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LONGMANS, GREEN, AND CO. LONDON, NEW YORK, BOMBAY, AND CALCUTTA LONGMANS CIVIL ENGINEERING SERIES NOTES ON CONSTRUCTION IN MILD STEEL EDITED BY HENRY FIDLER, M.I.C.E. NOTES ON BUILDING CONSTRUCTION Medium 8w. PART I. With 695 Illustrations, IQS. 6d. net. PART II. With 496 Illustrations, IDS. 6d. net. PART III. Materials. With 188 Illustrations, i8s net. PART IV. Calculations for Building Structures, With 551 Illustrations, 13^. net. LONGMANS, GREEN, AND CO. LONDON, NEW YORK, BOMBAY, AND CALCUTTA LONGMANS' CIVIL ENGINEERING SERIES NOTES ON CONSTRUCTION IN MILD STEEL ARRANGED FOR THE USE OF JUNIOR DRAUGHTSMEN IN THE ARCHITECTURAL AND ENGINEERING PROFESSIONS WITH ILLUSTRATIONS FROM WORKING DRAWINGS, DIAGRAMS, AND TABLES BY HENRY FIDLER, M.I.C.E. AUTHOR OF THE ARTICLE ON "DOCKYARDS" IN THE "ENCYCLOPEDIA BRITANNICA," AND EDITOR OF " NO^S ON BUILDING CONSTRUCTION*' LONGMANS, GREEN, AND CO. 39 PATERNOSTER ROW, LONDON NEW YORK, BOMBAY, AND CALCUTTA 1907 All rights reserved PREFACE IN the collection of "Notes" on Mild Steel and Constructional Steelwork, which form the contents of the present volume, no attempt has been made to treat the subject from the point of view of Applied Mechanics as ordinarily understood, nor are the theories of construction, nor the calculations for buildings or engineering structures referred to, except so far as may be required incidentally in connection with the subject-matter discussed, while the great range of the subjects upon which the Notes treat, and the severe limitations which are necessarily imposed, must form the only excuse which the writer has to offer for the obvious insufficiency of treatment of the items dealt with. It has been assumed that the junior draughtsman of the architectural or engineering professions has been, at least to some extent, properly grounded in the theory of construction, and that he has acquired an elementary knowledge of the determination of stresses in the structures with which he has to deal. It has, however, come within the experience of the writer that between the carefully calculated stress-sheet or correctly drawn graphic diagram, and the completion of a working drawing which shall successfully pass the ordeal of criticism in the girdermaker or bridge- or roof-builder's yard, there is sometimes found a gap, not always successfully bridged, and it becomes occasionally evident that the ability to produce, let us say, a correct graphic analysis of the stresses on a roof principal and the ability to design a sound riveted connection are not quite one and the same thing. It is true that excellence and soundness of design are not to be acquired from books alone, and that close study, observation, and 1 62822 vi PREFACE. experience must go hand-in-hand to arrive at that result. It is, however, the hope of the writer that the Notes now offered will assist the student, at all events, in the study and observation of such good examples of Steel Construction as may come within his reach, and in the practical application of a material which has taken, and is likely to maintain, so important a position in both Architectural and Engineering Construction. The education of the designer of Constructional Steelwork is not, however, completed even when to a sound knowledge of theory he has added to that knowledge the experience of the practical aspects of design. He will, if he be wise, endeavour, so far as opportunity may be given him, to trace back the previous history of the material he has been dealing with ; he will place himself, mentally and (as far as is possible to him) by personal observation, in touch with the centres of the Steel-making Industry, the Blast Furnace, the Cinder Heap, the " Sow " and her " Pigs," the dazzling radiance of the molten metal in the open hearth or the converter, the methods (to say nothing of the risks and anxieties) of the Steel Founder, the ruddy atmosphere of the Annealing Furnace, and the spectral shapes of castings, refracted by the waving and glowing gases as they undergo the ordeal which relieves internal stress and makes them ductile and tough, the Ingot, the Soaking Pit, the clangour, and hiss and roar of the Boiling Mills. The scene changes, and he will follow the completed sections and shapes to the Plater's yard, the Templet-maker's, Machine and Smith's shops, the Pickling or Galvanizing Tanks, and watch the processes whereby Drilling Machine, Punching Machine, Eiveting Machine, Pneumatic Hammer with its incessant rattle, Cold Saw with its halo of sparks, Hydraulic Press, and the like, shape and fashion his material into the form he has evolved on paper ; and perhaps he then becomes conscious, as the offspring of his thought grows into visible bodily shape before his eyes, that there are certain details in his design which he will take care to improve on a future occasion. Again the scene changes, the riveted sections of steelwork, the PREFACE. vii castings, the cases of bolts and nuts, the bags of rivets, have all left the contractor's yard, some by rail, some perchance by sea, and then the multitudinous practical requirements which surround the Erection of Constructional Steelwork become evident, whether the Structure be some Bridge of great span over a ravine or rapid river, a Skeleton Steel " Skyscraper " many stories high, a large Caisson or Lock Gate for a Dock Entrance, or whether it be the simpler and humbler forms of Builders' Ironwork, and the erection of a few simple columns, girders, or roof principals. All these things, and many more, noted with the observant eye, and the receptive and willing mind, will form so many rungs in the ladder whereby the junior draughtsman, be he Architect or Engineer, may climb, as regards this branch of his profession, to efficiency, success, and the honourable reward of his industry. The application of Steel to that mode of construction known as " Ferro- Concrete," " Armoured Concrete." or " Concrete Steel " demands separate treatment, and is not alluded to in this volume. This subject, together with that of the protection of Constructional Steelwork from the effects of fire, the present writer must leave until such period as time and opportunity may indicate. H. F. LONDON, November, 1906. CONTENTS CHAPTER I. MILD STEEL: ITS MANUFACTURE, PHYSICAL AND CHEMICAL QUALITIES. PAGE General remarks General appellation of "mild steel" Influence of small percentages of carbon Tabular statement showing the approximate per- centages of carbon and approximate ultimate tensile strength of various steels Influence of other chemical constituents Influence of carbon Influence of silicon Influence of phosphorus Influence of sulphur Influence of copper Influence of aluminium Influence of arsenic In- fluence of manganese Relationship between the chemical constitution of mild steel and its ultimate resistance to tension Proposed formulae For acid open-hearth steel For basic open-hearth steel Processes of pro- duction of mild steel The acid Bessemer The basic Bessemer The acid open hearth The basic open hearth General descriptions Tests of open- hearth steel Tests on mild steel angles On mild steel tees On mild steel flats On mild steel channels On mild steel rolled joists On mild steel zeds On mild steel trough flooring On mild steel round bars On mild steel rectangular bars On mild steel plates, lengthways and cross- ways On mild steel rivets On mild steel for bolts and nuts On mild steel forgings On mild steel for special purposes General results of mechanical tests Chemical analyses Comparative tests on wrought-iron bars, rectangular and round Microscopic analyses Remarks on the relative output of various processes of steel manufacture Cast steel General remarks Advantages and disadvantages in the use of cast steel Defects Blow-holes Examples of the use of cast steel Precautions as to use of cast steel of inferior quality Annealing of steel castings Table of methods employed by leading steel founders Tests and test bars Tables of tensile and bending tests on cast-steel bars Pawl racks Bollards Roller paths Rollers Machinery castings Sundry castings for various purposes Transverse strength of steel bars Chemical analyses of cast steel Transverse strength of cast-iron bars Chemical analysis of cast iron . 1 CHAPTER II. ROLLED SECTIONS IN STEEL AND THEIR MECHANICAL ELEMENTS, WITH GENERAL REMARKS ON THEIR USES AND COMBINATIONS. Angles Equal-legged Unequal-legged Round-backed Acute-angled Obtuse-angled Bulb-angles British standard sections Table of the CONTENTS. PAGE principal mechanical elements of equal-legged angles ; of unequal-legged angles Tees British standard sections Bulb tees Table of the prin- cipal mechanical elements of ordinary tees ; of bulb tees Rolled joists- - General remarks Proportions of web and flange thicknesses Standards of proportion British standard sections Table of the principal mechanical elements of rolled joists Channels Standards of proportions British standard sections Table of the principal mechanical elements of channels Zed angles General remarks British standard sections Table of the principal mechanical elements of Zed angles Other forms of sections Plates Bars Flats . 82 CHAPTER III. UPON CERTAIN APPLICATIONS OF RIVETED GIRDERWORK, WITH SOME REMARKS UPON RIVETS AND RIVET HOLES. General remarks Examples of various types of girderwork Remarks upon the design of riveted connections Fundamental rules and the study of good examples The making of rivet-holes Punching and the punch- ing machine Burrs, and the holes which they imply Drilled holes The templet system Making and use of templets Combined punched and drilled or rimered holes Rivets Shape and dimensions of rivet- heads Pan-heads Cup-heads Percentage of weight of heads and points Table of weights of heads and points Methods of riveting Hand riveting Hydraulic riveting Pneumatic riveting The pneumatic hand hammer and its applications Girderwork as applied to bridge construction Example of viaduct construction Cast-iron cylinders Details Lengths of cylinders Bottom lengths Upper lengths and cap Holding-down bolts of main girders Cylinder bracing Main girders Footway and flooring Cross girders Expansion arrangements Road- way Details in connection with mixed traffic- -Curbing Girderwork for machine or boiler shops, steel foundries, engine houses, etc. Traveller girders Travelling cranes and their loads Wheel pressures Crane wheels Table of weights of overhead travelling cranes- Analysis of total loads and resulting reactions of supports Minimum dimensions and clearances for overhead travelling cranes Headway required Truth of gauge of road for overhead travelling cranes Types of girders for roadway Sections of rails and methods of connection Roadway at walls of shops Details Lattice girderwork for roofing- Example and details of riveted connections Application of girderwork to the support of cast-iron water-tanks Consideration of the details of the tanks themselves General arrangements of such tanks Bottom and side plates Subdivision of tanks Plate flanges Tie-rods Arrangement of girderwork Details of roofing arrangements in connection with tanks- Gutters and gangways Connections of pipe-work, etc. Table of the weight of mild steel bolts and nuts 106 CONTENTS. x CHAPTER IV. ON THE PRACTICAL DESIGN OF COLUMNS AND STRUTS. PAGE General remarks The ideal column The practical column Variation of modulus of elasticity Transverse stress: examples Conditions of end connections : Hat ended, round ended, pin ended Experiments on columns of wrought iron and steel Wrought-iron rectangular bars and hollow tubes, flat ended Wrought-iron rectangular bars, pin ended Influence of size of pins Tests of wrought-iron riveted columns, flat and pin ended Table of results Analysis and remarks Mode of failure- Weakness at ends of columns Weakness of component parts of columns Buckling between rivets Maximum pitch of rivets compared with plate thickness Lattice members of columns Minimum scantlings Experi- ments on compressive resistance of various sections Angles and tees, flat ended Angles and tees, hinged and round ended Channels, joists, welded tubes, and Zed columns, flat ended Channels, joists, and tubes, hinge ended Wrought-iron latticed columns, piu ended Mild steel angles, flat ended Hard steel angles, flat ended Diagrams of results of formulae proposed by various authorities Practical sections of columns and struts Elementary forms Flat bars Angles - Tees Channels Channels in combination Kolled joists Rolled joists in combination Built-up sections of various types Zed-iron sections in combinations Combinations of channels and joists Special sections Phoenix columns Secondary attachments Comparison of sections Eelative economy and efficiency Relative amount of riveting Relative accessi- bility for painting Caution in the preparation of working drawings for columns Check on proportion of length to diameter Practical ex- amples of riveted mild steel columns Procedure with respect to the continuity or otherwise of columns in various floor lengths Buildings of several stories Theatre auditorium Skeleton steel construction in very lofty buildings Massive columns for engine-house construction carrying travellers and tanks Variations in type Columns for machine-shops and engineering works Complex columns of this type carrying traveller roads and roofing Foundations to columns Holding-down bolts Lateral stability Special cases for concrete foundations of lofty buildings Precautions to be observed in the fixing of foundation bolts .... 180 CHAPTER V. ROOF CONSTRUCTION IN MILD STEEL AND IRON. General remarks Development of roof construction in timber, cast iron ( wrought iron, wrought iron and steel, mild steel Classification of roof principals Members of roof principals Upper or compressive member or principal rafter Sections for principal rafter Shoes to rafter Ex- pansion apparatus Main tie or lower tension member; in timber roofs; in composite roofs; in wrought-iron roofs; in steel roofs Risks of defective smith- work Earlier steel tie-rods Present-day practice Flat bar ties Link tie-rods Occasional stiffening of main tie-rod in small roofs CONTENTS. PAGE Examples of tie-rods Intermediate bracing Struts Ties Purlins In- fluence of nature of roof covering upon the arrangements of purlins Details and sections of purlins Distance apart of main trusses Inter- mediate rafters Hoofing accessories The collection and disposal of rain- water or melted snow General arrangement of roof drainage Eoof guttering in cast iron or riveted steel; in lead Experiment on rate of discharge in gutters and cesspools Area of roof surface to be drained Examples of guttering and downpipes Expansion joints Stopped ends Lanterns, skylights, and ventilators General remarks Lantern standards Louvre blades Koof of flat pitch Examples of roof con- struction of various types Special type of roofing combined with vertical supports Details The testing of roof principals Conditions of practical testing in the contractor's yard Methods of measuring deformation and settlement Kemarks on cottering up Setting out of roof principals Scribing floor 269 CHAPTER VI. THE USE OF MILD STEEL AND IRON IN MARINE ENGINEERING. General remarks Design of iron piers or jetties Classification of jetties Those which are backed up by solid structure in the rear Those which are isolated Types of design of the second class Accessories of jetties Exposure and " fetch" Height of deck Details of pile work as influenced by conditions of soil or sea bottom Modes of sinking piles Difficulties as to finished lengths and levels of top of piles Make-up lengths Objec- tions to make-up lengths Sawing off of steel or iron sections Composite structures of cast iron and timber Example and description Bollards Crane roads Floating booms Description of cast-iron cylinder jetty with superstructure of steel girderwork Cylinder spacing Main box girders Cross girders Details of cylinders Flange joints Cap Make- up lengths Lowermost rings of cylinders Cutting edge Further adaptations of steelwork in marine engineering works Tie-rods to wharf walls Accessories to jetties or wharves Bollards Strength of bollards Details to suit special oases Anchorage Examples Fairleads and capstans Position and arrangement Foundations Caissons Varied applications of the term Caissons for dock entrances For foundations For the commencement or completion of breakwater structures Practical example of a caisson for breakwater construction General description Dimensions General arrangement Compartments Bulkheads Details of construction Valves Mooring rings Method of erection and launch- ing Launching ways Completion after launching Ballasting Weights Conditions of stability Composition of ballast Subsequent operations Towing into position Sinking Programme for concreting and succes- sive conditions of stability Titan cranes for block-setting Caissons for closing dock entrances General comparison between lock-gates and caissons TypeB of caissons Sliding Floating Comparison of types Advantages and disadvantages Functions as a bridge and as a dam Watertigntness Design of keels and stems Arrangement of sealing timber for floating caissons For sliding caissons Width of water seal Details of timber keels and mode of connection, etc. Consideration of CONTENTS. xiii PAGE pressures, reactions, and general stresses due to water pressure Position of decks and air-chamber Effects of corrosion and considerations of minimum scantlings General description of internal arrangement of floating caissons Bilge Air-chamber Stability and pendulum Upper and end chambers Scuttling tanks Upper deck and top tanks Dangers arising from excess of buoyancy Critical conditions Holding-down apparatus Frictional resistance to uplifting Coefficient of Friction Calculation for buoyancy and weight Kivet heads Percentage to be allowed Weights of immersed timber Subsidiary items Table of the weights of recently constructed caissons Ballast and stowage Com- position and densities of ballast Burr concrete ballast General descrip- tion of sliding caissons Arrangements of upper deck and camber deck Sliding ways Hauling mechanism Additional resistances due to currents or differences in water level Culvert area Extra sluices Position of hauling gear Tilting moments Sledge runners and rollers Combination of the two types in recent caissons Keels Boiler paths Boilers and rams Mode of operation during inward and outward journeys Details of roller path and roller Of hydraulic rams and mud-scrapers Handrailing Hauling chains Description and manu- facture Tests Tables of results of tests Modulus of elasticity of hauling chains Table of the weights of sliding caissons 338 CHAPTER VII. THE PROTECTION OF STEEL SURFACES FROM CORROSION. General remarks The destructive effects of oxidation Desirability of an exhaustive inquiry into the best methods of protection and the relative efficiencies of various coatings Effects produced by locomotive gases and other agencies Influence of these considerations upon certain types of construction Inaccessible positions Durability of foundation bolts, and the like, of marine structures Attrition of shingle Mill scale and its removal The process of pickling mild steel Proportions of acid bath Tanks Period of immersion Subsequent processes Coating of boiled oil Analyses of boiled linseed oil First coat of paint Oxide of iron paint Analyses of oxide of iron paint Analyses of lead colour or grey paints 428 INDEX . 441 CHAPTER I. MILD STEEL: ITS MANUFACTURE, PHYSICAL AND CHEMICAL QUALITIES. General remarks General appellation of " mild steel "Influence of small per- centages of carbon Tabular statement showing the approximate percentages of carbon and approximate ultimate tensile strength of various steels Influence of other chemical constituents Influence of carbon Influence of silicon Influence of phosphorus Influence of sulphur Influence of copper Influence of aluminium Influence of arsenic Influence of manganese Relationship between the chemical constitution of mild steel and its ultimate resistance to tension Proposed formulae For acid open-hearth steel For basic open-hearth steel Processes of production of mild steel The acid Bessemer The basic Bessemer The acid open hearth The basic open hearth General descrip- tionsTests of open-hearth steel Tests on mild steel angles On mild steel tees On mild steel flats On mild steel channels On mild steel rolled joists On mild steel zeds On mild steel trough flooring On mild steel round bars On mild steel rectangular bars On mild steel plates, lengthways and cross- ways On mild steel rivets On mild steel for bolts and nuts On mild steel forgings On mild steel for special purposes General results of mechanical tests Chemical analyses Comparative tests on wrought-iron bars, rectangular and round Microscopic analyses Remarks on the relative output of various processes of steel manufacture Cast steel General remarks Advantages and disadvantages in the use of cast steel Defects Blow-holes Examples of the use of cast steel Precautions as to use of cast steel of inferior quality Annealing of steel castings Table of methods employed by leading steel founders Tests and test bars Tables of tensile and bending tests on cast- steel bars Pawl racks Bollards Roller paths Rollers Machinery cast- ingsSundry castings for various purposes Transverse strength of steel bars Chemical analyses of cast steel Transverse strength of cast-iron bars Chemical analysis of cast iron. IT is the primary object of these notes to treat, as regards riveted work, of those combinations or assemblages of various rolled sections of steel which make up the constructional forms of steel- work to be dwelt upon in the pages following. The methods by which these sections, amongst which may be enumerated plates, bars, angles, tees, joists, channels, and the like, B 2 CONSTRUCTION IN MILD STEEL. are produced in the rolling mills from the original ingot is beyond the scope of this work. It is, however, very desirable that the student and designer of structural work should possess some elementary knowledge at least of the leading features of the chemical and physical qualities of his material as affected by the various processes of manufacture, especially as these last are frequently referred to in modern specifications for structural steel- work, and the designer may be called upon to select that process which he considers best suited for his purpose, unless, indeed, he adopts the somewhat undesirable course of ignoring all reference to methods of manufacture, and is content to accept what is offered without further inquiry. The following elementary and necessarily imperfect outline of these subjects has been therefore prepared, rather as an incentive to the student to prosecute further inquiry than as an attempt to treat even partially of a branch of metallurgy full of detail of absorbing interest. Before treating of the several processes of manufacture now in vogue, it is desirable to consider briefly some of those chemical constituents which go to make up that compound of iron and carbon which is denominated steel under its various sub-divisions of hard, medium, soft, or mild, The discussions which arose in the earlier days of modern steel manufacture as to the precise nomenclature of the various grades of steel, and especially as regards that quality of the metal now used for ordinary riveted structural work, have to-day less interest. The appellation of " mild steel " is perfectly well understood, and the limits of the chemical and physical qualities of this metal, while they are subject to a certain amount of latitude with regard to the precise purposes in view, are nevertheless practically settled by the general consent of engineers and manufacturers. The wonderful influence of a small percentage of carbon in com- bination with iron will at once attract the attention of the student, and the question of carbon content must now be entered upon. The tabular statement which follows is intended to show the gradual increase in percentage of carbon which accompanies the increasing hardness of steel ranging from the softest quality manu- factured, and applicable to those purposes which require great ductility, malleability, and welding properties, to those grades of steel standing at the summit of the scale of hardness, and used only for cutting instruments of the finest temper and edge. ITS PHYSICAL AND CHEMICAL QUALITIES. The student will observe that the entire range or scale of carbon content is but about 1 per cent. It is unnecessary, perhaps, to point out that there is no hard- and-fast boundary line to be drawn between the several groups or strata of steels. Any one group may be found to overlap its neighbour to some slight extent, but in the main the percentages here given indicate within narrow limits those which will be found in chemical analyses of the metal used for the various purposes described. TABLE No. 1. SHOWING THE APPROXIMATE PERCENTAGES OF CARBON AND APPROXIMATE ULTIMATE TENSILE STRENGTH OF STEEL USED FOR THE PURPOSES DESCRIBED. Class of material. Percentage of carbon. Approximate ulti- mate tensile strength in tons per sq. in. Extra soft steel for such purposes as boiler flues or plates exposed to flame, rivets, tin-plates, tubes for boilers, welding material and the like 0-06-0-125 22-26 Mild steel for ship-building, bridge- work, builders' girders, riveted columns, roof trusses, rolled joists, trough floor sections, and the like 0-125-0-250 26-32 Medium steel for tyres, axles, rails for permanent way, railway vehicle springs, and the like 0-30-0-55 35-45 High Carbon Steels. Various blacksmiths' tools, and as 1 weld steel for steeling l 0-65 Wood- working chisel steel 1 0-875 Paving-tool steel, screw taps, chisels gouges, etc. 1 Stocks and dies, draw-plates, etc. 1 .. Turning-tool steel, rock drills, mill picks, scrapers, and cutting tools 1-000 1-125 Up to about 60 tons per square inch. for hard metals l ... 1-250 Hard file steel l 1-375 Kazor steel, turning and planing knives, drills, turning gravers for very hard materials l 1-500 J 1 Skelton, "Economics of Iron and Steel." Also Thallner, " Tool Steel.' 4 CONSTRUCTION IN MILD STEEL. The above table is intended to exhibit broadly the relationship between carbon content and ultimate tensile resistance, but this relationship is not solely of this simple nature. The influence of the other chemical elements usually found in chemical analysis of mild steel, as affecting the practical working qualities and physical characteristics of the metal, must also be traced. The following elementary remarks upon this subject are mainly based upon the work of a well-known American authority ; and, except where otherwise mentioned, the passages in italics which follow are taken from the work referred to. 1 Influence of Carbon. " The ordinary steel of commerce is carbon- steel ; in other words, the distinctive features of two different grades are due for the most part to variations in carbon rather than to differences in other elements. "There are often wide variations in manganese, phosphorus, silicon, etc., but it is rarely that the carbon content does not determine the class to which the material belongs. " This selection of carbon as the one important variable arose primarily from the fact that primitive Tubal Cains could produce a hard- cut ting instrument with no apparatus save a wrought-iron bar and a pile of charcoal; and the natural developments in manufacture have led to the conclusion that a given content of carbon will confer greater hardness and strength, with less accom- panying brittleness than any other element. " There are certain exceptions to be taken to this statement in the case of hard steels made by manganese, chromium, or tungsten, but it may be accepted as true in soft steel. " It follows, therefore, that no limit should ever be placed to the carbon allowed in any structural material if a given tensile strength is specified. It is, of course, true that every increment of carbon increases the hardness, the brittleness under shock, and the sus- ceptibility to crack under sudden cooling and heating, while it reduces the elongation and reduction of area; but the strength must be bought at a certain cost, and this cost is less in the case of carbon than with any other element." Influence of Silicon. " The contradictory testimony concerning the effect of silicon on steel has been well summarized by Mr. Howe, 2 who records many examples of exceptional steels with 1 Campbell, " Manufacture and Properties of Structural Steel." 3 "The Metallurgy of Steel." ITS PHYSICAL AND CHEMICAL QUALITIES. 5 abnormal contents of silicon, and who fully discusses the theories advanced by different writers. " He finds no proof that silicon has any bad effect upon the ductility or toughness of steel, and he concludes that the bad quality of certain specimens is not necessarily due to the silicon content, but to other unknown conditions." In discussing the results of the investigation of Mr. Hadfield, 1 the following remarks are made by Mr. Campbell : " These results are of the highest value in showing that silicon cannot be classed among the highly injurious elements, for in similar proportion (the percentages of silicon in the investigations in question range from 0'21 to 5'08) phosphorus and sulphur would be out of the question, manganese would give a worthless metal, and carbon would change the bar to pig-iron. It will, therefore, be only reasonable to suppose that small quantities cannot exert a very deleterious influence." Finally, the same author remarks that " in steels containing less than 0'25 per cent, of carbon, the effect of small proportions of silicon upon the ultimate strength is inappreciable." Influence of Phosphorus. "Of all the elements that are commonly found in steel, phosphorus stands pre-eminent as the most undesir- able. It is objectionable in the rolling mill, for it tends to produce coarse crystallization, and hence lowers the temperature to which it is safe to heat the steel, and for this reason phosphoritic metal should be finished at a lower temperature than pure steel, in order to prevent the formation of a crystalline structure during the cooling/' " Aside from these considerations, its influence is not felt in a marked degree in the rolling mill, for it has no disastrous effect upon the toughness of red-hot metal when the content does not exceed 015 per cent." " The action of phosphorus upon the finished material may not be dismissed in so few words. Mr. Howe 2 has gathered together the observations of different investigators, and the evidence seems to prove that the tensile strength is increased by each increment of phosphorus up to a content of 0*12 per cent., but that beyond this point the metal is weakened. Whether this last observation be correct or not is of little practical importance, for it would be criminal to use a metal for structural purposes that contained as much as an average of 0*12 per cent, phosphorus." 1 "Alloys of Iron and Silicon." Journal 7. and S. L, vol. ii., 1889. 2 "The Metallurgy of Steel." 6 CONSTRUCTION IN MILD STEEL. "Below this point it is absolutely certain that phosphorus strengthens low steels, both acid and basic. . . . The same certainty does not pertain to any other effect of this metalloid. Mr. Howe has ably discussed the whole matter, and I herewith make quotations from the Metallurgy of Steel, and place them in the form of a summary. " (1) The effect of phosphorus on the elastic ratio, as on elon- gation and contraction, is very capricious. "(2) Phosphoric steels are liable to break under very slight tensile stress if suddenly or vibratorily applied. "(3) Phosphorus diminishes the ductility of steel under a gradually applied load as measured by its elongation, contraction, and elastic ratio when ruptured in an ordinary testing machine, but it diminishes its toughness under shock to a still greater degree, and this it is that unfits phosphoric steels for most purposes. " (4) The effect of phosphorus on static ductility appears to be very capricious, for we find many cases of highly phosphoric steel which show excellent elongation, contraction, and even fair elastic ratio, while side by side with them are others produced under apparently identical conditions but statically brittle. "(5) If any relation between composition and physical pro- perties is established by experience, it is that of phosphorus in making steel brittle under shock ; and it appears reasonably certain, though exact data sufficing to demonstrate it are not at hand, that phosphoric steels are liable to be very brittle under shock, even though they may be tolerably ductile statically. "The effects of phosphorus on shock-resisting power, though probably more constant than its effects on static ductility, are still decidedly capricious. . . ." " It is true that numerous cases can be cited of rails, plates, etc., containing from 0*10 to 0'35 per cent, of phosphorus, which have withstood a long lifetime of wear and adversity ; but in the general use of such metal there has been such a large percentage of mysterious breakages that it seems quite well proven that the phosphorus and the mystery are the same." On the subject of phosphorus, another authority l remarks as follows : "In the case of what may be called the treacherousness of phosphoric steel, it is difficult to fix a definite limit for the 1 F. W. Harbord, " The Metallurgy of Steel," 1904. ITS PHYSICAL AND CHEMICAL QUALITIES. 7 maximum content of phosphorus which can be safely allowed, but there can be no doubt that the lower this is, the safer the material, and for structural purposes 0*06 per cent, is quite as much as can be accepted with a feeling of security. In steel rails 0*08 per cent, of phosphorus may be permitted with safety." Influence of Sulphur. " Nothing is better established than the fact that sulphur injures the rolling qualities of steel, causing it to crack and tear, and lessening its capacity to weld. This tendency can be overcome in some measure by the use of manganese and by care in heating, but this does not in the least disprove that the sulphur is at work, but simply shows that it is overpowered. " The critical content at which the metal ceases to be malleable and weldable varies with every steel. It is lower with each associated increment of copper, it is higher with each unit of manganese, and it is lower in steel which has been cast too hot. " In the making of common steel for simple shapes, a content of 010 per cent, is possible, and may even be exceeded if great care be taken in the heating ; but for rails and other shapes having thin flanges, it is advantageous to have less than 0*08 per cent., while every decrease below this point is seen in a reduced number of defective bars. " It is impossible to pick out two steels with different contents of sulphur and say that the influence of a certain minute quantity can be detected, but it is none the less true that the effect of an increase or decrease of O'Ol per cent, will show itself in the long run, while each 0'03 per cent, will write its history so that he who runs may read. " The effect of sulphur upon the cold properties of steel has not been accurately determined, but it is quite certain that it is unim- portant. In common practice the content varies from 0*02 to O'lO per cent., and within these limits it seems to have no appreciable influence upon the elastic ratio, the elongation, or the reduction of area. It is more difficult to say that it does not alter the tensile strength, for a change of 1000 Ibs. per square inch can be caused by so many things that it is a bold venture to ascribe it to one variable. " In rivets, eyebars, and fire-box steel, the presence of sulphur is objectionable, for it will tend to create a coarse crystallization when the metal is heated to a high temperature, and reduce the strength and toughness of the steel. 8 CONSTRUCTION IN MILD STEEL. 9 " In other forms of structural material the effect of this element is probably of little importance." Another authority 1 states, "the real danger of using a high sulphur steel for structural purposes, even when it has not in any way to be worked hot, lies in the fact that, during rolling, numerous cracks are likely to develop, which close up and are quite imper- ceptible in the finished material. Nevertheless, these remain as flaws, and may form starting-points for rupture when the material is subjected to any sudden stress. . . . Probably material of this description is one of the most dangerous that can be employed by the engineer, the more so that the tensile strength and elasticity, as evidenced by elongation and reduction of area, will give no indications in the majority of cases that the material is in any way untrustworthy." " Starting with fairly good materials, with careful treatment manufacturers should have no difficulty in producing regularly a steel with about 0'06 per cent., and certainly 0'08 per cent, is the very maximum that should be allowed in any steel, either for rails or structural purposes." Influence of Copper. "Steel may contain up to 1 per cent, of copper without being seriously affected, but if at the same time the sulphur is high, say 0'08 to 010 per cent., the cumulative effect is too great for molecular cohesion at high temperatures, and it cracks in rolling. This tearing occurs almost entirely in the first passes of the ingot, so that it is of little importance to the engineer, who is concerned only with perfect finished material. In the purest of soft steels, containing not more than 04 per cent, of either phosphorus or sulphur, the influence of even 0*10 per cent, of copper may be detected in the less ready welding of seams during the process of rolling ; but ordinarily, when the sulphur is below 0*05 per cent., the copper injures the rolling quality very little, even if present in the proportion of 0*75 per cent. In all cases the cold properties seem to be entirely unaffected. "These conclusions are not founded on any limited series of tests or special alloys ; they are the fruit of years of experience in the making of millions of tons of cupriferous steels, and it is quite certain that any baneful influence of this constant companion would have been felt in the many investigations which have been made into the mechanical equation of structural metal." Influence of Aluminium. Experiments by Hadfield quoted by 1 F. W. Harbord, " The Metallurgy of Steel," 1904. ITS PHYSICAL AND CHEMICAL QUALITIES. 9 Campbell show that "after making allowances for the variations in other elements, it will be found that the aluminium has little effect upon the tensile strength, while it does not materially injure the ductility until a content of 2 per cent, is reached." Experiments by the latter author, however, appear to lead to the following conclusions : "(1) The addition of one-half of 1 per cent, of aluminium increases the tensile strength between 3000 and 8000 Ibs. per square inch, exalts the elastic limit to about the same proportion, and injures very materially the elongation and contraction of area. The effect both upon strength and ductility is more marked in the case of low than in high steels. " (2) The addition of another half of 1 per cent, does not have much effect upon the ultimate strength or the elastic limit, but it still further decreases the ductility of the metal." Influence of Arsenic. " The effect of arsenic upon steel was quite fully investigated several years ago by Harbord and Tucker. The conclusions given by them may be summarized as follows : "Arsenic, in percentages not exceeding 0*17, does not appear to affect the bending properties at ordinary temperatures, but above this percentage cold shortness begins to appear and rapidly increases. " In amounts not exceeding 0*66 per cent., the tensile strength is raised very considerably. It lowers the elastic limit, and decreases the elongation and reduction of area in a marked degree. It makes the steel harden much more in quenching, and injures its welding power even when only 0*093 per cent, is present. "These results have been corroborated by J. E. Stead, who found that between O'lO and 0*15 per cent, of arsenic in structural steel has no material effect upon the mechanical properties; the tenacity is but slightly increased, the elongation and reduction of area apparently unaffected. With 0*20 per cent, of arsenic the difference is noticeable, while with larger amounts the effect is decisive. When 1 per cent, is present, the tenacity is increased, and the elongation and reduction of area both reduced. This increase in strength and diminution in toughness continue as the content of arsenic is raised to 4 per cent., when the elongation and reduction in area become nil" Influence of Manganese. 1 " In considering the influence of this 1 F. W. Harbord, " The Metallurgy of Steel," 1901. io CONSTRUCTION IN MILD STEEL. metal on steel, it must be remembered that, unlike most of the- other constituents, it is not an impurity originally present which the metallurgical treatment has failed to remove, but is, at all events in the case of all steel used for structural purposes, an essential constituent especially added to deoxidise the decarbonized metal so as to prevent its being red short. The effect which manganese has upon the tenacity and ductility varies very con- siderably with the percentage of carbon in the steel, its influence being much more marked in the case of high than of low carbon steels. In the author's opinion, for mild steel and rail steel, the less manganese a steel contains above that required to insure solid ingots and freedom from red shortness the better, and with reason- able care taken during the manufacture, there should not be the slightest difficulty in obtaining these results with 0*4 to 0'5 per cent, of manganese in the finished product, at all events for mild steel made in the Siemens furnace. ... In the case of mild steel required for boiler plates and for bridges or other structural work, an increase of manganese has a very distinct hardening effect, and above 0*6 per cent, begins to be dangerous, and should not be allowed. The tendency amongst steel makers to bring up the tensile strength to the specification by increasing the manganese, instead of the carbon, is greatly to be deprecated, and notwith- standing the reported excellent records of mild steel plates with 1 per cent, of manganese, and steel rails containing more than this amount, engineers will be well advised to decline to accept such material." It will be evident from a consideration of the foregoing remarks that the relationship between the chemical constitution of mild steel and its ultimate resistance to tension must be of a complex character, and that the attempt to establish a satisfactory formula which shall equate the chemical and physical qualities of any given specimen of the material is surrounded with some difficulties. Several authors have proposed formulae to this end, but it will suffice here to quote some of the conclusions arrived at by Mr. Campbell as the result of elaborate investigations based on a large number of experiments. For the details and methods employed, the reader is referred to the works of that author. 1 These conclusions are as follows, converting pounds into tons per square inch : 1 " The Manufacture and Properties of Structural Steel ; " also the paper read before the Iron and Steel Institute at New York, October, 1904. ITS PHYSICAL AND CHEMICAL QUALITIES. ii The strength of pure iron, 1 as far as it can be determined from the strength of steel, is about 17*76 to 18*75 tons per square inch. An increase of '01 per cent, of carbon (determined by com- bustion) raises the tensile strength of acid steel about 0*44 tons per square inch, and of basic steel about 0'34 tons. The influence of manganese upon the tensile strength of acid steel is a variable quantity, depending not only upon its own percentage, but upon that of the carbon with which it is associated, and is indicated in the table which follows, for steels of from 010 to 0'40 per cent, of carbon. TABLE No. 2. ACID STEEL. Increase in tensile strength in tons per square inch corresponding to the percentages of manganese and carbon. El I Percent- age of Magna- nese. 0-42 0-44 0-46 0-48 0-50 0-52 0-54 0-56 0-58 0-60 0-10 0-07 0-14 0-21 0-28 0-36 0-43 0-50 0-57 0-64 0-71 015 0-20 0-11 0-14 0-22 0-28 0-32 0-42 0-43 0-56 053 0-72 0-64 0-86 0-75 1-00 0-86 1-14 0-96 1-28 1-07 1-43 0-25 0-18 0-36 0-54 0-72 0-90 1-07 1-25 1-42 1-60 1-78 0-30 0-21 0-42 0-63 0-84 1-08 1-29 1-50 1-71 192 2-14 0-35 0-25 0-50 0-75 1-00 1-25 1-50 1-75 2-00 2-25 2-50 0-40 0-28 0-56 0-84 1-14 1-42 1-71 2-00 2-28 2-56 2-85 Thus for a steel of 0'35 per cent, carbon and 0'52 manganese, the increase would be 1*50 tons per square inch. An increase of O'Ol per cent, of phosphorus raises the tensile strength of acid and basic steel about 0'44 tons per square inch. The following formulae give the ultimate strength of acid and basic open-hearth steel in terms of their principal chemical constituents, where C = 100 x per centage of carbon, P = 100 X per centage of phosphorus, Mn = manganese, x Mn = a coefficient for manganese in acid steel, of which the values are given in Table No. 2, y Mn = a coefficient manganese in basic steel, of which the values are given in Table No. 3, and E = a variable based on heat treatment. 1 The term " pure iron " is arbitrary, and intended to express simply the datum plane from which to start in order to find the strength of steel by a simple formula. " Absolutely pure iron never has been, and in all probability never will be, made." 12 CONSTRUCTION IN MILD STEEL. Formula for Add Open-hearth Steel. (Carbon estimated by combustion.) 17'85 + 0*44 C + 0'44 P +oj Mn + K = ultimate tensile strength in tons per square inch. Formula for Add Open-hearth Steel. (Carbon estimated by colour.) 1776 + 0-508 C + 044 P+o?Mn + R = ultimate tensile strength in tons per square inch. Formula for Basic Open-hearth Steel. (Carbon estimated by combustion.) 18-52 + 0'34C + > 44P+2/Mn + E = ultimate tensile strength in tons per square inch. Formula for Basic Open-hearth Steel. (Carbon estimated by colour.) 1875 + '366 C + 0'44P+7/Mn + B=ultimate tensile strength in tons per square inch. In the above formula, K, the variable for heat treatment, is zero, in angles and plates about f inch to J inch thick finished at a fairly high temperature. The influence of manganese upon the tensile strength of basic steel is given in the following table : TABLE No. 3. BASIC STEEL. Percentage Increase in tensile strength in tons per square inch corresponding to the percentages of manganese and carbon. Percentage of manga- 0-35 0-40 0-45 0-50 0-55 0-60 nese. O05 0-24 0-49 0*73 0-98 1-22 1-47 0-10 0-29 0-58 0-86 1-16 1-44 1-74 0-15 0-33 0-66 I'OO 1-33 1-66 2-00 0-20 0-37 0-75 1-13 1-61 1 89 2-27 0-25 0-42 0-84 1-26 1-69 2-11 2-54 0-30 0-40 0-93 1-39 1-87 2-33 2-81 0-35 0-51 1-02 1-53 2-05 2-56 3-08 0-40 0-56 1-12 1-67 2-23 2-79 3-35 ITS PHYSICAL AND CHEMICAL QUALITIES. 13 As an example of the application of the above formulae, let us assume a specimen of open-hearth acid steel of which the chemical analysis gives a percentage of carbon (estimated by combustion) of G'166, phosphorus 0'053, manganese 0'58; then by the formula we have Ultimate tensile] = 17'85 + (0'44x 100 X 0166) -f (044x100 strength in tons I xO'053) + l'00(seeTableNo.2) = 28'5 per square inch J tons. In steels containing less than 0*25 per cent, of carbon, the effect of small proportions of silicon upon the ultimate strength is inappreciable. Sulphur in ordinary proportions exerts no appreciable influence upon the tensile strength. It will be observed, from a comparison of the above formulae, that phosphorus causes an addition to the tensile strength for each O'Ol per cent, equal to that caused by carbon for each O'Ol per cent., and this consideration gives force to Mr. Campbell's remark that " it is well not to assume the truth of all tradition, but if there is one fact which seems demonstrated, it is that phosphorus will hide its true character in the testing machine, but will certainly make itself known at some future time." The great bulk of the material known as mild steel is, in Europe and America, produced by the following processes, viz. : The Acid Bessemer process ; The Basic Bessemer process ; The Acid Open-hearth process ; The Basic Open-hearth process. The process by which high carbon steels are produced, known as the " Crucible," need not here be further alluded to, as the quality of steel produced by this method is not that used in those forms of construction with which this work principally deals, being, in fact, chiefly used in the manufacture of machine tools and implements, cutting instruments of keen temper and fine edge, and for other similar purposes. With regard to the above-mentioned processes, it will be observed that they consist of two principal divisions, viz. the Bessemer and open-hearth (otherwise the Siemens or Siemens- Martin process), each division being further subdivided into the processes known as acid and basic. 14 CONSTRUCTION IN MILD STEEL. The authority previously quoted 1 has defined each of these methods of manufacture in general terms, as follows : " The acid Bessemer process consists in blowing air into liquid pig-iron for the purpose of burning most of the silicon, manganese, and carbon of the metal, the operation being conducted in an acid-lined vessel, and in such a manner that the product is entirely fluid." "The basic Bessemer process consists in blowing air into liquid pig-iron for the purpose of burning most of the silicon, manganese, carbon, phosphorus, and sulphur of the metal, the operation being conducted in a basic-lined vessel, and in such a manner that the product is entirely fluid." " The open-hearth process consists in melting pig-iron, mixed with more or less wrought-iron, steel, or similar iron products, by exposure to the direct action of the flame in a regenerative gas furnace and converting the resultant bath into steel, the operation being so conducted that the final product is entirely fluid." We have seen that the open-hearth process may be either acid or basic. Of the latter the same author says " The basic (open-hearth) process, as herein discussed, consists in melting a charge of pig-iron, or a mixture of pig-iron and low carbon metal upon a hearth of dolomite, lime, magnetite, or other basic or passive material, and converting it into steel in the presence of a stable basic slag by the action of the flame, with or without the use of ore, and by the addition of the proper recarbonizers, the operation being so conducted that the product is cast in a fluid state." Amplifying the above general description, the following essential points of difference may be noted. In the Bessemer process the high temperature required for combustion and to effect the necessary chemical changes is maintained by blowing air through the molten pig-iron. In the open hearth no such blowing through process takes place, the bath of steel being exposed to the direct influence of the flame and intense temperature produced by the use of the Siemens regenerative furnace, which forms an essential feature in this method of manufacture. When we next consider the essential differences which underlie the use of the terms " acid " and " basic," we find, however, points 1 H. H. Campbell, " The Manufacture and Properties of Structural Steel." ITS PHYSICAL AND CHEMICAL QUALITIES. 15 of detail which are of importance as regards the quality of the resultant material. The influences, mainly hostile, exerted by the elements of phosphorus and sulphur, but more especially the former, upon the physical qualities of the finished product have already been enlarged upon in the foregoing remarks. The extent, therefore, to which the elimination of these hostile influences can be carried by the various processes of steel manu- facture, having regard to the original quality of the ore used, must consequently claim our attention, if we are to make any selection as to the method by which the finished product desired is to be manufactured. It is beyond the scope of these notes to enter fully into the complete history of the changes which take place in the contents of the acid-lined Bessemer converter from the commencement to the end of the " blow." Suffice it to say that while the original carbon content has been burnt out until practically none is left, the ultimate desired percentage of carbon being obtained by recarbonization by means of the addition of spiegel or ferro manganese, the element of phosphorus remains at nearly the same percentage as that in the original stock of molten pig-iron or scrap at the commencement of the blow. For a given percentage of phosphorus in the finished product, it follows therefore that the original stock must contain no more phosphorus than that allowed at the finish. This implies the use of practically non-phosphoric ores for the acid process. The acid-lined open hearth in this respect stands on the same footing as the acid-lined converter, and the original stock must be of known composition so far as sulphur and phosphorus are concerned, for there is no appreciable elimination of these elements, and the finished product will show a percentage equal to the average of the material charged. In the basic Bessemer process the distinctive feature of the basic vessel is a lining which resists the action of basic slags. This is usually made of dolomite, or limestone containing a small proportion of magnesia. During the earlier stages of the process of combustion the chemical reactions in the metal of the basic converter are practically identical with the reactions in the acid vessel up to the point when the combustion of the carbon has been carried to 16 CONSTRUCTION IN MILD STEEL. its limit. From this point onwards to the end of the blow the comparison with the acid process ceases, and the distinctive feature of the basic system, viz. the combustion of the phosphorus and sulphur, begins. The initial content of phosphorus can be burnt out and reduced to a desirable limit. This dephosphorization is in a similar manner the characteristic feature of the basic open hearth as compared with the acid open hearth. In both these basic processes it is, then, possible to use an initial stock of pig or scrap having a higher percentage of the undesirable elements than is possible in the acid processes ; or, in other words, a less pure ore can be utilized. An important distinction between the converter and open- hearth system lies in the fact that whereas the initial charge of pig-iron or scrap can be converted into steel by the former process in from fifteen to twenty minutes, the same transformation by the latter process occupies some nine to twelve hours. In the opinion of many authorities, this difference of time exercises an important influence on the quality of the resulting material by reason of the fact that greater opportunities are afforded in the longer process of testing the quality at frequent stages of the process. 1 , The important question, by which of the processes can the best and most reliable mild steel be produced for structural purposes, is one which would probably be answered by British, American, or German steel makers from points of view not wholly unconnected with the great commercial interests involved in the supply and use, in their respective countries, of phosphoric or non-phosphoric ores. It may, however, be generally admitted that for uniformity of quality, and general excellence of material for all purposes where great reliability is essential, the product of the open hearth, either acid or basic, stands pre-eminent. In support of this view a series of tests is appended, repre- sentative of present-day open-hearth practice in this country, and similar tests might be multiplied almost indefinitely. The tests cover, it will be seen, a large range of sections of structural material, such as are commonly employed in every-day use, and they have been exhibited at some length in order that 1 Various modifications of the open-hearth process (involving the consideration of various points of steel works practice into which it is not necessary here to enter) are known as the Bertrand-Thiel process, the Talbot process, the Twynam process, and the Monell process. ITS PHYSICAL AND CHEMICAL QUALITIES. 17 the student may be assured of the practical application of the series to the work he may have under consideration. The tests are the samples of a large quantity of mild steel employed in ordinary structural work as represented and described in Chapters III. to VI., and are representatives of the material from which the majority of the girder- work, columns, roofing, etc., represented by the illustrations in this volume, have been manu- factured. 1 The material was supplied under ordinary commercial conditions by some seven or eight firms in both England, Wales, and Scotland, and are therefore fairly indicative of present practice in open- hearth work in Great Britain. The material was supplied under the following specification All mild steel required for structural purposes is to be of British manufacture, made by the open-hearth process, either acid or basic. To be cleanly rolled and true to the thicknesses and sections specified, free from scale, laminations, cracked edges, and every other defect. The edges of all plates to be cleanly sheared, except where otherwise specified, and truly square. The surfaces of finished plates to be quite fair and flat, except where otherwise directed. All steel to be of such strength and quality that it shall not fracture under tensile stresses or with elongations less than those shown in the following table : Tensile strength in tons per Description of material. square inch. Elongation in 8-inch length. Not less than Not more than Per cent. Rivet aud bolt steel 26 30 25 Strips cut lengthwise from beams, angles, tees, channels, and bars, both square and round 26 30 20 Strips cut lengthwise or cross- wise from plates 26 30 20 1 These tests, together with the chemical analyses, were carried out by Mr. R. H. Harry Stanger, Assoc. M. Inst. 0. E., A. M. I. Mech. E., Broadway Testing Works, Westminster. C i8 CONSTRUCTION IN MILD STEEL. Samples selected for testing as specified above are to be planed parallel for a length of 8 inches. The sectional area to be fractured is, whenever possible, to be not less than J square inch. The steel must also be capable of bearing the following tests : Rivets. Pieces of rivet steel, heated uniformly to a low cherry red, and cooled in water of 82 Fahrenheit, must stand bending double in a press to a curve of which the inner diameter is equal to the diameter of the bar tested. Bending cold without fracture in the manner shown in Fig. 1, where the line AB equals one diameter of the rivet. Bending double when hot, and hammered till the two parts of the shank touch in the manner shown in Fig. 2 without fracture. Flattening of the rivet head while hot in the manner shown in Fig. 3 without cracking at the edges. The head to be flattened FIG. i. FIG. 2. FIG. 3. until its diameter is two and a half times the diameter of the shank. The shank of the rivet to be nicked on one side, and bent over to show the quality of the material. Bolts and Nuts. Pieces cut from a bar, heated uniformly to a low cherry red and cooled in water at 80 Fahrenheit, must stand bending in a press to a curve of which the inner radius is equal to the radius of the bar tested. A sample bolt is to be slightly notched and bent over to show the quality of the material. When the bolts are of sufficient length in the plain part to admit of being bent cold, they must stand bending in a press to a curve of which the inner radius is equal to the radius of the bolt tested without fracture. When the bolts are not of sufficient length in the plain part to admit of being bent cold, the screwed part should stand bending cold without fracture, as follows : ITS PHYSICAL AND CHEMICAL QUALITIES. 19 J inch diameter, and under, through an angle of 35 above J inch and under 1 inch 30 1 inch and above 25 Beams, angles, channels, tees, etc. Strips cut lengthwise, 1 in. wide, heated uniformly to a low cherry red and cooled in water of about 80 Fahrenheit, must stand bending double in a press to a curve of which the inner radius is one and a half times the thickness of the steel tested. This steel is also to stand such forge tests, both hot and cold, as may be sufficient in the opinion of the inspector to prove soundness of material and fitness for the work. Plates. Strips cut lengthwise or crosswise, 1J inch wide, heated uniformly to a low cherry red, and cooled in water of about 80 Fahrenheit, must stand bending double in a press to a curve of which the inner radius is one and a half times the thickness of the steel tested. Such other tests as may be considered necessary by the inspector to determine the quality of the steel plates are also to be carried out. Samples will be taken as often and in such a manner as the inspector may consider necessary, and in the event of a sample proving unsatisfactory, it will be in the power of the inspector to reject the whole of the steel represented by such sample. Steel Castings. Steel castings to be sound, true, and clean, and free from honeycomb. Pieces of 1 inch square, taken from each cast or blow of steel, to have a breaking strain of 26 tons per square inch, with an elongation of not less than 10 per cent, in a length of 8 inches. A test piece, 1 inch square, shall be capable of bending cold in a press or over a slab or block with a fair surface, with the edge with a rounding of 1J inch radius, through an angle of 45. The castings to be thoroughly annealed by being put in a special furnace and carefully heated up to a bright cherry-red and then allowed to cool gradually. The castings are not to be taken out of the furnace until sufficiently cool to admit of them being easily handled without covering. The duration of time from heating to cooling to be not less than seven days. The castings to be afterwards slung and tested by hammering to ensure soundness. All castings to be chipped and dressed to remove roughness or inequalities. All test pieces required are to be properly shaped and prepared for testing at the contractors' cost. 20 CONSTRUCTION IN MILD STEEL. TABLES OF THE RESULTS OF PHYSICAL TESTS ON THE ULTIMATE TENSILE STRENGTH AND ELONGATION OF OPEN-HEARTH MILD STEEL FOR ORDINARY STRUCTURAL WORK. TABLE No. 4. TESTS ON MILD STEEL ANGLES. No. of test. Description of section tested. Ultimate tensile strength. Tons per sq. inch. Ultimate elonga- tion in 8 inches. Per cent. Remarks. Mild steel angles. 1 2 9" X 31" x 1" 8" X 3f x f " 28-0 30-2 26-0 22-0 Bending tests satisfactory 3 99 99 29-1 26-0 9 99 4 99 99 30-0 29-0 91 99 5 7" x 4" X f" 29-9 27-0 6 99 99 28-7 28-0 99 7 7" X 31" X f 28-7 26-0 99 99 8 7" X 31" X 1" 28-5 25-0 9 10 7" X 3" X f 99 99 30-8 30-7 25-0 26-0 {Excess strength slight, elongation good, so allowed 11 6 i" x 41" x f " 30*1 25-0 Bending tests satisfactory 12 6" X 6" X U" 27'2 23-0 13 6" X 6" X |" 26-6 23-0 14 6" X 4" X 1" 28-1 26-0 H 15 99 99 28-6 24-0 99 9 16 6" X 31" x l" 27-32 29-5 99 9 17 6" X 3" X f 26-3 23-0 99 9 18 9> 99 28-1 27-5 99 9 19 9 99 31-3 23-0 Somewhat above the speci- fied maximum, but the elongation being good, the test was allowed 20 6" x 3" X f" 28-7 27-0 Bending tests satisfactory 21 99 99 28-7 27-0 99 99 22 99 99 28-6 24-0 99 99 23 99 99 28-4 22-0 99 99 24 5" X 5" X f " 279 27-0 99 9> 25 5" X 5" X f 29-7 25-0 26 5" X 31" X 1" 29-9 25-0 99 99 27 3" NX Ql" \S 3" X <% X 29-8 25-0 99 99 28 99 99 29-6 23-0 99 99 ITS PHYSICAL AND CHEMICAL QUALITIES. 21 No. of test. Description of section tested. Ultimate tensile strength. Tons per sq. inch. Ultimate elonga- tion in 8 inches. Percent. Remarks. Mild steel angles. 29 5" X 31" X f" 29-8 28-0 Bending tests satisfactory 30 55 55 28-6 27-0 55 31 55 11 28-1 24-0 55 32 29-2 25-0 55 55 33 55 >-, 29-5 27-0 55 55 34 29-4 I 24-0 55 55 35 5" x 3" X f" 29-4 26-0 5 5> 36 55 ,, 29-6 26-0 55 M 37 41" x 4" x f 28-6 25-0 5 5 38 ! 28-7 24-0 55 55 39 41" x 31" X f 40 4" x r x f" 26-8 28-0 29-1 29-0 5> 55 55 55 41 29-3 26-0 55 J) 42 4" x 4" X f 27'7 29-0 5? 55 43 j 55 30-3 24-0 >5 55 44 55 55 27-4 32-0 5 55 45 4" X 4" X 1" 28-2 30-0 55 JJ 46 55 ) 29-7 28-0 55 55 47 4" X 31" x f " 28-9 26-0 55 55 48 4" X 4" X 1" 29-9 27-0 >5 55 49 55 55 28-2 26-0 55 55 50 4" x 3" X f 29-2 23-0 55 55 51 4" X 3" X |" 27-5 25-5 5 55 52 55 55 27-7 26-0 55 55 53 55 55 27-9 21-0 55 55 54 55 55 27-4 34-0 55 55 55 55 55 27-7 26-0 )5 5 56 55 55 28-0 23-0 51 55 57 55 55 28-2 27-0 55 55 58 55 55 27-8 24-0 J5 55 59 55 55 28-8 27-0 55 55 60 55 55 30-0 25-0 5> ' 61 4" X 3" X f 28-3 25-0 55 55 62 55 5 28-2 29-0 55 55 63 55 5 28-9 25-0 55 55 64 ! 9Q.7 55 5 4* 23-5 J5 55 65 55 15 27-7 290 55 5) 66 55 55 28-2 27-0 55 5 67 55 55 27-8 29-0 55 5 68 4" X 3" X A" 29-0 21-5 55 5* 69 3f X 31" X f" 29-8 27-0 55 55 70 J' 55 29-1 25-0 55 55 71 55 }5 28-7 29-0 55 55 72 >? 5 27-7 29-0 55 5 22 CONSTRUCTION IN MILD STEEL. No. of test. Description of section tested. Ultimate tensile strength. Tons per sq. inch. Jltimate elonga- tion in 8 inches. Per cent. Remarks. Mild steel angles. 73 3" X 3J" X f" i 27-8 1 26-0 Bending tests satisfactory 74 28-7 29-0 75 27-7 29-0 76 3J" X 3" x i" 29-0 26-5 35 55 77 55 55 27-8 30-0 55 55 78 55 55 28-2 32-0 53 55 79 55 55 28-0 25-0 80 55 55 261 30'0 55 33 81 55 55 26-5 30'0 55 55 82 55 35 27-4 28'0 55 83 ,, 26-3 28'0 55 55 84 35 55 26-7 31'0 55 55 85 35 55 26-6 28'5 55 35 86 35 35 26-7 28-5 33 35 87 35 55 27-6 32'0 88 28-6 25'0 55 55 89 55 55 28-9 27-5 55 33 90 55 3' 30-0 25'0 33 55 91 29-9 28-0 3' 33 92 33 35 28-7 27-0 33 33 93 55 55 29-3 26-0 35 53 94 55 55 29-1 25-0 35 55 95 55 55 30-0 24-0 55 55 96 53 55 291 27'0 5' -5 97 55 33 30-1 25-0 Excess strength slight, elongation good, so allowed 98 99 3f X 31" X i" si" x si" x f 30-3 27-6 25-0 27-0 Round backed Bending tests satisfactory 100 35 5> 28-5 26-0 55 55 101 55 55 28-2 27-0 33 35 102 55 33 28-4 28-0 33 53 103 Ol" v> q" v> 1" o^ X o X ^ 28-5 24-0 55 55 104 33 33 30-2 24-0 55 55 105 33 35 28-1 28-0 '5 3) 106 3f X 3" X f 29-1 26-0 55 55 107 99 99 29-1 26-0 55 35 108 3" X 3" X |" 27-0 23-0 55 3? 109 35 55 26*5 29-0 33 31 110 55 35 29-2 27-0 35 55 111 112 35 53 55 35 30-7 30-9 27*0 25-0 {Excess strength slight, elongation good, so allowed 113 35 ,3 27-9 25-5 Bending tests satisfactory ITS PHYSICAL AND CHEMICAL QUALITIES. No. of test. Description of section tested. Ultimate tensile strength. Tons per sq. inch. Ultimate elonga- tion in 8 inches. Percent. Remarks. Mild steel angles. 114 3" x 3" x y 28-7 27-5 Bending tests satisfactory 115 55 55 27-2 27-0 51 116 55 55 27-7 26-0 51 117 29-4 27-0 55 118 3" X 3" X f" 27'2 26-0 55 119 55 55 28-2 28-0 15 120 55 55 28'9 29-0 15 55 121 55 55 29-8 29-0 55 51 122 55 55 27-5 28-0 5 55 123 55 55 28-5 25-0 55 55 124 55 55 29-1 27-0 55 55 125 3" X 2J" X f" 29-8 25-0 55 55 126 26-8 25-0 15 55 127 26-4 22-5 55 ., 128 3" X 2f x A" 26-1 33-0 55 55 129 2f x 2f x y 28-4 26-0 15 55 130 21" X 2J" X f 27-0 29-0 55 131 27-3 30-0 55 55 132 55 5) 29'7 27-2 55 55 133 55 55 27-0 25-0 51 55 134 55 55 28-9 26-0 55 55 135 2" X 2f x &" 29-4 21-0 55 5 136 55 55 28'9 22-0 55 , 137 55 55 28-7 23-0 55 5 138 55 55 29-6 20-0 1 139 55 55 30-0 28-0 55 1 140 21" X 21" X y 28-9 22-0 1, 1 141 2f X 2f X f 29-0 20-0 11 | 142 5> 55 29-3 25-0 5 51 143 >5 15 28-3 24-0 15 15 144 >5 55 28*1 24-0 55 5 145 Ol" v f > 1 " V 5 " 4 *1 **4 * 16 28-6 21-0 55 5 146 55 55 27-5 22-0 55 5 147 55 55 28-7 21'0 55 , 148 55 55 27'3 25-0 ,, 5 149 55 55 28-8 22-0 }> 5 150 2" x 2" X A" 31-1 22-0 Excess strength, but elongation good, so allowed 151 152 55 55 0" v 1 1" V 3 " A J- 2 A g 26-0 30'7 30-0 20-0 Bending tests satisfactory Excess strength slight, elongation good, so allowed CONSTRUCTION IN MILD STEEL. TABLE No. 5. TESTS ox MILD STEEL TEES. Ultimate Ultimate "NY> of tensile elonga- llU. OI test. Description of section tested. strength. Tons per tion in Remarks. 8 inches. ! sq. inch. Percent. Mild steel tees. 1 6" X 4" X i" 27-6 j 26-0 Bending tests satisfactory 2 6" X 3" X |" 28-6 27-0 5J 55 3 55 55 27-4 29-0 55 55 4 55 55 28-1 27-5 55 55 ' Somewhat above the 5 6 ;; 55 55 31'3 30-5 23-0 28-0 specified maximum, but the elongation being good the test was allowed. 7 55 26-85 31-5 Bending tests satisfactory 8 55 29-7 27'0 55 55 9 55 55 29-3 25-0 55 55 10 ^ 55 29-4 28-0 55 55 11 55 55 31'4 22-0 Somewhat above the specified maximum, but the elongation being good the test was allowed. 12 55 55 29-5 31'0 Bending tests satisfactory 13 5 55 28-6 31-0 55 5 14 55 27-6 32-0 55 15 55 55 27-6 25-0 55 55 16 6" X 3" X f" 30-7 25-0 Somewhat above the specified maximum, but the elongation being good the test was allowed. 17 55 27-4 27-5 Bending tests satisfactory 18 55 55 29-5 26-0 55 55 19 55 55 29-6 27-0 55 55 20 55 55 27-1 29-0 55 55 21 5"X 3" X f" 29-3 29-0 55 *5 22 5) 55 29-3 26-0 55 J> 23 55 55 29-3 31-0 24 55 55 29-5 28-5 55 >5 25 5"X 2f X f 28-7 27-0 55 55 26 55 55 29-7 25-0 55 5 27 55 55 27-3 31-0 15 55 28 55 55 28-5 28-0 55 57 29 55 55 29-4 29-0 5> 55 ITS PHYSICAL AND CHEMICAL QUALITIES. No. of test. Description of section tested. Ultimate tensile strength. Tons per sq. inch. Ultimate elonga- tion in 8 inches. Per cent. Remarks. Mild steel tees. 30 5"x2l"xf" ! 29-2 21-5 Bending tests satisfactory 31 4" X 4" X J" 29-7 28-5 ., 32 jj jj 28-8 29-5 jj j 33 jj jj 28-9 28-0 JJ 5J 34 JJ )5 29-3 30-0 JJ J) 35 1J JJ 28-2 27-0 JJ J> 36 JJ JJ 295 35-0 JJ J) 37 27-8 25-0 JJ JJ 38 27-3 32-0 JJ JJ 39 JJ JJ 27-5 330 JJ U 40 4" X 4" X f 29-7 26-0 JJ ) 41 29-3 27-5 JJ JJ 42 jj jj 28-9 28-0 JJ JJ 43 %j jj 27-7 28-0 JJ J* 44 jj jj 29-1 27-5 JJ JJ 45 jj jj 27-3 30-0 JJ JJ 46 jj jj 27-5 32-0 J1 J> 47 jj jj 27-1 27-0 5J JJ 48 jj jj 27-6 28*0 JJ JJ 49 jj jj 27-7 280 JJ U 50 jj jj 27-6 27-0 JJ J> 51 jj j j 27-6 27-0 JJ J) 52 jj jj 28-6 24-0 JJ JJ 53 29-2 27-0 JJ JJ 54 jj jj 30-3 22-0 JJ JJ 55 jj j 29-4 25-0 JJ JJ 56 4" X 31" X 1" 28-3 26-0 JJ JJ 57 4" X 3" X |" 29-3 27-5 JJ J) 58 2f X 21" X f 27-2 27-5 JJ JJ 59 nil v -1 1 it ^ 3 " & X IgT X YQ 28-7 15-0 Broke on the datum point 60 30-0 21-5 The following test, No. 60, quite satisfactory, bend- ing tests satisfactory 26 CONSTRUCTION IN MILD STEEL. TABLE No. 6. TESTS ON MILD STEEL FLATS. No. of tent. Description of section tested. Ultimate iMMtti strength. Tons per square inch. Ultimate elongation in 8 inches. Per cent. Remarks. Mild steel flats. 1 2 i8f x y 11 29-4 29-2 29-0 29-5 Bending tests satisfactory 11 ,) 3 16" x y 28-9 29-0 11 11 4 11 28-8 28-0 11 11 5 11 27'7 28-0 11 11 6 11 28-0 30-0 11 ,, 7 16" X f 29-0 27-0 11 11 8 29-7 27-0 11 11 9 M 28-6 25-0 11 11 10 11 28-0 29-0 11 11 11 14" X f" 30-5 26-0 11 11 12 27-8 28-0 11 11 13 14" X y 27'i) 29-0 11 11 14 11 28-7 26-0 11 11 15 11 29-7 26-0 11 11 16 11 28-9 29-0 11 11 17 11 28'9 28-0 11 11 18 11 29-7 27-0 11 11 19 14" X f" 28'8 28-0 11 11 20 12" X f" 28-5 28-0 11 11 21 > 29-8 25-0 11 11 22 12" X ff 27-4 28-0 11 11 23 12" X y 31-2 23-0 Although the tensile strength is above that specified, the elongation and bending tests are satisfactory. The mate- rial was accepted 24 12" X J" 25'2 28-0 Tensile strength below that specified, but fur- ther tests were satisfac- tory, so allowed 25 12" x y 28'1 28-5 Bending tests satisfactory 26 11 26-0 30-0 > 27 11 28'7 290 11 it 28 11 27'9 25-5 11 11 29 11 26'8 29-0 11 it ITS PHYSICAL AND CHEMICAL QUALITIES. 27 No. of tost. Description of section tested. Ultimate tonsil.- strength. Tons per square inch. Ultimate elongation in 8 inches. Per cent. Remarks. Mild steel flats. 30 12" X |" 31-3 21-0 Although the tensile strength is above that specified, the elongation and bending tests are satisfactory. Material / was accepted 31 1 1" X f 27-2 28'5 Bending tests satisfactory 32 ii" x y 27-0 32-0 33 11 28-1 31-0 > 34 Jf 29-5 30-0 85 M 29-3 27-0 36 10" x r 30-0 29-0 37 10" x f 29-5 28-0 >j > 38 n 29-9 29-0 ? i > 39 N 28-7 26-0 40 28-5 28-0 41 5J 28-4 27-0 j 42 9" X 1" 29-5 21-0 > 43 9" x f " 30-6 29-0 > 44 9" X |" 28-3 27'0 45 9" X f 28'6 250 i 46 8^ X |" 27-2 27-0 47 M 27-4 29-0 48 8f X f " 29-0 26-5 . 49 N 27-4 2D-0 50 81" x i" 29-0 26-0 n 51 30-0 30-0 > > 52 N 30-4 26-0 53 gl" x ^" 29-6 29-0 ,, 54 3!" x !/' 28-0 30-0 > n 55 8" X |" 27'2 24-0 > 56 ii 26'6 24-0 57 8" X ^" 30-5 26-0 > n 58 7i" X |" 27-0 31-0 j> J> 59 7f X |" 27-0 31-0 60 f 7" w " / X g 27-2 26-0 61 7" X |" 28-5 29'0 > 62 7" X |" 28-6 33-0 63 28-5 28-0 64 n 29-7 22-0 65 N 30-2 27-0 66 61" X f 26-7 28-0 n > 67 6" X f 28-8 28-0 68 6" X |" 26-7 31-0 > 28 CONSTRUCTION IN MILD STEEL. No. of test. Description of section tested. Ultimate TTI*.: tpnsilp Ultimate tensile elongation strength. . g f ^ Ions per , p f square inch. Per cent - Remarks. Mild steel flats. 69 Kl vx 1" 2 ^^ 2 27-2 30'0 Bending tests satisfactory 70 51" x -Z_" 27-7 27-0 71 5" X 1" 27-6 25-0 11 11 72 5" X " 28-8 26'0 n 11 73 5" X &" 31-2 20-0 The forge tests being satisfactory, and, having in view the thinness of the bar, the material was accepted 74 5" X % 27-1 23-0 Bending tests satisfactory 75 4" x |" 28-5 25-0 11 11 76 4" X f 29-7 24-0 11 11 77 3" X H" 30-0 21-0 11 11 78 3f X If 28-4 27-0 11 11 79 ol// v L* 2 * 2 28-0 28-0 11 11 80 28-2 25-0 11 11 81 11 28-2 24-0 11 11 82 11 30-0 23-0 11 11 83 28-6 28-0 11 11 84 M 28-7 25-0 11 11 85 >5 27-8 28-0 11 19 86 11 27-7 26-0 11 11 87 28-6 24-0 11 5 88 31" X f" 29-7 22-0 11 11 89 3" X 1" 28-3 28-0 91 11 90 3" X I" 26-4 25-0 11 11 91 3" X f 29-2 24-0 11 11 92 3" X f 29-5 25-0 11 11 93 11 29-4 230 11 11 94 19 28-6 22-0 11 11 95 11 29-1 21-0 11 11 96 11 29-9 20-0 11 11 97 3" X f 29-0 24-0 J 11 98 n 28-6 28-0 ' 91 99 2J" X |" 27-7 23-0 11 11 100 2f X f " 29-3 21-0 11 11 101 ol" V, 1" "^ x\ 7T 30-1 20-0 11 11 102 2i" X f" 26-0 25-0 11 11 103 2 o 31*4 31-0 Somewhat above the speci- fied maximum, but the elongation being good the test was allowed 104 21" v " 27-9 26-0 Bending tests satisfactory 105 4" X F 27'3 24-0 11 11 ITS PHYSICAL AND CHEMICAL QUALITIES. 29 Ultimate Ultimate No. of test. Description of section tested. strength. Tons per square inch. elongation in 8 inches. Per cent. Remarks. Mild steel flats. 106 2" x 1" 29-0 28'0 Bending tests satisfactory 107 2" x f" 28-1 27-0 108 26-7 27-0 109 if x V 28-2 27-0 TABLE No. 7. TESTS ON MILD STEEL CHANNELS. No. of test. Description of section tested. Ultimate tensile strength. Tons per sq. inch. Ultimate elonga- tion in 8 inches. Per cent. Remarks. Mild steel channels. 1 15" x 4" @ 42 Ibs. 29-3 25-0 Bending tests satisfactory 2 12" x 31" @ 31 Ibs. 29-3 24-0 jj jj 3 10" X 4 X f 26-6 24-0 > jj 4 JJ JJ 27-0 25-0 j 5 10" x 4" X 1'" 30-3 30-0 j> >j 6 10" X 3" @ 26 Ibs. 27-8 28-0 jj 7 jj j 28-3 26-0 jj jj 8 9" X 3| X \ 29-5 26-0 jj jj 9 jj jj 28-2 26-0 jj jj 10 9" X 3" @ 15-45 Ibs. 29-9 25-0 11 jj jj 30-1 26-0 jj jj 12 jj 29-8 27-0 jj 13 J> U 29-5 27-0 jj jj 14 JJ JJ 29-6 27-0 jj jj 15 JJ J' 29-5 25-0 jj jj 16 JJ JJ 29-4 25-0 jj jj 17 8"X3| X l" 30-2 22-0 jj jj 18 29-5 25-0 19 7}" X 2T X 201 Ibs. 26-3 30-0 n jj 20 7f X 2|" " 28-3 21-0 jj jj 21 )} 28-7 24-0 jj jj 22 jj 28-1 23-0 jj 23 7f X 2f x 151 Ibs. ! 26'0 28-0 jj jj 24 ! 29-0 24-0 u j> CONSTRUCTION IN MILD STEEL. Ultimate Ultimate No. of test. Description of section tested. tensile strength. Tons per elonga- tion in 8 inches. Remarks. sq. inch. Per cent. Mild steel channels. 25 7" X 3f X " 29-1 27-0 Bending tests satisfactory 26 55 55 29-8 22-0 55 55 27 55 55 29-0 26-0 55 55 28 55 55 28*3 24-0 55 55 29 55 55 29-5 24-0 55 55 30 55 55 28-8 28-0 >5 55 31 55 55 29-6 21-0 J5 55 32 5) 55 28-3 25-0 55 55 33 >5 5 30-0 23-0 55 55 34 7" X 2if" X iV' X y 28-1 23-0 5 55 35 6" X 3" X J" 28-7 29-0 " TABLE No. 8. TESTS ON MILD STEEL ROLLED JOISTS. No. of test. Description of section tested. Ultimate tensile strength. Tons per sq. inch. Ultimate elonga- tion in 8 inches. Per cent. Remarks. Mild steel rolled joists. 1 16" x 6" @ 62 Ibs. 28-6 30-0 Bending tests satisfactory 2 14" X 6" @ 57 Ibs. 30-6 25-0 55 55 3 5 55 28-2 27-0 55 55 4 14" X 6" @ 46 Ibs. 27-4 21-0 55 '5 5 27-4 30-0 ) 55 6 13" X 5" @ 40 Ibs. 29-7 22-0 55 55 7 > J5 29-4 24-0 55 55 8 >5 55 29-6 23-0 5 55 9 55 55 29-6 22-0 55 55 10 12" x 6" @ 54 Ibs. 29-7 23-0 55 55 11 55 55 28-4 24-0 55 55 12 55 55 28-3 25-0 55 55 13 28-0 22-0 55 55 14 55 55 28-8 28-0 55 15 15 5 55 28-9 28-0 55 55 16 55 28-8 24-0 55 55 17 ., 28-6 21-0 55 55 ITS PHYSICAL AND CHEMICAL QUALITIES. 31 No. of test. Description of section tested. Ultimate tensile strength. Tons per sq. inch. Ultimate elonga- tion in 8 inches. Per cent. Remarks. Mild steel rolled ioists. 18 i 12" x 6" @ 54 Ibs. 29-3 28-0 Bending tests satisfactory 19 11 11 28-3 22-0 11 11 20 11 11 29-4 24-0 11 11 21 11 11 29-0 24-0 n >i 22 11 11 28-0 28-0 11 11 23 12" X 6" @ 44 Ibs. 28-2 29-0 11 > 24 > 11 28-6 29*0 11 11 25 12" X 5" @ 32 Ibs. 28-6 26-0 11 11 26 11 28-2 23-0 i 11 27 27-7 25-0 11 11 28 i -,-, 11 28-8 28-0 11 11 29 10" x 6" @ 45 Ibs. 27-7 31-0 11 11 30 11 ' 27-7 29-0 11 11 31 > ?5 28-8 30-0 11 11 32 11 " 29-1 30-0 11 11 33 5 ' 27-8 29*0 11 11 34 5 28-1 35-0 11 11 35 28-2 33-0 11 11 36 > 27-7 28-0 11 11 37 r 5 27-8 30-0 11 11 38 > 5 27-8 29-0 11 11 39 > 27'5 30-0 11 11 40 > > 27-2 31-0 11 11 41 ) 27-5 32-0 11 11 42 >J 5> 27-8 34-0 11 11 43 30-0 27-0 11 11 44 ?> 29-3 27'0 11 11 45 > 27-1 26-0 11 11 46 > > 27-3 29-0 n 11 47 J 26-7 30-0 11 11 48 1> > 26-6 27-0 11 11 49 10" x 5" @ 33 Ibs. 27-4 30-0 11 11 50 27-3 29-0 11 11 51 10" X 5" @ 29 Ibs. 30-5 22-0 11 11 52 ?> 30-2 24-0 11 11 53 )) ) 29-8 27-0 11 11 54 9" X 7" @ 58 Ibs. 28-2 28-0 11 11 55 > '27-8 28-0 11 11 56 5 26-2 34-0 11 11 57 8" X 5" @ 30 Ibs. 29-5 26-0 11 11 58 8" X 4" @ 20 Ibs. 29-1 24-0 11 11 59 7" X 3f @ 16 Ibs. 27-0 23-0 11 60 ?> > 28-2 22-0 11 > 61 6" x 5" @ 25 Ibs. 29-1 29-0 11 11 CONSTRUCTION IN MILD STEEL. No. of test. Description of section tested. Ultimate tensile strength. Tons per sq.inch. Ultimate elonga- tion in 8 inches. Percent. Remarks. Mild steel rolled joists. 62 6" x 3" @ 13 Ibs. 30-0 23-0 Bending tests satisfactory 63 J 29-2 27-0 J V 64 29-8 30-0 > 65 30-8 29-0 It 5> 66 5 } 28-7 22-0 5 5 67 J 28-4 26-0 1 1 68 5" x 41" @ 18 Ibs. 31-9 24-0 M ?> 69 28-6 22-0 H ' 70 5" X 3" @ 15 Ibs. 30-0 26-0 > 71 29-9 23-5 > 72 5" x 3" @ 10 Ibs. 29-5 23-0 > 5J TABLE No. 9. TESTS ON MILD STEEL ZED-ANGLES. No. of test. Description of section tested. Ultimate tensile strength. Tons per sq. inch. Ultimate elonga- tion in 8 inches. Per cent. Remarks. Mild steel zeds. 1 8" X 3J" X 3f X F 29-5 21-0 Bending tests satisfactory 2 30-0 22-0 > )? 3 28-8 23-0 5 > 4 27-8 23-0 5 29-5 22-0 > > 6 296 23-0 1* 7 29-5 22-0 1) > 8 29-8 22-0 J 9 6" X 3J" X 3" X f 30-0 20-0 > 10 > >< 29-6 23-0 11 ?> 28-9 21-0 > 1) ITS PHYSICAL AND CHEMICAL QUALITIES. 33 TABLE No. 10. TESTS ON MILD STEEL TROUGH FLOORING. No. of test. Description of section tested. Ultimate tensile strength. JJSS Ultimate elonga- tion in 8 inches. Percent. Remarks. Mild steel trough 1 flooring plates. I Specimens represent-) } ing the material 5 28-6 27'0 Bending tests satisfactory 2 n 28-8 24-0 3 j> 28-3 28-0 4 28-7 26-0 5 > 30-0 29-0 ?> > 6 > 29-2 27-0 7 28-9 31-0 8 28-7 28-0 > 9 28-8 30-0 > )? 10 j 28-7 26-0 i> ? 11 5> > 28-4 24-0 > 12 28-5 27-0 > 13 30-1 27-0 14 29-6 25-0 TABLE No. 11. TESTS ON MILD STEEL BOUND BARS. No. of test. Description of section tested. Ultimate tensile strength. Tons per sq. inch. Ultimate elongation in 8 inches. Per cent. Remarks. Mild steel round bars. 1 6^" diameter 29-2 24-0 Bending tests satisfactory 2 O )) 29'4 22-0 )> 3 5-" 28'4 26-0 4 5 27-3 26-0 5 5) 28-0 25-0 6 29-7 24-0 7 l 28-4 26-0 8 27-3 26-0 9 J> > 28-0 25-0 10 29-7 24-0 34 CONSTRUCTION IN MILD STEEL. No. of test. Description of section tested. U teS e Ultimate S i Remarks. Mild steel round bars. 11 4f" diameter 28-4 26-0 Bending tests satisfactory 12 4" ,, 27-6 30-0 H 11 13 11 > 29-1 26-0 n u 14 11 ?> 29-5 25-0 11 11 15 > 27-5 27-0 11 11 16 11 11 27-2 36-0 11 it 17 11 27-6 30-0 11 11 18 4" 30-0 23-0 11 tt 19 3f 30-3 26-0 11 it 20 > 28-4 24-0 11 i) 21 5' 28-8 25-0 11 11 22 31" "4 11 28-4 28-0 11 11 23 s|" 28-2 21-0 11 11 24 # 28-1 24-0 11 it 25 99 " 31-0 15-0 11 11 26 j> 99 28-2 22-0) Further tests from the 27 19 59 28-6 23-0 bars from which No. 25 28 99 99 27-8 21-5) was taken 29 11 29-3 24-0 Bending tests satisfactory 30 > 29-1 25-0 11 n 31 5> 11 30*0 27-0 n 32 5> } 29-8 28-0 11 11 33 Q" * 28-6 26-0 11 n 34 >j i) 29*3 27-0 11 11 35 29-2 28-0 11 11 36 11 _ > 30-0 26-0 11 37 > 11 29-1 26-0 }> i> 38 30-0 25-0 n 11 39 29-7 28-0 40 > J5 29-3 21-0 11 11 41 > J 28-8 27-0 n 11 42 > ) 30-0 25-0 11 11 43 11 11 28-7 27-0 11 5> 44 2f 28-8 30-0 it 11 45 > > 291 31-0 11 11 46 11 11 29-3 28-0 11 11 47 it 11 29-0 26-0 11 11 48 11 11 29-2 27-0 11 11 49 11 11 28-9 28-0 11 11 50 05" ^8 > 29-4 31'0 11 11 51 of" ^2 28-2 24-0 11 11 52 > J> 27-9 25-5 n 11 53 ) 29-0 25-0 11 ITS PHYSICAL AND CHEMICAL QUALITIES. 35 No. of test. Description of section tested. Ultimate tensile strength. Tons per sq. inch. Ultimate elongation in 8 inches. Per cent. Remarks. Mild steel round bars. 54 2J" diameter 27-9 24-0 Bending tests satisfactory 55 28-1 25-0 > 56 ) 11 28-9 26-0 Tests Nos. 51 to 65 in- 57 ,, 28-5 22-0 clusive are the tests for 58 30-5 22-0 the tie rods shown in 59 28-4 25-0 Figs. 369-372. See also 60 28-4 25*0 test No. 67. 61 }> J> 27-3 23-0 Bending tests satisfactory 62 > 5J 27-0 23-0 63 26-6 32-0 > 64 )> 26-5 31-0 65 27-2 32-0 > 66 n\n 4 " 29-8 26-0 ?J 67 * >J 29-7 27-0 j > 68 If" 29-0 26-0 69 11 )) 29-8 26'0 70 ,, 29-7 27-0 > 71 ) 29-5 27'0 72 l 28-4 26-0 73 Ig 29-3 23-0 74 If" 28-8 23-0 > 75 > 30-0 24-0 i> 76 If 27-9 31-0 77 r 26-8 28-0 > > 78 1 27-1 32-0 > jj TABLE No. 12. TESTS ON MILD STEEL KEGTANGULAR BARS. No. of test. Description of section tested. Ultimate tensile strength. Tons per sq. inch. Ultimate elongation in 8 inches. Per cent. Remarks. Mild steel rectan- gular bars. ; 1 7" X 4" rectangular 28-0 29-0 Bending tests satisfactory 2 28-2 31'0 > > 3 ' 28-3 30-0 4 28-8 31-0 > CONSTRUCTION IN MILD STEEL. No. of test. Description of section tested. Ultimate tensile strength. Tons per sq. inch. Ultimate elongation in 8 inches. Per cent. Remarks. Mild steel rectan- gular bars. 5 7" X 4" rectangular 28-3 32-0 Bending tests satisfactory 6 6" X 4" 28-7 28-0 5> 1 7 >j 27-7 28-0 5> 8 4f square 27-9 28-0 9 4" square 30-0 28-0 10 " 27-7 24-0 11 N 27-0 20-0 12 5" X 2f 27-7 31-0 > > 13 3|" square 29-7 26-0 14 3|" square 28-4 22-5 J 15 27-9 23-0 5) J 16 M 27-0 22*5 17 n 29-8 27'0 18 3" square 29-7 26-0 i> > 19 2|" square 29'4 24-0 20 M 29-6 22*0 ,, ,, 21 21" square 29-5 27-0 22 3" X If 28-0 22-0 )) )' 23 2f square 29-5 26-0 > > 24 n 29-8 25-0 n 25 2" square 27-5 27*0 > ' 26 27 If square 31" X If 26-4 28-0 30-0 27-0 TABLE No. 13. TESTS ON MILD STEEL PLATES. Ultimate Ultimate No. tensile elonga- of Description of section tested. strength. tion in Remarks. test. Tons per 8 inches. sq. inch. Per cent. Mild steel plates, tested lengthways of 1 the plate, f thick 27-1 29-0 Bending tests satisfactory 2 > 27-1 34-0 > 3 i) 27-6 29-0 > 4 27-5 29-0 ) 5 n 26-9 27-0 i? >> ITS PHYSICAL AND CHEMICAL QUALITIES. 37 No. of test. Description of section tested. Ultimate tensile strength. Tons per sq. inch. Ultimate elonga- tion in 8 inches. Per cent. Remarks. Mild steel plates, tested lengthways of the plate. 6 f" thick 28-0 28-0 Bending tests satisfactory 7 ti 28-3 31-0 11 11 8 f" thick 29-3 27'0 n 11 9 it 28-5 27-0 11 11 10 27-4 26-0 it 11 11 11 28-3 29-0 11 11 12 H 28-0 29-0 11 n 13 29-2 29-0 11 11 14 28-1 33-0 11 15 * !> 26-6 32-0 11 16 27-8 31-0 11 >i 17 28'7 27-0 ?i 11 18 11 28-1 30-0 it i* 19 11 27-4 26-0 11 11 20 11 27-7 30-0 11 11 21 J" thick 29-5 26-0 11 11 22 it 26-9 26-0 11 >} 23 11 28-0 27-0 11 ! 24 29-1 27-0 11 ! 25 n 28-3 27-0 11 1* 26 11 29-1 29-0 27 11 28-7 28-0 11 1' 28 29-6 25-0 11 11 29 it 27-8 32-0 11 11 30 27-7 26-0 ! Chequer or ribbed \ 31 plates for flooring [ 28-6 31-0 11 11 4" thick ) 32 M 28-4 27-0 11 11 33 M 30-7 26-0 11 11 34 29-4 30-0 35 w 29-1 26-0 11 11 36 M 28-1 26-0 11 11 37 29-0 28-0 38 f thick 28-2 27-0 11 11 39 11 29-4 26-0 11 ! 40 11 26-6 31-0 11 '1 41 n 28-6 28-0 11 '1 42 ~ 4 28-2 23-0 11 11 43 H 28-5 27-0 It 11 44 w 28-3 26-0 It 1 ' 45 11 28-4 24-0 11 51 CONSTRUCTION IN MILD STEEL. No. of test. Description of section tested. Ultimate tensile strength. Tons per sq. inch. Ultimate elonga- tion in 8 inches. Per cent. Remarks. Specimens Nos. 46 to 78 Mild steel plates, tested cross ways of are from similar plates to those represented by the plate. Nos. 1 to 30. 46 f thick 28-0 25-0 Bending tests satisfactory 47 55 28-1 27-0 >5 48 55 27-8 29-0 ^ 49 27-0 30-0 ,, J? 50 55 27-9 24-0 5' 51 f " thick 28-7 26-0 > 55 52 55 28-2 26-0 > 55 53 55 28-7 26-0 55 54 ,, 28-3 26-0 55 55 55 28-6 29-0 5 56 28-0 29-0 > 5 57 ) 26-7 25-0 55 58 55 27-3 28-0 >5 55 59 >5 28-0 26-0 >' 60 27-3 25-0 5 >5 61 55 28-2 26-0 5 15 62 " thick 27-0 20-0 55 5 63 55 27-4 28-0 55 5 64 55 29-1 27-0 5 5 65 55 29'3 24-0 ,, 66 55 29-5 25-0 5 55 67 55 27-8 26-0 >5 55 68 55 28-2 27-0 55 ' 69 w 29-3 24-0 55 70 55 262 26'0 5 55 71 55 27-7 26-0 55 55 72 55 28-3 29-0 5? 5) 73 II 29-3 24-0 55 55 74 55 26-2 26'0 55 > 75 55 27-7 26-0 5 55 76 55 28-3 29-0 55 *5 77 55 27-8 27-0 55 78 M 29-0 25-0 55 11 79 f thick 28-5 25-0 5) 55 80 55 30-1 27-0 >J )> 81 5) 27-2 26-0 15 82 w 28-6 25-0 5* 5) 83 55 27-9 25-0 1) 84 55 29-1 26-0 >5 5 85 55 29-2 22-0 55 55 86 27-9 22-0 55 55 ITS PHYSICAL AND CHEMICAL QUALITIES. 39 No. of test. Description of section tested. Ultimate tensile strength. Tons per sq. inch. Ultimate elonga- tion in 8 inches. Per cent. Remarks. Mild steel plates, tested crossways of the plate. 87 f" thick 28-5 25-0 Bending tests satisfactory 88 99 28-8 26-0 99 99 89 99 28-5 25-0 99 99 90 / 30-1 27-0 99 99 91 if thick 28-4 24-0 99 99 92 99 28-9 25-0 99 N 93 H 28-4 26-0 99 M 94 99 28-7 25-0 99 99 The following tests represent mild steel plates of various thicknesses, from f" to |", tested length- 95 ways and crossways Mild steel plates 28-4 25-0 Tested lengthways 96 9 99 28-7 23-0 99 crossways 97 9 29-4 24-0 99 lengthways 98 9 9> 29-6 25-0 99 crossways 99 9 91 27*8 28-0 99 lengthways 100 ) 9 28-0 27-0 99 crossways 101 9 > 29-1 28-0 99 lengthways 102 j 9 29-2 27-0 99 crossways 103 9 29-8 30-0 99 lengthways 104 29-8 26-0 99 crossways 105 > 28-8 29-0 99 lengthways 106 29-1 25-0 99 crossways 107 9 9 28-6 26-0 9> lengthways 108 28-6 27-0 |J crossways 109 1 9 29-1 24-0 99 lengthways 110 9 ) 29-7 23-0 99 crossways 111 5 9 29-0 28-0 99 lengthways 112 29-2 27-0 99 crossways 113 99 99 29-0 26-0 99 lengthways 114 29-9 27-0 99 crossways 115 99 9 28-6 30-0 99 lengthways 116 99 > 28-9 26-0 99 crossways 117 99 9 28-8 28-0 99 lengthways 118 28-7 25-0 99 crossways 119 99 9 29-3 27-0 99 lengthways 120 99 J 29-3 26-0 99 crossways CONSTRUCTION IN MILD STEEL. No. of test. Description of section tested. 121 Mild steel plates. 122 55 5' 123 55 55 124 55 55 125 15 5 126 55 55 127 55 15 128 55 55 129 5 SJ 130 5 55 131 5 15 132 5 55 133 5 55 134 5 135 5 136 55 1 137 55 ) 138 15 5 139 5 * 140 5 141 f 55 142 55 143 5 55 144 5 51 145 5 146 5 55 147 > "5 148 5 55 149 5 55 150 5 55 151 5 55 152 ) 5 153 5 5 154 5 1 155 5 5 156 5 5 157 5 158 5 55 159 55 55 160 55 55 161 55 55 162 5 55 163 164 165 Ultimate tensile strength. Tons per sq. inch. Ultimate elonga- tion in 8 inches. Per cent. I bCinarks. 29-4 25-0 Tested lengthways 29-0 25-0 N cross way s 28-6 26-0 n lengthways 28-7 24-0 it crossways 27-8 26-0 55 lengthways 27-8 24-0 55 crossways 29-8 25-0 5 lengthways 29-3 24-0 i crossways 28-3 26-0 i lengthways 28-9 27-0 5 crossways 28-6 28-0 lengthways 28-6 25-0 i crossways 28-8 26-0 i lengthways 28-7 22-0 55 crossways 29-1 28-0 55 lengthways 29-3 23-0 55 crossways 28-2 28-0 55 lengthways 28-6 24-0 crossways 29-5 26-0 55 lengthways 29-3 27-0 55 crossways 29-4 25-0 55 lengthways 29-3 23-0 55 crossways 27-8 27-0 51 lengthways 28-0 28-0 55 crossways 28-2 30-0 5 lengthways 27-7 23-0 5 crossways 28-7 29-0 > lengthways 29-1 28-0 5 crossways 29-0 28-0 5 lengthways 29-1 27-0 * crossways 28-8 28-0 5 lengthways 29-1 24-0 55 crossways 29-0 26-0 55 lengthways 29-0 25-0 55 crossways 28-4 26-0 5) lengthways 28-8 23-0 55 crossways 29-7 30-0 55 lengthways 29-4 24-0 55 crossways 29-4 25-0 55 lengthways 29-5 26-0 55 crossways 29-2 26-0 55 lengthways 29-5 27-0 55 crossways 28-6 25-0 1J lengthways 28-8 23-0 55 crossways 29-4 25-0 55 lengthways ITS PHYSICAL AND CHEMICAL QUALITIES. No. of test. Description of section tested. Ultimate tensile strength. Tons per sq. inch. Ultimate elonga- tion in 8 inches. Per cent. Remarks. 166 Mild steel plates. 29-4 25-0 Tested crossways 167 29-5 23-0 lengthways 168 i 29-6 25-0 crossways 169 28-3 30-0 lengthways 170 yi 9 28-6 28-0 crossways 171 28-9 27-0 lengthways 172 / 28-8 24-0 crossways 173 j ) 29-4 26-0 lengthways 174 , , 29-2 26-0 crossways 175 ) i 28-3 29-0 lengthways 176 , , 28-4 28-0 crossways 177 9 29-0 25-0 lengthways 178 J> 5 29-1 27-0 crossways 179 ,, ,, 29-2 26-0 lengthways 180 " " 29-2 25-0 croesways TABLE No. 14. TESTS ON MILD EIVET STEEL. No. of test. Description of section tested. Ultimate tensile strength. Tons per sq. inch. Ultimate elongation in 8 inches. Per cent. Remarks. Mild rivet steel. 1 J" diameter 26-4 30-0 Bending tests satisfactory 2 27-5 27-0 3 ^ 26-1 27-3 t > >> 4 26-1 28-4 For the' chemical analysis of Test No. 4, 'see p. 52 5 H 26-3 28-7 Bending tests satisfactory 6 27-2 30-0 > 7 w 27-0 31-0 1 4* 8 M 27-7 28-0 I* 9 M 27-8 28-0 10 ^ 27-2 21-0 y 11 n 28-2 29-8 ' > 12 )} 28-9 28-5 f 13 ? 28-4 28-9 9 42 CONSTRUCTION IN MILD STEEL. No. of test. Description of section tested. Ultimate tensile strength. Tons per sq. inch. Ultimate elongation in 8 inches. Per cent. Remarks. Mild rivet steel. (The tensile strength of 14 |" and |" diameter 25-1 33-5 this rivet steel is slightly below the specified mini- 15 D 25-6 31-0 mum, but in view of the 16 9 24-8 33-0 \ good elongation and the 17 99 26-2 34-7 satisfactory shop cold i and temper tests the \ rivets were accepted 18 9* 29-6 31-0 Bending tests satisfactory 19 99 29-5 31-0 >9 99 20 f" diameter 25-8 27-5 99 99 21 99 27-4 35-0 99 99 22 1* 28-2 30-0 9 99 23 f" diameter 27-3 27-0 99 99 24 99 28-0 26-0 99 99 /The tensile strength of Tests Nos. 25 to 29 is somewhat high, but the 25 If 31-2 25-5 elongation is good, and 26 }| 31-3 27-0 the large number of 27 |} 31-5 25-5 mechanical tests (bend- 28 9) 32-5 25-0 ing, flattening down, 29 5} 31-6 25-8 etc.) made, showed the metal to be of high class quality, and the rivets V were accepted 30 Pan-head rivets 26-6 25-0 Bending tests satisfactory 31 Snap-head rivets 27-8 20'0 ii 32 N 29-9 24-0 99 99 33 99 30-0 23-0 99 99 34 II 24-6 25-0 It 99 35 36 37 38 Steel rivets (various) 99 99 9 99 99 99 25-3 25-1 26-4 25-7 31-0 32-0 30-0 31-0 Flattening and bending (hot and cold) tests gave satisfactory results 39 Steel rivets ~" diam. 29-6 28-0 Bending tests satisfactory 40 99 51 30-0 32-0 99 41 99 99 29-8 31-0 >9 42 ft" diam. 29-6 32-0 M 43 9> 99 30*0 32-0 99 44 9) 99 29-8 27'0 99 45 9 99 29-2 34-0 91 46 |f" diam. 28-7 31-0 99 47 99 99 29-2 32-0 99 48 9) >9 28'0 32-0 99 ITS PHYSICAL AND CHEMICAL QUALITIES. 43 TABLE No. 15. TESTS ON MILD STEEL FOR BOLTS AND NUTS. No. of test. Description of section tested. Ultimate tensile strength. Tons per sq. inch. Ultimate elongation in 8 inches. Per cent. Remarks. 1 Bolt and nut steel. 29-4 25-0 Bending tests satisfactory 2 29-1 30-0 3 > 28-4 32-0 5> 4 28-9 28-0 5 > > 27-0 31-0 6 > 29-1 30-0 J 7 > ' 26-6 26-0 8 " 29-4 25-0 5> 9 5 29-1 30-0 >J 10 > 26-6 26-0 11 26-9 30-0 12 J> > 27-3 28-0 13 55 1) 25-7 29-0 > 5 14 26-1 27-0 15 J ' 29-9 27-0 16 27-3 29-0 17 27-7 31-0 18 " 28-3 31-0 I, TABLE No 16. TESTS ON MILD STEEL FORCINGS AND OTHER SPECIAL STEELS. ! Ultimate No. tensile Ultimate of test. Description of section tested. strength. ; extension. Tons per ; Per cent. Remarks. sq. inch. Mild steel forgings. 1 Shackles 30-6 35-0 Extension on 2 inches 2 w 31-4 37'0 3 ?J 31-7 22-5 8 4 ?J 31-6 29-0 4 5 n 31-6 20-0 8 6 Lifting bolts 30-8 36-0 2 7 > 29-3 23-0 !! 4 44 CONSTRUCTION IN MILD STEEL. No. of test. Description of section tested. Ultimate tensile strength. Tons per sq. inch. Ultimate extension. Per cent. Remarks. 8 Mild steel forgings. Crossheads 28-8 41-0 Extension on 2 inches 9 n 28-9 23-5 55 10 Lifting beams 31'6 37-0 55 55 11 5 55 30-9 37-0 55 55 55 12 55 55 31-5 23-5 4 13 Crane post 26-7 23-5 55 8 14 55 5 29-5 26-0 55 55 55 15 55 55 25-4 29-6 55 55 55 16 Connecting rod 27-9 32-0 55 ^ 17 Sprocket wheel spindles 26-3 35-0 55 " 55 For details of this wheel, see Figs. 413-416. ( Blooms 8J" square 1 X 10' 0" and 7" 27-8 26-0 Extension on 8 inches I square X 14' 6" ) 19 Engine forgings 28-4 26-0 55 55 55 20 55 55 28-4 26-0 55 55 55 21 55 55 28-5 28-0 55 55 55 22 55 55 28-5 30-0 55 55 55 23 55 55 28-3 27-0 55 55 55 24 55 55 28-4 28-0 55 55 55 25 55 55 29-9 25-0 55 55 55 26 55 55 28-9 26-0 55 55 55 27 55 55 27-2 23-0 55 55 11 28 55 55 30-0 25-0 55 55 55 29 55 55 27-3 28-0 55 55 55 30 55 55 27-9 27-0 55 11 55 31 Piston-rod forgings 28-5 24-0 55 55 55 32 55 55 27-4 26-0 55 55 55 33 55 55 28-5 25-0 55 ' ' 34 Shaft forging 27-6 28-0 55 15 55 35 Forged pins 26-2 29-0 55 5 >5 36 99 99 26-3 29-0 51 J5 55 37 Steel tyres and axles 36-0 30*0 i Bending tests cold and \ tempered satisfactory 38 55 55 36-5 28-0 55 5 55 39 55 55 39-0 28-0 55 '5 55 40 55 55 38-0 29-0 55 55 55 41 55 55 39-6 27-0 55 55 55 42 55 55 40-0 25-0 55 55 55 Extension taken on 3" for 43 Steel tyres 44-2 26-0 tests 37 to 42 inclusive, 44 55 44-1 20-0 and on 2" for tests 43 [ to 52 inclusive 45 Steel crane posts 30-6 35-0 Bending tests satisfactory ITS PHYSICAL AND CHEMICAL QUALITIES. 45 No. of test. Description of section tested. Ultimate tensile strength. Tons per sq. inch. Ultimate extension. Per cent. Remarks. Mild steel forgings. 46 Steel crane posts 32-2 29-0 Bending tests satisfactory 47 32-8 29-0 ) 48 j> 31-8 33-0 5 5> 49 jj 32-8 32-0 J 5J 50 5 32-2 35-0 55 5> 51 36-8 20-0 55 > 52 > 33-4 31-0 J 55 No. 52 is a re-test of No. 51 53 Spring steel 3" X f" 45-1 21-0 Not considered satisfac- tory. 54 ) 52-9 13-0 Replace of No. 53. Ex- tension taken on 6" for - Nos. 53, 54 NOTE. Tests Nos. 1 to 12 represent material used in the construction of plant for marine works, such as Titans or Goliahs, for the handling of large concrete blocks, etc. TABLE No. 17. TESTS ON MILD STEEL FOR SPECIAL PURPOSES. Ultimate No. tensile Elonga- of test. Description of material. strength. Tons per sq. inch. tion in 8 inches. Per cent. Remarks. Mild steel for special purposes. 1 2 3 4 (Hot drawn weldless^ steel hexagonal -t couplings for tie V bolts (screwed right 1 and left-handed) J 26-42 26-27 26-00 27-05 22-0 24-5 23-0 19-5 For the details of these couplings, see Figs. Nos. 369, 370. Steel bars for nuts for bolts. 5 2" diameter 28-9 28-0 6 03" 29-9 28-0 7 4- 26'2 24-0 4 6 CONSTRUCTION IN MILD STEEL. No. of test. Description of materials. Ultimate tensile strength. Tons per sq. inch. Elonga- tion in 8 inches. Per cent. Remarks. Steel flats for links for hauling chains. 8 6J" X |" X 12' 1" 31-2 23-0 \ 9 55 55 31-5 23-0 Bending tests satisfactory. 10 11 55 55 55 55 31-9 31-5 24-0 24-0 This steel was specified to have an ultimate 12 55 55 31-1 25*0 tensile resistance of not 13 55 55 31-2 22-0 less than 30 or more 14 55 55 32-7 21-0 than 33 tons per square 15 55 55 32-5 22-0 inch, with 20 per cent. 16 55 55 31*0 24-0 extension in 8 inches. 17 55 55 31-0 23-0 For the details of the 18 55 55 31-0 24*0 links of the chain made 19 55 55 31-2 22-0 from this steel, see 20 55 55 31-9 20-0 Figs. 410, 411, 422, 423. 21 55 55 32-2 24-0 See also Chemical Ana- 22 55 55 31-9 26-0 lysis, No. 19, p. 54, 23 55 55 31-9 22-0 24 25 Flanged nuts for chains 55 55 28-9 27-0 28-0 31-0 (Stamped out under the hammer. See Figs. 411, 1 423. 26 Flanged nuts for chains 30-4 31-0 Bending tests satisfactory 27 55 55 30'4 30-0 55 55 28 55 55 28-9 28-0 55 55 29 Lewis bolts f " 29-1 30-0 55 55 30 55 55 26'6 26-0 55 55 31 55 -4' 28'4 32-0 55 55 32 Cotter bolts 2" 291 30-0 55 55 It is apparent from a consideration of the foregoing results, and from numberless experiments of a similar class which might be quoted, that the present-day processes of steel-making have resulted, especially so far as open-hearth steel is concerned, in a material remarkable for its uniformity of quality, its high tensile resistance, and for the excellent elongation shown by the tests. The highest quality of wrought-iron bar now obtainable may perhaps compare with mild steel favourably as regards ultimate extension, when it has been obtained from the best makers, but will be found to fall considerably below steel in ultimate tensile resistance, while inferior brands of wrought iron can offer no such comparison. ITS PHYSICAL AND CHEMICAL QUALITIES. 47 An instance of the great advance shown by the newer material may be found in the tests of plates. In the old days the tensile resistance of wrought-iron plates across the grain was con- siderably below that lengthways of the grain, while the ultimate extension crossways frequently did not exceed 5 per cent. ; a fact which had to be carefully borne in mind in the use of wrought-iron plate across the grain. The results of the tests on mild steel plates are given in the foregoing table, No. 13. It will there be seen that the average ultimate tensile strength of plates tested lengthways, Tests Nos. 1 to 45, is 28-07 tons per square inch, while the same resistance of plates tested crossways, Tests Nos. 46 to 94, is 28*03 tons per square inch. The average ultimate extension lengthways is 28*5 per cent, in 8 inches, and crossways is 26'23 per cent., showing a slight difference in extension in favour of plates tested lengthways. Tests Nos. 95 to 180 are the results on plates tested length- ways and crossways under a different contract, but a comparison of the averages gives a similar result to the foregoing series. The average ultimate tensile strength tested lengthways is 28*82 tons per square inch, and tested crossways is 28*93. The average ultimate elongation in 8 inches, tested lengthways, is 27'00 per cent., tested crossways is 25*28. A third series of fifty-eight experiments, representing some 200 tons of plates from f inch to f inch thick, give results in accordance with the foregoing. The ultimate tensile resistance lengthways is 2 8 '24 tons per square inch, with an ultimate extension in 8 inches of 28'6 per cent. Tested crossways, the re- sults are 28*05 tons per square inch and 26 '7 per cent, extension. All three series exhibit a practical uniformity in ultimate tensile strength, whether tested lengthways or crossways, and a difference of from 7 to 9 per cent, in the ultimate extension in favour of the lengthways tests. Chemical Analysis. Eeference has already been made to the relation between -the chemical constitution and the mechanical properties of mild steel, the difficulties surrounding the problem of ascertaining exactly what that relationship is, and of estimating the ultimate strength of a given sample from an analysis of its chemical constituents. The resulting formula, arrived at after an exhaustive examination of the subject by an eminent American authority, has also been given on p. 12. The following examples of chemical analyses are given, not by 4 8 CONSTRUCTION IN MILD STEEL. way of elucidating the formulse above referred to (they are, for this purpose, insufficient in number), but as practical examples of the form of analysis met with in ordinary work, and were made on the same constructive material, the mechanical tests of which have been given in the preceding tables. The chemical analysis and the mechanical test were in all cases made from the same test piece. The variations to be observed are those usually found in practice. 1. Chemical analysis of sample representing f" mild steel plate Per cent. Carbon ... ... 0-200 Silicon 0-019 Sulphur 0-064 Phosphorus ... ... 0-046 Manganese ... ... ... ... 0*565 Iron (by difference) 99-106 100-000 Tensile test of the above sample Ultimate strength, 28-1 tons per square inch. Elongation, 30'0 per cent, in 8 inches. Bendiog tests satisfactory. 2. Chemical analysis of sample representing -J" mild steel plates Carbon Silicon Sulphur Phosphorus Manganese... Iron (by difference) Per cent. 0-178 0-014 0-074 0-049 0-497 99-188 100-000 Tensile tests of the above sample Ultimate strength, 27*5 tons per square inch. 00. A > ?> ^ * J " Elongation, 25-0 per cent, in 8 inches. 26-0 Mean ultimate strength, 27'9 tons per square inch. Mean elongation, 25*5 per cent, in 8 inches. Bending tests satisfactory. ITS PHYSICAL AND CHEMICAL QUALITIES. 49 3. Chemical analysis of sample representing f" mild steel plate Per cent. Carbon 0-220 Silicon 0-014 Sulphur 0-069 Phosphorus 0'050 Manganese 0*497 Iron (by difference) 99-150 100-000 Tensile test of the above sample Ultimate strength, 26-6 tons per square inch. Elongation, 31-0 per cent, in 8 inches. Bending tests satisfactory. 4. Chemical analysis of sample representing J" mild steel plate Per cent. 0-178 0-014 0-060 0-056 0-450 99-242 100-000 Carbon Silicon Sulphur Phosphorus Manganese ... Iron (by difference) Tensile test of the above sample Ultimate strength, 27*7 tons per square inch. Elongation, 28*0 per cent, in 8 inches. Bending tests satisfactory. 5. Chemical analysis of sample representing mild steel plate- Per cent. Carbon 0-154 Silicon 0-011 Sulphur 0-084 Phosphorus 0'059 Manganese... ... ... ... ... 0*454 Iron (by difference) 99-238 100-000 Tensile test of the above sample Ultimate strength, 29*8 tons per square inch. Elongation, 27-0 per cent, in 8 inches. Bending tests satisfactory. 50 CONSTRUCTION IN MILD STEEL. 6. Chemical analysis of sample representing mild steel flat Per cent. Carbon 0-201 Silicon ... ... 0-003 Sulphur 0-035 Phosphorus 0035 Manganese ... ... ... ... ... 0*650 Iron (by difference) 99-076 100-000 Tensile test of the above sample Ultimate strength, 28-4 tons per square inch. Elongation, 31-0 per cent, in 8 inches. Bending tests satisfactory. 7. Chemical analysis of sample representing 12" X f" mild steel flat Per cent. Carbon 0-170 Silicon 0-015 Sulphur ... 0-079 Phosphorus 0-043 Manganese... 0-720 Iron (by difference) ... 98-973 100-000 Tensile test of the above sample Ultimate strength, 28*7 tons per square inch. Elongation, 2 9 -5 per cent, in 8 inches. The amount of sulphur in this sample is somewhat large, but in other respects the composition is normal, and the bending tests were satisfactory. 8. Chemical analysis of sample representing 5" X 5" x f " mild steel angle Per cent. Carbon .. ... 0-116 Silicon 0-023 Sulphur 0-034 Phosphorus 0-042 Manganese ... ... ... ... ... 0*684 Iron (by difference) 99-101 100-000 ITS PHYSICAL AND CHEMICAL QUALITIES. Tensile test of the above sample Ultimate strength, 29-1 tons per square inch. Elongation, 28'9 per cent, in 8 inches. Bending tests satisfactory. 9. Chemical analysis of sample representing 3J" x 3" x mild steel angle Per cent. 0-165 0-061 0-060 0-063 0-360 99-291 100-000 Carbon Silicon Sulphur ... Phosphorus Manganese... Iron (by difference) Tensile test of the above sample Ultimate strength, 29-2 tons per square inch. Elongation, 24-0 per cent, in 8 inches. Bending tests satisfactory. 10. Chemical analysis of sample representing 3" x 3" x mild steel angles Per cent. Carbon 0-316 Silicon 0-053 Sulphur 0-053 Phosphorus 0-056 Manganese ... ... ... 0-360 Iron (by difference) ... 99' 162 100-000 Tensile test of the above sample Ultimate strength, 28-5 tons per square inch. Elongation, 25*0 per cent, in 8 inches. Bending tests satisfactory. 11. Chemical analysis of sample representing 3" x 3" x steel angles Carbon . Silicon Sulphur Phosphorus Iron (by difference) Per cent. 0-198 0-072 0-047 0-062 0-342 99-279 100-000 CONSTRUCTION IN MILD STEEL. Tensile test of the above sample Ultimate strength, 29-2 tons per square inch. Elongation, 24'0 per cent, in 8 inches. Bending tests satisfactory. 12. Chemical analysis of sample representing 3" X 3" X steel angles Carbon Silicon Sulphur Phosphorus ...... Manganese... Iron (by difference) ...... Tensile test of the above sample Ultimate strength, 28*7 tons per square inch. Elongation, 23-5 per cent, in 8 inches. Bending tests satisfactory. 13. Chemical analysis of sample representing mild steel for rivets Per cent. 0-200 0-080 0-069 0-067 0-468 99-116 100-000 Per cent. 0-130 0-026 0-055 0-056 0-360 99-373 100-000 Carbon Silicon Sulphur ... ... Phosphorus Manganese... Iron (by difference) Tensile test of the above sample Ultimate strength, 26-1 tons per square inch. Elongation, 28'4 per cent, in 8 inches. 14. Chemical analysis of sample representing 7" X J" flats- Per cent. Carbon Silicon ... ... Sulphur Phosphorus Manganese ... Iron (by difference) 100-000 ITS PHYSICAL AND CHEMICAL QUALITIES. 53 Tensile test of the above sample Ultimate strength, 28*0 tons per square inch. Elongation, 22-0 per cent, in 8 inches. Bending tests satisfactory. 15. Chemical analysis of sample representing 2J" -f f" flats Per cent. Carbon 0'176 Silicon 0-010 Sulphur 0-073 Phosphorus 0'042 Manganese... 0*688 Iron (by difference) 99*011 100-000 Tensile test of the above sample Ultimate strength, 28*80 tons per square inch. Elongation, 31 -0 per cent, in 8 inches. Bending tests satisfactory. 16. Chemical analysis of sample representing 2^" -f 2J" angles Per cent. Carbon 0-169 Silicon 0*026 Sulphur 0-083 Phosphorus 0*050 Manganese ... ... ... ... ... 0*410 Iron (by difference) 99-262 100-000 Tensile tests of the above sample Ultimate strength, 29-3 tons per square inch. Elongation, 25*0 per cent, in 8 inches. Ultimate strength, 27*8 tons per square inch. Elongation, 24*0 per cent, in 8 inches. 17. Chemical analysis of a sample representing %" thick mild steel plate Per cent. Carbon 0*190 Silicon 0*020 Sulphur 0*072 Phosphorus 0*064 Manganese ... ... ... ... ... 0*612 Iron (by difference) 99*042 100-000 54 CONSTRUCTION IN MILD STEEL. Tensile tests of the above sample Lengthways, Ultimate strength, 28'6 tons per square inch. Elongation, 27'0 per cent, in 8 inches. Crossways, Ultimate strength, 28'8 tons per square inch. Elongation, 24'0 per cent, in 8 inches. 18. Chemical analysis of a sample representing f" thick mild steel plate Per cent. Carbon 0-154 Silicon ... ... 0-009 Sulphur 0-067 Phosphorus ... ... 0-057 Manganese... ... 0-468 Iron (by difference) 99-245 100-000 Tensile tests of the above sample Lengthways, 28-9 tons per square inch. Elongation, 26'0 per cent, in 8 inches. Crossways, 28*6 tons per square inch. Elongation, 28-0 per cent, in 8 inches. 19. Chemical analysis of a sample representing 6J" X f " flats, used in the manufacture of links for hauling chains Per cent. Carbon 0-238 Silicon 0-046 Sulphur 0-057 Phosphorus 0-070 Manganese 0'652 Iron (by difference) 98*937 100-000 Results of tensile tests of the above sample (Analysis No. 19) Breaking strain. Elongation in 8 inches. Tons per square inch. Per cent. 32-2 26-0 This specimen is from the same class of material represented in Tests Nos. 8 to 23 inclusive (Table No. 17), under the heading of "Steel for Special Purposes." It represents a class of steel slightly higher in ultimate tensile strength, and having a slightly lower percentage of elongation than the bulk of the material represented in the tables. The processes through which the steel went in the ITS PHYSICAL AND CHEMICAL QUALITIES. 55 manufacture of the finished link (shown in Figs. 410, 422) proved the excellence of the material. 20. Chemical analysis of a sample representing 3" X 3" x |" mild steel angles 100-000 Carbon ... Silicon Sulphur Phosphorus Manganese ... Iron (by difference) Tensile tests of the above sample Ultimate strength, 28'3 tons per square inch. Elongation, 25*0 per cent, in 8 inches. Bending tests satisfactory. 21. Chemical analysis of a sample representing 3|" X 3^" x f " mild steel angles Per cent. Carbon 0-128 Silicon 0-042 Sulphur ... ... ... 0-053 Phosphorus ... ... ... ... 0*069 Manganese... ... ... ... ... 0-635 Iron (by difference) 99*073 100-000 Tensile tests of the above sample Ultimate strength, 29-8 tons per square inch. Elongation, 27*0 per cent, in 8 inches. Bending tests satisfactory. 22. Chemical analysis of a sample representing plate mild steel Carbon Silicon Sulphur Phosphorus Manganese... Iron (by difference) Per cent. 0-206 0-038 0-081 0-043 0-637 98-995 100-000 56 CONSTRUCTION IN MILD STEEL. Tensile tests of the above sample Lengthways, 27-2 tons per square inch Crossways, 2 7 '8 tons per square inch. Elongation, Lengthways, 2-70 per cent, in 8 inches. Crossways, 25'0 per cent, in 8 inches. Bending tests satisfactory. For comparison with the foregoing mechanical tests and chemical analyses of mild steel, the following table of the results of mechanical tests on wrought-iron bars, rectangular and round, is appended. The material here indicated represents good present- day practice in the manufacture of wrought iron, and is of as high a quality as could be readily obtained under ordinary commercial conditions. As the manufacture of wrought-iron plates is no longer of the importance that once belonged to it, no comparison between the old and the modern material need in this respect be instituted. TABLE No. 18. EESULTS OF PHYSICAL TESTS ON WEOUGHT-IRON BARS, BECTANGULAR AND BOUND. Description of section tested. Ultimate No. tensile Elongation of strength. in 8 inches. Remarks. test. Tons per Per cent. sq. inch. Wrought-iron bars. 1 i 3J" square from ) ! O0 . \ 6' 11" to 7' 8" long/ 12-0 2 3 4 5 6 7 8 n 11 11 11 11 11 11 M 11 11 11 11 ft 11 22-8 20-3 22-1 22-5 22-5 22-3 22-5 17*0 8-0 27-0 24-0 27-0 26-0 27-0 These bars were specified to have not less than , 22 tons ultimate tensile strength per square inch, and 10 per cent, elongation in 8 inches 9 11 11 22-3 26-0 10 n 11 24-1 21-0 11 11 11 23-6 22-0 Forge tests were satis- factory 12 11 > 23-5 23'0 13 > J 23-3 23'0 14 M 23'3 24-5 n 15 11 n 22-3 24-0 16 11 i 22-6 27-5 ITS PHYSICAL AND CHEMICAL QUALITIES. 57 No. of 17 18 19 20 21 22 23 24 25 26 27 28 29 '30 31 32 33 34 35 36 Description of section tested. Ultimate tensile strength. Tons per sq. inch. Elongation in 8 inches. Per cent. Remarks. Wrought-iron bars. I 3l" square from ) \6' 11" to 7' 8" long } 22-9 21-5 l Forge tests were satis- ( factory 23-2 24-0 N Wrought-iron flats. 8J" X 21" , 23-0 27-0 41" X 1-" 3|" X if" 22-7 23-1 26-0 25-0 Wrought-iron round bars. 4" diameter 22-6 29-0 !' 4f H 3|" 22-7 23-1 28-0 23-0 Specified to have not less than 22 tons ultimate 2" 23-9 27-0 tensile strength, and 1J" 22-8 34-0 10 per cent, elongation 23-0 28-5 . 24-9 16-0 24-9 20-0 , 25-4 13-0 For the chemical analysis f 22-9 28-0 from drillings from 23-1 28-0 tests Nos. 28 to 36 in- L" 8 ' 26-3 15*0 clusive, mixed well to- 24-1 17-0 gether, see below. ' ^ 26-2 26-0 23-9 18-0 The following chemical analysis of a mixture of the samples whose mechanical tests are described by tests Nos. 28 to 36 inclusive (Table No. 18) is of interest, when compared with the analyses of mild steel given above. Chemical analysis of a sample representing wrought-iron round bars | inch to 1 J inch diameter Carbon Silicon Sulphur Phosphorus Manganese... Slag Iron (by difference) Per cent. 0-042 0-118 0-030 0-237 0-162 0-878 98-533 100-000 58 CONSTRUCTION IN MILD STEEL. The results of the tensile tests are given in the Table No. 18, tests Nos. 28 to 36 inclusive, the mean ultimate tensile strength being 24*6 tons per square inch, and the mean ultimate elongation 20*1 per cent, in 8 inches, ranging from 13 to 28 per cent. The student will observe in the above analysis the low percentage of carbon and manganese, the high percentage of phosphorus, and last, but not least, the presence of slag to the extent of nearly 1 per cent. ; the material is, however, of good quality. The foregoing remarks on the mechanical tests and chemical analyses required for the determination of the quality and strength of structural mild steel could hardly be considered complete, even in the elementary form in which they have been presented, without a reference to that important branch of laboratory investigation, the microscopic examination of the structure of metals. More than a reference to this subject is not, however, within the scope of these notes, the subject demanding the discussion of refinements of methods and of results which are beyond the more rough-and- ready determinations of commercial tests and analyses. The results to be obtained from microscopic investigation give ample promise of high scientific value in the future, in the determination of the general equations subsisting between the mechanical qualities, chemical constituents, and microscopic structure of the specimens examined, but for the everyday re- quirements of the designer of structural steel-work, this method has not yet superseded the more ordinary process of mechanical testing and chemical analysis above referred to, especially when the comparatively small area of surface of section examined under even moderately high powers is taken into consideration, while the amount of material to be accepted or rejected is measured in tons. The following remarks contained in the presidential address of the Iron and Steel Institute for 1901 1 are suggestive as to the pos- sible issue in the near future not only of the competition at present existing between the Bessemer and open-hearth processes, but also of that between the acid and basic subdivision of the latter process : " Notwithstanding all that has been done chiefly in the direc- tion of securing larger output and greater regularity in the pro- duct, the waste in the Bessemer process remains practically the 1 Iron and Steel Institute. Presidential address by Mr. William Whitwell, May, 1901. ITS PHYSICAL AND CHEMICAL QUALITIES. 59 same as it was in the early days. Although the purposes for which Bessemer steel (acid and basic) is now being used have increased enormously fully one-half the make in this country being used for other purposes than railway material it seems probable that by reason of cheaper methods of producing steel, the Bessemer processes will have in future much more serious com- petition than has been the case in the past. The recent modifi- cation of the open-hearth process by Bertrand-Thiel and by Talbot, aided, as they are certain to be, by the labour-saving appliances already in successful operation, seem to indicate that we are now on the verge of effecting still greater economies in our steel-pro- ducing methods, and unless some means can be devised of reducing the waste in the Bessemer converters, the Bessemer processes, which have served the world so well in the past, are likely to be superseded. "For regularity and reliability of product the Siemens acid steel process stands pre-eminent. By far the greater part of the open-hearth steel in this country is made by this process, owing to the facilities for obtaining a cheap and efficient supply of hematite pig-iron, and so long as such conditions continue to exist it will undoubtedly hold its own. But the basic open-hearth process is advancing with rapid strides, and is seriously challenging the position of the acid process as regards the cheapness of its product ; and this fact, coupled with what I have already said on the question of the pure ore supply, would seem to point to the conversion of many acid hearths into basic at no very distant date. In the developments of the iron and steel industries in the future the basic Siemens process will no doubt claim most attention." In connection with the remarks of the authority above quoted, the following comparison of the total outputs of steel in the United Kingdom, Germany, and the United States for the year 1899 will be found of interest : The total amount of steel manufactured in Great Britain in the year mentioned was 4,855,325 tons. Of this amount 1,825,074 tons were produced by the Bessemer process and 3,030,251 tons by the open-hearth process. Of the Bessemer process 71 '6 per cent, was acid and 28*4 per cent, basic steel. Of the open-hearth process 90-3 per cent, was acid and 9'7 per cent, was basic steel. The Bessemer process produced in 1899 about 37 per cent, of the whole amount manufactured, whereas ten years previously, in 1889, its percentage of the gross output was 60. 60 CONSTRUCTION IN MILD STEEL. In Germany the total production of steel in 1899 amounted to 6,290,434 metric tons. Of this amount 63'2 per cent, was basic converter, 2 6 '9 per cent, basic open-hearth, and 9'9 per cent, was acid Bessemer. In the United States for the same year the total production of steel was 10,662,170 tons of 2240 Ibs. Of this amount 717 per cent, was Bessemer, 27*7 per cent, was open-hearth, and 1*2 per cent, crucible and special steel. Of the open-hearth steel 70*6 per cent, was basic and 29*4 per cent, was acid steel. In 1902 the total production of steel in the United States amounted to 14,994,200 tons, of which 5,687,729 tons were open-hearth, or nearly 38 per cent, of the total quantity. Of the open-hearth steel 21 per cent, was acid and 79 per cent, basic. In 1904, the total production of steel in the United States amounted to 13,859,887 tons, of which 56'6 per cent, was Bessemer, 42-7 per cent, was open-hearth, and 0*7 per cent, was crucible or special steel. Of the open-hearth steel manufactured in the United States in 1904, 86'4 per cent, was basic and 13'6 per cent, was acid. Practically all the Bessemer steel was acid. In Great Britain, the total production of steel in 1904 was 5,026,879 tons, of which 35*4 per cent, was Bessemer and 64*6 per cent, was open-hearth. Of the open-hearth steel manufactured in Great Britain in 1904, 79 '6 per cent, was acid and 20 '4 per cent, was basic. Cast Steel. This most valuable material has of late years come into prominent use in a variety of forms, although in ordinary building construction the expense attending its adoption has been, and still is, the principal obstacle to its extended use in that direction. A material possessing some four times the direct tensile resistance of ordinary cast iron, and a range of elasticity to which cast iron offers but little parallel, appears at first sight an ideal metal to be cast into constructional forms. But, as above stated, the high price of steel castings at present forms an effective commercial obstacle to any rivalry with the cheaper metal in ordinary construction. There are also other facts to be taken into account which somewhat discount the advantages of increased strength and elasticity. These are, in the present stage of the art of steel-founding, first, the want of finish on the exterior of the casting, the roughness of the surface contrasting somewhat unfavourably with the smooth finish obtainable on the skin of a good casting in iron a result commonly supposed to be due to the high temperature ITS PHYSICAL AND CHEMICAL QUALITIES. 61 of cast steel, and its injurious effect upon the surface of the mould exposed to the intense heat and attrition of the molten metal. The second defect, of a more vital nature, is one which probably causes the inspectors and users of this material consider- ably more anxiety than the want of external finish. It consists in the .almost invariable presence of gas-holes, or, as would be called in iron castings, air- or blow-holes, more or less numerous, mainly of small dimensions, but frequently not showing themselves on the surface of the casting until machining has revealed their existence, and possibly not even then. The judgment of the inspector will frequently be exercised as to the extent to which such defects may be considered to affect the soundness of the casting, and an indiscriminate rejection of work on this ground only is generally considered an impracticable course to adopt in the present condition of steel founding. The problem will again and again present itself to the mind of the inspecting official as to how far a gas-hole manifesting itself on the surface, let us say of a machined casting, may extend into the body of the work, what may be its cubic capacity or its ramifica- tions, and to what extent is it likely to interfere with the practical soundness of the casting, and with its fitness for the purpose for which it has been designed ? When the depth of such a defect cannot be well ascertained by pricking with a wire, owing possibly to its crooked shape, a measure of its cubic capacity may be obtained by pouring water into the hole, and observing the volume of water absorbed. But when every allowance has been made for the defects above mentioned, it must still be conceded that the high tensile resistance, elasticity, and toughness of this material render it extremely valuable under certain conditions. But little is at present known as to its compressive resistance in the form of long columns, or in the compression flange of simple girders, and the proportions of girder flanges -determined by the early and well-known experiments of Hodgkinson would probably require considerable modification in the use of cast steel for simple H -shaped girders. In machinery and engine work the use of cast steel is extensive and various. Spur wheels of all sizes up to large diameters are in frequent use, though the high rate of shrinkage of cast steel as compared with cast iron gives some little trouble in this direction occasionally. 62 CONSTRUCTION IN MILD STEEL. Mitre wheels, small gearing and clutches, and generally details exposed to severe shock are all instances of its use. In ship construction we have perhaps the finest examples of the use of this material in large and complicated castings often of several tons in weight, as in rambow castings, screw frames (known in the shipbuilding yard as " spectacles "), rudder frames, and the like. In the Table of tests which follows, a considerable variety of purposes to which this material has been applied will be observed. Thus in Table No. 20, tests Nos. 1 to 40, we find a series of tests of steel castings used for pawl racks in slipways for hauling craft up for repairs having a displacement of some 200 tons or more. The racks having to resist the shock of the pawls in the event of the hauling apparatus giving out, were required to be of a tough and very strong material, and cast steel was used for the purpose. In Table No. 20, tests Nos. 41 to 97, we have a series of tests on cast-steel bollards for mooring purposes on a wharf or breakwater wall. Tests Nos. 270 to 272 are the results from castings for wheels to bogie waggons carrying concrete blocks of 50 tons weight. These are small wheels of crucible cast steel. Tests Nos. 98 to 193 are from steel castings for the roller paths of large sliding caissons for dock entrances, these paths being laid under water. Tests Nos. 194 to 226 are from the roller castings themselves. Specimens from cast-steel cylinders for hydraulic rams, and their covers, together with various other items of machine con- struction, also find their place in the tables. In several cases the details of these castings are found in the illustrations referred to, in order that the student may fully realize the class of work to which the tests have reference. It is perhaps unnecessary to remark that when cast steel is specified, it is desirable to be sure that cast steel is supplied. All is not cast steel that is called by that name. An examination of tests Nos. 1 to 8 in Table No. 20 will show considerable fallings off in the metal offered from the specified standard, but the improved results successively indicated in tests Nos. 9 and onward show the beneficial result of a steady adherence to the requirements of the specification. The tests applied to steel castings usually consist of tensile and bending tests on specimens cast on the castings and cut off ITS PHYSICAL AND CHEMICAL QUALITIES. 63 for that purpose after annealing. Large castings are frequently hammered, or let fall from a height, to test their soundness. The annealing of steel castings is frequently adopted, the castings being re-heated in a specially constructed furnace, and allowed to cool gradually for certain specified periods. All the tests enumerated in the following tables are on annealed speci- mens. The bending tests are commonly carried out on square or round bars bent cold by an hydraulic press over a curved block, the radius of which is specified, and it is well for the student in drawing up his requirements in this particular to be clear as to the meaning of the clause defining the angle through which the bar is to bend. Thus to specify that a bar shall bend to an angle of 45, appears to leave it an open question as to whether it shall bend through an angle of 45 or through an angle of 135. The use of the term "interior angle," or, better still, the figured diagram, will, however, leave the requirement intelligible and free from dispute. Considerable variations will be observed in the tables with respect to the angles bent through, as compared with the ultimate elongation in tensile tests, and the causes of this variability are not very obvious. It is possible, however, that they are partly due to differences of conditions in the process of annealing. The following table, No. 19, shows, in general terms, the practice with respect to annealing of steel castings, position of test-pieces, etc., of five of the leading cast-steel manufacturers in this country at the present time. 6 4 CONSTRUCTION IN MILD STEEL. I e $ .2^ fl "S5 ^ ^r2'i rg ~*^ gj,fr - s - 2 g I" 2 P & I ^ .-a i'g I P r . S. Cj W rt 00 00 " 1? .3 C^ S *H I I CQ S-slI ^".a.sal!^e s ^3 ^g oo^Orrt S^O $1^9 I fl-1'"3 o> S o-g 35 II g |J j |^ gg^a a ^ c8 H cS-^pH 53-+^ PrH-f3Cr<^2 P O 11^1 Nll| I frill O QQ < 8.9 a &S o 2^ .i - l ^ 1.9 G 1 j H -3 -3 i.Sgg^3 il|J fr oo ~ nl S8 li p oo oo o O * M 3 3 P M'S^ g-as p*-p i* Sill .^ q O ri4 1 ^^ r4 Sfl 2 "3 2 5 'S W) 3 .gi ITS PHYSICAL AND CHEMICAL QUALITIES. 65 The great advantage possessed by cast steel over cast iron in the ductility exhibited even by the smallest angle bent through, given in the table, is sufficiently obvious. Fig. 4 is an elevation of a typical specimen of cast-steel test bar nominally 1 inch square, bent by hydraulic pressure over a block having a radius of 1 J inch, to an interior angle of 70, and remaining unbroken. Fig. 5 is a section of the bar on the line a-b, showing the FIG. 5. Scale, half full size. FIG. 6. Scale, half full size. FIG. 4. Scale, half full size. section of the bar, with its square edges machined or filed off. (The whole bar was machined.) Fig. 6 gives the section through the bend of the bar on the line c, d, and shows the flow of material due to the process, the concave fibres in compression being laterally extended, while the convex surface is contracted, accompanied by a slight hollowness in the sides, the whole figure well exhibiting the ductility of the material. The tensile tests are made in the usual way on specimens which are sometimes 8 inches in length between the shoulders, but more commonly 2 inches in length, the latter dimension being that usually preferred by the steel founder, as being more advan- tageous from his point of view. F 66 CONSTRUCTION IN MILD STEEL. TABLE No. 20. TENSILE AND BENDING TESTS ON CAST-STEEL BARS. All bars machined approximately 1 inch square (with the exceptions described) for bending tests, and prepared in the usual way for tensile tests. Bending tests were made over a block having a radius of 1J inch, and were bent cold under hydraulic pressure. All specimens, both for bending and tensile tests, were annealed with the castings which they were intended to represent. The material for the greater part of the castings was supplied under the specification given on p. 19. No. of test. Description of casting. Ultimate tensile strength. Tons per sq. inch. Elongation in 8 inches. Per cent. Elongation in 2 inches. Per cent. Angle through which test- piece was bent. Degrees. Remarks. 1 2 3 4 5 6 7 8 | Pawl 1 1 racks ( 11 v> 11 11 11 M 5 18-7 18-7 19-8 22-5 24-0 24-2 23-3 21-8 5-0 \ 3-1 3-7 2-25 4-25 3-75 2-75 2-5 ' ... ... All these results being so much below the spe- cified require- ments, the castings repre- sented were rejected 9 11 32-5 14-75 ... ... Good fracture 10 11 26-75 10-50 ... . . . 11 11 11 37-50 16-75 ... ... 11 12 11 26-90 9-75 . . . .. . 11 13 11 27-50 15-75 .. . . .. 11 ( Below the spe- 14 11 29-75 8-0 ... ... j cified elonga- [ tion 15 11 32-1 18-75 ... ... Good fracture 16 1 32-2 20-5 ... ... 11 17 1 33-6 20-0 ... ... 11 18 1 33-9 20-75 ... ... 11 19 1 33-85 1 1*0 ... .. . 11 20 1 32-45 12-0 .. ... 11 21 1 31-5 22-2 ... ... 11 22 } 81-1 13-5 ... ... 11 23 }J 31-1 21-25 ... ... 11 24 11 30-9 23-25 ... ... 11 ITS PHYSICAL AND CHEMICAL QUALITIES. 67 No. of test. Description of casting. Ultimate tensile strength. Tons per sq. inch. Elongation in 8 inches. Per cent. Elongation in 2 inches. Per cent. Angle through which test- piece was bent. Degrees. Remarks. 25 i Pawl } \ racks f 29-1 23-0 ... ... Good fracture 26 11 29-0 23-5 ... ... 11 27 11 30-2 19-75 ... ... 11 28 11 28-6 19-5 ... ... it 29 29-8 23-1 ... ... 11 30 11 29-2 19-5 ... ... 11 31 11 31-0 23-0 ... ... 11 32 11 30-4 24-5 ... ... 11 33 11 32-1 21-8 ... ... 11 34 H 32-0 20-5 ... ... 11 35 n 31-5 19-0 ... ... 11 36 11 32-0 21-75 ... ... 11 37 11 31-75 24-75 ... ... 11 38 11 33-25 21-5 ... ... 11 39 11 27-85 ... ... ... Broke outside datura points These speci- mens were cut from the racks themselves, 40 11 34-15 22-25 ... ... and not from runners cast at the same time as the racks 41 1 Bollards 31-8 ... 26-0 2 105 42 11 31-02 26-0 95 43 11 32-8 ... 21-0 90 44 11 31-5 ... 21-5 115 45 11 33-25 ... 20-0 110 46 11 32-9 ... 20-5 120 47 11 31-9 ... 15-0 90 48 11 31-8 ... 17-0 88 49 11 31-55 ... 15-0 87 50 11 32-4 ... 16-5 105 51 11 32-6 ... 16-0 100 52 11 31-85 ... 16-0 102 1 Test Nos, 41 to 63 inclusive for bending were made on bars I inch to \% inch square. Bending tests Nos, 64 to 97 inclusive were made on 1 inch diameter round bars. 2 Specimens for testing in tension were from 0'74 to 0"81 inch in diameter, and from 0-43 to 0'51 square inch in area. 68 CONSTRUCTION IN MILD STEEL. No. of test. Description of casting. Ultimate tensile strength. Tons per sq. inch. Elongation in 8 inches. Per cent. Elongation in 2 inches. Per cent. Angle through which test- piece was bent. Degrees. Remarks. 53 Bollards 29-6 16-0 110 54 30-4 ... 14-0 115 55 >> 29-4 ... 18-0 105 56 11 32-6 ... 18-0 105 57 55 32-75 ... 17-0 110 58 55 31-80 ... 17-0 105 59 55 32-75 ... 18-0 95 60 55 32-90 ... 19-0 105 Sound 61 11 31-8 ... 17-0 110 5 62 1 31-6 ... 18-0 105 Broke 63 1 31-3 ... 16-0 100 Sound 64 1 33-5 .. . 19-0 96 i 65 1 34-6 ... 18-5 105 Broke 66 1 33-4 ... 14-5 95 55 67 1 34-8 ... 18-0 105 Sound 68 1 28-8 .. . 18-0 100 Broke 69 1 30-0 ... 16-0 100 Sound 70 1 28-8 ... 19-0 113 Broke 71 5 33-8 .. . 16-0 100 Sound 72 5 34-3 .. . 16-0 90 M 73 5 30-9 ... 24-0 90 5 74 5 30-6 ... 23-0 90 55 75 5 30-5 ... 25-0 90 51 76 | 33-3 ... 26-0 90 51 77 5 32-0 ... 26-0 90 55 78 5 32-9 ... 22-0 95 55 79 5 32-2 ... 23-0 90 If 80 , 32-4 ... 26-0 90 55 81 1 32-2 ... 23-0 90 55 82 5 32-5 ... 20-0 90 55 83 1 32-0 .. . 27-0 90 55 84 > 30-8 ... 24-0 90 51 85 5 32-3 ... 23-0 90 5 86 5 33-0 ... 30-0 90 55 87 5 33-8 ... 25-0 90 55 88 n 33-0 ... 28-0 90 55 89 33-7 ... 21-0 90 55 90 ) 34-2 ... 27-0 90 55 91 55 33-9 ... 22-0 90 5? 92 55 34-2 ... 26-0 90 5 93 n 32-2 ... 25-0 90 55 94 55 35-2 ... 21-0 90 55 95 55 34-2 ... 23-0 90 55 96 55 33-1 ... 23-5 90 !5 97 55 33-2 ... 23-0 90 55 ITS PHYSICAL AND CHEMICAL QUALITIES. 69 No. of test. Description of casting. Ultimate tensile strength. Tons per sq. inch. Elongation ! Elongation in 8 inches. """ * ?er n ce. Angle through which test- piece was bent. Degrees. Remarks. | ( Roller 1 || 98 path 32-2 ... 19-0 45 Sound (castings ' 99 j 29-6 ... 28-0 50 jj LOO 29-0 ... 14-0 50 jj L01 31-3 19-0 50 99 [02 28-9 ... 13-0 51 >5 103 5J 33-5 11-5 ... 45 Broke L04 J 31-0 . . . 28-0 50 Sound L05 29-1 12-5 ... 50 LOG jj 30-3 ... 29-0 50 107 j 29-1 ... 31-0 60 108 ?J 27-3 ... 19-0 60 109 J 29-4 12-0 ... 70 Broke 110 31-3 ... 28-0 57 Sound [11 ?5 33-2 10-5 ... 50 Broke 112 5J 29-5 20-0 ... 75 ?? [13 31-8 21-0 ... 70 > [14 30-2 ... 30-0 .50 [15 28-8 26-0 ... 48 Sound [16 27-0 13-5 ... 51 9) [17 jj 29-4 13-5 ... 75 Broke [18 jj 32-2 ... 16-0 45 Sound [19 M 29-2 25-0 ... 50 > [20 Jj 29-3 15-0 ... 55 Broke [21 M 29-5 16-0 ... 50 Sound L22 JJ 33-3 ... 18-0 50 Broke [23 JJ 31-6 15-0 ... 40 ) [24 N 31'7 ... 14-0 35 [25 j> 31-6 14-0 ... 80 L26 Jj 34-0 13-0 ... 70 L27 JJ 31-7 ... 29-0 125 > [28 jj 29-2 ... 25-0 100 > [29 JJ 31-6 14-0 ... 125 Sound [30 JJ 29-9 ... 15-0 70 Broke [31 JJ 29-6 10-0 ... 90 132 JJ 30-6 15*0 ... 90 Sound [33 JJ 29-7 12-0 ... 135 ii [34 n 30-7 ... 24-0 145 [35 JJ 33-3 13-0 ... 65 Broke [36 JJ 34-2 14-0 ... 140 Sound [37 1) 29-1 11-0 ... 145 j> 1 The details of these roller paths are given in Figs. 403, 404, and a descrip- tion will be found on p. 410. CONSTRUCTION IN MILD STEEL. No. of test. Description of casting. Ultimate tensile strength. Tons per eq. inch. Elongation in 8 inches. Per cent. Elongation in 2 inches. Per cent. Angle through which test- piece was bent. Degrees. Remarks. Boiler ) 138 path 29-9 ,,, 12-0 45 Broke castings/ 139 55 33-7 ... 16-0 50 55 140 55 29-7 10-0 ... 70 55 141 55 30-5 ... 30-0 55 55 142 > 30-5 15-0 130 55 143 H 29-7 10-0 ... 70 55 144 55 31-2 11-0 ... 75 55 145 5 28-1 .,, 28-0 145 55 146 31-1 ... 15-0 80 55 147 55 29-8 12*0 ... 75 55 148 30-2 ... 20-0 145 Sound 149 26-1 ... 8-0 85 Broke 150 55 27-8 ... 10-0 70 55 151 55 29-6 ... 18-0 70 55 152 11 29-2 ,. , 23-0 95 55 153 55 31-5 ... 19-0 95 55 154 55 31-2 ... 16-0 90 Sound 155 55 29-6 ... 10-0 90 Broke 156 55 27-9 17-0 ... 100 55 157 5 29-9 ... 24-0 75 55 158 J 30-5 ... 19-0 55 55 159 55 32-1 ... 21-0 60 J5 160 55 32-4 ... 20*0 105 5 161 5> 28-5 ... 10-0 45 55 162 n 33-9 ... 24-0 45 55 163 n 30-5 ... 17-0 105 5> 164 5> 28-0 ... 21-0 70 55 165 )j 30-2 ... 29-0 52 Sound 166 n 31-7 15-0 ... 75 Broke 167 55 31-0 ... 16-0 110 Sound 168 5 30-0 13-0 ... 95 55 169 9) 32-2 12-0 ... 90 5 170 |f 29-2 19-0 ... 70 Broke 171 55 31-5 ... 17-0 65 Broke 172 55 27-1 10-0 ... 65 55 173 D 28-7 ... 15-0 80 Sound 174 55 27'6 13-0 ... 60 Broke 175 55 27-7 25-0 ... 55 55 176 59 32-9 ... 15-0 80 55 177 95 30-2 ... 20-0 135 Sound 178 55 31-2 li'-o ... 75 Broke 179 55 28-9 11-0 ... 62 55 180 55 30-1 13-0 ... 52 M ITS PHYSICAL AND CHEMICAL QUALITIES. No. of test. Description of casting. Ultimate tensile strength. Tons per sq. inch. Elongation in 8 inches. Per cent. Elongation in 2 inches. Per cent. Angle through which test- piece was bent. Degrees. Remarks. 181 (Roller pathj 1 castings j 28-4 11-0 ... 76 Broke 182 28-3 12-0 ... 67 183 11 28-7 10-0 ... 122 Sound 184 32-2 ... 26-0 65 Broke 185 11 28-0 10-0 ... 95 M 186 11 31-2 ... 25-0 77 11 187 11 30-0 11-0 ... 75 11 188 11 32-0 15-0 ... 145 Sound 189 11 27-5 18-0 ... 40 Broke 190 11 27-6 8-0 ... 60 i) 191 11 27-9 8-0 ... 87 M 192 11 28-8 8-0 ... 67 11 193 11 30-3 15-0 ... 85 11 194 195 ( Roller 1 } \ castings J 29-2 33-5 ll'o 26-0 50 45 Sound Broke 196 11 28-8 26-0 ... 48 Sound 197 11 29-5 16-0 ... 50 ii 198 11 28-7 ... 34-0 49 11 199 ,, 28-7 34-0 ... 64 Broke 200 ,, 30-5 14-5 ... 135 Sound 201 11 29-5 18-5 65 Broke 202 11 29-6 13-5 ... 85 11 203 11 31-0 14-5 ... 60 11 204 11 25-4 12-0 ... 75 11 205 11 27-3 10-0 ... 80 11 206 ,, 27-9 12-5 ... 75 11 207 28-3 ... 19-0 150 Sound 208 11 25-4 13-5 ... 80 Broke 209 11 29-4 13-5 ... 115 11 210 11 29-6 19-0 ... 95 11 211 11 29-7 16-0 ... 110 11 212 11 28-0 13-5 ... 60 11 213 29-3 13-5 ... 70 11 214 31-1 14-0 ... 105 Sound 215 ,, 28-0 20-0 ... 90 Broke 216 11 29-2 ... 24-0 45 11 217 ,, 29-0 ... 26-0 55 11 218 ,, 29-2 ... 26-0 50 11 219 29-4 ... 25-0 50 11 220 11 28-9 ... 28-0 45 11 1 The details of these rollers are given in Figs. 405, 406, and a description will be found on p. 412. CONSTRUCTION IN MILD STEEL. Ultimate Angle No. of test. Description of casting. tensile strength. Tons per Elongation n 8 inches. Per cent. Elongation in 2 inches. Per cent. through which test- piece was bent. Remarks. sq. inch. Degrees. 221 ( Roller | ( castings j 27-3 ... 19-0 60 Sound 222 31-3 ... 19'0 50 51 223 55 33-5 11-0 ... 45 Broke 224 55 28-9 at 28-0 45 Sound 225 55 29-1 12-0 ... 50 >> 226 55 27-3 ... 19-0 60 5J Castings for machinery 227 Oast steel l 32-9 14-0 ... 50 Broke Cylinders for. 228 hydraulic 31-8 13-0 ... 90 Sound rams 229 5 34-2 10-0 ... 90 55 230 55 27-8 20-02 ... 90 ? 231 55 28-9 21-0 ... 90 55 232 5) 28-2 22-02 ... 90 5> 233 55 26-6 ... 15-0 90 M 234 55 29-6 ... 34-0 164 ?> 235 55 28-4 ... 26-0 155 55 236 5 35-0 ... 21-0 73 Broke 237 Pinions 33-0 ... 25-0 85 n 238 99 34-7 ... 27-0 90 Sound 239 99 28-2 . . . 35-0 180 j 240 99 35-6 ... 15-0 85 241 99 34-2 . . . 12-0 60 5> 242 Bevel pinions 31-6 ... 8-5 55 ... 243 5> 32-2 ... 12-0 3 ... ... 244 Wheels 36-4 ... 22-0 83 55 245 Clutches 30-2 .. . 12-0 78 Broke 246 99 32-0 17-0 74 55 247 99 32-9 18-0 68 248 Crank discs 28-2 ... 35-0 164 ? 249 5 29-6 ... 34-0 73 )) 250 i Stuffing-box \ 31'6 31-0 180 55 \ covers j 251 5) 31-4 ... 29-0 180 5) 252 > 29-0 ... 30-0 180 Sound 1 These cylinders are referred to on p. 415. 2 Extension on 6 inches. 3 Re-test of No. 242. ITS PHYSICAL AND CHEMICAL QUALITIES. 73 No. of test. Description of casting. Ultimate tensile strength. Tons per Bq. inch. Elongation ! in 8 inches. Per cent. Elongation in 2 inches. Per cent. Angle through | bent. Degrees. 253 (Sundry small) \ castings / 31-3 28-0 ... 57 Broke 254 N 27-0 13-5 ..i 51 Sound 255 32-2 ... 16-0 45 n 256 29-2 25-0 ... 50 257 M 29-6 ... 28-0 86 J5 258 M 31-2 11-0 ... 75 Broke 259 M 33-8 11-5 ... 115 M 260 55 32-6 10-5 ... 120 n 261 55 28-9 ... 21-0 55 Sound 262 M 33-9 ... 24-0 145 Broke 263 M 33-0 ... 25-0 90 264 M 29-6 ... 28-0 135 Sound 265 w 33-9 ... 24-0 45 Broke 266 27-0 13-0 ... 51 Sound 267 | Brackets for | \sliding doors/ 30-5 18-5 ... ... ... 268 36-0 15-7 ... ... ... 269 M 29-8 17-5 ... ... i (Crucible cast- 270 271 steel wheels / for bogie 35-0 39-0 ... 30-0 26-6 ... On 2" On 3" 272 1 waggons to carry50-ton 36-5 ... 29-3 ... ^ loads 6-0 (test 273 Pinion 3 2 '6 ... piece de- 90 Sound fective) 274 J} 31-6 ... 25-0 90 275 ^ 31-4 ... 32-0 45 55 276 M 34-0 ... 16-0 105 277 H 33-0 ... 20-0 105 278 M 32-0 ... 28-0 90 279 55 29-7 ... 14-0 60 Broke 280 Bevel wheel 33-0 ... 27-0 90 Sound 281 N 33-8 ... 30-0 95 282 39-0 ... 20-0 90 55 283 Running wheel 34-8 ... 27-0 45 284 Curb ring 35-6 ... 23-0 45 M 285 )t 35-0 ... 23-0 90 N 286 37-0 ... 22-0 60 287 32-0 ... 32-0 90 288 /Sundry cast-i ] ings for vari-1 27'6 8-5 65 Broke I ous purposes] 74 CONSTRUCTION IN MILD STEEL. No. of test. Description of casting. Ultimate tensile strength. Tons per sq. inch. Elongation in 8 inches. Per cent. Elongation in 2 inches. Per cent. Angle through which test- piece was bent. Degrees. Remarks. 289 Sundry cast-j ings forvari-I 30-5 18-0 77 Broke ous purposes) 290 jj 31-2 it. 25-0 60 M 291 j> 32-2 26-0 87 JJ 292 jj 32-2 26-0 95 >J 293 H 29-4 15-0 ... 87 ft 294 jj 29-8 ... 21-0 85 Sound 295 jj 28-0 10-0 90 M 296 JJ 30-5 ... 18-0 65 Broke 297 JJ 30-8 ... 24-0 87 jj 298 JJ 32-5 19-0 ... 75 M 299 JJ 29*4 16-0 ... 90 jj 300 JJ 29-8 15-0 ... 65 j 301 JJ 29-2 ... 18-0 118 Sound 302 29-2 ... 15-0 55 Broke 303 JJ 31*5 ... 21-0 60 j 304 JJ 30-9 ... 22-0 63 jj 305 JJ 31-2 ... 20-0 58 >j 306 JJ 31-9 ... 14-0 59 jj The following experiments on the transverse resistance to bending of cast-steel bars are of interest, more especially as similar tests are, so far as the writer knows, somewhat rare. TABLE No. 21. THE TRANSVERSE STRENGTH OF CAST-STEEL BARS. The bars were of the nominal dimensions of 2" x 1", planed all over, the load being applied at the centre of the specimen, and the greater dimension of the bar being vertical. Distance between supports = 36 inches. No. of specimen. Dimensions. Span. Load applied. Deflection in inches. Remarks. Pounds. Tons. (1120 0-5 0-06) Permanent set at I. 1-958" x 0-963" 3'0" 2240 13360 1-0 1-5 0-11 0-211 1-5 ton of 0-07 inch. ITS PHYSICAL AND CHEMICAL QUALITIES. 75 Load applied. No. of specimen. Dimensions. Span. Deflection n inches. Remarks. Pounds. Tons. 1120 0-5 0-07) Permanent set at II. 1-954" X 0-978" 3'0" 2240 1-0 0-13 1-5 ton of 0-07 3360 1-5 0-25J inch. /Permanent set at [1120 0-5 0-07 1-0 ton of 0-03 in oil III. 2-00" X I'OO" 3'0" 2240 ^3360 4480 1.5891 1-0 1-6 2-0 2-63 0-15 0-61 2-30 Specimen bent 1 through 70, but not broken; slight cracks visible. 11120 0-5 0-09^ Permanent set at 2240 1-0 0-15 1-0 ton of 0-02 IV. 2-05" X 1'05" 3'0" 3360 1-5 0-25 \ inch. 4480 2-0 1-59 Specimen broke at 5980 2-67 Break] 2-67 tons. 1120 2240 0-5 1-0 0-06^1 0-12 Permanent set not noted V. 2-00" X I'OO" 3'0" 3360 4480 5600 6720 1-5 2-0 2-5 3-0 0-17 0-62 1-79 3-31 Specimen bent through 64, but did not break. The chemical analyses of the bars referred to in the foregoing table are as follows : BARS Nos. I. AND II. Carbon Silicon Sulphur Phosphorus Iron (by difference) Per cent. 0-250 0-086 0-073 0-065 0-911 98-615 100-000 Ultimate tensile strength = 31-2 tons per square inch. Ultimate elongation = 10-0 per cent, in 8 inches. Angle bent through (1 inch square) = 90. ?6 CONSTRUCTION IN MILD STEEL. BARS Nos. III. AND IV. Per cent. Carbon 0-265 Silicon 0-320 Sulphur 0-082 Phosphorus 0*042 Manganese ... ... ... ... 0*637 Iron (by difference) 98-654 100-000 Ultimate tensile strength = 28*86 tons per square inch. Ultimate elongation = 22-5 per cent, in 2 inches. Contraction of area = 22-0 per cent. BAR No. V. Per cent. Carbon 0-415 Silicon 0-187 Sulphur 0-067 Phosphorus 0'036 Manganese ... ... ... ... 0*511 Iron (by difference) 98-784 100*000 Ultimate tensile strength = 35-6 tons per square inch. Ultimate elongation = 15*6 per cent, in 2 inches. Angle bent through (1 inch square) = 85. The chemical analyses of two specimens of cast-steel bars not submitted to a transverse test are as follows : Carbon Silicon Sulphur Phosphorus ... Manganese Iron (by difference) ... 100-000 100-000 Ultimate tensile strength (a) = 28*9, (6) = 28-2 tons per square inch. Ultimate elongation (a) = 21 per cent, in 8 inches, (6) = 35 per cent, in 2 inches. Angle bent through (1 inch square) (a) = 90, (6) = 180. JTS PHYSICAL AND CHEMICAL QUALITIES. 77 Chemical analysis of cast- steel brackets for sliding doors Per cent. Carbon 0'488 Silicon 0-269 Sulphur 0-085 Phosphorus 0'070 Manganese... ... ... ... ... 0'421 Iron (by difference) 98-667 100-000 The ultimate tensile strength of this metal was 36'0 tons per square inch, and the ultimate elongation was 15*7 per cent, in 8 inches. (Test No. 268, Table No. 20.) The series of tests which follows on the transverse strength of cast-iron bars is but a selection from a number of tests made in different foundries, and covering a wide range of constructive practice. The material represented was used for bridge and jetty cylinders, bollards, machinery castings, various details in con- nection with bridge construction, penstock frames and doors, and the like. The variations shown are characteristic, but the general average indicates that the standard of strength and elasticity aimed at in the specification has been generally attained, and fairly represents good modern foundry practice in this class of work. TABLE No. 22. THE TRANSVERSE STRENGTH OF CAST-IRON TEST-BARS LOADED AT THE CENTRE, ON SUPPORTS 36 INCHES APART. Nominal size of bar, 2 inches deep x 1 inch wide. No. of Test. Actual dimensions of test-bar as cast. Inches. Actual breaking load at centre. Pounds. Deflection at fracture. Inches. Equivalent breaking load of 2" X 1" bar calculated in the proportion of BD*. Pounds. Depth. Breadth. 1 2 2-06 2-08 1-06 1-07 3046 2934 0-33 0-30 2715 2540 l 3 2-11 1-05 3203 0-30 2744 i 4 2-06 1-07 4278 0-35 3770 1 Flaw on underside. CONSTRUCTION IN MILD STEEL. No. of Test. Actual dimensions of test-bar as cast. Inches. Actual breaking load at centre. Pounds. Deflection at fracture. Inches. Equivalent breaking load of 2" X 1" bar calculated in the proportion of BD*. Pounds. Depth. Breadth. 5 2-06 1-06 3875 0-30 3452 6 2-1 I'l 2329 0-25 19211 7 2-06 1-07 5734 0-55 5040 2 8 2-04 1-02 4726 0-40 4457 9 2-07 1-09 4300 0-50 3683 10 2-07 MO 3472 0-28 29471 11 2-06 1-08 3516 0-30 3069i 12 2-08 1-06 5465 0-50 4768 13 2-07 1-07 2822 0-15 2462i 14 2-06 1-08 4009 0-35 3500 15 2-07 1-06 4054 0-33 3500 16 2-05 1-06 3584 0-30 3218 17 2-10 1-07 4278 0-35 3626 18 2-00 1-00 3940 0-41 3940 19 2-00 1-00 3800 0-44 3800 20 2-00 1-00 3780 0-41 3780 21 2-00 1-00 3830 0-38 3830 22 2'00 1-00 4490 0-44 4490 23 2-00 1-00 4320 0-39 4320 24 2-01 1-06 3113 0-45 2909 25 2-02 1-00 3875 0-40 3800 26 2-00 1-00 3300 0'41 3300 27 2-00 1-00 3390 0-41 3390 28 2-00 1-00 3290 0-41 3290 29 2-00 1-00 3150 0-38 3150 30 2-00 1-00 3140 0-37 3140 31 2-00 1-00 3160 0-38 3160 32 2-00 1-00 4010 0*47 4010 33 2-00 1-00 3820 0-42 3820 34 2-00 1-00 3390 0-43 3390 35 2-00 1-00 3550 0-46 3550 36 2-00 1-00 3360 0-45 3360 37 2-00 1-00 3820 0-42 3820 38 2-00 1-00 3640 0-41 3640 39 2-00 1-00 3710 0-42 3710 40 2-00 1-03 4050 0-43 3927 41 2-00 1-00 4210 0-49 4210 42 2-00 1-03 3490 0-40 3384 43 2-00 1-00 3610 0-43 3610 44 2-00 1-00 3780 0-41 3780 45 2-00 1-00 3710 0-45 3710 46 2-00 1-00 3674 0-43 3674 47 2-00 1-00 3150 0-35 3150 48 2-00 1-00 3000 0-29 3000 Flaw on underside. 2 Flaw on upper half. ITS PHYSICAL AND CHEMICAL QUALITIES. 79 No. of Test. Actual dimensions of test-bar as cast. Inches. Actual breaking load at centre. Pounds. i Equivalent breaking Deflection at K load f 2 ," *}". fracture. Inches. gS& Depth. Breadth. BD". Pounds. 49 2-00 1-00 3350 0-40 3350 50 2-00 1-00 3100 0-30 3100 51 2-12 1-07 4233 0-35 3519 52 2-06 1-09 3785 0-30 3274 53 2-11 1-05 3248 0-25 2781 1 54 2-07 1-07 4278 0-35 3736 55 2-06 1-07 4188 0-32 3690 56 2-12 1-08 4435 0-40 3654 57 2-00 1-00 3303 0-28 3303 58 2-00 1-00 3472 0-30 3472 59 2-00 1-00 3610 0-33 3610 60 2-00 1-00 3582 0-36 3582 61 2-00 1-00 3580 0-415 3580 62 2-00 1-00 3990 0-454 3990 63 2-00 1-00 3200 0-390 3200 64 2-00 1-00 3530 0-416 3530 65 2-00 1-00 3889 0-455 3889 66 2-00 1-00 3950 0-450 3950 67 2-00 1-00 3580 0-437 3580 68 2-00 1-00 3750 0-455 3750 69 2-00 1-00 3640 0-437 3640 70 2-00 1-00 3528 0-375 3528 71 2-00 1-00 3696 0-437 3371 72 2-00 1-00 4032 0-437 3371 73 2-00 1-00 4032 0-437 3371 74 2-00 1-00 3360 0-437 3360 75 2-00 1-00 3528 0-375 3528 76 2-00 1-00 3808 0-437 3808 77 2-00 1-00 3584 0-375 3584 78 2-00 1-00 3528 0-375 3528 79 2-00 1-00 3360 0-437 3360 80 2-00 1-00 3416 0-375 3416 81 2-00 1-00 3584 0-437 3584 82 2-00 1-00 3304 0-375 3304 83 2-00 1-00 3584 0-437 3584 84 2-00 1-00 3360 0-375 3360 85 2-00 1-00 3426 0-437 3426 86 2-00 1-00 3696 0-375 3696 87 2-00 1-00 3864 0*375 3438 88 2-00 1-00 3528 0-375 3528 89 2-00 1-00 3584 0-375 3584 90 2-00 1-00 3696 0-500 3472 91 2-00 1-00 3192 0-343 2902 92 2-00 1-00 3472 0-406 3270 2 1 Flaw on underside. 2 Retest of No. 91. 8o CONSTRUCTION IN MILD STEEL. No. of Test. Actual dimensions of test-bar as cast. Inches. Actual breaking load at centre. Pounds. Deflection at fracture. Inches. Equivalent breaking load of 2" X 1" bar calculated in the proportion of BD 2 . Pounds. Depth. Breadth. 93 2-00 1-00 3304 0-375 3158 94 2-00 1-00 3248 0-406 3102 95 2-00 1-00 4144 0-500 4020 96 2-00 1-00 3472 0-437 3360 97 2-00 1-00 3584 0-375 3360 98 2-00 1-00 3360 0-406 3304 99 2-00 1-00 3584 0-437 3528 100 2-00 1-00 3584 0-437 3472 In tests Nos. 69 to 100 the dimensions of the test-bar are nominal only. In all cases the breaking load is reduced in the last column in the proportion of BD 2 . It is not unusual to find specifications for cast-iron work which combine a specified ultimate resistance in direct tension with a specified transverse breaking load on a standard bar. The discrepancy between the calculated fibre stress (using the ordinary formula) and the ultimate resistance in direct tension has been long known from the days of the earlier experimenters to the present time, and much has been written upon the subject, including the influence of the form of cross-section upon the ratio. The subject, which is one of great interest, and affects not only cast iron, but also the permissible working fibre stress in small wrought- iron and mild steel beams, cannot be further alluded to here, but the practical lesson to be drawn as regards the drawing up of specifications for the strength of cast iron appears to be, that where the ultimate transverse resistance is stipulated, it is wiser to avoid direct reference to the ultimate tensile resistance, or vice versa. Either standard of strength may be chosen, but not both, unless the purchaser is prepared to establish to his own satisfaction, and that of the contractor, the precise ratio which in any given bar should obtain between ultimate transverse resistance and ultimate tensile strength. It is customary to find the test-bar as cast to vary fractionally both in breadth and depth from the nominal dimensions, and it therefore becomes necessary to allow for the variation in the observed breaking load, and to reduce to a common standard in the proportion of breadth X depth 2 . This has been done in the ITS PHYSICAL AND CHEMICAL QUALITIES. 81 foregoing table, and the mean value of the breaking load at the centre of a bar 2 inches deep by 1 inch wide, on supports 36 inches apart, is found to be from the above experiments (omitting those with flaws on the underside) 3568 Ibs., and the mean deflection at the centre, O394 inch. The test-bar may also be found to vary from a true rectangular shape, being thicker at top than at bottom, and the way in which such a bar is placed in the testing machine should be observed, Numerous published chemical analyses of cast iron will be found in the literature of this subject, but the following analysis of a test-bar of the dimensions given in the foregoing table will serve to afford the student a fair idea of the chemical differences between cast iron and cast steel. The analysis presents no very marked difference from the normal composition of cast iron, save that the proportions of manganese and phosphorus are somewhat high. CHEMICAL ANALYSIS OF CAST-IRON TEST-BAR. Per cent. Graphite 2-215 Combined carbon ... ... ... ... 1-802 Silicon 2-028 Sulphur 0-101 Phosphorus 1'192 Manganese ... ... ... ... 0*965 Iron (by difference) 91-697 100-000 The test-bar from which the analysis was taken gave a breaking weight of 28 cwt. at centre of standard bar (2" X 1" at 36" span) with | inch deflection. CHAPTEK II. ROLLED SECTIONS IN STEEL AND THEIR MECHANICAL ELE- MENTS, WITH GENERAL REMARKS ON THEIR USES AND COMBINATIONS. Angles Equal-legged Unequal-legged Round-backed Acute-angled Obtuse- angled Bulb-angles British standard sections Table of the principal mechanical elements of equal-legged angles ; of unequal-legged angles Tees British standard sections Bulb tees Table of the principal mechanical elements of ordinary tees; of bulb tees Rolled joists General remarks Proportions of web and flange thicknesses Standards of proportion British standard sections Table of the principal mechanical elements of rolled joists Channels Standards of proportions British standard sections Table of the principal mechanical elements of channels Zed angles General remarks British standard sections Table of the principal mechanical elements of Zed angles Other forms of sections Plates Bars Flats. IT is proposed in this chapter to give a short description of the principal rolled sections in steel commonly used in ordinary c,/ /* ' Ox / S \ N X X \ ^ \ \ X W\Vv\X\?Cv oo^Vk^y -;T - b d, FIG. 7. FIG. 8. riveted construction, with tables of their principal mechanical elements, and some practical remarks on their use. Angles, The angle-steel, or, to use the older nomenclature, the angle-iron, is perhaps the most commonly in use among all those sections of material which go to make up riveted work. It may be "equal-legged," as in Fig. 7, or "unequal-legged," as in Fig. 8. ROLLED SECTIONS IN STEEL. 83 The equal-legged angle in its ordinary form has a rectangular outline with a square corner on the outside, the interior faces being sometimes slightly tapered with a connecting round in the inner corner, and the edges rounded off to a quadrant of small radius. These tapers and the radii of the roundings are not quite the same in all section books, varying with the shape of the rolls of the respective makers, although proposals for the adoption of a uniform standard in this as in other sections have not been wanting. These proposals have now assumed a definite form in this country, by the issue of the " British Standard Sections," compiled under the direction of the Engineering Standards Committee in 1904, and to these sections the attention of the student is directed ; and in the work entitled " Properties of British Standard Sections " will be found the standard sizes, thicknesses, slopes of taper, and radii of connecting curves, together with tables of the mechanical elements of the standard sections. The unequal-legged angle presents the same general character- istics, while its name speaks for itself. Both the equal- and unequal-legged section is, in the British standard section, of uniform thickness, without taper. Variations from these forms are found in the acute-angled angle and the obtuse-angled angle, used where oblique connections of riveted work have to be made. The use of acute-angled angles is attended sometimes with the difficulty of getting the rivets into the acute angle, which must be borne in mind in these cases, it being sometimes necessary, if the angle of connection is very acute, to use a bent plate of sufficient dimen- sions in lieu of an angle. Both equal- and unequal-legged angles are also rolled with a round back, as in Fig. 9. They are most commonly used to effect the splice in the main angles of plate or lattice girders, an example of which is given in Fig. 101, the round back of the connecting angle FlG 9> fitting into the interior rounding of the main angles to be spliced. This method of splicing the main angles of a riveted plate girder is the one most commonly adopted, and leads to the consideration of the net sectional area of the angles to be spliced, the corresponding thickness of the angle " cover," which 84 CONSTRUCTION IN MILD STEEL. must necessarily be greater than that of the main angles, and as a consequence the spaces left for the rivets, their heads, and the amount of metal left outside them. When, however, angles are used for ties or struts, either singly or in pairs, as in roof trusses, it becomes a simple matter to splice each leg of the angle with a flat of suitable width and thickness. Another variation in the equal- or unequal-legged angle is that in which the legs are rolled of equal thickness without taper, and the edges and corners, both internal and external, are square and sharp. This, however, is usually considered a special section, and not frequently adopted in ordinary riveted work. A section of angle-iron used frequently in the frames of ship or caisson work, as beams subject to transverse stress, is the so- called bulb-angle, shown in Fig. 10. This angle is usually unequal-legged, the object of the bulb being to increase the moment of inertia of the beam in the plane of its greatest depth as a beam, while it also serves the purpose of thickening and rounding the edge of the angle where exposed to passing traffic, etc. The bulb may be rolled on one side of the longest limb as shown, or on the opposite side. FIG. 10. The sectional area of the bulb varies slightly with different makers, but is standardized in the British standard section. According to the usual practice, the vertical limb or web with the bulb is made parallel, the taper being given to the other limb of the angle. In the British standard section of bulb-angle, both limbs are of uniform thickness, there being no taper. If the section be increased beyond a certain minimum thickness the dimensions of the sides are increased proportionately, while the bulb retains the same projection from the face of the web. The uses of angle-steels are multifarious. In addition to their primary function of connecting members of a structure in planes at right angles to one another, such as the web and flanges of a plate girder, or in oblique connections, they are also found used to a great extent either as beams, struts, or ties. As beams we find them in purlins to roofs, as secondary beams in a variety of structures, in the framing to sides of corrugated iron sheds, and the like. As struts they are employed in the members of ROLLED SECTIONS IN STEEL. 85 lattice girders, in the compression members of roof principals, and as secondary bracing where some lateral stiffness is required in a number of cases. As ties they appear more or less suc- cessfully in the tension members of light trusses, but their effective use in tension is somewhat qualified by the necessity of securing them in many cases by one leg only. This remark also applies under similar conditions to their use as struts. In this latter capacity they will be further referred to in the chapter on columns. The selection of the dimensions and scantlings of angles will be determined by a variety of considerations depending on the use to which they are put. As connecting members simply we shall find their dimensions ruled to a large extent by the size of rivets employed, the bearing stress allowed, and so on ; as beams, by their moment of inertia; as struts, by their least radius of gyration. But in most cases considerations of rivet spacing in connections, etc., will be ruling factors in the design ; and the young draughts- man will in this, as in so many other cases, be wise in drawing all doubtful details full size, or to a large scale, before he finally determines his section. The following tables give the dimensions, weight per foot run, sectional area, moments of inertia, and least radii of gyration for equal-legged, unequal-legged, and bulb-angles in steel : TABLE No. 23. THE PRINCIPAL MECHANICAL ELEMENTS OF EQUAL-LEGGED ANGLES l (See Fig. 7). Section. Equal-legged angles. Area in sq. inches. Weight in Ibs. per foot lineal. Approximate moment of inertia about axis a 6, Approximate least radius of gyration, Distance of axis a-b from farthest edge of section. Fig. 7. AXIS C~ (*. Inches. 8" X 8" X 1 15-00 51-00 88-98 1-56 5-63 8" X 8" X 1 13-23 44-98 79-46 ... 5-68 8" X 8" X | 11-44 38-89 70-04 1-57 5-72 8" X 8" X f 9-61 32-67 59-80 ... 5-77 8" X 8" X J 7-75 26-35 48-65 1-58 5-87 7" X 7" X 1" 13-00 44-20 58-16 1-36 4-89 1 In this and the following tables the effects of taper and of the circular curves connecting members are ignored. The values are therefore approximate, but of sufficient accuracy for practical purposes. 86 CONSTRUCTION IN MILD STEEL. Section. Equal-legged angles. Area in sq. inches. Weight in Ibs. per foot lineal. Approximate moment of inertia about axis a 6, Fig. 7. Approximate least radius of gyration, axis c d. Distance of axis a b from farthest edge of section. Inches. 7" X 7" X |" 11-48 39-05 52-10 4-93 7" X 7" X |" 9-94 33-79 45-86 1-37 4-98 7" X 7" X f" 8-36 28-42 39-14 ... 5-02 7" X 7" X f 6-75 22-95 32-00 1-38 5-06 6" X 6" X 1" 11-00 37-40 35-46 1-18 4-13 6" X 6" X F 9-73 33-10 31-88 . 4-18 6" X 6" X f 8-44 28-69 28-12 1-19 4-22 6" X 6" X f" 7-11 24-17 24-11 4-27 6" X 6" X 1" 5-75 19-55 19-90 1-20 4-31 51" X 51" X |" 8-86 30-12 24-07 1-06 3-81 51" X 51" X I" 7-69 26-14 21-32 3-85 5f X 51" X f 4" X 51" X f 6-48 5-25 22-05 17-85 18-03 15-19 1-08 3-90 3-94 5" X 5 ft X f 6-94 23-59 15-75 0-98 3-48 5" X 5" X f" 5-86 19-92 13-56 ... 3-52 5" X 5" X l" 4-75 16-15 11-24 1-00 3-56 41" X 41" X f " 5-23 17-80 9-72 0-87 3-14 A l" v 4-L" v 1" ^TQ A J-o A Q 4-25 14-45 8-00 ... 3-19 ^1" v, ^1" y JTJ/ 41" v 4.1" s/ &" 4- 2 X *2 X I 3-75 3-23 12-74 11-00 7-18 6-27 0-88 3-21 3-23 4" X 4" X f" 4-61 15-67 6-65 0-78 2-77 4" X 4" X f 3-75 12-75 5-56 ... 2-81 4" X 4" x A" 3-31 11-25 4-96 ... 2-84 4" X 4" X f" 2-86 9-72 4-35 0-79 2-86 3f X 3f X f" 3-98 13-55 4-32 0-68 2-40 31" X 3|" X i" 3-25 11-05 3-64 2-44 3|" X 3|" X &" 2-87 9-76 3-24 2-46 3f X 3f X f 2-48 8-45 2-88 0-69 2-48 3J" X 3f x |" 3-00 10-20 2-85 0-64 2-25 3J" X 3f X fe" 2-65 9-02 2-58 2-28 3f X 3f X f 2-30 7-82 2-25 0-65 2-30 3" X 3" X f 2-75 9-35 2-22 0-58 2-07 3" x 3" X &" 2-43 8-27 1-99 ... 2-09 3" X 3" X f 2-11 7-17 1-75 0-59 2-11 2f " X 2f x f 2-50 8-50 1-67 0-53 1-87 2f X 2f" X A" 2-21 7-53 1-51 1-90 2 y 2 y " 1-92 6-53 1-33 0-54 1-92 21" X 2|" X ^" 2-00 6-79 1-11 0-49 1-71 91" v 21" V " 2 ^2 *> 8 1-73 5-90 0-98 1-74 2-" X 2-" X 5 -" 1-47 4-98 0-85 0-50 1-76 2f X 2f X f 1-55 5-26 0-70 0-44 1-55 2J" X 21" x A" 1-31 4-45 0-61 0-45 1-57 2" X 2 " X f 1-36 4-62 0-48 0-39 1-36 9" \/ 9" \x 6 " Z X ^ X j-g 1-15 3-92 0-42 0-40 1-38 4 X A^ X jg 1-00 3-39 0-27 0-34 1-20 ROLLED SECTIONS IN STEEL. Section. Equal-legged angles. Area in sq. inches. Weight In Ibs. per foot lineal. Approximate moment of inertia about axis a b, Fig. 7. Approximate least radius of gyration, axis c d. Distance of axis a 6 from farthest edge of section. Inches. if" x if x f 0-81 2-76 0-23 0-34 1-22 11" x I 1 " X --" 0-84 2-86 0-16 0-30 1-01 if x if xj 1 0-69 2-34 0-14 0-30 1-03 if x if x f 0-56 1-91 0-077 0-24 0-85 If X If X f 0-29 0-98 0-044 0-24 0-89 V s X 1" X f 0-44 1-49 0-037 0-19 0-66 1" X 1" X f 0-23 0-78 0-022 0-19 0-70 3" v 3'/ v- 1" 4 X 4 X 8 0-17 0-58 0-008 0-15 0-51 TABLE No. 24. THE PRINCIPAL MECHANICAL ELEMENTS OF UNEQUAL-LEGGED ANGLES (See Fig. 8). Section. Unequal-legged angles. Area in sq. inches. Weight In Ibs. per foot lineal. Approximate moment of inertia about axis a ft, Fig. 8. Approximate least radius of gyration about axis c d. Distance of axis a 6 from farthest edge of section. Inches. 14" X 3f X f 8-50 28-90 160-0 0-94 8-19 11' X 3" X f 6-75 22-95 78-5 0-81 6-47 10" X 3f X f 6-50 22-10 63-5 0-92 6-10 9" X 3f X |" 6-00 20-40 48-0 0-90 5-56 8" X 4f X f" 8-81 29-96 57-1 0-96 5-16 8" X 4f X f 7-42 25-23 48-6 0-96 5-21 8" X 4f X 6-00 20-40 39-8 0-96 5-25 8" X 3f X f 6-80 23-11 42-5 0-73 4-96 8" X 3f X f 5-50 18-70 33-5 0-73 5-02 8" X 3" X f 6-48 22-05 40-2 0-73 4-84 8" X 3" X f 5-25 17-85 32-6 0-73 4-89 7f X 3" X f 6-17 20-98 33-7 0-71 4-57 7f X 3" X |" 5-00 17-00 27-5 0-71 4-62 7" X 4" X f " 7-69 26-14 37-87 0-85 4-50 7" X 4" X f" 6-48 22-05 32-24 0-85 4-54 7" X 4" X f 5-25 17-85 26-62 0-86 4-58 7" X 3f X f" 6-17 20-98 30-73 0-75 4-43 7" X 3f X f 5-00 17-00 25-33 0-75 4-47 7" X 3" X f 5-86 19-92 27-9 0-76 4-30 7" X 3" X f 4-75 16-15 22-9 0-76 4-35 7" X 3" X f" 3-61 12-27 17-6 0-77 4-40 6f X 4f X f 6-41 22-05 27-56 0-95 4-34 61" x 4^-" X -" 5-25 17-85 23-49 0-96 4-38 6|" X 4f X |" 3-98 13-55 17-68 0-96 4-43 6f X 4" X |" 6-17 20-98 26-36 0'84 4-26 88 CONSTRUCTION IN MILD STEEL. Section. Unequal-legged angles. Area in sq. inches. Weight in Ibs. per foot lineal. Approximate moment of inertia about axis a &, Fig. 8. Approximate east radius of gyration about axis c d. Distance of axis a b from farthest edge of section. Inches. 6f X 4" X f 5-00 17-00 21-42 0-85 4-30 6f X 4" X f 3-80 12-91 16-81 0-85 4-34 6f X 3f X f 5-86 19-92 24-99 0-79 4-15 6f X 3J" X f 4-75 16-15 20-37 0-80 4-19 6f X 3|" X f" 3-61 12-27 16-15 0-80 4-24 6f X 3" X f 5-55 18-86 24-35 0-78 4-03 6f X 3" x f 4-50 15-30 18-75 0-79 4-08 6i" X 3" X f 3-42 11-63 14-35 0-79 4-13 6" x 5" X 1" 8-86 30-12 30-13 1-03 4-04 6" X 5" X f 7-69 26-14 26'46 1-04 4-08 6" x 5" X f 6-48 22-05 22-68 1-04 4-13 6" X 4" x f" 6-94 23-59 24-62 0-87 3-92 6" x 4" X f" 5-86 19-92 21-25 0-88 3-96 6" X 4" X f 4-75 16-15 17-45 0-88 4-01 6" X 3f x f 5-55 18-86 20-18 0-79 3-87 6" X 3f" x f 4-50 15-30 16-63 0-80 3-92 6" X 3f X f/ 3-97 13-48 14-74 0-80 3-94 6" X 3" X f 5-23 17-80 18-92 0-76 3-76 6" X 3" X f 4-25 14-45 15-68 0-77 3-81 6" X 3" x f 3-23 11-00 12-12 0-77 3-85 5f X 4" x f " 5-55 18-86 16-37 0-86 3-67 5|" X 4" X f 4-50 15-30 13-64 0-87 3-72 5f X 4" X |" 3-42 11-63 10-51 0-87 3-78 5f x 3|" X f " 5-23 17-80 15-84 0-79 3-59 5f X 3" X |" 4-25 14-45 13-04 0-80 3-63 4" X 3f X |" 3-23 11-00 10-07 0-80 3-67 5f X 3' 1 x f" 4-92 16-73 14-91 0-67 3-49 5J" X 3" x |" 4-00 13-60 12-28 0-68 3-53 5f" X 3" X |" 3-05 10-36 9*53 0-68 3-57 5" X 4f X f " 5-55 18-86 13-10 0-89 3-45 5" X 4f x f 4-50 15-30 10-88 0-90 3-50 5" X 4|" x |" 3-42 11-63 8-44 0-90 3-54 5" X 4" X f 5-23 17-80 12-55 0-85 3-38 5" X 4" x V 4-25 14-45 10-45 0-86 3-42 5" X 4" X f 3-23 11-00 8-12 0-86 3-46 5" X 3f X f 4-92 16-73 12-03 0-75 3-30 5" X 31" X 1" 4-00 13-60 10-02 0-76 3-34 5" X 3|" X |" 3-05 10-36 7-79 0-76 3-39 5" x 3" X f 4-61 15-67 11-36 0-65 3-21 5" X 3" x f 3-75 12-75 9-45 0-66 3-25 5" X 3" x |" 2-86 9-72 7-31 0-66 3-29 4i" X 4"xf 4-92 16-73 9-37 0-80 3-08 4f" x 4" X |" 4-00 13-60 7-87 0-81 3-13 4f X 4" x f 3-05 10-36 6-05 0-81 3-17 4 f X 3f x f 4-61 15-67 8-83 0-74 3-01 ROLLED SECTIONS IN STEEL. 89 Section. Unequal-legged angles. Area in sq. inches. Weight in Ibs. per foot lineal. Approximate moment of inertia about axis a b, Fig. 8. Approximate least radius of gyration about axis c d. Distance of axis a b from farthest edge of section. Inches. 4f X 3f x f 3-75 12-75 7-33 0-75 3-05 4f X 3f x |" 2-86 9-72 5-71 0-75 3-09 4f X 3" x f 4-30 14-61 8-50 0-65 2-91 4f X 3" X f 3-50 11-90 7-02 0-66 2-96 4f x 3" X f 2-67 9-08 5-49 0-66 3-00 4f X 2f X f 3-25 11-05 6-03 0-62 2-86 4JL" v 91" v/ 3" ~*>2 ^ 1 ^ S 2-48 8-45 5-17 0-62 2-90 4" X 3f X f 4-30 14-61 6-36 0-72 2-70 4" x 3f X f 3-50 11-90 5-31 0-73 2-75 4" X 3f X f 2-67 9-08 4-16 0-73 2-79 4" x 3" X f 3-98 13-55 6-01 0-64 2-63 4" X 3" X f 3-25 11-05 5-03 0-65 2-67 4" X 3" X f" 2-48 8-45 3-95 0-65 2-71 4" X 2f x f 3-00 10-20 4-72 0-56 2-58 4" X 2f x |" 2-30 7-81 3-79 0-50 2-62 3f X 3" X f 3-00 10-20 ' 3-45 0-63 2-37 3f X 3" X f 2-30 7-81 2-71 0-63 2-42 3f X 2f X f 2-75 9-35 3-25 0-55 2-29 3f" x 2f X f 2-11 7-17 2-57 0-55 2-33 3f X 2f X f 2-02 6-85 2-46 0-53 2-29 3f X 2f x &" 1-70 5-78 2-10 0-53 2-32 3" X 2f" X f 2-63 8-93 2-16 0-55 2-03 3" X 2f X f 2-02 6-85 1-78 0-55 2-08 3" X 2f x f 2-50 8-50 2-09 0-53 2-00 3" X 2f x f 1-92 6-53 1-64 0-53 2-04 3" x 2" x " 1-47 4-98 1-32 0-44 1-98 3" X 2" X f ' 1-19 4-04 1-07 0-44 2-01 2f X 21" x " 1-39 4-72 0-82 0-45 1-73 2f X 2f X f 1-13 3-83 0-68 0-45 1-75 91" \x O" v> 5 " ^ X ^ X 77 1-31 4-45 0-79 0-43 1-69 2f X 2" x f 1-06 3-61 0-65 0-43 1-71 2f X If X f 0-94 3-19 0-46 0-34 1-52 2" X If X f 0-88 2-98 0-33 0-35 1-37 2" X H" X f 0-81 2-76 0-31 0-32 1-34 2" X 1'"' X &" 0-53 1-79 0-21 0-25 1-26 if x if x f 0-75 2-55 021 0-29 1-19 if x if x f 0-39 1-32 0-12 0-29 1-23 4" x if x f 0-63 2-13 0-13 0-26 1-00 if x if x I" 0-33 1-12 0-070 0-26 1-04 If X 1" X f 0-26 0-88 0-040 0-21 0-85 i| x |;; x ^ 0-25 0-85 0-039 0-20 0-83 0-23 0-78 0-028 0-20 0-76 1" X f X f" 0-20 0-68 0-019 0-16 0-67 3" y I" y I" 4X3X3 0-14 0-47 0-007 o-n 0-48 90 CONSTRUCTION IN MILD STEEL. Tees. The tee-steel, or tee-iron, ranks perhaps next to the angle in general utility. Its general form is shown in Fig. 11. The proportions of top table to stem or web are very variable, and the error of misde- scription of the dimensions is one very fre- quently found on drawings, rectified, it may be, by dimensioning the members, but the young draughtsman will do well to remember that a 6" X 3" tee is by no means the same thing as a 3" X 6" tee. He will probably ascertain this to his cost if he specifies the one in mistake for the other, in the absence of a figured section. The width of top table FIG. 11. . ,, *L. n , -, is the dimension first quoted. The top table and stem are usually both slightly tapered, and connected by roundings of small radius, the corners of the extremities of the limbs being sometimes rounded and sometimes square. A variation sometimes found is when the top table is of uniform thickness and the stem tapered, or vice versa. The British standard section of tee has the top table and the web tapered, the edges of the top table being rounded off beneath, while the edge of the web is square. Tees are commonly used as beams, as in the case of purlins, secondary bearers in fire-proof floors, and the like. As struts they are a favourite section for the compression members of roof trusses of moderate span, lattice girders, etc., also as stiffeners to the webs of plate girders. As ties their use is more limited, there being some difficulty in making such an end connection as will effectively bring into play the whole cross-section of the metal. Tee struts will be further referred to in the chapter on columns. The proportions of tees to be adopted in any particular detail will, apart from the value of their moments of inertia when used as beams, or of their least radius of gyration when used as struts, be frequently ruled by the dimensions and spacing of their riveted or bolted connections. Thus, to take a familiar example, the tee stiffener to the web of a plate girder will require a width of top table or flange sufficient to take the rivets required in a joint of the web plating, which again will be ruled by the shearing stresses in the web, and the number and diameter of the rivets required. Or supposing, in the case, let us say, of a footbridge with timber floor secured to tee bearers by bolts or coach-screws, the ROLLED SECTIONS IN STEEL. top table of the tee must be of width enough to receive screws or bolts of the diameter required, with (a) a sufficient amount of metal outside the hole, and (6) sufficient space between the stem and hole for the nut of the bolt or head of the coach-screw. Such elementary considerations may bear the aspect of truisms, but careful attention to points of detail such as these will always be found to characterize sound ironwork design. Bulb Tees. A tee section with a bulb rolled on the lower extremity of the stem constitutes the useful section known as " bulb tee " or " deck beam." This section is used to a considerable extent in shipbuilding, I C and occasionally in purlins and similar beams. The moment of inertia is increased by the bulb, which also forms a finish to the lower edge of the stem, which is usually rolled with parallel sides, the top table or flange having a taper similar to the flange of a rolled joist. The area of the bulb and relative thickness of stem and flange vary somewhat in different rolling mills, but are standardized in the British standard section. The following tables give the dimensions, sectional area, weight per foot run, greatest moment of inertia, position of centre of gravity, and least radius of gyration, for ordinary tees and for bulb tees of average proportions of stem, flange, and bulbs. TABLE No. 25. THE PRINCIPAL MECHANICAL ELEMENTS OF ORDINARY TEES (See Fig. 11). FIG. 12. Section. Ordinary tees. Table X web. Area in sq. inches. Weight ia Ibs. per foot run. Greatest moment of inertia about axis a b. Fig. 11. Distance of centre of gravity above lower edge. Approximate least radius of gyration about axis c d. 7" X 31" X f 7-31 24-86 6-12 2-63 7" X 31" X f 6-17 20-98 5-28 2-68 7" X 31" X 1" 5-00 17-00 4-30 2-72 ,,, 7" X 31" X " 4-40 14-97 3-96 2-75 1-65 7" X 31" X f 5-94 20-19 3-83 2-40 ... 7" X 31" X l" 4-81 16-36 3-17 2-44 1-62 6f X 6f X f 9-19 31-24 35-16 4-61 ... 9 2 CONSTRUCTION IN MILD STEEL. Section. Ordinary tees. Table x web. Area in sq. inches. Weight in Ibs. per foot run. Greatest moment of inertia about axis ab. Fig. 11. Distance of centre of gravity above lower edge. Approximate least radius of gyration about axis c d. 6J" X 6f X f 7-73 26-30 31-06 4-64 64" x 6i" x 4" 6-25 21-25 25-70 4-68 1-50 61" X 6" X |" 8-81 29-96 28-78 4-28 61" x 6" X f 7-42 25-23 24-71 4-33 6f X 6" X j" 6-00 20-40 20-36 4-38 1-50 6" X 5" X f 7-69 26-14 16-72 3-59 6"X 5" X f 6-48 22-05 14-40 3-63 ... 6" X 5" X 4" 5-25 17-85 11-92 3-68 ... 6" x 5" X f" 3-98 13-55 9-22 3-72 1-33 6" x 4" x f 5-86 19-92 7-53 2-97 6" X 4" X |" 4-75 16-15 6-20 3-02 6" X 4" X f 3-61 12-27 4-91 3-06 l'-34 6" X 3f X f" 5-55 18-86 5-09 2-72 ... 6" X 3f X |" 4-50 15-30 4-27 2-67 1-38 6" X 3f X f 3-42 11-63 3-34 2-71 1-38 6" X 3" X f " 5-23 17-80 3-22 2-26 6" X 3" X f 4-25 14-45 2-70 2-31 6" X 3" X f 3-23 11-00 2-10 2-35 1-40 5" X 4" X f " 5-23 17-80 7-14 2-88 ... 5" X 4" X 4" 4-25 14-45 5-76 2-93 ... 5" x 4" X f 3-23 11-00 4-64 2-97 1-10 5" X 34" X f 4-92 16-73 4-82 2-55 ... 5" X 3|" X f 4-00 13-60 4-00 2-59 < 5" X 34" X f 3-05 10-36 3-19 2-64 1-12 5" X 3" X F 4-61 15-67 3-06 2-20 ... 5" X 3" X 4" 3-75 12-75 2-59 2-25 5" X 3" X f " 2-86 9-72 2-00 2-29 1-14 " x 2f x 4" 3-50 11-90 1-51 1-89 5" X 2f x f" 2-67 9-08 1-19 1-94 1-16 44" x 44" x |" 5-23 17-80 9-72 3-14 ... 44" x 44" x f 4-25 14-45 8-00 3-19 ... 44" x 44" x f 3-23 11-00 6-27 3-23 0-88 4g X 3^ X i" w 3-75 12-75 3-92 2-55 ... lz X "2 X Ye 3-31 11-25 3-51 2-57 ... 44" x 34" x |" 2-86 9-72 3-07 2-60 0-90 44" x 24" x 4" 3-25 11-05 1-47 1-83 ... A"ljf \^ 01" v/ 7 f *2 ^S ^2 *^ 16 2-87 9-76 1-32 1-85 .. 44" x 24" x |" 2-48 8-45 1-17 1-88 0-92 4" X 5" x 4" 4-25 14-45 10-45 3-42 ... 4" X 5" X f 3-23 11-00 8-00 3-46 0-76 4" X 44" X f 4-00 13-60 7-80 3-12 .. . 4" X 44" X |" 3-05 10-36 6-08 3-17 0-80 4" x 4" X f 4-61 15-67 6-65 2-77 ... 4" x 4" X f 3-75 12-75 5-56 2-81 ... 4" x 4" X |" 2-86 9-72 4-20 2-86 0-82 ROLLED SECTIONS IN STEEL. 93 Section. Ordinary tees. Table X web. Area in 6(1. inches. Weight in Ibs. per foot run. Greatest moment of iuerlii about axis a b. Fig. 11. Distance of centre of gravity above lower edge. Approximate least radius of gyration about axis c d. 4" X 3f X f 3-50 11-90 3-81 2-50 4" X 3f X Jr" 3-09 10-51 3-41 2-52 4" X 3f X f" 2-67 9-08 2-98 2-54 0-86 4" x 3" X f 3-25 11-05 2-43 2-17 4" X 3" X " 2-87 9-76 2-18 2-19 4" X 3" X f 2-48 8-45 1-90 2-22 0-88 4" X 2f X f 3-00 10-20 1-42 1-83 ... 4" X 21" X ^" 2-65 9-02 1-28 1-85 ... 4" X 2f X |" 2-30 7-81 1-13 1-88 0-90 3f X 3f X f 3-25 11-05 3-64 2-44 ... Ql// v/ Ql" v/ ^ " ^ X Og X Y 2-87 9-76 3-24 2-46 3f X 3f X |" 2-48 8-45 2-80 2-48 0-72 3f X 3" X f 3-00 10-20 2-33 2-12 3f X 3" X A" 2-65 9-02 2-22 2-14 ... 3f X 3" X |" 2-30 7-81 1-84 2-17 0-74 3f X 2f X ^" 2-43 8-27 1-23 1-82 3f x 2f X f" 2-11 7-17 1-09 1-84 3f X 2f X A" 1-78 6-04 0-93 1-86 0-76 3" X 3f X ^ 2-65 9-02 3-08 2-40 ... 3" X 3f X f 2-30 7-81 2-71 2-42 0-60 3" X 3" X #' 2-43 8-27 1-99 2-09 3" X 3" X f 2-11 7-17 1-75 2-11 3" X 3" X ^r" 1-78 6-04 1-50 2-08 0-62 3" X 2f x ' 2-21 7-53 1-18 1-77 3" x 2f X f" 1-92 6-53 1-04 1-79 3" X 21" X " 1-62 5-51 0-87 1-82 0-64 3" X If X f 1-55 5-26 0-23 1-11 ... 311 ^ I 1" vx 5 " X la X je 1-31 4-45 0-20 1-13 0-68 21" X 21" X f 1-73 5-90 0-98 1-74 ... 2f X 21" X ' 1-47 4-98 0-84 1-76 2f X 21" X f 1-19 4-04 0-68 1-78 0-50 2f X 2f X f' 1-55 5-26 0-65 1-53 2f X 2f X %' 1-31 4-45 0-59 1-57 !!! 2f x 2f X f 1-06 3-61 0*49 1-61 0-46 O" xx 0" xx 3" A X * X $ 1-36 4-62 0-42 1-36 ... 2" x 2" X ^" 1-15 3-92 0-39 1-41 ... 2" x 2" X f 0-94 3-19 0-33 1-46 0-41 2" x If X f" 1-17 3-98 0-20 1-04 2" X If X A" 1-00 3-39 0-18 1-06 2" X If X f 0-81 2-76 0-15 1-08 6-40 2" X If X f 2'^X IJ'^X ^" 0-75 0-57 2-55 1-95 0-09 0-07 0-92 0-94 0-40 ^ x\ 4 ^ 4 0-81 2-76 0-24 1-22 ... If X If X ft" 0-62 2-11 0-20 1-23 0-36 If X 2^ X f 0-81 2-76 0-31 1-33 ... 94 CONSTRUCTION IN MILD STEEL. Section. Ordinary tees. Table X web. Area in sq. inches. Weight in Ibs. per foot run. Greatest moment of inertia about axis a, b. Fig. 11. Distance of centre of gravity above lower edge. Approximate least radius of gyration about axis c-d. 11" \s 9" \s 3 " ^ X A X "IQ 0-62 2-11 0-25 1-36 0-29 1 1" \x 1 1" sx l" 13 X If X 4 1-' X 1-' X " 0*69 0-53 2-34 1-79 0-12 0-11 1-03 1-05 0-30 if x if x f 1 1" xx 1 Ht vx ^ " 0-56 0-45 1-90 1-53 0-07 0-06 0-85 0-88 0-24 1" X 1" X -&-" J x\ 1 *> 16 0-34 1-15 0-03 0-67 1" X 1" X f" 0-23 0-78 0-02 0-71 0-20 TABLE No. 26. THE PRINCIPAL MECHANICAL ELEMENTS OF BULB TEES (See Fig. 12). Greatest Distance of Approximate Depth X table X thick- ness of web and table. Area in sq. inches. Weight in Ibs. per foot lineal. moment of inertia about axis ab. axis a & from farthest edge of least radius of gyration about axis Fig. 12. section. c-d. i 12" X 6f X J" 11-67 39-68 202-2 6-80 1-07 lU" X 6f X fj" 10-02 34-07 164-4 6-30 1-07 ir x 6" x -^ 9-07 30-84 151-7 6-07 0-99 10" X 6" X ^" 8-33 28-33 120-0 5-72 0-99 9" X 5|" X A" 7-43 25-26 80-2 5-21 0-91 9" X 5- X " 6-70 22-78 76-5 5-06 0-86 8|" x 5f X%' 6-33 21-52 64-5 4-90 0-86 8' 1 X 5f X &" 6-70 22-78 56-3 4-85 0-92 8" X 5' 1 X -j^ 5-91 20-10 51-2 4-67 0-82 7 X 5 X ~QQ 5-32 18-10 34-3 4-25 0-82 ft" \s 4-i" V 8 " w ** *1 ^ 20 4-68 15-91 20-4 3-63 0-74 5" X 4" x 4" 2-46 8-36 10-0 3-16 0-66 3" X 3" X ^r" 1-71 5-81 2-2 1-86 0-49 Rolled Joists. This well-known, most useful, and deservedly popular section is shown in Fig. 13. The web is most commonly rolled with parallel sides, the flanges being tapered, and connected to the web with roundings in the internal corners. The proportion of web thickness to flange thickness, the amount of taper on the latter, the radii of the roundings, have been, as in other sections, variable with different ROLLED SECTIONS IN STEEL. 95 makers. These proportions exert some influence on the precise values of the moments of inertia and resistance, and the manu- facturers of this section frequently give in their trade catalogues the mechanical ele- r \ ments and exact proportions of the sec- tions rolled by them. This course is com- mendable in preference to the compilation of tables of strengths in which the data of the calculations are absent. In the British standard section the thickness of web and flanges, the taper of the latter, and the radii of the con- necting curves, are all standardized, and the mechanical elements of the standard section will be found in the publication FlG 13 previously referred to. The depths of this section as usually found in the market range from 3 inches to 24 inches, and the width of flange from 1J inch to 8 inches. This width of flange has recently been exceeded in continental rolling mills, and the section thus produced offers considerable advantages in column design owing to the increase of the least radius of gyration, and in the arrangement of details in connections, where the additional space afforded is often very convenient. Notwithstanding the width of flange the section can be very cleanly rolled, right out to the edge of the flange, and straight and true in its length. The proportions of depth and width require careful con- sideration when selection is being made of a section suitable for the purpose in view. The economy of this section as regards riveting, and the facility with which, aided by the table of strengths obligingly furnished by the manufacturer, the selection of a section for strength can be made, undoubtedly contribute to the favour in which the rolled joist is held. It is questionable, however, as a matter of taste, how far the indiscriminate use of the section, especially in the largest sizes, contributes to the artistic appearance, if it may be so called, of well-designed ironwork, and it must be confessed that economy of both cost in manufacture and painstaking in design are frequently attained at the expense of appearances. It is to be feared, however, that any regard for appearances in structural steelwork, if it implies 96 CONSTRUCTION IN MILD STEEL. any increase in cost, real or imaginary, will in these competitive days be regarded by many as an economic heresy. No universally recognized standard of proportion of the flanges and web of rolled joists had, up to a recent period, been arrived at by manufacturers. Published lists of sections show considerable variation in the proportion of web thickness to flange width, of web thickness to height of joist, of mean thickness of flange as compared with width, or with height of joist. The thickness of web is found to range between seven and twelve hundredths of the flange width in joists of 3^ inches width of flange and upwards, and may be taken to average about eight hundredths. In joists under 3J inches in flange width the web will average about one- tenth of flange width. The mean thickness of flange is equally variable, and will be found to range between five and nine hundredths of the height of joist in joists above 6 inches high. In shallower joists the mean flange thickness will range from eight to twelve hundredths. The maximum moment of inertia of the cross-section will increase in value per unit of area as the web becomes thinner, but the student need not be reminded that the moment of inertia is not the only standard of the ultimate actual strength of the joist. Apart from the practical requirements of the rolling mill the web must be thick enough not only to withstand the usual web stresses, but also to resist the effects of corrosion, and to assist the top flange to resist the buckling tendency under com- pression which is found in practice to limit the strength of the joist when not supported laterally, the compression flange under these conditions usually failing by lateral flexure before the full tensile resistance of the metal in the lower flange has been attained. Within the usual limits of variation of web thickness as rolled by different manufacturers, the maximum value of the moment of inertia compared with the total sectional area or weight per foot run will be attained when the flange thickness is from nine to ten hundredths of the height of the girder, but the economic efficiency is practically equally as great between the limits of six and twelve hundredths, and the lower value of flange thickness is the one more usually found in joists above 6 inches in height. The following table is based upon an assumed web thickness of 0'08 (width of flange) in all joists above 3J inches wide, and 010 (width of flange) in joists under that width. The values of the ROLLED SECTIONS IN STEEL. 97 moments of inertia (taken about the axis a b) are given for varying proportions of flange thickness, and these will be found to cover the variations usually found in practice. The radii of gyration (for use in column and strut design) are given about the axes a I and c d respectively. TABLE No. 27. THE PRINCIPAL MECHANICAL ELEMENTS OF ROLLED JOISTS. (See Fig. 13.) Flange thickness "De^tFdTjoistT Section of joist. Area in square inches. Weight in IDS. per foot run. Moment of inertia about the axis a &. Fig. 13. Radii of Axis a 6. gyration. Axis c d. Distance of axis a b from farthest edge of section. 0-05 20" X 7J" 25-8 88 1646-4 7-92 1-60 10-00 0-06 > 28-56 97 1864-8 8-08 1-72 ,J 0-05 19f" X 7J" 24-59 84 1530-0 7-85 1-60 9-87 0-06 M 27-25 93 1735-8 7-99 1-66 M 0-05 18" X 7" 21-67 74 1120-2 7-20 1-50 9-00 0-06 }J 23-99 81 1268-8 7-27 1-60 M 0-05 17f X 6f" 20-57 70 1029-2 7-09 1-49 8-87 0-06 > 22-80 78 1165-7 7-11 1-55 0-05 16" X 6" 16-51 56 674-3 6-38 1-22 8-00 0-06 18-27 62 763-8 6-40 1-25 ?j 0-05 16" X 5" 13-76 46 561-9 6-42 1-10 8-00 0-06 > 15-23 52 636-5 6-46 14 M 0'05 15f X 6f 16-55 56 656-4 6-30 35 7-87 0-06 18-35 62 743-7 6-37 41 0-05 15" X 6" 15-48 53 555-6 5-98 30 7-50 0-07 18-79 64 700-0 6-10 35 tt 0-05 15" X 5|" 14-19 48 509-3 5-97 21 7-50 0-07 17-22 58 641-7 6-10 26 j, 0-05 15" X 5" 12-90 44 463-0 5-98 00 7-50 0-06 > 14-28 49 524-5 6-05 04 0-05 14" X 6" 14-45 49 451-8 5-62 30 7-00 0-06 5 15-99 54 511-7 5-65 35 0-05 14" x 5f 13-24 45 414-1 5-60 1-21 7-00 0-06 14-66 50 469-0 5-64 1-26 j, 0-05 13" X 5" 11-18 38 301-4 5-18 1-10 6-50 0-06 > 12-37 42 341-4 5-24 1-14 V 0-06 12" X 61" 14-85 51 349-1 4-84 1-49 6-00 0-07 16-29 55 388-3 4-88 1-54 J? 0-06 12" x 6" 13-71 47 322-2 4-85 1-35 6-00 0-08 16-36 56 392-8 4-92 1-40 98 CONSTRUCTION IN MILD STEEL. ;e thickness ith of joist. Section of joist. Area in square inches. Weight in Ibs. per foot run. Moment of inertia about the axis 06. Radii of gyration. Distance of axis a 6 from farthest edge of section. if Fig. 13. Axis Axis B a b. c-d. 0-06 12" X 5J" 12-56 43 295-4 4-86 1-26 6-00 0-08 11 11 14-99 51 359-9 4-90 1-33 0-05 12" X 5" 10-32 35 237-1 4-80 1-10 6-00 0-06 99 11-42 38| 268-5 4-85 1-15 it 0-07 10J" X 5" 10-96 37 200-1 4-27 1-18 5-25 0-08 11 11 11-93 41 219-3 4-29 1-21 M 0-05 10J" X 4|" 8-37 281 140-3 4-08 1-04 5-125 0-06 19 9-25 3l| 159-0 4-17 1-09 5) 0-06 10" X 6" 11-42 381 186-5 4-04 1-38 5-00 0-08 > 13-63 46-5 227-3 4-08 1-46 M 0-05 10" X 5" 8-60 29 137-2 3-99 1-10 5-00 0-08 11 it 11-36 38J 189-4 4-08 1-21 0-06 10" X 41" 8-57 29 139-8 4-03 1-03 5-00 0-08 99 10-22 35 170-5 4-08 1-09 0-06 4" X 4J" 8-12 271 119-6 3-88 1-03 4-75 0-08 11 9-70 33 145-8 3-90 1-09 11 0-06 91" X 4" 7-04 24 98-4 3-74 0-91 4-625 0-08 11 19 8-40 281 119-9 3-78 0-96 0-07 9" X 7" 13-15 44| 176-4 3-66 1-65 4-50 0-09 11 11 15-47 521 209-5 3-68 1-73 0-06 9" X 51" 9-40 32 124-6 3-64 1-26 4-50 0-08 11 11 11-24 38 151-9 3-68 1-33 0-06 9" X 4" 6-84 231 90-6 3-64 0-92 4-50 0-08 99 91 8-18 28 110-5 3-67 1-08 11 0-06 9" X 3" 5-61 19 70-4 3-55 0-66 4-50 0-08 11 11 6-59 221 85-0 3-59 0-70 11 0-06 81" X 3" 5-15 17} 54-3 3-25 0-66 4-125 0-08 6-04 20J 65-5 3-29 0-70 M 0-06 8" X 6" 9-14 31 95-5 3-23 1-37 4-00 0-08 10-90 37 116-4 3-27 1-45 11 0-06 8" X 5" 7-61 26 79-5 3-23 1-15 4-00 0-08 11 91 9-09 31 97-0 3-27 1-21 11 0-06 8" X 4" 6-09 20| 63-6 3-23 0-92 4-00 0-08 7-27 24 77-6 3-27 0-97 11 0-06 7" X 4" 5-33 18 42-64 2-83 0-92 3-50 0-08 91 6-36 21 t 51-98 2-86 1-08 11 0-05 7" X 3|" 4-51 15| 35-29 2-80 0-83 3-50 0-06 5-00 17 39-97 2-83 0-86 11 0-06 61" X 31" 4-15 14 26-56 2-53 0-80 3-125 0-08 > > 4-96 17 32-37 2-56 0-85 11 0-06 61" X 3" 3-88 131 23-60 2-47 0-66 3-125 0-08 11 11 4-57 151 28-47 2-50 0-70 11 0-06 6f X 2" 2-60 8 15-73 2-46 0-44 3-125 POLLED SECTIONS IN STEEL. 99 ?e thickness th of joist. Section of joist. Area in square inches. Weight in Ibs. per foot Moment of inertia about the axis 06. Radii of gyration. Distance of axis 06 from farthest edge of B 8 1 run. Fig. 13. section. 1" Axis Axis PI 06. c d. 0-08 6f x 2" 3-05 101 18-98 2-49 0-47 3-125 0-07 6" X 5" 6-26 37-33 2-45 1-18 3-00 0-09 55 55 7-37 25 4 44-34 2-45 1-24 55 0-06 6" X 4J" 5-14 171 30-21 2-43 1-03 300 0-08 55 55 6-13 21 36-83 2-46 1-09 55 0-06 6" X 3" 3-74 12- 20-87 2-37 0-66 3-00 0-08 55 55 4-39 15 25-19 2-39 0-70 55 0-06 6" X 2" 2-49 81 13-92 2-36 0-44 3-00 0-08 55 55 2-93 10 16-79 2-39 0-47 55 006 5f X 2" 2-29 73 10-72 2-16 0-44 2-75 0-08 55 55 2-68 9| 12-94 2-19 0-47 55 0-06 51" X If 1-63 51 6-99 2-07 0-33 2-625 0-08 99 99 1-92 61 8-44 2-09 0-36 55 o-io 5" X 5" 6-60 221 27-55 2-04 1-25 2-50 0-12 99 99 7-52 251 31-05 2-04 1-29 if o-io 5" X 41" 5-94 201 24-79 2-04 1-13 2-50 0-12 55 55 6-75 23 27-94 2-04 1-16 55 0-08 5" X 41" 4-83 161 20-13 2-04 1-03 2-50 o-io 55 55 5-61 19 23-42 2-04 1-07 55 0-08 5" X 3" 3-66 121 14-58 2-00 0-70 2-50 o-io 4-20 141 16-85 2-00 0-73 55 0-08 4" x if 2-03 6- 7-29 1-90 0-41 2-375 o-io 55 55 2-33 8 8-42 1-90 0-44 55 0-08 4" X 3" 2'93 10 7-46 1-60 0-70 2-00 o-io 55 55 3-36 111 8-62 1-60 0-73 55 0-07 4" x 2" 1-81 61 4-50 1-58 0-45 2-00 0-09 55 55 2-09 7- 5-37 1-60 0-48 55 0-06 4" X If 1-45 5 4 3-61 1-58 0-38 2-00 0-09 55 55 1-83 6f 4-70 1-60 0-42 5 0-08 3f X 3" 2-56 8- 5-00 1-39 0-70 1-75 o-io 55 55 2-94 10 5-78 1-40 0-73 J5 0-08 31" X If 1-28 41 2-50 1-39 0-35 1-75 o-io 55 55 1-47 5 2 2-89 1-40 0-37 55 0-11 3" X 3" 2-68 91 3-86 1-19 0-74 1-50 0-13 55 55 3-00 101 4-29 1-19 0-76 55 0-08 3" X 11" 1-09 3 ! 1-57 1-20 0-35 1-50 o-io 55 55 1-26 4 1-82 1-20 0-37 55 0-08 3" X If 0-91 3 1-31 1-20 0-29 1-50 o-io 55 55 1-05 % 1-51 1-20 0-30 55 It is customary to specify the width of flange and total depth coupled with the weight per foot lineal of the rolled joist required, ioo CONSTRUCTION IN MILD STEEL. and this is doubtless the most desirable course to pursue. It leaves, however, the exact relative thicknesses of web and flanges an open question, though the total sectional area is of course governed by the weight per foot. If, on the other hand, the designer specifies the thickness of web or flange, he must in all probability be prepared to accept the section rolled by some one particular maker, and in such a case he will do well to follow the dimensions given in the trade section books. These remarks do not of course apply to the use of the British standard section, where the thicknesses of web and flanges for the given depth, width, and weight are standardized. As regards the values of the moment of inertia given in the above table, and based upon the proportions of web and flange stated, it may be remarked that for any weight per foot lineal of joist of any one particular section not found in the table, the moment of inertia for that weight may for approximate calculations be taken as simply proportional to the weight per foot. The value of the least radius of gyration will not be found to vary materially for any practical variation of the section within the limits usually rolled. Channels. This section is represented in Fig. 14. The web is rolled with parallel sides, the flanges are tapered and connected to the web with rounded internal angles, C, \ and this is the type of the British standard section. Increase of weight beyond the minimum section is obtained mainly by an i increase in web thickness. This section is frequently used as a beam O in small bearers, as a strut in the compression members of lattice girders and roof trusses, i i and in riveted columns, while it is occasion- ally useful in certain connections as taking the place of two angles. j If a small section of channel is required FlG 14 having a rivet through the web, as, for example, in the case of two channels crossing one another, back to back, and riveted together, care must be taken in the selection to secure one wide enough to permit of the formation of the point of the rivet. For this reason in such cases a small angle will frequently be found preferable to a small channel. ROLLED SECTIONS IN STEEL. 101 As in rolled joist sections so in channels, no generally re- cognized standard of proportionate thickness in web or flanges appears to have been attained prior to the establishment of the British standard section. In the majority of cases the thickness of web and flanges is similar or nearly so, but occasional sections are found where the thickness of flange is greater than that of the web. Any increase in weight over the normal or minimum section is obtained by thickening the web, the flange thickness remaining practically constant. In the following table the thickness of web and flanges is assumed as uniform all over. The standard thickness of the British standard channel shows a flange thickness greater than that of the web, and the student is referred to the " Properties of British Standard Sections" for the corresponding mechanical values. TABLE No. 28. THE PRINCIPAL MECHANICAL ELEMENTS OF CHANNELS. (See Fig. 14) Section of channel. Area in square inches. Weight in Ibs. per foot run. Moment of inertia about the axis a b. Fig. 14. Radii of Axis a-b. gyration. Axis c d. Distance of axis a b from farthest edge of section. 15f X3"xf 10-37 351 308-2 5-45 0-74 7-87 15" X 4" xf" 13-59 393-8 5-38 1-01 7-50 12" X 4" X 1" 9-50 32| 187-8 4-45 1-14 6-00 12" X 31" X 1" 9-00 30f 171-2 4-36 0-97 6-00 12" X 3" X #' 7-48 25-| 138-5 4-30 0-81 6-00 12" X 21" x f 8-00 27J 138-1 4-15 0-62 6-00 llf X 3" X 1" 8-43 28| 150-5 4-22 0-81 5-93 10" x 4" X ^r" 7-50 25 i 107-8 3-79 1-17 5-00 10" X 3" X " 6-62 22| 87-8 3-64 0-83 5-00 10" X 21" x /' 6-18 21 77-8 3-55 0-66 5-00 9 F X 31" X #' 6-66 22| 87-5 3-62 0-88 4-94 nl" v/ '-}!" v 7 " 4 ^ iF ^ TF 6-72 22f 81-0 3-47 1-00 4-62 9" X 31" x ' 6-62 991 "2 75-7 3-38 1-00 4-50 9" X 3" X f 5-34 181 59-4 3-33 0-86 4-50 9'^ X 2i" X f 4-96 17 52-4 3-25 0-68 4-50 4- "2" ^LO 5-41 181 48-0 2-98 0-68 4-12 8" X 3f x |" 7-00 23| 63-58 3-10 1-00 4-00 8" X 2f x f 6-00 20| 49-50 2-87 0-68 4-00 8" X 2f x f" 4-40 15 36-45 2-88 0-61 4-00 102 CONSTRUCTION IN MILD STEEL. Moment of Distance Section of channel. Area in square inches. Weight in Ibs. per foot run. inertia about the axis a b. Radii of gyration. a b from farthest edge of Fig. 14. Axis a b. Axis c of. section. 8" sx 9'' sx 3" X ^J X ^ 4-22 14 i 33-73 2-83 0-51 4-00 7f X 3f X |" 7-18 24 1 64-60 3-00 1-13 3-94 7 C x 3 ^,' x C 6-56 22| 56-10 2-92 0-91 3-94 ' X ^"j X "8 4-55 15| 37-69 2-88 0-68 3-94 7" X 3f X |" 6-50 22J 46-04 2-66 1-10 3-50 7" X 3" X f 6-00 20| 40-75 2-61 0-88 3-50 7" X 2" X f 3-84 13 24-10 2-51 0-53 3-50 6" X 4" X |" 6-50 22| 35-54 2-34 1-24 3-00 6" X 3f X f 4-59 15- 25-31 2-34 1-01 3-00 6" x 3" X f" 4-22 14| 22-34 2-30 0-91 3-00 6" X 2f X f 3-84 13J 19-37 2-24 0-73 3-00 6" X 2" X |" 3-47 12 16-40 2-17 0-55 3-00 6" x If X A" 2-78 9 1 12-89 2-15 0-42 3-00 5f X 2f X f 4-75 16J 20-87 2-10 0-71 2-87 cj v 9i" v 1" *-^o ^\ ^o ^ S 3-65 12^ 15-68 2-07 0-74 2-75 5|" X 2f X f 4-94 17 2 18-32 1-92 0-86 2-56 5" X 2" X |" 3-09 10 \ 10-43 1-84 0-58 2-50 5" X If X f 2-72 9J 8-42 1-76 0-40 2-50 4f X 2" X |" 2-90 10 8-05 1-66 0-58 2-25 41" x i-' x f" 2-53 8| 6-45 1-60 0-41 2-25 4" x 2f x f " 3-14 10| 7-81 1-57 0-75 2-06 4" X If X ^" 2-14 7- 4-73 1-49 0-42 2-00 4" X If X &" 2-00 1 4-19 1-45 0-41 2-00 3f" X If" X f" 2-15 z 3-42 1-26 0-43 175 3" X If X f 1-37 4| 1-75 MS 0-45 1-50 2-" x 1 -- '-" y -" 1-06 Si 0-81 0-87 0-35 1-18 8 1 C> ^ 4 21" x If X f 1-06 3- 0-74 0-83 0-38 1-12 2" X If X f 0-94 3J 0-50 0-73 0-33 1-00 If" X f" X &" 0-49 1| 0-18 0-61 0-18 0-87 11" x 1-" X ^" 0-68 2} 0-23 0-58 0-38 0-75 4" x f^x ^ 0-49 If 0-14 0-53 0-22 0-75 Further reference will be made to the use of channels in the practical design of columns or struts. Zed Angles. This useful section is shown in Fig. 15. It is largely used in the frames of ship and caisson work, having a considerable moment of inertia for its weight, as compared with angles or tees, with ample width of flange for riveted con- nections. The web is rolled with parallel sides, the flanges having a taper and being connected to the web by curves at the internal ROLLED SECTIONS IN STEEL. 103 V^VXXNftXV CL \ I 1 ^\SSvVsSS^v ct\ I i FIG. 15, angles. In the British standard section the flanges have no taper, but are of uniform thickness. Increase of weight beyond the minimum section is obtained by thickening the web, the width of flange being slightly increased. ^ ' The section is frequently rolled with a uniform thickness of web and flange, the latter being tapered as above described, and the quoted thickness being the mean between that of the root and of the point of the flange. The flanges of the British standard section have a thickness in excess of that of the web. Occasionally the flanges are rolled of unequal width ; this is a convenience where additional width is required for heavy riveting, and in those cases where the lesser width of flange is sufficient for the riveted attachments, then the increased width of the other flange yields a larger moment of inertia. The thicknesses given in the following table are approximately those to which the various sections are rolled as a minimum ; for other thicknesses than those given, the moment of inertia may be taken for approximate calculations as proportional to the sectional area or weight for each section. The table on page 104 gives the dimensions, sectional area, weight per foot lineal, moments of inertia, radii of gyration, etc., for Zed angles. Further reference will be made to the use of Zed angles in the practical design of columns or struts. In the preceding pages the sections which have been described and of which the tables of the principal mechanical elements have been given, viz. angles, equal and unequal-legged, tees, bulb tees or deck beams, rolled joists, channels, and Zed angles, are those which may be called the elementary or standard sections, which in combination with plates and bars are most ordinarily employed in riveted constructional steelwork. It is not possible to consider in detail the very numerous forms of rolled sections, other than those above mentioned, employed for special purposes. These include, for example, the varied sections of railway bars (bull- headed, bridge, and flat-footed), fish plates, tramway rails, guard 104 CONSTRUCTION IN MILD STEEL. TABLE No. 29. THE PKINCIPAL MECHANICAL ELEMENTS OF ZED ANGLES. (See Fig. 15.) Section of Zed angle. Depth X flanges. Area in square inches. Weight in Ib8. per foot run. Moment of inertia about the axis a b. Radii of Axis gyration. Axis Distance of axis a b from farthest edge of Fig. 15. a b. c d. section. 10" X 31" X 31" X 1" 8-00 271 109-41 3-70 1-20 5-00 8" X 31" X 3|" X 1" 7-00 23| 63-58 3-10 1-28 4-00 7" X 3|" X 31" X I" 6-50 221 46-04 2-66 133 3-50 7" X 3' 1 X 3" X f ' 4-59 15^ 32-34 2-65 1-13 3-50 6" X 3f X 31" X f" 4-59 15- 25-31 2-34 1-41 3-00 6" X 3" X 3" X f 4-22 141 22-34 2-30 1-15 3-00 5|" X 31 X 31" X f 4-40 15 2 20-61 2-16 1-43 2-75 51" X 3" X 3" X f" 4-03 18-15 2-12 1-17 2-75 5" X 3|" X 31" x f" 4-22 14f 16-47 1-95 1-46 2-50 5" X 3" X 3" X f 3-84 13 2 14-46 1-94 1-20 2-50 4" X 3" X 3" X f 3-47 11? 8-49 1-56 1-26 2-00 rails, sections of trough flooring (usually formed in hydraulic presses), quadrant sections for pile- work, half-round, segmental, or cope steels, sash-bars, and fancy and other sections. The mechanical elements of square, round, hexagonal, and octagonal bars have not been given in the tables, as these can be easily obtained by the usual arithmetical processes. With respect to the use of plates and bars, it is sufficient to point out that the dimensions to which these can now be rolled are amply sufficient to meet all legitimate demands of the designer of constructional steelwork. Various makers have their own standard maximum dimensions to which plates, sheets, or flats can be rolled, and it is customary to assign a limit of superficial area for each thickness of plate, which is not exceeded without entering into special arrangements. Thus for a |-inch plate, the limit of area is given by one authority as 135 square feet, the maximum length of plate being 42 feet, and the maximum width 7 feet 6 inches, it being understood that maximum length and maximum width are not rolled together, but that, given the length, the width is such as not to exceed the limit of area, or vice versa. Again, for a plate f inch thick, a limit of 250 square feet is given, ROLLED SECTIONS IN STEEL. 105 the maxima of length and width being 56 feet and 10 feet re- spectively. With respect to flats, usually so called when the width does not exceed 12 inches to 15 inches, the available length obtainable without joint will usually be found to meet all practical require- ments, as other considerations, such as the maximum length permissible for transport or shipment, very frequently rule the case. CHAPTER III. UPON CERTAIN APPLICATIONS OF RIVETED GIRDERWORK, WITH SOME REMARKS UPON RIVETS AND RIVET-HOLES. General remarks Examples of various types of girderwork Remarks upon the design of riveted connections Fundamental rules and the study of good examples The making of rivet-holes Punching and the punching machine Burrs, and the holes which they imply Drilled holes The templet system Making and use of templets Combined punched and drilled or rimered holes Rivets Shape and dimensions of rivet-heads Pan-heads Cup-heads Percentage of weight of heads and points Table of weights of heads and points Methods of riveting Hand riveting Hydraulic riveting Pneu- matic riveting The pneumatic hand hammer and its applications Girder- work as applied to bridge construction Example of viaduct construction Cast-iron cylinders Details Lengths of cylinders Bottom lengths Upper lengths and cap Holding-down bolts of main girders Cylinder bracing Main girders Footway and flooring Cross girders Expansion arrangements Roadway Details in connection with mixed traffic Curbing Girderwork for machine or boiler shops, steel foundries, engine-houses, etc. Traveller girders Travelling cranes and their loads Wheel pressures Crane wheels Table of weights of overhead travelling cranes Analysis of total loads and resulting reactions of supports Minimum dimensions and clearances for over- head travelling cranes Headway required Truth of gauge of road for over- head travelling cranes Types of girders for roadway Sections of rails and methods of connection Roadway at walls of shops Details Lattice girder- work for roofing Example and details of riveted connections Application of girderwork to the support of cast-iron water-tanks Consideration of the details of the tanks themselves General arrangements of such tanks Bottom and side plates Subdivision of tanks Plate flanges Tie rods Arrangement of girderwork Details of roofing arrangements in connection with tanks Gutters and gangways Connections of pipe-work, etc. Table of the weight of mild steel bolts and nuts. RIVETED girderwork in general covers so wide an area of con- structive practice, and its application is found in so many different directions, that it is hopeless to deal adequately with the subject in one chapter of such a collection of notes as the present. All that can here be done is to offer to the student some examples of the application of girderwork in one or two particular directions, RIVETED GIRDERWORK AND RIVET-HOLES. 107 accompanied by a few remarks on some practical aspects of rivets and rivet-holes. Nor can the theory of the beam be in any way entered on. The methods of determining bending moments, either by graphic or analytic methods, the theory of shearing forces, and of stresses in triangulated or latticed structures, together with the processes of apportioning the sectional areas of metal required, and of determining the correct lengths of flange-plates, etc., must be assumed to have been acquired in greater or less degree by the reader of these notes. The same remark must also be taken to apply to what may be called the theory of riveted joints in the application of safe limits of shear and bearing stresses, 1 The examples of various types of girderwork which are given in the illustrations which follow are all of comparatively small span, not exceeding 60 feet, as the consideration of girders of very large span does not enter within the limits of these notes. Thus in Figs. 66 and 73 we have examples of ordinary single- plate web-girders to carry traveller rails, while in Figs. 244 and 245 we have details of a double-webbed or box-girder for the same purpose. Figs. 116 and 117 show details of single- webbed plate-girders carrying tank-work above, forming a portion of the roof over an engine-house, and it will be convenient to consider, in connection with these girders, such details of the tanks themselves as will be found practically useful to the draughtsman. In Figs. 33 and 51 are given details of single- web plate- girderwork for bridge construction of the type described, and in Figs. 360 and 361 are found details of box and single-web girders used in jetty construction. Figs. 82 to 101 show some details of lattice girders for roof construction, especially those details of riveted connections which are all important in these as in other branches of girderwork. It is somewhat difficult to describe in so many words all the mental processes which attend the design by an experienced draughtsman of a well-thought-out riveted connection, and yet 1 Among the numerous treatises which have been issued on these subjects the student may profitably consult Part IV. of "Notes on Building Construction," in addition to more advanced works on the same subjects ; " Bridge Construction," by Prof. T. Claxton Fidler (Griffin); and as regards riveted joints, Prof. Unwin's " Machine Design " (Longmans). io8 CONSTRUCTION IN MILD STEEL. there is no detail associated with the design of structural steel- work which will more reveal the efficiency or otherwise of the designer than this. It is true that all the mechanical elements which form the basis of the design of the connection may be present to his mind the total stress, the number and area of rivets, the bearing areas, may all have been correctly determined and provided for, but there will often remain a residuum of conditions to be met outside theoretical requirements as to which there may be a right way or a wrong way of procedure. The experienced draughtsman will almost instinctively choose the right way, although he might find a difficulty in explaining in a few words the reasons for his choice. Oblique connections of all sorts will generally tax the ingenuity of the draughtsman more than those which are square, and if the conditions on one side of the girder or the connection differ in some way from those on the other, it is always desirable to remember both ends of the rivet, and not that end only which is represented on the plane of the paper. There are not wanting in public places evidences of the want of this precaution, which may serve as examples to the junior draughts- man of a wrong method of procedure, of how not to design a riveted connection. The fundamental rules which, after the proper determination of the mechanical elements of the strength of the joint has been made, will govern the general design are: the grouping of the assemblage of rivets on the centre line or line of action of force of the connected members ; the reduction to a minimum of loss of section; the proper pitch of rivets, which for certain classes of joints sometimes requires to be as close as possible to avoid clumsiness ; l the minimum distance from edge of rivet-hole to edge of member to avoid any risk of bursting out ; and, lastly, the accessibility of all parts and the provision of sufficient space under all conditions for the operations of riveting and holding up. These rules, if carefully followed and intelligently applied, should lead to satisfactory design. But the study of good examples will be more instructive to the young draughtsman than verbal instructions, however complete, and it is hoped that some assistance will be 1 In water-tight work and for boilers or receivers rivet spacing is governed by practical consideration of caulking, and the necessity for a sound water or steam or air-tight joint. RIVETED GIRDERWORK AND RIVET-HOLES. 109 derived from the examples figured in the following pages, where the riveting is distinctly shown, although the general scale of the construction may be but small. The student who, in the course of his inspection of the methods and practice of a girder-maker's or bridge-building yard, observes the process of work carried on by the punching machines, will find one of the results of that operation to consist of a heap, under the FIG. 16. FIG. 17. machine, of punchings, or, as they are usually called, "burrs," 1 being the circular discs of metal forced out of the plate or bar in the operation of forming a "punched" rivet-hole. The precise shape and size of the burrs will vary with the diameter of rivet to be employed and the thickness of the material through which the hole is made, but in general will exhibit the features shown in Figs. 16, 17, which are f full-size sections through burrs from punched holes intended for a | -inch rivet through a |-inch plate or bar, the precise features of the upper and under surfaces of the burr varying with the type of punch employed, the flow of material prior to, or simul- taneous with, the final shear- Fw> 18> ing of the circumferential area being shown by the bulging of the under surface of the burr as shown. If the student now lays, say, three of these burrs together, so that their circumferences are in close contact, as shown in Fig. 18, it at once becomes evident that the burrs are not portions of 1 For the use of "burrs" in the formation of special concrete in ballast of maximum density, see p. 402. no CONSTRUCTION IN MILD STEEL. cylinders, but portions of cones, the angle of the cone being determined by the amount of clearance between the punch and the die, the greater the clearance the greater being the departure from a truly cylindrical form. Thus, as the burr is conical, the hole in the plate or bar is also conical, and we arrive at one of the distinctive features of a punched hole. Callipered measurements from burrs will show an average difference of about ^ inch between the larger and smaller diameters of the burr, being j equivalent to a rate of slope in | the side of the cone of about 1 in 8, in plates of from f inch to | inch thick. It is true that in those cases where two bars or plates are to be riveted together (and two only), as shown in Fig. 19, and i the holes have been punched FIG. 19. from the meeting or " faying " surfaces, the double cone pro- duces an approximation to a double countersink, and is not so far objectionable, as it possesses in itself a certain element of Fia. 20. I FIG. 21. strength to resist pulling apart of the plates, even if the heads and points were absent. But where the number of thicknesses to be riveted together exceeds two, we have a condition of affairs which may assume a variety of shapes according to circumstances, as sketched in Figs. 20, 21, although by a use of the conical drift, which can hardly be called legitimate, some approximation to a roughly RIVETED GIRDERWORK AND RIVET-HOLES. in cylindrical hole may be obtained at the cost of a considerable amount of rough usage and distress of the surrounding metal. Thus far we have assumed the axis of the conical holes to be perfectly straight, or, in other words, that the holes have been truly centred one over the other in all the thicknesses passed through. If this be not so, the conditions become aggravated, the quality of the work deteriorates in the same degree, while the illegitimate use of the drift becomes still more pronounced. The ideal rivet-hole is truly cylindrical, each hole in each thickness of plate or bar being exactly concentric with the adjacent holes, so that the axis of the cylinder remains perfectly straight and square to the plane of junction, whatever be the number of thicknesses joined. These conditions are only perfectly attained when the holes are drilled through all the thicknesses of plates at one operation, and this method is frequently adopted in special cases, or where the conditions or importance of the work render such a course desirable, multiple drills being sometimes employed, by which the position of a number of holes can be simultaneously and very accurately determined with respect to each other. But for the ordinary run of structural steelwork with which we are here mainly concerned, a process such as this is found costly or inconvenient, and other means must be adopted to secure not only that the holes in separate plates shall be truly concentric when assembled together, but also that their pitch or position with respect to each other shall be accurate. In punched work the holes in each individual plate or bar are punched separately, and this is also the case with drilled work, except in the special cases above mentioned. It is, therefore, in the assembling of these separate parts together prior to the insertion of the rivet that the accuracy or want of accuracy of the methods adopted becomes evident, and the examination of the holes for rivets or other connections becomes an important part of the duty of those who may be charged with the inspection of riveted steelwork. In the bulk of structural steelwork of good quality the method by which the accuracy of the setting out of rivet-holes is main- tained is that known as the " templet " system, and the " templet shop " in a bridge-building or girder-building yard occupies an important position, inasmuch as the care with which the work is set out in this shop is a very powerful factor in the ultimate quality of the finished work. The templets employed are _ OF THE " \ UNIVERSITY J OF / 112 CONSTRUCTION IN MILD STEEL. sometimes of iron, but generally of wood, and the setting out of templet work may be described as careful full-size draughtsman- ship on wood, each rivet-hole being accurately set out in its correct position, whether it be a hole near the edge of a plate, a hole in an angle cover, or in any other position required, and bored through the thickness of the templet, to suit the size of a centre punch, which, being passed through the hole in the templet with a blow from the hammer in the hand of the plater, marks, as shown in Fig. 22, upon the surface I of the steel plate or bar I the centre of the rivet- hole which is subsequently punched or drilled out. The next stage of the process is one which at first sight appears to offer opportunity of error which would go far to destroy the original accuracy of the templet, for as the bar or plate (frequently of considerable dimensions and weight) is passed through the punching machine, the operation of placing the centre-punch mark exactly under the centre of the punch de- mands skill of eye and hand (assisted sometimes by certain mechanical de- vices, such as racks, etc.) on the part of the mechanic in charge of the machine. A very considerable degree of accuracy may nevertheless be attained, as is proved when good work of this class is assembled together. Excellent work can be produced by a system which stands intermediate between punched and drilled work and partakes of some of the advantages of both. Each rivet-hole is first punched out, the largest diameter of the punched hole being from -^ inch to inch less than the diameter of the finished drilled hole. The plate or bar is then transferred from the punching machine to the I I I FIG. 22. RIVETED GIRDERWORK AND RIVET-HOLES. I*- drilled to-punched* drilling machine, and the punched hole is enlarged, or rimered, to the finished diameter required, as shown in Fig. 23. It follows that the conical hole has dis- appeared, together with a certain zone of metal which may have been overstrained or distressed in the process of punching, and is replaced by a truly cylindrical hole. As, however, the point of FIG. 2 3. the drill, or rimer, in entering the punched hole is guided in direction by that hole, the axes of the punched and drilled holes remain the same for all practical \*--l'/a - -H I K-*{-+| I hole. FlG - 24. FIG. 25. FIG. 26. purposes, and any material error in position of the punched hole is not modified in the process of drilling. I ii4 CONSTRUCTION IN MILD STEEL. Notwithstanding, as above stated, excellent work is produced by this method, and the accuracy of the holes when assembled together can be made to fulfil all requirements of first-class work, though not equal to that which would result from the process of drilling through all thicknesses at once. Certain roughnesses left on the surface of the steel plate or I* /% -H /" hole. FIG. 27. % hole FIG. 28. 3 hole. FIG. 29. bar at the edges of the holes as the tool enters or emerges from the hole should be scraped off before the meeting surfaces are placed together for riveting, as they tend to prevent close contact. Details of the mechanical tests of mild steel for rivets are given in Table No. 14, p. 41, and the chemical analysis of a sample for the same purpose will be found on p. 52. A comparison of the rivets manufactured by various makers RIVETED GIRDERWORK AND RIVET-HOLES. 115 and commonly used in constructional steelwork will show certain variations in the shape and dimensions of the heads. Figs. 24 to 32 have been drawn and measured from actual specimens as manufactured and used by well-known firms in this country. As a rule, mild steel rivets have heads and points somewhat heavier than those employed for wr ought-iron rivets. Figs. 24, 25, 26, show pan-headed rivets, and Figs. 27, 28, 29, show one type of cup-headed rivets, while Figs. 30, 31, 32, show cup-headed rivets of somewhat different shape. For the % rivet. FIG. 30. ^ rivet . FIG. 31. FIG. 32. combination of punched and rimered holes above described there will be a difference of about ^ i nc ^ between the diameters of the hole and the rivet to allow for entry. The student will consequently appreciate the distinction between a rivet figured for, say, 1 inch hole, and a rivet figured as 1 inch diameter, and as by the terms of most specifications the rivet is to fill the hole, a rivet, say, of f| diameter may for purposes of calculation be reckoned as 1 inch diameter when completed. In the estimation of weights of structural steelwork the weights of the heads and points of rivets (except where countersunk) must u6 CONSTRUCTION IN MILD STEEL. be allowed for. The actual percentage will vary slightly in different classes of work, being greatest in those cases where the riveting is heavy relatively to the thicknesses of plates connected and the pitch close. About 4^ per cent, will, as a rule, be found sufficient for heavy girderwork, but a more reliable estimate in individual cases is arrived at by counting the rivets where prac- ticable and allowing the values given in the following table, in which the point or snap of the rivet is assumed to be of the same weight as the type of cup-head shown in Figs. 27, 28, 29. TABLE No. 30. THE WEIGHT OF HEADS AND POINTS OF MILD STEEL RIVETS. Diameter of rivet i" 2 511 8 3" 4 T_n 1" Weight of head and point of rivet in pounds per hundred rivets 9 13 24 35 50 Tables of the weights of mild steel b^lts and nuts are given at the close of this chapter. While the older-fashioned methods of hand-riveting are still employed in those situations or under those conditions which require them, yet the great bulk of riveting is now carried out by machine- work, the power employed being usually either hydraulic or pneumatic. In the former process a steady pressure is applied to the heated rivet, which, if allowed to remain on long enough, produces a thorough filling up of the hole in a manner wliich cannot be surpassed. In the pneumatic or compressed air method the process may either be one of steady pressure, or of a succession of rapid blows produced by the tool known as the pneumatic hand, hammer, which, albeit somewhat noisy, has proved its efficiency in this direction, while similar processes are applied to caulking, drilling, and other mechanical work. A pneumatic holder-up is also used in connection with the hand-hammer, but is often replaced by the older hand method where convenience requires. Some difference of opinion exists as to which of the methods, hydraulic or pneumatic, as applied to hand-hammers, produces the soundest work in closing up the rivet. There is no doubt that good work can be produced by either mode, and the formation of RIVETED GIRDERWORK. 117 the snap-head by the hand-hammer can be completed with great neatness and finish. The pneumatic hand-hammer also finds a place in certain processes as much associated with architecture as engineering, being used in the dressing and carving of stonework. Girderwork as applied to Bridge Construction. It is obviously impossible in a collection of notes such as the present to deal even in the most elementary manner with the details of bridge construction in steel. The subject is one of immense extent, and the details of even one such structure of the first class and of very large span would suffice to fill a volume of itself. The example here chosen is selected merely as typical of the application of plate girderwork to a comparatively small structure of short spans, but as the work includes some other useful details of various kinds, it will be further discussed. The structure in question forms a viaduct connecting certain outlying jetties and wharves with the mainland. The roadway is therefore designed to carry a mixed traffic of foot passengers, railway lines, and ordinary road vehicles, together with certain provision made for pipe-work, such as hydraulic mains, etc. This combination required an arrangement of road- bed or bridge-floor adapted to meet the requirements of the conditions above described. Fig. 33 gives an elevation of one span of the viaduct, which is formed of a pair of heavy plate girders supported on cast-iron cylinders placed 60 feet apart longitudinally, and 25 feet 9 inches centre to centre transversely, as shown in Fig. 34, which is a cross- section of the viaduct at the centre of one of the spans, the clear width of roadway between main girders being 24 feet. The cast-iron cylinders were constructed in lengths of 6 feet in height as a rule, certain special or make-up lengths being supplied to reach the prescribed finished level at the girder-beds in accordance with the slightly varying depths to which the cylinders were sunk, determined by the nature of the strata reached, and by the amount of settlement of the cylinder under the prescribed test-load. These lengths of cylinder were each cast in one complete ring without vertical joint. This method of construction can be easily carried out up to about 10 feet or thereabouts in diameter. For larger diameters it is usual to cast them in segments with vertical u8 CONSTRUCTION IN MILD STEEL. joints, a system which offers some advantages for shipment abroad. The bottom lengths are 7 feet 6 inches in diameter. Above these RIVETED GIRDERWORK. 119 is the taper length shown in Figs. 33 and 34, leading to a reduction in diameter for the uppermost lengths which maintained a uniform FIG. 34. Scale 1 inch = 12 feet. diameter of 4 feet 6 inches up to the level of the capping which forms the capital of the column. The lowermost of the bottom lengths is furnished with a cutting edge, as shown in Fig. 35, for con- venience in penetrating the strata through which the cylinder has to pass, being sunk by the combined processes of undercutting at the cutting edge, and forcing down by dead weight applied at the top, the interior of the cylinder being kept dry by the use of the compressed air system, an air-lock being used for passage into and out of the PETA "- OF CUTTING EDGE ' 1 The enlarged diameter at the bottom of the cylinder affords facilities for the necessary excavation. 120 CONSTRUCTION IN MILD STEEL. The lengths of cylinders were stiffened by internal vertical ribs as shown in Fig. 36, which also shows the nature of the horizontal \\ -j M\J\ Fia. 36. Scale | inch = 1 foot. Fio. 37. Scale 3 inches = 1 foot. RIVETED GIRDERWORK. 121 joint and bolted connection between the bottom lengths, the section of the joint being further shown in detail in Fig. 37. It will be observed that between every bolt a triangular stiffening bracket is cast connecting the flange with the metal skin of the cylinder. The flanges are machined for their entire width, while all the bolt-holes are drilled, ensuring sound work and the precise duplication of the joints. The water-tightness of these joints is secured by the use of canvas and red lead, or by an indiarubber ring about \ inch FIG. 38. Scale \ inch = 1 foot. diameter placed between the machined faces and squeezed out by the bolting up of the joint. It has occasionally happened that either from the existence of initial cooling stresses in the casting, or from certain inequalities of stress arising from the forcing down of the cylinder through hard and difficult strata, the bottom length of cylinders such as those now under consideration have cracked more or less seriously during the process of sinking, and this has led some designers to adopt a riveted form of construction for the lowermost length. The horizontal joint between the lower lengths and the taper or conical length next above them is shown in Fig. 38. The joints of the upper lengths of reduced diameter are similar to that shown in Fig. 37. 122 CONSTRUCTION IN MILD STEEL. The upper portion of the cylinder at the level of the capping and girder bedstones is shown partly in elevation and partly in section FIG. 39. Scale | inch = 1/oot. in Fig. 39. The moulded cap or capital is cast separately from the RIVETED GIRDERWORK. 123 cylinder length, is of ^-inch metal, cast in a convenient number of segments, and is bolted to the top length of cylinder in the manner shown in Fig. 41, which shows a detailed section of the moulding, while Fig. 40 shows the internal elevation at a joint of the segments. Within the capping, a hard stone girder-bed of the dimensions shown in Fig. 39 is inserted, resting upon the concrete with which the cylinders are filled, to receive the ends of the 60-feet main girders. The general levels of the work in the vicinity of the viaduct FIG. 40. Scale \\ inch = 1 foot. FIG. 41. Scale 1 inch = 1 foot. did not permit of any greater headway above high-water mark and the underside of the main or cross-girders than that shown in Fig. 34. In such cases, not infrequent in jetty work, it becomes desirable to counteract a possible uplifting force from beneath caused by the displacement of floating craft, such as barges, which may by mischance have been caught underneath the girders on a rising tide, and tending to displace the girderwork above them. This is effected by the holding-down bolts 2 inches in diameter, shown in Fig. 39, passing through the bottom flange of the main girders and the bedstones, and carried down a sufficient distance 124 CONSTRUCTION IN MILD STEEL. into the concrete filling of the cylinder, and having at their lower ends the cast-iron ribbed washer-plates shown in Fig. 42 and Fig. 43. These bolts are carefully fixed in position by templets, and with their cast-iron washers embedded in the concrete as the filling progresses, the girder-beds being slipped over them. To allow for possible errors in the levels of setting, the screwed ends are kept well above the nuts as shown. This is a wise precaution wherever foundation bolts are liable to displacement by sinking during the progress of the work, and allows a margin of error in 1 3E 1 1 X ~1 5 j 1 V _ __ l ._ t >- : o " o' o o 3 ; a -' a: j! ... _ u * \rv a v 1 *t - z a HJ /^ i ?x V , LJ Z { o 1 c-^i ' ^*t: '" '^i^r The side plates are connected with the bottom plates by the angle pieces shown in Figs. 102, 103, 104, and on a larger scale in Fig. 109. The angle pieces in this case are shown 1 64 CONSTRUCTION IN MILD STEEL. with a square corner in the angle. This form, which offers a certain simplicity in the pattern-making, would not be a good one for heavier pressures of water, and an angle or connecting FIG. 110. Scale | inch = 1 foot. piece having a circular quadrant section is frequently used, in accordance with the well-known principle regulating the best form of cast-iron construction under heavy pressures, such, for RIVETED GIRDERWORK AND WATER-TANKS. 165 example, a.s the bottoms of hydraulic rams. Such considerations, however, are not to the point in such a case as the present, where the head of water is inconsiderable. The tank is divided into two halves by a partition of plates similar to the side plates, as shown in Figs. 110 and 111. This division serves the purpose of providing a reserve of water storage when one-half of the tank is laid dry for cleaning or repairs, but it sometimes implies the use of a double set of supply, outlet, and overflow pipes, while the partition itself must be capable of resisting water pressure on alternate sides. The connection of the division plates with the sides and bottom is formed by a FIG. ill. Scale i inch = 1 foot. double angle piece, cast in one, as shown in Figs. 110 and 111. The junction at the vertical corners of the tank are also formed by single angle pieces, as shown in plan in Fig. 112. The whole of the bottom and side plates are provided with ilanges round their edges, as shown in the illustrations, of sufficient depth (in this case 2-J inches) to accommodate the size of the bolts used in connection. All the meeting surfaces of these flanges are, in good work, machined where they are in contact, a chipping or planing fillet being provided for that purpose, in such wise that when fitted together a caulking space of about J inch in width is left between the flanges, which space is filled up with iron cement i66 CONSTRUCTION IN MILD STEEL. to form a perfectly watertight joint. The flanges are stiffened by a gusset piece between every bolt, the bolt-holes being cored out to receive galvanized bolts. Occasionally the holes are left square, and the bolts provided with square necks. Upon the efficiency of the caulked cement joint the proper watertightness of the tank mainly depends. It will be observed that, in the tank under consideration, the flanges are turned inside the tank, and not outwards. This is not RIVETED GIRDERWORK AND WATER-TANKS. 167 an invariable rule, and there are arguments for and against the practice. As regards the strength of the plates, the method shown has the advantage, for experiment has shown that a cast-iron tee-shaped section loaded transversely is stronger with the table downwards than upwards, in accordance with the laws governing the relative resistances in compression and tension of cast-iron sections. On the other hand, the use of the flange turned inwards converts the bottom of the tank into a number of independent pockets without drainage from one to the other, when the tank is laid dry for cleaning purposes. This disadvantage can, however, be met, if necessary, by lining the tank bottom to the level of the top of the flange with Portland cement mortar. FIG. 113. FIG. 114. Scale 3 inches = 1 foot. The necessary resistance of the side plates to the bursting pressure of the water is provided in the case under consideration by wrought-iron heavily-galvanized tie-rods, placed at an angle of about 45, and connecting the top of the side plates with the flanges of the bottom plates. One such rod is provided at every joint in the side, end, and partition plates, as shown in Figs. 102, 104, and 110. These rods are forged with jaws of sufficient width to embrace the pair of flanges at each joint, as shown in Figs. 113 and 114, which show the fork or jaw in plan and elevation. They are bolted at both ends to the flanges of the side and bottom plates, a convenience afforded by the method of turning the flanges inwards. The con- nection of the tie-rod to the top of the side plates is shown in 1 68 CONSTRUCTION IN MILD STEEL. Fig. 115. The side plates are further stiffened by a horizontal flange on the upper edge, as shown in Figs. 105 and 115. In deeper tanks than that shown, the rods are frequently carried horizontally across from one side to the other, at intervals apart depending upon the pressures. In all cases of cast-iron tanks these tie-rods are of vital importance to the security of the FIG. 115. Scale 3 inches = 1 foot. tank, and hardly too much attention can be paid to their design, fitting, and subsequent maintenance. The total weight of such a tank as that above described, when filled with water, being considerable, careful consideration of the supporting framework of girders is desirable. This framework is shown in Figs. 102, 103, 104, 110, and consists of main riveted plate girders carrying cross riveted plate girders, which last support rolled joists, the whole being of mild steel. The general RIVETED GIRDERWORK AND WATER-TANKS. 169 arrangement of this girderwork is shown in the figures. The main girders are supported at one end upon the main walls of the building, of which the tank forms a portion of the roof, the other end being carried upon a steel riveted column, which is described in Chapter IV., p. 231. The connection of the main girders over the column is shown in Fig. 110. The cross girders are supported by the main girders, and their connections are shown 32 '-11% SECTION FIG. 116. Scale 1 inch = 1 foot. FIG. 117. Scale 1 inch = 1 foot. in sectional plan in Fig. 110, and in elevation in Fig. 102. The depths of the main and cross girders are so regulated that the upper surfaces of the rolled joists which rest upon the latter are in the same horizontal plane as the upper surface of the top flange of the main girder. The cross-section of the main girder at the centre is shown in Fig. 116, and at the end in Fig. 117. It will be observed that, as the number of plates in the upper flange fall off i ;o CONSTRUCTION IN MILD STEEL. towards the ends, the level is preserved by means of the 8|" X |" packing strips, shown in Fig. 117, forming together, with the upper surfaces as aforesaid of the rolled joists, which are carefully straightened and levelled in the press, the plane surface upon which the cast-iron bottom plates of the tank are bedded, the actual contact being made .30 Id*. er foot. SECTION AT OF cboss FIG. 118. Scale \\ inch = 1 foot. FIG. 119. Scale 1 inch = 1 foot. by the 1-inch deep fillets cast on the underside of the plates, as shown in Figs. 103 and 116. These fillets are chipped or machined until true and even contact is obtained. FIG. 120. Scale inch = 1 foot. The cross-section of the rolled joist is shown in Fig. 118, and that of the cross girder at the centre in Fig. 119. The bearing of the main girder on the wall is shown in Fig. 104 in elevation, and in sectional plan in Fig. 120. The bearing on the RIVETED GIRDERWORK AND WATER-TANKS. 171 column is shown in Fig. 110. The bearings of the rolled joists on the wall are shown in Figs. 121 and 122. The object sought to be obtained in the arrangement of girder- work above described is to prepare a practically rigid and even bed for a tank constructed of a material (cast iron) not well adapted to resist cross strains arising from excessive or unequal deflection, and FIG. 121. Scale I inch = 1 foot. in which it is of prime importance to preserve the joints from starting and becoming leaky. To prevent undue deflection or alteration in shape arising from the difference between a full and empty tank, it is desirable either to give the supporting girders an ample proportion of depth to 1 hole* FIG. 122. Scale f inch = 1 foot. span, if space will allow, or otherwise to keep the working stresses low, by extra metal in the flanges. It has been above remarked that in cases where tanks of this class form a portion of the roof of the building, and are associated with ordinary roofing details, some special arrangement for forming a weathertight connection between the two becomes necessary. Certain methods by which this may be effected are illustrated in Figs. 123, 124, and 125. 172 CONSTRUCTION IN MILD STEEL, In Fig. 102 the tank is shown abutting on a roof principal of the type described in Chapter V., p. 302, carrying a cast-iron gutter shown in detail in Fig. 272 ; and it is necessary to form a watertight connection between this gutter and the side of the tank. A similar detail occurs in Fig. 104, where a gutter runs round between the tank and the parapet wall. In both these cases the object desired is obtained by the use of the special connection shown to a larger scale in Fig. 123, which consists of a weathering flange cast on the outside of the side plates of the tank in the position shown, and having a vertical lip or feather overlapping the gutter, which is tucked in under the flange, as shown. All direct attachment between the tank and the gutter is avoided, either being left free to expand or contract independently of the other. The gutter work is carried completely round the tank as shown in plan in Fig. 112, which also shows the arrangement of the weathering flange at the corners of the tank. RIVETED G1RDERWORK AND WATER-TANKS. 173 Other methods of attaining the same end are shown in Figs. 124 and 125. In Fig. 124 a gangway is provided between the tank and the parapet wall for painting or repairs, floored as shown, and covered FIG. 124. Scale f inch = 1 foot. with a small lean-to roof of zinc and boarding, draining direct into the tank. In Fig. 125 connection is made with the gutter of a neighbour- ing roof in the manner shown, a lining of boarding covered with 174 CONSTRUCTION IN MILD STEEL. zinc being attached to the tank and the gutter in such a way as to prevent wet from getting down into the building. All the details connected with the hydraulic pipework re- quired in connection with such tanks as those above described cannot here be described. In general three sets of pipes supply, 24% OjZlHC On, l&df 3) I l_ FIG. 125. Scale i inch = 1 foot. discharge, and overflow will be required, and it is usual to effect the junction of these pipes with the tank by means of special provision in one or more of the bottom or side plates, these being especially stiffened up for that purpose. But in cases where lofty stacks or considerable lengths of pipes are required, the expansion RIVETED GIRDERWORK AND WATER-TANKS. 175 and contraction of such pipes due to temperature changes should be borne in mind, and not allowed to visit themselves upon the connections to the plates of the tank, with alternating stresses. Automatic or electric tell-tales of water-level will also be required. Weights of Mild Steel Bolts and Nuts. The following table of the weights of mild-steel bolts and nuts may be found useful in the process of estimating weights of steel-work and fastenings. The heads and nuts are hexagonal, of the usual Whitworth standard size ; that is, the depth of the head is seven-eighths of the diameter of the bolt, and the depth of the nut is equal to the diameter. The dimensions of the head and nut across the flats or over the angles of the hexagon are those usually given in the published tables of sizes of Whitworth standard. Any departure from the above proportions of head and nut will of course modify to some extent the weights given in the tables. The table may also be used for the calculation of weights of similar bolts in other materials than mild steel by proportioning in the ratio of the specific gravities of the material used. The length of the bolt is in all cases measured from under head to point, and the lengths have been extended to 30 inches in the table to meet the ordinary cases of long bolts used in the connection of heavy timber framing. For longer bolts, such as foundation bolts and the like, special calculations must be made, using the values of the weight of heads and nuts given at the head of the table. The weight of washers is not included, and must be allowed for separately. CONSTRUCTION IN MILD STEEL. TABLE No. 32. THE WEIGHT OF MILD STEEL BOLTS AND NUTS m POUNDS PER HUNDRED. HEXAGON HEADS AND NUTS. Diameter of) bolt. $ i" 4 A- SL" 8 TV i" 9 " T6 r 4 v 8 Weight of ) head and nut ( 2-83 4-48 7-53 11-71 16-61 22-82 29-4 49-7 74-5 hundred. Length in inches under W eight of bolts and nut s in po unds pe r hundi ed. head to point. 1" 4-22 6-65 10-6 16-0 22-2 29-9 38-1 62-2 ll" 4-57 7-19 11-4 17-0 23-5 31-6 40-3 65-3 1-' 4-92 7-73 12-2 18-1 24-9 33-4 42-4 68-5 100 if 5-27 8-28 13-0 19-1 26-3 35-1 44-6 71-6 104 2" 5-61 8-83 13-8 20-2 27-7 36-9 46-8 74-7 108 21" 5-96 9-37 14-5 21-3 29-1 38-7 49-0 77-9 113 0?" 2 6-30 9-91 15-3 22-3 30-5 40-4 51-1 81-0 117 2f 6-65 10-45 16-1 23-4 31-9 42-2 53-3 84-1 121 3" 7-00 10-99 16-9 24-5 33-3 43-9 55-5 87-2 125 31" 7-35 11-53 17-7 25-5 34-7 45-7 57-6 90-4 130 3f 7-70 12-08 18-5 26-6 36-1 47-5 59-8 93-5 134 3|" 8-05 12-63 19-3 27-7 37*5 49-2 62-0 96-6 138 4* 8-39 13-18 20-1 28-7 38-9 51-0 64-2 99-7 142 41" 8-74 13-72 20-8 29-8 40-2 52-7 66-3 102-9 147 4" 9-09 14-26 21-6 30-9 41-6 54-5 68-5 106-0 151 4J" 9-44 14-80 22-4 31-9 43-0 56-2 70-7 109-0 155 5* 9-78 15-35 23-2 33-0 44-4 58-0 72-8 112-0 160 5f 10-13 15-89 24-0 34-1 45-8 59-8 75-0 115-0 164 * 10-48 16-43 24-8 35-1 47-2 61-5 77-1 118-0 168 5f 10-83 16-98 25-5 36-2 48-6 63-3 79-3 121-0 172 6" 11-18 17-53 26-3 37-2 50-0 65-1 81-5 125-0 177 61" 11-53 18-07 27-1 38-3 51-4 66-8 83-7 128-0 181 61" 11-88 18-61 27-9 39-4 52-8 68-6 85-9 131-0 185 6-" 12-22 19-15 28-7 40-4 54-2 70-3 88-0 134-0 189 7 12-56 19-70 29-5 41-5 55-6 72-1 90-2 137-0 194 * 7z" 12-91 20-24 30-2 42-6 57-0 73-9 92-4 140-0 198 2 13-26 20-78 31-0 43-6 58-4 75-6 94-6 143-0 202 7f 13-60 21-33 31-8 44-7 59-7 77-4 96-7 147-0 206 8" 13-95 21-88 32-6 45-7 61-1 79-1 98-9 150-0 211 81" 14-30 22-42 33-4 46-8 62-5 80-9 101-0 153-0 215 81" 14-65 22-96 34-1 47-9 63-9 82-7 103-0 156-0 219 8 15-00 23-50 34-9 48-9 65-3 84-4 105-0 159-0 223 WEIGHT OF BOLTS AND NUTS. 177 Diameter of/ i// bolt. 1 A" r A" i" A" f" 1" I" Weight of ) head and nut f O.QQ 1.1ft together per > ~ bd 4 4y 7-53 11-71 16-61 22-82 29-4 49-7 74-5 hundred. ) Length in inches under head to point. W eight of bolts and nuts in po unds pe r hundr ed. 9" 15-34 24-05 35-7 50-0 66-7 86-2 108-0 162-0 228 91" 15-69 24-59 36-5 51-1 68-1 87-9 110-0 165-0 232 9f 16-04 25-13 37-3 52-1 69-5 89-7 112-0 168-0 236 9f 16-39 25-67 38-1 53-2 70-9 91-5 114-0 172-0 240 10" 16-73 26-22 38-9 54-3 72-3 93-2 116-0 175-0 245 101" 17-08 26-77 39-6 55-3 73-7 95-0 118-0 178-0 249 10-' 17-43 27-32 40-4 56-4 75-0 96-7 120-0 181-0 253 io|" 17-78 27-86 41-2 57-5 76-4 98-5 123-0 184-0 258 11 18-13 28-40 42-0 58-5 77-8 100-3 125-0 187-0 262 llf 18-48 28-94 42-8 59-6 79-2 102-0 127-0 190-0 266 llf 18-83 29-48 43-5 60-7 80-6 103-8 130-0 193-0 270 llf 19-18 30-03 44-3 61-7 82-0 105-5 132-0 197-0 275 12" 19-53 30-58 45-1 62-8 83-4 107-3 134-0 200-0 279 13" 20-92 32-75 48-3 67-1 89-0 114-4 142-0 212-0 296 14" 22-31 34-92 51-4 71-3 94-5 121-4 151-0 225-0 313 15" 23-70 37-09 54-5 75-6 100-1 128-4 160-0 237-0 330 16" 25-09 39-26 57-6 79-8 105-7 135-5 168-0 250-0 347 17" 26-48 41-43 60-8 84-1 111-3 142-5 177-0 262-0 364 18" 27-87 43-60 63-9 88-3 116-8 149-5 186-0 275-0 381 19" ... 67-1 92-6 122-4 156-6 194-0 287-0 398 20" ... ... 70-2 96-8 127-9 163-6 203-0 300-0 415 21" 73-3 101-1 133-5 170-6 212-0 312-0 432 22" ... ... 76-4 105-3 139-1 177-7 220-0 325-0 449 23" ... ... 79-6 109-6 144-6 184-7 229-0 337-0 466 24" ... ... 82-7 113-9 150-2 191-8 238-0 350-0 483 25" 363-0 500 26" 375-0 517 27" 388-0 534 28" 400*0 551 29" 413-0 568 30" 425-0 585 178 CONSTRUCTION IN MILD STEEL. TABLE OF THE WEIGHT OF MILD STEEL BOLTS AND NUTS IN POUNDS PER HUNDRED. HEXAGON HEADS AND NUTS. Diameter of bolt. i" ; ii" ir If" li" If" if H 2" Weight of head) and nut together V 106 148 195 251 324 403 495 600 725 per hundred. ) Length in inches under head to point. Weigl lit of b( Dlts anc I nuts i n poun ds per liundrec [. 2" 149 204 2-" 155 212 273 347 2-" 161 219 281 357 450 549 2f 167 226 290 368 462 564 682 3* 173 233 299 378 474 579 699 835 992 3z" 178 240 308 389 487 593 716 855 1014 olW o^- 184 247 316 400 500 608 733 875 1036 3f" 189 254 325 410 512 623 750 894 1058 4" 195 261 334 420 524 638 768 913 1081 4-" 200 267 342 431 537 653 785 933 1103 4!" 206 274 351 441 549 667 802 952 1125 4" 212 281 360 451 562 682 819 972 1148 5' 1 217 288 368 461 575 697 836 991 1170 5-" 223 296 377 472 588 712 853 1011 1192 5 228 303 386 483 600 726 870 1031 1214 * 234 310 395 493 612 741 887 1050 1236 6" 239 317 404 504 624 756 904 1069 1259 6-" 245 324 412 515 637 771 921 1089 1281 8" 251 331 421 526 650 785 938 1109 1304 6z" 256 338 429 536 663 800 955 1129 1326 7" 262 345 438 546 676 815 972 1148 1348 7 i 267 352 447 557 688 830 989 1168 1370 ~2 273 359 455 567 700 844 1006 1187 1393 7f 278 367 464 578 712 859 1023 1207 1415 8'' 284 373 473 588 724 873 1040 1226 1437 81" 289 380 481 598 737 888 1057 1245 1459 8f 295 387 490 609 749 903 1074 1265 1482 8f 301 394 499 620 762 918 1091 1284 1504 9* 306 401 508 630 774 932 1108 1304 1526 91" 312 408 517 641 787 947 1125 1323 1548 9f 318 416 525 651 800 962 1142 1343 1571 9^" 323 423 534 662 812 977 1159 1363 1593 10 329 430 542 672 825 991 1176 1382 1615 10f 334 437 551 683 838 1006 1193 1402 1637 WEIGHT OF BOLTS AND NUTS. 179 Diameter of bolt. \" ir u" If" li" ( If" If IF 2" Weight of head ) and nut together V j 106 148 195 251 324 403 495 600 725 per hundred. j i Length in inches under head to point. Weigl it of be )Its anc nuts i n pounc Is per 1 iiindred . ioj" 340 444 559 694 850 1021 1210 1421 1659 lOf 345 451 568 704 863 1035 1228 1441 1681 11" 351 458 577 714 875 1049 1245 1460 1704 11J" 356 465 586 725 887 1064 1262 1480 1726 111" 362 472 595 736 900 1079 1279 1499 1748 llf 367 479 603 746 913 1094 1296 1519 1770 12" 373 486 612 756 925 1108 1313 1539 1793 13" 395 514 646 799 975 1168 1381 1617 1882 14" 418 542 681 841 1024 1227 1449 1695 1971 15" 440 570 716 883 1074 1285 1517 1774 2060 16" 462 598 751 925 1124 1343 1585 1852 2149 17" 484 627 786 967 1175 1403 1654 1930 2238 18" 507 655 821 1008 1225 1461 1722 2008 2327 19" 529 683 855 1051 1274 1520 1790 2087 2416 20" 551 711 890 1093 1325 1578 1858 2165 2505 21" 574 739 925 1135 1374 1637 1926 2243 2595 22" 596 767 960 1177 1425 1696 1994 2321 2684 23" 618 796 995 1219 1474 1754 2062 2399 2773 24" 640 824 1029 1261 1525 1813 2130 2477 2861 25" 662 852 1064 1303 1575 1872 2198 2555 2950 26" 684 880 1098 1345 1625 1931 2266 2633 3039 27" 707 908 1133 1387 1675 1990 2334 2711 3128 28" 729 936 1168 1429 1725 2048 2402 2790 3217 29" 751 964 1202 1471 1775 2107 2470 2868 3306 30" 774 993 1237 1513 1826 2166 2539 2947 3395 CHAPTER IV. ON THE PRACTICAL DESIGN OF COLUMNS AND STRUTS. General remarks The ideal column The practical column Variation of modulus of elasticity Transverse stress : examples Conditions of end connections : flat ended, round ended, pin ended Experiments on columns of wrought iron and steel Wrought-iron rectangular bars and hollow tubes, flat ended Wrought-iron rectangular bars, pin ended Influence of size of pins Tests of wrought-iron riveted columns, flat and pin ended Table of results- Analysis and remarks Mode of failure Weakness at ends of columns Weakness of component parts of columns Buckling between rivets Maximum pitch of rivets compared with plate thickness Lattice members of columns Minimum scantlings Experiments on compressive resistance of various sec- tionsAngles and tees, flat ended Angles and tees, hinged and round ended Channels, joists, welded tubes,'and Zed columns, flat ended Channels, joists, and tubes, hinge ended Wrought-iron latticed columns, pin ended Mild steel angles, flat ended Hard steel angles, flat ended Diagrams of results of formulje proposed by various authorities Practical sections of columns and struts Elementary forms Flat bars Angles Tees Channels Channels in combination Rolled joists Rolled joists in combination Built-up sections of various types Zed-iron sections in combinations Combinations of channels and joists Special sections Phoenix columns Secondary attachments Com- parison of sections Relative economy and efficiency Relative amount of riveting Relative accessibility for painting Caution in the preparation of working drawings for columns Check on proportion of length to diameter Practical examples of riveted mild steel columns Procedure with respect to the continuity or otherwise of columns in various floor lengths Buildings of several stories Theatre auditorium Skeleton steel construction in very lofty buildings Massive columns for engine-house construction carrying travellers and tanks Variations in type Columns for machine-shops and engineering works Complex columns of this type carrying traveller roads and roofing Foundations to columns Holding-down bolts Lateral stability Special cases for concrete foundations of lofty buildings Precautions to be observed in the fixing of foundation bolts. CONSISTENTLY with the principle adopted throughout these notes, the theory of the strength of columns, as viewed from a mathe- matical standpoint, will not be entered upon. This subject has been frequently dealt with by numerous and able writers, and the PRACTICAL DESIGN OF COLUMNS AND STRUTS. 181 student is referred to their works for further information on this branch of the subject. The ideal column or strut is perfectly straight, is subjected to a purely compressive stress in the direction of its length, while the compressing force is usually assumed to be truly axial ; the modulus of elasticity of the material of which the column is com- posed is also supposed to be uniform not only in every cross- section, but in every part of a cross-section. The practical column of everyday experience falls short, how- ever, in a considerable degree from all these ideal conditions, notwithstanding the care with which the designer may have striven to realize them. His column is, it is true, as straight, perhaps, as ordinary workmanship can ensure, but the modulus of elasticity of his material may vary slightly not only in every separate cross- section, but even in different portions of the same cross-section, a physical fact which may, in the life history of the column, deter- mine incipient flexure and perhaps the direction in which that flexure may extend towards the goal of ultimate resistance and failure if the loading be carried to this extent. So far, again, as the axial direction of loading is concerned, the practical column is often, from the very conditions of the design, exposed to transverse stresses arising either from the bending moment set up by eccentric loading, or even from its own weight, as in the case of inclined struts, such as sheer legs or the jibs of cranes. Vertical columns may also be subject to severe transverse stress where exposed to wind pressure, as, for example, in columns supporting large roofs, or forming the supports of lofty sheds or other buildings. The cast-iron piles of a marine jetty may be instanced as an example where the transverse stresses set up by the force of waves may perhaps be more important than the vertical loading they are called upon to endure. In many cases these transverse stresses have, as far as possible, to be foreseen and allowed for, and the absence of such a provision may, as in the case of crane jibs of considerable radius, have serious results arising from cross strains imposed upon them, let us suppose, by the exigencies of erection or repair. In addition to the above may be stated the risks of transverse shock, as in the case of columns exposed to wheeled traffic, or to loads piled up against them in such manner as to cause bending stresses in addition to the vertical loading to which they are sub- jected. In short, it is not too much to assert that the possibilities 182 CONSTRUCTION IN MILD STEEL. of transverse stress in any column should be always present to the mind of the designer, and will go far in guiding his judgment in the determination of that always important point, viz. the ratio of diameter or least dimension to length, and to which further reference will be made. The ideal column may further be supposed to be either flat ended, round ended, or pin ended, and theoretical deductions have been drawn as to the mode of failure of columns of a certain length under each of these conditions. But in practice it is not always easy in many cases to assert with confidence under which of the above heads a column or strut should be classed, and, as we shall see in the experiments about to be described, neither pin-ended nor flat-ended columns invariably fail in the mode in which it might be reasoned that they should do. It is not therefore surprising, from a consideration of the foregoing, to find that most formulae professing to give the ultimate strength of a column or strut are based upon constants derived from experimental research, although it must be confessed that up to the present time the experimental data available, especially as regards mild steel, do not by any means cover the whole of the ground, or solve all the problems which will present themselves to the designer in the course of his practice. It is proposed, then, to give in the few pages following a summary in a graphic form of some of the principal experiments on columns of wrought iron and steel so far as they approximate to the ordinary conditions of practical construction to be followed by working details of column construction, with explana- tory remarks. In Fig. 126 are plotted the experiments on the compressive resistance of wrought- iron rectangular bars and hollow circular tubes, carried out by Eaton Hodgkinson, and described in the Appendix to the Report of the Commissioners appointed to inquire into the application of iron to railway structures, and carried out in 1846-47. The rectangular bars varied in length from 3f inches to 10 feet, with a sectional area ranging from T04 to 5*8 square inches. They were tested in a vertical position, with their ends made perfectly flat and well bedded against two parallel and horizontal crushing surfaces. The proportions of length to least radius of gyration were in several cases extreme, and beyond the PRACTICAL DESIGN OF COLUMNS AND STRUTS. 183 range of practice ; as, for example, in the case of a bar 10 feet long and half an inch thick. Katios beyond the value of 400 to 1 ; ^ / O / 1 CO t 1 o >8 ^ "S / ^ CO V ^ *o CN ^s S + ? a o 1 "^V V) ^ u & s. H II / 1 CVJ -rl V ^ & *,V> Q~ ^ S Is 1 US / k i g ^ M 1 / S CM 1 ^^ ^^ 1 | \ X O "NL 5^ i 1 qg + ^ f 1 1 If] | O -f- * 3 / i o 1 3 / ab ^ o | XO 1' o ! o < S* 00 1fJ2t I V^L &??< p */# d LO ~r SliOJ -P=r~l / , r -ri mBi T-rH r ^^ 'Wl'tl in ") j 8 ) \f M 1 | c > U ) o 1 84 CONSTRUCTION IN MILD STEEL. are not plotted in the diagram, but the dotted mean curve has been laid down, with the aid of experiments, with a value of - beyond that limit. In this diagram, as in those to be further described, all the individual experiments are plotted, and the reader is in a position to judge for himself of the probable accuracy of the dotted mean curve, which has been drawn to represent the average value of the ultimate resistance to compression for various proportions of length to least radius of gyration. In these experi- ments all the rectangular bars, with the exception of those having a value of -, less than 50 to 1 failed by flexure. r' J The circular tubes ranged from 1J inches to 6| inches in diameter, and from 2 feet 4 inches to 10 feet in length, the sectional area of the tubes ranging between 0*44 square inch to 2*9 square inches, and the thickness of metal from ^ inch to | inch. Fig. 127 gives the results of a series of tests l made at Water- town Arsenal on wrought iron rectangular bars, forty-seven in number, nominally 3 inches square (varying from 8*70 to 8 '94 square inches in area), and of various lengths from 2 feet 6 inches to 15 feet, centre to centre of pins. The iron of which the bars were manufactured was found to have an average ultimate tensile strength of 22 -56 tons per square inch, with an elastic limit in tension of 10*67 tons, an elongation in 20 inches of 21 J- per cent., with a contraction of area of 31 per cent. Chemical analysis gave the following results : carbon, 0*05 ; phosphorus, 0*22 ; sulphur, 0-048 ; silicon, 0*084 ; manganese, 0*218. In those experiments which are plotted in Fig. 127, the bars were in each case provided with 1 J-inch diameter pins at each end, arranged as shown in the figure. The bars were tested horizontally, the pins being vertical, while the weight of the longer bars was counter- weighted. In all cases failure took place through lateral flexure, and in every case but one the plane of flexure was perpendicular to the axis of the pins that is to say, in the plane in which the ends of the bar were free to move round the pin. It is to be observed that up to a length of about 24 diameters, or a proportion of length to least radius of gyration of about 83 : 1, 1 Report of tests, Watertown Arsenal, 1883. PRACTICAL DESIGN OF COLUMNS AND STRUTS. 185 the lateral flexure was gradual and without sudden springing, but that beyond this length, after the flexure had attained a certain 05 1 1 4-4 * gS cu 6 !G o in O in 186 CONSTRUCTION IN MILD STEEL. amount, a sudden increase of deflection occurred, accompanied by a rapid fall in resisting power. This fact is perhaps not without value in the consideration of the proper proportion of length to least dimension, and is an argument in favour of an increased factor of safety in long columns. Selecting bars of the same length, and tested under the same conditions, except as regards the nature of the end bearings, we are enabled to make the following comparisons, each result being the mean of two experiments : Ultimate load in tons per square inch. Length in inches. 90 120 Two li" pin ends. One flat end and one li" pin end. Two flat ends. 11-03 11-22 11-68 9-12 9-89 10-15 We may also observe the influence of the size of the pin from the following results, each being, as before, the mean of two experi- ments : Ultimate load in tons per square inch. inches. I" pins. lupins. lupins- 11" pins. 21" pins. 120 7-27 8-18 9-12 9-57 9-89 It will be seen that the pin-ended strut, with 2^-inch pins, gives a result similar to that with one flat end and one pin end, and is not much below the strut with two flat ends, the tendency of increasing the size of the pins being to approximate to the conditions of a flat-ended strut, when the frictional conditions of the pin surface in contact remain the same. The observed deflections of flat-ended bars 10 feet in length in the above series, when loaded beyond their limit of ultimate resistance, give a curve which closely approximates to that required by theory, being of triple flexure, while the tangent to the curve at the ends is nearly, if not quite, square to the plane of the abutting surface. PRACTICAL DESIGN OF COLUMNS AND STRUTS. 187 Pin-ended bars give indication of an approximation to the same curve, the difference in the form of curve becoming less as the size of the pin increases. The well-known series of tests on wrought-iron riveted columns carried out at the Watertown Arsenal, Mass., in 1883, will next be considered. 1 This series of tests comprised seventy- four columns of varying sections and lengths, as follows : Six pin-ended columns of the type of section shown in Fig. 165, and consisting of two 6 -inch channels, connected by a solid plate web 6" X y and four angles 1-J" X 1" X f s ", with i-inch iron rivets at 6-inch pitch. These columns were respectively 10, 15, and 20 feet in length, centre to centre of pins, two columns of each length being tested. Six pin-ended columns of the type of section shown in Fig. 165, but consisting of two 8-inch channels, connected by a plate web 8" X f fi " and four angles 2" X 2" X J". These columns were 13 feet 4 inches, 20 feet, and 26 feet 8 inches in length, centres of pins. Six columns of the type of section shown in Fig. 152, and consisting of two 6 -inch channels, and two web plates 10" X -", forming a box or closed section, the rivets being |J-inch diameter at 6-inch pitch. These columns were 10 feet 8 inches, 15 feet, and 20 feet in length, centres of pins (when pin ended) ; four were tested with pin ends and two with flat ends. Six columns of the type of section shown in Fig. 152, and consisting of two 8 -inch channels, and two web plates 12|" x f 6 ", forming a box or closed section, the rivets being f-inch diameter at 6-inch pitch. These columns were 14 feet, 20 feet, and 26 feet 8 inches in length, two being flat ended and four pin ended. Six columns of the type of section shown in Fig. 163, and consisting of two flange plates 9" X }', two web plates 5|" X ", and four angles 1|" X 1J" X T 3 6 ", the rivets being JJ-inch diameter at 6-inch pitch. These columns were 10 feet, 15 feet, and 20 feet in length, centres of pins. Six columns of the type of section shown in Fig. 163, and consisting of two flange plates 12" x fy", two web plates 7 }/ X fy", and four angles 2" x 2" X J", the rivets being ^-inch diameter at 6-inch pitch. These columns were 14 feet, 20 feet 8 inches, and 1 Report of tests on the strength of structural material made at the Watertown Arsenal, Mass., 1883. 1 88 CONSTRUCTION IN MILD STEEL. 26 feet 8 inches in length, four being tested as flat ended and two pin ended. Six columns of a similar section to that shown in Fig. 163, but with flange and web plates ^ inch thick. The lengths similar to those last described. Four were tested as flat ended and two as pin ended. Six columns of the type of section shown in Fig. 150, and consisting of two 8-inch channels, with open lattice webs of 2" x I" flats, riveted to the flanges of the channels. The lengths of the columns were 13 feet 4 inches, 20 feet, and 26 feet 8 inches, centres of end pins. Six columns of similar section to that shown in Fig. 150, but with a swelled outline, the distance between the channels at the centre being from 1| inch to 2| inches greater than at the ends. The lengths similar to those last described. Four columns of the section shown in Fig. 150, and consisting of two 10-inch channels, with open lattice webs of 24" x f" flats, riveted to the flanges of the channels. The lengths of the columns were 16 feet 8 inches and 25 feet, centres of pins. Four columns of similar section to that shown in Fig. 150, but with a swelled outline, the distance between the channels at the end being from 2J inches to 3J inches greater than at the ends. Lengths similar to those last described. Six columns of a special section of the type shown in Fig. 151, but consisting of two 10 -inch channels, with an open lattice web of 2" X |" flats on one side, and a solid plate web 13" X f on the other. The centre of gravity of this section not being the centre of figure, the placing of the pins in the alternate centres showed the effect of eccentricity of loading with results which will be further referred to. Six columns of a section similar to the last, but consisting of two 8-inch channels, with an open lattice web of 2" x J" flats on one side, and a solid plate web 12" x |" on the other. These also afforded a similar opportunity of comparing the results of con- centric and eccentric loading. Of the above seventy-four columns, sixteen were tested with flat ends, the remainder being tested with pin ends. The pins were in all cases 3J inches diameter, the ends of the columns being reinforced with extra plates and closer riveting, in order to provide sufficient bearing area and resistance to the local stresses set up in the neighbourhood of the pin. PRACTICAL DESIGN OF COLUMNS AND STRUTS. 189 The columns were tested horizontally, and were counter- weighted at the middle. Compressions and sets were measured on a gauged length by a micrometer. The load was gradually applied, and the ultimate load recorded was the maximum which the column was capable of maintaining, although considerable distortions may have previously taken place. The results of the tests are given in the following table : TABLE No. 33. THE ULTIMATE KESISTANCE TO COMPKESSION OF WROUGHT-IRON PIN-ENDED AND FLAT-ENDED COLUMNS. Number of experi- ment. Description of column. Length centre to centre of pins. Inches. Length divided by radius of gyration. Condition of end bearing. P = pin ended. F = flat ended. Ultimate strength. Tons per square inch. 1 120-2 62-3 P 13-49 2 Type section. 120-7 62-3 P 14-01 3 Fig. 165. Mean 180-0 93-2 P 11-23 4 sectional area = ' 180-0 93-2 P 9-40 5 9-91 sq. inches 240-0 124-3 P 8-65 6 240-1 124-3 P 7-24 7 160-1 38-8 P 13-82 8 Type section. 160-0 66-1 P 14-06 8 Fig. 165. Mean 240-0 96-7 P 11-80 10 sectional area = 240-0 96-7 P 10-06 11 15-90 sq. inches 320-0 129-0 P 8-79 12 320-1 129-0 P 7-84 13 127-9 46-1 F 14-16 14 Type section. 127-9 46-1 F 14-98 15 Fig. 152. Mean 180-0 65-0 P 14-43 16 sectional area = 180-1 65-0 P 14-82 17 11*46 sq. inches 240-0 86-6 P 13-37 18 240-0 86-6 P 13-03 19 167-8 47-1 F 15-60 20 Type section. 167-8 47-1 F 15-89 21 Fig. 152. Mean 240-0 67-4 P 14-32 22 sectional area= ' 240-0 67-4 P 14-40 23 17-85 sq. inches 320-0 81-4 P 11-82 24 320-0 81-4 P 11-29 1 90 CONSTRUCTION IN MILD STEEL. Number of experi- ment. Description of column. Length centre to centre of pins. Inches. Length divided by radius of gyration. Condition of end bearing. P = pin ended. F = flat ended. Ultimate strength. Tons per square inch. 25 119-9 49-3 P 13-98 26 Type section. 120-0 49-3 P 14-15 27 Fig. 163. Mean 180-0 74-0 P 14-13 28 sectional area= j 180-0 64-0 P 13-71 29 9*41 sq. inches 240-0 98-7 P 12-92 30 240-0 85-4 P 13-34 31 y 167-9 50-9 F 14-66 32 Type section. 167-6 50-8 F 15-65 33 Fig. 163. Mean 247-6 75-0 F 14-73 34 sectional area= \ 247-8 65-5 F 15-40 35 15'87 sq. inches 319-9 96-9 P 12-51 36 320-0 129-5 P 12-46 37 i , 167-7 51-1 F 15-03 38 Type section. 167-7 51-1 F 14-76 39 Fig. 163. Mean 247-6 75-4 F 14-74 40 sectional area= 247-6 75-4 F 15-15 41 2 1-1 2 sq. inches. 320-0 103-2 P 11-50 42 r 320-1 103-2 P 11-58 43 159-2 35-2 P 15-14 44 Type section. 159-27 35-2 P 16-35 45 Fig. 150. Mean 239-6 53-0 P 15-23 46 sectional area= 239-6 53-0 P 14-91 47 7 '71 sq. inches. 319-9 107-3 P 14-11 48 319-85 107-3 P 13-33 49 159-9 35-3 P 15-33 50 Type section. 159-9 35-3 P 14-97 51 Fig. 150. Mean 239-7 80-4 P 14-91 52 sectional area = 239-7 53-0 P 15-35 53 7'61 sq. inches. 319-8 107-3 P 13-76 54 319-92 85-3 P 13-73 55 56 Type section. Fig. 150. Mean 199-84 200-0 50-3 50-3 P P 15-06 15-48 57 sectional area = 300-0 61-8 P 15-01 58 12*14 sq. inches. 300-0 61-8 P 14-48 PRACTICAL DESIGN OF COLUMNS AND STRUTS. 191 Number of experi- ment. Description of column. Length centre to centre of pins. Inches. Length divided by radius of gyration. Condition of end bearing. P = pin ended. F = flat ended. Ultimate strength. Tons per square inch. 59 60 Type section. Fig. 150. Mean 199-25 199-50 41-0 41-0 P P 13-89 14-28 61 sectional area = 300-2 45-2 P 14-65 62 1 2-21 sq. inches. 300-15 75-6 P 14-61 63 300-0 P 11-69 64 65 Type section. Fig. 151. Mean ( 300-0 300-0 P P 12-57 7-77 66 sectional area = 300-0 P 7-71 67 1 7*40 sq. inches. 307-75 F 15-30 68 307-87 F 14-88 69 247-94 F 14-58 70 71 Type section. Fig. 150. Mean 247-94 240-25 F P 15-12 7-25 72 sectional area = 240-0 P 8-58 73 1 2'65 sq. inches. 240-25 P 12-35 74 240-25 P 13-66 Among the practical lessons to be deduced from these experi- ments, we may first observe that when the ratio of length to least radius of gyration exceeded 120 to 1, sudden lateral springing of the column occurred at or very close to the point of ultimate resistance. This may be compared with the similar phenomenon in the case of 3-inch rectangular bars referred to on p. 184. It might very naturally have been concluded that in pin- ended columns failure by lateral flexure would take place in a plane at right angles to the axis of the pin, especially when that plane coincided with the plane of the least moment of inertia and radius of gyration. This method of failure did actually occur in some twenty-four cases, but it is worthy of remark that in fourteen cases, although the plane of lateral flexure was at right angles to the axis of the pin, it was also in the plane of the greatest radius of gyration, not the least. It is for this reason that the fourth column of the table is headed, " Length divided by radius of gyration," not least radius of gyration, the proportion of _ being calculated on that radius in the IQ2 CONSTRUCTION IN MILD STEEL. plane of which failure took place. It is further to be noted that in several cases failure occurred in a plane parallel to the axis of the pins. Such cases should be classified under the heading of fixed-ended struts rather than pin-ended, and even under this condition the plane of failure was not invariably that of the least value of r. It is not difficult to discover from the results of these experi- ments, and others which will be referred to, the great importance of avoiding structural weakness at the ends of a column which first receive the stress, whether it be a pin-ended, fixed-ended, or a flat- ended connection. The concentration of stress, and what appears to be in some cases of short columns a certain flow of material under extreme loads, may constitute this the weak point in the entire column strength. In the case now before us the end of the column is strengthened by the addition of three extra eye-plates on each side, forming a total thickness of metal of 3| inches and a total bearing surface for the 3 \ -inch diameter pin of 11 '81 square inches. The stress through the eye-plate is transmitted to the body of the column by the rivets, which have a collective shearing area of 8 '4 square inches. But this column (No. 42 in the table) failed by the shearing of these rivets, which did not fill the holes, the longest rivets having the most clearance. Another source of weakness was found to be the bending of the pin, when the unsupported length was too great, accompanied in some cases by the elongation of the pin-holes. Eiveted columns of the type now under consideration may be stated to consist of a number of component parts, the nature of those components and their liability to individual failure varying with the details of design of the column. It is conceivable that the ultimate strength of a column will be determined by that of its component parts, and that the full strength of the column as a whole will not be attained when local weakness of the component is present. An example of local weakness at the ends of a column has already been described, and this view is further confirmed by an analysis of the experiments upon the box-shaped columns of the types shown in Fig. 163. Of thirty experiments carried out on this type, nine failed by the buckling of the plates between the rivets, and some instructive details may be gathered upon the important point of the proper pitch of rivets in a riveted column required to ensure the maximum PRACTICAL DESIGN OF COLUMNS AND STRUTS. 193 resistance, especially when the column is short. The buckled plate may be considered as a fixed-ended rectangular column, subject to compression in the length of the whole column, the length of this subsidiary or component column being the pitch of the rivets. If, further, this subsidiary column is supposed to be subject to a compressive stress per square inch equal in intensity to that sustained by the whole cross-section, we shall then have the relations expressed in the following table, in which are given the pitch of rivets both crosswise and lengthwise, the thickness of plates, i.e. the least dimension of the column, the ratio of - both of the component and entire columns, and the ultimate strength per square inch, all as derived from the experiments, all the columns excepting the last (No. 38) having failed by buckling the plates between the rivets. TABLE No. 34. THE INFLUENCE OF EIVET PITCH ON THE ULTIMATE STRENGTH OF COLUMNS. Pitch of rivets in inches. Value of 1 Nature of Number of experi- ment. Mean thickness of plates. r Ultimate strength. Tons per square inch. end con- nection. p _pin ends. v flat "ends. Crosswise. Lengthwise. Plate between rivets. Entire column. 25 7-5 6 0-22 95 49-3 13-98 P 26 7-5 6 0-26 80 49-3 14-15 P 13 8-0 6 0-26 80 46-1 14-16 F 14 8-0 6 0-26 80 46-1 14-98 F 19 10-5 6 0-28 74 47-1 15-60 F 32 10-25 6 0-31 67 50-8 15-65 F 31 10-25 6 0-32 65 50-9 14-66 F 34 10-25 6 0-33 63 65-5 15-40 F 37 10-25 6 0-44 47 51-1 15-03 F 38 10-25 6 0-49 42 51-1 14-76 F It will be observed from the above figures that the 6-inch pitch of rivets represented, so far as the buckling of the plates is concerned, a column of greater length in proportion to its least radius of gyration than the column taken as a whole. This preponderance of slenderness is maintained in the first seven o 194 CONSTRUCTION IN MILD STEEL. experiments, decreasing as the plates thicken; in the next two the proportions of - are nearly alike, and it may have been a matter of uncertainty whether the column would fail as a whole by lateral flexure, or by buckling as they did between the rivets. In the last case, however, the thickening of the plate to 0*49 inch has altered the relative proportions of -, and the plate between the rivets is stronger than the column as a whole. Failure takes place, not by buckling of the plate, but by lateral flexure of the whole column, the plates buckling subsequently to the maximum load being attained. The ultimate resistances to buckling may be compared with the results of Hodgkinson's experiments on flat- ended rectangular bars shown in Pig. 126. The foregoing analysis is subject to the uncertainty which attaches to the influence which the crosswise pitch may have exerted upon the ultimate buckling resistance, but it at least serves to show that the pitch of riveting should not be overlooked in the design of columns, especially those which, by reason of their ratio of -, may be expected to give a high ultimate resistance. In the particular cases cited, it is evident that half an inch was practically the minimum thickness of plate required to prevent buckling with a 6-inch pitch ; or, vice versa, that 6 inches was the maximum pitch allowable for J-inch plates, when the ratio of length to least radius of gyration for the entire column was about 50 to 1. We may now refer to the results of the experiments of the latticed columns, Nos. 43 to 74 inclusive, of the table on page 190, of which the types are shown in Figs. 150, 151. We obtain from this series some light on the important and difficult sub- ject of the minimum section required for the lattice members of columns of this type and dimension ; the evidence is, it must be admitted, only of a limited and negative character, but is valuable as far as it goes. These lattice bars formed a single triangulated system, arranged at an angle of about 60 degrees, and secured to the flanges of the channel irons by one f-inch or f-inch rivet, the breadth of the bars being 2 inches and 2J inches respectively, and the thickness | inch. In the absence of any statement in the record of tests to the contrary, we may assume that bars of these scantlings were PRACTICAL DESIGN OF COLUMNS AND STRUTS. 195 sufficient to develop the full strength of columns of the lengths and dimensions shown in the table. The percentage of weight of material used to resist what may be termed the secondary stresses in a column, to counteract local flexure, to provide sufficient bearing area at the ends, or in other ways to meet local weakness, in comparison with the total net theoretic weight of the section subject to direct compression, must always claim attention in a preliminary estimate of the weight of any column or strut, and will vary in accordance with the special conditions of each case. It is obvious that the reduction to a minimum of the scantlings of such a system of latticing as that just referred to is desirable on economical grounds, although the practical conditions of riveted connections and the thickness judged necessary for resisting corrosion will limit the extent to which such reduction can be carried. We may now lastly observe from experiments Nos. 63 to 74 inclusive the influence of eccentric loading upon the ultimate strength of the column. Comparing experiments 63 and 64 with 65 and 66, we have two sets of columns, similar in length, cross-section, and details of ends, and differing only in the position of the point of application of the load. In the former (Nos. 63 and 64) the load is applied at the centre of gravity of the unsymmetrical cross-section, with a mean ultimate resistance of 12*13 tons per square inch. In the latter (Nos. 65 and 66) the load is applied at the centre of figure, 1*60 inches out of the centre of gravity, or, say, one-fifth of the width of the column, with a mean ultimate resistance of only 7*74 tons per square inch. The reduction of strength due to eccentric loading is therefore in this case 36 per cent. Again, comparing Nos. 73 and 74 with Nos. 71 and 72, we find a mean reduction of 39 per cent., the eccentric loading being about one-sixth of the width of the column from the centre of gravity of the section. It is noteworthy that a measurable amount of lateral flexure is observed at a much earlier stage in the history of the test in the case of the eccentric load, and the total loads required to cause a given degree of lateral flexure are much less in the eccentric load than in the case of that applied at the centre of gravity, a result which is in consonance with theoretical requirements. If we endeavour to trace the influence of the form of cross- 196 CONSTRUCTION IN MILD STEEL. section upon the ultimate strength as between the H-shaped, the box with plate webs, and the box with lattice webs, it is found that there is little difference between the two latter, the lattice- webbed column being practically as strong as the plate-webbed for all values of -. The H-shape appears, however, to fall short of the ultimate resistances of the other sections, more especially as the value of ~ becomes greater. Further evidence is, however, required. The results of the pin- and flat-ended experiments are plotted in Fig. 128. It is not surprising, from a consideration of the foregoing remarks, that the average results are to be represented rather by an area than by a mean line, the varying elements of resistance in a built-up column being more likely to show con- siderable variations in strength than solid rectangular plates or bars, or simple rolled sections. Comparing pin-ended with flat-ended columns, we find, with nearly equal values of -, that the pin-ended columns give an ultimate resistance but little less than that of flat ends. Thus the mean of experiments 31, 32, 37, and 38 is 15-02 tons per square inch, while the mean of Nos. 25, 26, 45, 46, 52, 55, and 56 is 14' 8 8 tons per square inch. It is probable that the size of pins was not without influence in the ultimate resistance of the pin-ended columns, while, on the other hand, the local buckling of the plates in some of the flat-ended specimens probably lowered the resistance of those columns as a whole. The well-known experiments of Mr. James Christie, M.Am.- Soc.C.E., on wrought-iron and steel struts, are plotted in Figs. 129 to 132, and Figs. 134, 135, but for a complete description of the whole of the details of these valuable series of experi- ments the student is referred to the original record. 1 In Fig. 129 are plotted the results of compression tests on flat- and fixed-ended angles and tees, these forms of struts being of the type-sections shown in Figs. 142 and 147. The angles experi- mented upon ranged in section from 1" X 1" X J" to 4" X 4" x f ", while the lengths of the struts ranged from 5}" to 15' 5f", giving a proportion of - which varied between 14 and 481. 1 Transactions of the American Society of Civil Engineers, vol. xiii., April, 1884. PRACTICAL DESIGN OF COLUMNS AND STRUTS. 197 The tees, of which the experimental compressive results are plotted in the same figure, varied from 1" X 1" to 4" X 4" in 8 cu i 8 o o o o ii it 000 00 $ 3O O o oo 00 <* O OC 3 CO 8 &UOJT U2 in (\j O (VI in in 198 CONSTRUCTION IN MILD STEEL. section, and from 6" to 15' Of" in length, giving a proportion of - ranging between 14 and 420. n ^ aa I f + 8 S s? Jdd SUOJ. ^ lO CVJ s PRACTICAL DESIGN OF COLUMNS AND STRUTS. 199 The results of experiments on fixed- ended angles are plotted in the same figure. The fixing of the ends was obtained by means of clamps, and it is probable that the theoretical conditions of a fixed-ended strut were more nearly obtained in this series than in flat-ended struts. It will be observed from the diagram that when exceeds about 150, the fixed-ended struts show generally a greater compressive resistance than the flat-ended. Fig. 130 gives the results of compression tests upon hinged and round-ended angles and tees, both sections being plotted in the same figure. In this case, in the large majority of instances, the hinged ends consisted of ball and socket bearings, a semi- spherical ball of from 1 inch to 2 inches in diameter bearing upon a semi-spherical socket, the specimens being so arranged that the centres of balls were as nearly as practicable coincident with the centre of gravity of the cross-section. The influence of the size of the ball (probably due, although lubricated, to frictional resistance in the socket) may be traced in one or two instances in this set of experiments. For example, a 2J" x 2J" angle, 5 feet 4^ inches in length, with 2-inch diameter ball, failed at 12 '44 tons per square inch, while an angle of the same section and length, with 1-inch diameter ball, failed at 8*18 tons per square inch. Again, an angle 3" x 3" x -//, 15 feet 3| inches in length, with 2-inch ball, failed at 2'66 tons per square inch, while the same bar with 1-inch ball failed at 1*31 tons per square inch. Another angle, 2" X 2" X 1%", 15 feet 4^ inches in length, with 2-inch ball, failed at 071 ton per square inch, while the same bar with 1-inch ball failed at 0*62 ton per square inch. The loss of strength produced by slight eccentricity of loading also becomes evident in two tests ; an angle, 2" x 2" x T %", 8 feet 3J inches long, properly centred, with 1-inch ball and socket ends, failed at 3*16 tons per square inch ; improperly centred, it failed at 1*77 tons per square inch. Again, an angle, 1" x 1" X ", 5 feet 3 inches long, with 1-inch ball and socket, properly centred, failed at 2 '5 8 tons per square inch; a similar bar, slightly out of centre, failed at T30 tons per square inch. Considerable diversity of results is apparent in the hinged-ended specimens, possibly due to varying frictional resistances between the ball and socket, or pin and bearing, and the results are best expressed by an area, rather than a mean line. 20O CONSTRUCTION IN MILD STEEL. The round-ended specimens were arranged with a semi-spherical ball-bearing on a flat plate. Frictional resistances may be assumed * + s 4- "*D 00 H ** CO ^44- 4- O o 00 1 4- o 4- o a fc* CA n \\ + 4- 4- 44-0 OSJ i I 5 to fe3 8" I 1-s 4- 4- * O ^ VJ . CM 2 1 I**) ^> j>< (V 4 4 * o 1 o 1 M^ M^ 4- \ I 4- 4- 4- T< ^ lO ' 1 4- *" 4 Hf o 4- 1 5 O 4- 4- 4- 4-4- * OO | 1 ^ Q^. r 4 4- 1 -k) CO 4> 4. 4, 1 uj a sonl *s * > o PRACTICAL DESIGN OF COLUMNS AND STRUTS. 201 to have been absent in this case, and the ends being free to turn upon their bearings, the general results give a somewhat more regular mean line than those of the hinged-ended struts. The line lies, however, obviously along the lower fringe of the hinged-ended area. Fig. 131 gives the results of compressive tests upon wrought- iron flat-ended channels, joists, welded tubes, and Zed columns. The channels ranged from 2 inches to 12 inches in depth, and from 6 inches to 15 feet in length. The beams ranged from 4 inches to 15 inches in depth, and from 6 feet 6 inches to 22 feet in length. The tubes were 2*37 and 2*87 inches in outer diameter, and from 3 feet 5 inches to 15 feet in length. The results of similar sections, but hinged-ended, are shown in Fig. 132. In this series, the influence exerted upon the ultimate strength by the precise conditions of the " hinged-end " are well shown. Thus a welded tube, 3'5 inches external diameter, 15 feet in length, did not fail at 10'5 tons per square inch with a 2 -inch pin end, but, with 2 -inch ball and socket, failure took place at 6-3 tons per square inch, and with 2-inch ball and plate (round- ended, with practically no frictional resistance) at 5*0 tons per square inch. The result of eccentricity of loading is also shown by a tube of the same diameter and length, with 2-inch pin, set one-tenth of an inch out of centre, which failed at 8 '4 tons per square inch. The quality of wrought-iron used by Mr. Christie in the fore- going tests was as follows: ultimate breaking stress in tension = 21*8 tons per square inch ; elastic limit = 14*3 tons ; elongation in 8 inches = 18 per cent. Among the flat-ended specimens plotted in Fig. 131 are shown the results of tests on Z columns with one lattice web carried out by Mr. C. L. Strobel. 1 These tests were fifteen in number, and the section of the column was of the' type shown in Fig. 168, con- sisting of four Z irons, 2^" x 3" x 2J" x &'' connected by a single lattice web. The lengths of the columns ranged from 10 feet 11 J inches to 28 feet. The columns were tested horizontally, the lattice web being in a vertical plane. The ends abutted squarely against the castings of the testing machine, without the interposition of shoes, and the mode of failure was uniformly 1 Transactions of the American Society of Civil Engineers, vol. xviii. 2O2 CONSTRUCTION IN MILD STEEL. the same, by flexure in the direction of the least radius of gyration, in conformity with theory. (\J in PRACTICAL DESIGN OF COLUMNS AND STRUTS. 203 The section appears to yield good results, having regard to its simplicity of construction and accessibility for painting. Tensile 10 in 204 CONSTRUCTION IN MILD STEEL. tests of the iron used in the Z sections gave an ultimate tensile strength of from 22'0 tons to 24'0 tons per square inch, with an elongation of from 11 '3 to 22 '7 per cent. In Fig. 133 are plotted the results of tests upon pin-ended lattice columns of the Detroit Bridge and Iron Company, made at Watertown Arsenal. 1 These columns were of the type section shown in Fig. 150, consisting of two channel bars, connected together with a double web of lattice bracing. The channels were of sections 6 inches, 8 inches, 10 inches, and 12 inches wide, with flanges of from If inch to 2 inches deep. The channels were spaced from 6 inches to 8 inches apart, back to back, strengthened with reinforcing plates at the ends to provide bearing for the pin connections, the pins being 3 inches and 3 \ inches diameter. The columns failed usually by deflection in the direction of the least radius of gyration. It will be observed from the figure that 3-inch diameter pins give lower results than 3J-inch diameter, a result in accordance with the tests on 3-inch rectangular bars with pin ends, described on p. 186. Fig. 134 gives the results in graphic form of Mr. Christie's experiments 2 on flat-ended angles of mild steel, which were carried out under similar conditions to those on wrought iron previously described. The steel employed had an average carbon content of about 0'12 per cent., with an ultimate tensile resistance of about 28*3 tons per square inch, and an ultimate elongation of about 23' 6 per cent, in 8 inches. Fig. 135 gives the results of similar experiments on flat-ended angles of hard steel, having an average carbon content of 0'36 per cent., and an ultimate tensile resistance of about 45 tons per square inch, and an ultimate elongation of 17^ per cent, in 8 inches. The number of published experiments on the ultimate com- pressive resistance of mild steel columns is, notwithstanding the extent to which this material has been employed in this direction, not so complete or extensive as those upon wrought-iron columns, and a series of further experiments on full-sized built-up columns of various sections is yet a desideratum. As an example of such tests, the following may be quoted 3 : 1 Lanza, " Applied Mechanics." 2 Transactions of the American Society of Civil Engineers, vol. xiii., August, 1884. 3 Ibid., vol.fxxi. PRACTICAL DESIGN OF COLUMNS AND STRUTS. 205 Two columns of the type shown in Fig. 163, but with the lower flange plate replaced by open latticing, were tested to 8 | g I 3 <3 J? : [^T^r?^''^^ "S3 " !!! A. FIG. 181. Scale inch =r 1 foot. f. 0" 'o o'o V \ o 8 o \ o * \ o *l o o o o o .* fe X * o o *5 X ?J ^ o < >\ o FioTm 4 " Scale 4 inch = 1 w r-*f* *. M foot. 228 CONSTRUCTION IN MILD STEEL. These figures then illustrate a case where the continuity of the column structure has been broken in order to meet girder require- ments. But it must not be supposed that this is an example to be followed where the conditions are not similar. H FIG. 183. Scale 1 inch = 1 foot. In cases of buildings of several stories, where the column is considerable height, in segments of the various floor spacings, PRACTICAL DESIGN OF COLUMNS AND STRUTS. 229 and where the accumulation of load on the lower columns is heavy, a sound judgment would lead to the conclusion that the continuity of the column is of the first importance, and that all FIG. 184. Scale 1 inch = 1 foot. details of girder connections should be made to give way to it. Such a case might be conceived to arise in the columns supporting 230 CONSTRUCTION IN MILD STEEL. the various box and gallery tiers in a theatre auditorium, and where the safety of the audience demands that the utmost care be FIG. 186. Scale 1 inch = 1 foot. _* V- 5 X -e t I ffit& -f*- SECTIONAL PLAN AT H-H. .SECTIONAL PLAN ATJ-J FIG. 185. Scale 1 inch = 1 foot. taken in the design of all column details. Even in this case the continuity of the column has not in practice always been preserved, PRACTICAL DESIGN OF COLUMNS AND STRUTS. 231 although by the use of divided girders carrying the box tiers and forming the projecting cantilever portions, this desirable end could easily be secured. Another illustration of the importance of column continuity is found in the very lofty structures erected on the principle known as skeleton steel construction, as commonly practised in the United States. Here the consideration of transverse stresses due to wind pressure, and the necessity of preventing lateral flexure or oscillation, leads to very careful consideration of the column connections, and the best practice demands as much continuity of the column members as can be practically attained, the girder seatings being as a rule bracketed off the columns. We may have, then, two leading ideas which point to the desirability of column continuity, the accumulation of vertical loading, and the possibility of lateral flexure or oscillation in the building as a whole. Figs. 187, 188 give details of the base of a column of similar type to the foregoing, i.e. of girder section, of the type shown in Fig. 162. In this case no cast-iron bed-plate is used, the base of the column being arranged to bear directly upon concrete or stonework. We may next examine the details of a massive column of the type shown in Fig. 166, used in the interior of an engine-house, and supporting a heavy load arising from two lines of traveller girders, together with the load of girders and cast-iron tank above, the details of which are considered on pages 158 to 171. It will be seen from Figs. 189 and 190 that at the level of the capping or bracketing supporting the traveller girder, the column is gathered in, and reduced in section to the dimensions shown on Fig. 191, which is a plan of the top of the traveller girder seatings looking down. The upper column is of the same type of section as the lower portion, and possesses great stiffness in all directions. Fig. 189 is a front section on the line E of Fig. 191, and Fig. 190 is a section on the line DD of Fig. 191. It will be observed that the traveller girder seatings are borne, as it were, upon the shoulders of the lower portion of the column, while the continuity and rigidity of the column as a whole is well maintained. The clearance between centre of traveller rail and face of column is 9 inches, less the projection of the rivet heads (see the remarks on this detail in Chap. III., p. 137), a clearance which is sufficient for the type of traveller used in this instance. 232 CONSTRUCTION IN MILD STEEL. The normal section of the lower portion of the column below traveller girder seatings is shown in Fig. 192, and of the upper FIG. 187. Scale inch = 1 foot. on, tt*v&er* of 'JZajse, pLatt, to &e, Coivntersmtk. NOTE. The holding-down bolts to this column are four in number, li" diameter, with flat bar washer plates 1" thick, and 3" diameter washers, as shown in detail in Figs. 179, 180, p. 226. FIG. 188. Scale | inch = 1 foot. PRACTICAL DESIGN OF COLUMNS AND STRUTS. 233 portion in Fig. 194, the side elevation and plan of cap to upper portion of column being shown in Figs. 195, 196. In columns of this type, where the height is considerable, it is DetazL* of Clip tx> be, FIG. 189. Scale \ inch = 1 foot. sometimes desirable to introduce plate and angle stiffeners, similar to the stiffeners in the web of an ordinary plate girder, for the purpose of preventing distortion or flexure in the outer corner angle irons. This detail is shown in Figs. 192, 193. 234 CONSTRUCTION IN MILD STEEL. A column performing similar functions to the one last described, and of similar type, is shown in Figs. 197 to 205. The method of effecting the connection between the upper and /. 7 SECTION FIG. 190. Scale \ inch = 1 foot. lower sections of the column at the level of the traveller girder is shown in Figs. 197 and 198, which is a variation from the design shown in Figs. 189 and 190. The normal section of the lower PRACTICAL DESIGN OF COLUMNS AND STRUTS. 235 portion of the column is shown in Fig. 200, together with the details of the stiffener shown in plan in Fig. 200, and in elevation U*^ . ' __ PLAN AT B.B. CIROERS OMITTED FIG. 191. Scale g inch = 1 foot. DETAIL OF STIFFENERS IN LOWER COLUMN""" FIG. 192. Scale 1 inch = 1 foot. 236 CONSTRUCTION IN MILD STEEL. in Fig. 201. Details of the base of this column are shown in Figs. 202, 203, 204, and 205, with lewis bolts securing the column to a masonry bedstone. r FIG. 193. Scale \ inch = 1 foot. FIG. 194. Scale 3 inch = 1 foot. FIG. 195. Scale | inch = 1 foot. 2 4-' ;r-^J ^ . ^>- ~^~T^ (jib dib ' PLAN OF CAP FIG. 19G. Scale inch = 1 foot. PRACTICAL DESIGN OF COLUMNS AND STRUTS. 237 A column, of which the simple elementary type is shown in Fig. 157, is shown in detail in Figs. 206 to 215 inclusive. This column consists, in its lower portion, of two rolled joists """i """^ !o i ( |O 1 ( !o I ( iO ta 1 c 1 1 o h . ,0 IN b ( o i H o ( .,\4 O OTO FIG. 209. Scale \ inch = 1 foot. the arrangement of the details and connections being determined by the conditions of the site and the peculiarities of loading. It forms one of a row of columns dividing two adjacent bays of an extensive range of factories, boiler-shops, etc., the bay on one hand having a high-level traveller road, with high-level 246 CONSTRUCTION IN MILD STEEL. roof, and on the other hand a low-level traveller road, with low- level roof. Together with the provision for these traveller and ., 2 -r-^ PLAN AT B-B FIG. 210. Scale \ inch = 1 foot. 0.0 2 r o o O.O !o!!o! - H--I- o o o o Fia. 211. Scale i incb = 1 foot. PRACTICAL DESIGN OF COLUMNS AND STRUTS. 247 roof loads a system of bracing is also attached for the purpose of carrying the various ranges of main and counter shafting, with ft rras&etv 3jk diaZ u* ;*__/ J{ /. PLAN AT C-C. FIG. 212 (Scale \ inch = 1 foot). plates PLAN AT A-A FIG. 213 (Scale jf inch = 1 foot). 2 4 8 CONSTRUCTION IN MILD STEEL. electric motors attached to the column, 'required for the varied machine tools to be used in the shops. The variety of loading and of detail of connection thus required rendered the design of these columns somewhat complex, and the results are not without their value to the student. The general arrangement of the columns, -4- *. \ o! I \j I pi o v I rb! o o\ #?--.*- JOi 'O! .x, r :>. ><*. IN & k ^- !/ PLAN OF CAP. FIG. 215. Scale \ inch = 1 foot. FIG. 214. Scale | inch = 1 foot. and of the traveller girders, roof girders and roof principals asso- ciated with them, is shown in Figs. 216, 217, the bracing for countershafting, which supplied longitudinal stiffness to the rows of columns, being omitted for the sake of clearness. Fig. 218 is a front elevation and Fig. 219 a side elevation of the base of the column. A plan of the base looking down is given in PRACTICAL DESIGN OF COLUMNS AND STRUTS. 249 FIG. 210 (Scale 1 inch = 10 feet). 250 CONSTRUCTION IN MILD STEEL. Fig. 220. It will be observed that the column is held down by eight foundation bolts, the details of which are shown in Fig. 221 and to which further reference will be made. FIG. 217 (Scale 1 iuch = 10 feet;. PRACTICAL DESIGN OF COLUMNS AND STRUTS. 251 A longitudinal section of the base is also shown in Fig. 222. The normal section of the lower portion of the column is given in Fig 223, from which it will be seen that the weight-bearing section consists of two girder-shaped riveted sections, each consist- FIG. 218. Scale \ inch = 1 foot. ing of a solid web 20" X i", four angles 3J" X 3" X i", and two plates 8" x J". The sections are prevented from twisting by a braced arrangement of flat bars 3" X |", arranged as shown, and spaced at intervals up the column, while the pair of girder sections 252 CONSTRUCTION IN MILD STEEL. are united by a latticed web of angle irons riveted to the back of the girder webs as shown in Fig. 219, thereby converting the pairs FIG. 219. Scale | inch = 1 foot. PRACTICAL DESIGN OF COLUMNS AND STRUTS. 253 of vertical columns into one braced vertical cantilever, capable of resisting transverse flexure, and with a very large moment of inertia in the plane of the latticed web ; while in a plane at right angles thereto, and in the longitudinal axis of the traveller roads, the girder sections constituting the columns have each a large resistance to flexure in that plane. This lower section of the column is continued up to the level of the lower traveller road, provision for which is made as shown in Fig. 224, one girder section being stopped off to carry the lower ir K n P^-jjpgf:^ 3 -A- ^4 JL3 J.J FIG. 220. Scale | inch = 1 foot. traveller girder, while the other girder section is continued up unbroken to carry the higher traveller as shown in Figs. 217, 225. It will be seen in Fig. 224 that at the level of the lower traveller seating a new vertical member commences, intended to carry the roof loading above. The base of this roof column is arranged to rest upon the arrangement of plates and angles shown in Fig. 224, by which means the roof load is divided between the twin girder sections of the lower portion of the column. Re- ferring again to Fig. 225, we see that while the column section 254 CONSTRUCTION IN MILD STEEL. is stopped at the level of the upper traveller road, the roof column is continued upwards to the summit of the entire column, the total height from the under side of the column being 46 feet 5 inches. The section of the column between the levels of the lower and upper traveller ways is shown in Fig. 230. FIG. 221. Scale \ inch = 1 foot. The student will observe that the clearance between the faces of columns and the centre line of traveller rail is in this case 11 inches, and he will be in a position to appreciate the influence which this dimension has on the arrangement of details in cases of this kind. PRACTICAL DESIGN OF COLUMNS AND STRUTS. 255 Fig. 226 is a sectional plan on line FF at the level of the lower traveller girder seating shown in elevation in Fig. 224, while FIG. 222. Scale | inch = 1 foot. Fig. 227 is a section on GG, Fig. 224. Fig. 228 is a section through DD (Fig. 225), and Fig. 229 is a section at CO, looking down upon the seating of the upper traveller girder. FIG. 223. Scale f inch = 1 foot. The uppermost portion of the column above the upper traveller road, carrying the lattice roof girder, has sections, which are shown 2 5 6 CONSTRUCTION IN MILD STEEL. in Figs. 231 and 232, while the detail of the bolted connection between column and roof girders is shown in Figs. 85, 86. The details of the girders themselves are alluded to, together with those 1 vIS I I 1 '! hfljt; i i-p- .. /4\ . 1 1 J /+\ I i /^r\ /-\ II i ' /^\ i /t\ i ' tKtN'H^ f^rGK'j>k>r-e j - TfreH !!r%;i ufepi ! i ; M J=L J=U FIG. 235 (Scale | inch = 1 foot). Fio. 236 (Scale 1 inch = 24 feet). 262 CONSTRUCTION IN MILD STEEL. top of the column is divided between several rows of columns, the whole being enclosed between masonry walls of a substantial character. Consequently the amount of holding-down power FIG. 237. Scale 1 inch = 16 feet. required to resist such a moment was not excessive, and the group of eight foundation bolts shown in detail in Fig. 221 provided a sufficient resistance. The arrangement of these bolts PRACTICAL DESIGN OF COLUMNS AND STRUTS. 263 is shown in plan in Fig. 235, and it will be observed that their washers, in this case, consist of simple steel flats, 1 inch thick, arranged as shown. Under other conditions of construction, however, the question of lateral stability of the whole structure against wind pressure may be of greater importance, and require special provision to ensure sufficient resistance to an overturning moment. Especially may this be the case where the building is lofty 264 CONSTRUCTION IN MILD STEEL. and the enclosing walls composed of timber or corrugated sheet- iron, or both combined, having no great weight in themselves, and therefore requiring a sufficiency of stability in the column anchorages. i An instance of this class is illustrated in Fig. 236, showing a cross-section of a building designed to carry 70-ton travellers at a height of rail level of 41 feet 4 inches above ground, the elevation of one bay of the building being shown in Fig. 237. PRACTICAL DESIGN OF COLUMNS AND STRUT. 265 In this case the columns of riveted wrought iron rest upon massive concrete foundations, carried down to a reliable stratum underlying soft alluvial deposit. The section of this column, which is 49 feet in total height, is of the type shown in Fig. 167, and the details of the base and anchorages are shown in Figs. 238, 239, 240, 241, 242, and 243. It will be seen that the holding-down bolts resisting overturning FIG. 240. Scale inch = 1 foot. moments transversely to the building are 3 inches in diameter, of mild steel, with circular cast-iron washers, while sufficient stability in the longitudinal direction of the building is afforded by bolts 2^ inches in diameter. The attention of the student is directed to the means by which the heavy anchorage bolts take hold upon the riveted column base. 266 CONSTRUCTION IN MILD STEEL. The detail of the cap of the column and the seating provided for the traveller girders is given in Fig. 244, and the section of the traveller girders showing elm timber sleeper forming continuous FIG. 241. Scale \ inch = 1 foot. bearer to rail in Fig. 245, the timber being notched to the stepping up of the plates in top flange, the traveller girder in this case being of uniform depth, and not fish-bellied. FIG. 242. Scale \ inch = 1 foot. In such a case as the foregoing, the fixing of heavy anchorage bolts during erection requires careful attention to ensure that the bolts themselves do not sink beyond their true level when concrete PRACTICAL DESIGN OF COLUMNS AND STRUTS. 267 is being deposited around them, as in such an event the screwed portion of the bolts may be found insufficient in length to pass FIG. 243. Scale \ inch = 1 foot. FIG. 244. Scale \ inch = 1 foot. through the whole depth of the nut, a contingency which points to the desirability of an ample margin of length in the bolt and its screwed portion, the labour of cutting off excess length in such 263 CONSTRUCTION IN MILD STEEL. conditions being preferable to any loss of strength in the hold on the nut. FIG. 245. Scale | incli = 1 foot. The accuracy of position of all anchorage bolts in plan should be secured by the use of templets. CHAPTER V. KOOF CONSTRUCTION IN MILD STEEL AND IRON. General remarks Development of roof construction in timber, cast iron, wrought iron, wrought iron and steel, mild steel Classification of roof principals- Members of roof principals Upper or compressive member or principal rafter Sections for principal rafter Shoes to rafter Expansion apparatus Main tie or lower tension member ; in timber roofs ; in composite roofs ; in wrought-iron roofs ; in steel roofs Bisks of defective smith-work Earlier steel tie-rods Present-day practice Flat bari ties Link tie-rods Occasional stiffening of main tie-rod in small roofs Examples of tie-rods Intermediate bracing Struts Ties Purlins Influence of nature of roof covering upon the arrangement of purlins Details and sections of purlins Distance apart of main trusses Inter- mediate rafters Roofing accessories The collection and disposal of rainwater or melted snow General arrangement of roof drainage Roof guttering in cast iron or riveted steel ; in lead Experiment on rate of discharge in gutters and cesspools Area of roof surface to be drained Examples of guttering and down-pipes Expansion joints Stopped ends Lanterns, skylights, and venti- lators General remarks Lantern standards Louvre blades Roofs of flat pitch Examples of roof construction of various types Special type of roofing combined with vertical supports Details The testing of roof principals Conditions of practical testing in the contractor's yard Methods of measuring deformation and settlement Remarks on cottering up Setting out of roof principals Scribing floor. IT is impossible, within the limits of a single chapter in a collection of " Notes " such as the present, adequately to deal even with the main features of roof construction in mild steel or iron. All that the writer can hope to accomplish is to offer such suggestive remarks on the subject as may assist the student to a fuller consideration of this branch of practical construction, and lead him to a careful study of the numerous existing examples. It will be assumed that the student has made himself acquainted with the usually accepted theories as to wind pressure, and the conditions of loading of a roof truss arising from dead load of structure, weight of snow, and wind pressure, whether the latter be considered as acting vertically, normal to the slope of 270 CONSTRUCTION IN MILD STEEL. the roof, horizontally, equally or unequally distributed ; and that he is acquainted with the usual methods of calculations of stresses, such as graphic analysis and the method of sections. Nor can the extensive subject of the nature and properties of the various kinds of roof coverings, such as slate, tiling, glass, zinc, copper, lead, corrugated iron, felt, and the like, be considered, except so far as they may influence the arrangement and detail of the metallic structure which is designed to support them. 1 The history of the development of roof construction from its earlier forms in timber, and through the further stages of cast iron, wrought iron, with various cast-iron details, then wrought iron practically alone, wrought iron with steel tie-bars, and lastly, as at the present time, in mild steel, with occasionally some admixture in detail of the other two metals, would doubtless be both interesting and instructive, but practical consideration can only here be given to the final stage of mild steel. Eoof principals may be roughly divided into four main divisions, viz. : (a) Principals with straight upper rafters, of varying degrees of pitch. (6) Principals with curved or polygonal upper rafters. (c) Principals of special constructions, including the arch, arch with one, two, or three hinges, or of the " sickle " type indicated in Fig. 345, usually employed only in large spans. (d) To the above may be added another class sometimes employed in covering large areas, in which lattice girders with parallel booms, and sometimes of large span, are placed side by side, and roofed over with intermediate principals, usually of the first type de- scribed above, but occasionally of a special class. In this class the upper boom of the main lattice girder supports a valley gutter for its entire length, or a series of ridges and valleys is arranged to cover the inter- mediate space. A further subdivision may also be taken to include a type of roof covering where the conditions require a cantilever method of construction, such as large verandahs, or the form frequently 1 The student will find valuable assistance in the subjects of roofing materials in Vol. I. and in the Calculation of Stresses and the Theory of Roof Loading in Vol. IV. of "Notes on Building Construction.*' ROOF CONSTRUCTION IN MILD STEEL AND IRON. 271 met with in railway station platforms, where the position of the supporting columns at some distance from the edge of the plat- form necessitates the continuation of the roof truss in the form of a cantilever. In all such cases the deflection of the cantilever portion must be carefully borne in mind, in order that the con- struction, guttering, etc., at the eaves may maintain their true and horizontal lines. Another arrangement of roof principals has been suggested, dividing them into two classes, intended to cover all roof structures, namely, the one in which the reactions of the supports of the prin- cipal are in a vertical direction, and the other in which the reactions are at an angle with the vertical, the first class being self-contained without horizontal thrust, the second those with a horizontal thrust, and dependent upon the resistance of the abutments for their stability. This distinction would, however, appear to fail unless the loading of the principal is purely vertical in both classes. Where the assumptions as to wind pressure include a horizontal com- ponent, as in the case of wind pressure taken normal to the slope of the roof, other considerations present themselves, and the reactions of one or both supports, even in self-contained structures, must contribute a corresponding and opposing force. Eoof principals of the class (a) or (6) present three main features in their design, viz. : The upper or compressive member, usually denominated the principal rafter, either straight, curved, or polygonal, as the case may be. The lower or tension member, denominated the main tie, or, in timber roofs, the tie beam. The intermediate bracing of struts and ties, fulfilling similar functions to those of the web of lattice girders. The upper or compressive member, or principal rafter, will have its scantlings determined in the first instance by the laws governing the strength of long columns or struts, the length of the column under consideration being determined in a vertical plane by the distance between the apices or points of junction of the intermediate bracings. In a longitudinal direction, however, the column will be free to deflect laterally between the points of support of the purlins, assuming the latter to offer a sufficient resistance to lateral flexure of the principal as a whole ; but, as remarked further on, roof principals in course of erection or 272 CONSTRUCTION IN MILD STEEL. testing are, in the temporary absence of purlins or roof coverings, somewhat flexible in a plane at right angles to their elevations, owing to the smallness of their dimensions in that plane as compared with their span. Security in this respect is obtained by a properly designed system of what is called wind bracing, being an arrangement of diagonal braces from the heel or shoe of one principal to the ridge or summit of another, whereby the possibility of the overturning of a series of roof principals like a pack of cards is obviated. Where the length of roof is not great, and the roof is enclosed between stout gable walls at the ends, or is hipped, the addition of wind bracing is not so imperative. It will be found, however, in practical design, that the scantlings of the principal rafter will be ruled by other considerations than those of columns or strut area alone, even if the compressive stresses be purely axial, in the direction of the length of the column. If, on the other hand, the column is subjected to transverse stress arising from the position of the purlin not being precisely over the junction of a brace, a con- dition which will frequently arise in roofs of small span, then the stresses arising from the bending moments must be con- sidered in connection with those arising from purely compressive stress, and the area or moment of inertia of the section increased accordingly. The construction of skylights or ventilating lanterns with standards attached to the principal rafters, examples of which will be given later on, will frequently influence the choice of section, and impose a minimum dimension in order that the bolted or riveted attachments may be properly made. Thus, for example, a tee-steel section for the principal rafter may be selected, giving a sufficiency of area for the calculated stresses, but the top table of which may be too narrow to receive the bolts required to connect a cast-iron louvre standard of the type shown in Fig. 265. Or again, the section may not be suitable to properly arrange the details required at the connection of the rafters at the apex of the principal. Mistakes in points of detail such as these (upon which much of the success in design depends) will be usually avoided if the student is careful to draw each detail in cross-section as well as in elevation. The details of connection of the purlins with the principal ROOF CONSTRUCTION IN MILD STEEL AND IRON. 273 rafter must also be considered and allowed for. Where wind bracing is adopted, the scantlings required for connection to the top table or web of the rafter must be remembered. The sections commonly used in the construction of the principal rafter are various, and adapted to the span, distance apart of principals, load, and working stress allowed. Thus for roofs of small span, and where precise symmetry about a central axis is not necessary, a single angle (Fig. 142) may be used. For roofs up to about 40 to 50 feet span a single tee section (Fig. 147) is commonly adopted. A section of double angles (Fig. 143) is very convenient for connection, and affords more space for bolted or riveted details in the top tables. A built-up tee section of plates and angles is convenient for larger spans, as in Fig. 146, with the addition of a vertical web plate. A section of double channels (Fig. 150) has been used for spans of from 90 to 100 feet, while the built-up channel sections shown in Fig. 163, with flat bar lattice bracing, have been used in a roof of about 120 feet span. Eoofs of still larger spans, up to 200 feet or more, have been constructed with principal rafter sections of the types shown in Fig. 151, or in Fig. 162, with additional flange plates top and bottom. The details of the lower or shoe end of the upper rafter are variable in character, depending largely on the span of the principal, and the scantlings of the main tie. If this latter is of heavy section, the connection at the heel of the principal becomes of corresponding importance, and demands careful consideration. For roofs of moderate span, say up to 60 feet or thereabouts, the lower end of the principal rafter terminates in, and is connected to, a shoe which forms the seating of the principal upon the wall, column, or girder, as the case may be. Formerly this shoe was of cast iron of various forms, and some defective details may be discovered in those forms of shoe in which the method of connection of the main tie involved tension upon certain portions of the cast iron. In present-day practice these cast-iron shoes have generally been superseded by shoes of a simple form in mild-steel riveted work. A few examples of shoes of this type, with their connection to the main tie, are shown in Figs. 280, 286 to 293, 298 to 302. In roofs of large span the expansion and contraction of the structure under changes of temperature have to be provided for and in these cases the place of the ordinary shoe is frequently taken by a system of rocker plates and rollers resembling the T 274 CONSTRUCTION IN MILD STEEL. ordinary expansion apparatus of a girder of large span, although it may be questioned whether such rollers, not easily accessible as a rule to inspection, do not frequently become rusted up to an extent which interferes with their efficiency. The Main Tie or Lower Tension Member. The form of section to be given to this important member of a roof-truss, especially of the classes (a) and (&) above alluded to, will largely influence the details of connections and the general type of construction, and will always be found to demand careful consideration. In timber roofs this member takes the form of a simple rectangular beam, as the functions of this tie are usually as much to resist transverse stress due to the weight of ceiling rafters, or possibly of a floor, as to resist in tension the spreading effort of the rafters. In composite roofs of timber and iron combined the practice has usually been to employ wrought-iron tie-rods of circular section. In wrought-iron roofing for moderate spans, and even up to spans of very considerable dimensions, the general practice for many years was in favour of the round rod or circular section. This form admitted of a nice adjustment of cross-sectional area to theoretical requirements, and so far represented an economical construction, while the appearance was light, and the nature of the material offered no special difficulties or risks in the manufacture of eyes and jaws or in the welding processes which usually accompany those details, provided only that the smith-work was properly and soundly done. In many roofs of large span heavy circular rods were used with screwed ends and coupled connections, with a view probably of avoiding the risks of defective smith-work in such large jaws or eyes as the size of section demanded. Eecent events have, however, thrown some light upon the general policy of providing a single member only to act as the main tie in roofs of large span, and it may be doubted whether, in view of possible hidden flaws arising from defective smith- work, a duplication of this important member in a large roof -truss is not desirable. Upon the introduction of steel into roof construction some attempts were made to utilize the material possessing a high tensile resistance, by employing it in the main tie, while constructing the remainder of the truss in wrought iron. In the early days ROOF CONSTRUCTION IN MILD STEEL AND IRON. 275 of steel construction a harder grade of steel, with higher carbon content, was in vogue, and difficulties manifested themselves in the smithing of jaws and eyes. In some cases the difficulty was met by the use of a ferrule of soft wrought iron being welded on the steel rod, and the whole smithed out to the desired form ; while in other directions steel tie-rods with plain screwed ends, involving no smith-work or welding, were used, the connections being of a special character, consisting of coupling boxes designed to give the required connections at junctions with intermediate braces, etc. With the more general use of mild steel of a lower carbon content, and more amenable to smith-work, a new set of conditions has arisen, and the present-day practice is in favour of the use of mild steel throughout the entire truss, with such occasional use of cast iron in special details, such as lanterns, skylights, and guttering, as is desirable. Some designers, however, prefer, in the case of round-rod ties, to use wrought iron, on the ground of greater security in the welds, reserving mild steel for the remainder of the truss, thus reversing the procedure of an earlier date; but the tendency as a rule has been to abandon the circular section, and to adopt for moderate spans the flat-bar tie with riveted connections. This form of tie is less economical than the circular section, inasmuch as a loss of one rivet-hole in the cross-section is involved ; the appearance, although not objectionable, is not so light as the round rod, but, on the other hand, the method of construction is cheap, involving no smith-work, while the riveted connections are as a rule of simple type. If the slight increase of weight in the flat-bar type is set against the greater economy in manufacture, it is probable that the difference of cost in the two types, flat-bar section and circular section, is not very appreciable. In roofs of large span, the ordinary suspension-bridge link with swelled eyes and pin connection has been employed with good results both in wrought iron and steel. In this case all the precautions necessary, both as to methods of manufacture and in the design of the proper shape of head and dimensions of pin connection, are as applicable as in the case of suspension-bridge design, or in the lower chords of trussed girders, with eye-bar tension members. Hitherto we have regarded the main tie as subject to direct tension only, and this assumption is probably correct for all roofs of large span and of considerable dead load in proportion to any 276 CONSTRUCTION IN MILD STEEL. inequality or obliquity of loading or wind pressure which may come upon them. Certain cases may, however, arise, especially in roofs of small span in very exposed situations, where it is expedient to stiffen the main tie as against any small element of compression which may arise from an extreme horizontal component of wind pressure, or where the roof principal performs the function of a strut or tie between the heads of lofty columns, acting as a gauge- keeper between the parallel rails of a traveller gantry, or trans- mitting a proportion of wind pressure in a lofty building from one side to the other. Again, such a stiffening of the main tie may be desirable in the case of roof principals spanning the interval between lattice roof girders possessing but little transverse stiffness, and where a certain amount of stiffness in the tie-rod is desirable on general grounds. Considerations of this kind will occasionally lead to the adoption of angle or tee, or other stiffened section, for the main tie, although, of course, the economy of section as for a purely tension member is lost, owing to the practical difficulties in connection with end connections, which lead to an inequality of tensile stress over the entire cross-section. It is unnecessary to remark that where a tie is subjected to transverse stress, as from supported loads, the weight of a ceiling or floor, or the like, then the form of section must be one specially adapted to meet these conditions. Some examples of the use of the circular section of tie-rod, with the details appertaining thereto, are given in Figs. 290 to 295. The treatment of flat-bar ties in mild steel is indicated in Figs. 280 to 289, and of the stiffened form of tie in certain cases in Figs. 270 to 279. The Intermediate Bracing of Struts and Ties. The design of the struts forming portion of the intermediate bracing in trussed principals will be governed by the laws of long columns, and they will generally be found to be free from the transverse stresses which may sometimes affect the sectional area required in the main rafters ; but, considered as columns, due allowance must be made for the imperfect seating or fixing of the ends of the struts, due to the exigencies of design in certain types of construction. Where a bond-fide pin end can be obtained at both ends of the strut, the strut can then be more certainly classed under pin- or round-ended columns, and calculated accordingly. But it frequently happens that the line of thrust is, from the nature ROOF CONSTRUCTION IN MILD STEEL AND IRON. 277 of the connections, not axial, and the loss in strength should be allowed for accordingly. These considerations lead to the adoption of a low working resistance, or of a large factor of safety, if the strength of the strut is calculated from the usual formulae. The variation of stress in the bracing caused by unequal loading will, of course, have received attention in the preparation of the stress diagram. The form of section for struts will vary with the dimensions of the principal, and the position occupied in the truss. The section may be a simple angle or tee, two tees back to back, kept apart by cast-iron distance pieces, and riveted through, two flats treated in similar manner (see Fig. 141) ; while a section consisting of four angles, arranged as shown in Fig. 144, and kept in position by special castings, has been used with success in some of the largest examples of the bow-string truss in this country. Tubular struts are occasionally used, but require connections at their ends of a somewhat special character. The use of cast iron for struts was frequent in roofs of old-fashioned design, but has been replaced in modern roof-work in wrought iron or steel by the types above referred to. The ties are usually constructed as pure tension members, and may be of any of the sections previously alluded to and used for the main tie, as round or flat bars. In some cases, however, angles are employed both for struts and ties, with riveted connections, and in this way an effective and economical truss (economical, that is, in cost of construction) is obtained. As all the bracing members are thus capable of resisting compressive stresses, the changes of sign in stress in the bracing arising from unequal loading are met. Purlins. The arrangement and construction of these important members of a roof structure must now be considered, and it will be found that the class of roof covering to be adopted will have considerable influence on their design. Thus, if a covering of slates or tiles be used without boarding or battens, the purlins will take the form of angle laths, spaced at a distance corresponding with the gauge of the slates or tiles, which are wired to them. This is a common form of covering in gas-retort houses or similar structures. Again, if slates, zinc, lead, or copper are laid on boarding, then the distance apart of the purlins will be regulated by the maximum 278 CONSTRUCTION IN MILD STEEL. span, which can be assigned to the boarding, allowing for dead and live loads, and with a proper amount of stiffness, or absence of undue deflection. Or if zinc be laid with Italian corrugations upon wood rafters, then the maximum span allowable for the rafters will determine the pitch of the purlins ; while if one or other of the numerous patent forms of glazing be adopted, it will be found necessary to accommodate the spacing of the purlins to the details of the system employed, including also consideration of the maximum length of sheet-glass to be used, and the allowable span of the sash-bars. A similar condition will be found to prevail when zinc is laid on boarding with drips, and the length from drip to drip will be ruled by the standard length of zinc sheet to be used, allowance being made for the length of sheet taken up in forming the drip, tucks, overlaps, etc. Generally, conditions such as those outlined above will govern the pitch and setting out of the purlins, and following thereon the arrangement of the bays of intermediate bracing, and the sub- division of the main rafter. The details and sections of the purlins themselves will be dependent upon the load to be carried, and their span, that is, the distance apart of the main trusses. This latter dimension usually varies with the span of the roof, although in many cases other considerations may govern the distance apart of main principals, such as the distance apart of column foundations (when ruled by local circumstances), the arrangement of the piers in supporting walls, and the like. Thus, for spans up to, say, 40 feet, a very usual distance centres of principals is from 6 to 10 feet. Principals of spans of 100 to 200 feet are commonly spaced 25 to 35 feet apart, while trusses of such exceptional spans as 300 feet or upwards may be from 50 to 70 feet apart. The purlins in structures of such dimensions as the latter are lattice girders, of considerable depth and weight ; those of, say, 25 to 35 feet in span may consist of trussed angles or tees, or occa- sionally rolled joists, while those of 6 to 10 feet span are usually either single angles, tees, channels, or rolled joists of light section. Where the main principals or trusses are as much as 25 feet apart, intermediate rafters resting upon the purlins are frequently adopted, thus subdividing the spaces to be covered, and resulting in a span which can be met by one or other of the roof coverings above referred to. ROOF CONSTRUCTION IN MILD STEEL AND IRON. 279 Purlins of considerable span, such as 25 feet, when consisting of braced beams or lattice girders, and arranged so that the plane of the web of the girder is normal to the slope of the main rafter, which is frequently the case, are subject to a twisting moment, due to their centre of gravity having a lever arm about the point of support, which should not be overlooked. This consideration points to the desirability of so arranging for heavy purlins that their webs lie in a vertical plane, and this will usually lead to the adoption of vertical members in the system of intermediate bracing in the main truss. Such vertical members are also useful in the case of hipped roofs, and simplify attachments. Such considerations will, however, only apply in the case of purlins of considerable span and weight. Roofing Accessories The collection and disposal of Rain-water or Melted Snow Skylights and Ventilators. The arrangement of the general scheme of roof drainage, and of the principal and secondary gutters, with their cesspools and downpipes or spouts, should always receive the very careful attention of the designer. The material used most frequently for roof guttering and rain- water pipes in iron constructions is cast iron, although occasionally riveted steel gutters are used in special situations. In timber roofing for ordinary building construction, timber guttering, lined with lead or zinc, is commonly used, but to this latter form of construction further attention need not here be given. 1 The disposal of rain-water, and the necessary dimensions to be given to gutters and down-spouts for the safe drainage of any given area of roof, constitute an important branch of the science of applied hydraulics, combined with due consideration of the meteorological conditions of the site as regards the maximum rainfall to be provided for, especially if the roof is to be designed for tropical climates, where excessive rainfalls, occurring over greater or lesser periods of time, are to be anticipated, and must be duly and efficiently met, with a sufficient margin of safety against overflow and flooding. The purely hydraulic questions connected with the flow of water in channels, and through orifices which have to work under the widely varying conditions met with in practice, cannot here be dealt with, and it is probable that much of the design of this important branch of roof construction has been carried on by empirical, or more or less rule-of-thumb, methods, based, no 1 See " Notes on Building Construction," vol. i. 280 CONSTRUCTION IN MILD STEEL. doubt, on practical experience, but with which the ordinarily accepted rules and formulae of applied hydraulics have had little to do. Experimental evidence on many points connected with the design of guttering, cesspools, and drainpipes is, so far as the writer is aware, to some extent lacking, and it is much to be desired that correct information on these subjects should be extended. The figures detailed in Table 35, and showing the average results of a considerable number of careful experiments on the rate of discharge of guttering, cesspools, and downpipes of a certain type of design, are therefore presented as a small contribution to the SECTION ON A.B. SECTION ON C.D. i Fio. 246. Scale 1 inch = 1 foot. FIG. 247. Scale 1 inch = 1 foot. general subject, and are, of course, applicable only to the precise details described. They may serve perhaps to bring out some of the conditions with respect to flow and discharge which are to be met with in practice. The gutter experimented upon is shown in Fig. 247, the flanged joints being partly internal and partly external, as shown in Fig. 248. A similar section of gutter is shown in Fig. 250 with flanges wholly on the outside, as shown in Fig. 251. These flanges are machined, bolted, and made watertight with rust cement, the section of joint being of similar type to that in Fig. 257. ROOF CONSTRUCTION IN MILD STEEL AND IRON, 281 The connection of the normal run of gutter, with its cesspool, which occurs at a stopped end, is shown in Figs. 246 to 249. SIDE ELEVATION. FIGS. 248, 249. Scale 1 inch = 1 foot. Fig. 246 is a section on AB, and Fig. 247 a section on CD in Fig. 248. It will be observed that the outlet and downpipe are arranged out of centre of the gutter, in order to clear the supporting lattice 282 CONSTRUCTION IN MILD STEEL. girder below, and the detail illustrates one of those practical con- ditions in the design of gutterwork to which purely hydraulic con- siderations have occasionally in some degree to give way. Fig. 248 is a plan, and Fig. 249 an elevation of the cesspool. The actual section of valley gutter, with its cesspool and down- pipe forming one complete bay of roof drainage, was tested in position in the roof with the results detailed in the following table, the gutter being filled successively to the depths shown, and the contents allowed to discharge themselves freely through the apertures shown in the figures by the removal of suitably arranged plugs or valves. TABLE No. 35. TABLE SHOWING THE EESULTS OF EXPERIMENTS TO ASCERTAIN THE KATE OF DISCHARGE OF KAIN-WATER FROM THE GUTTER, CESSPOOL, AND DOWNPIPE SHOWN IN FIGS. 246 TO 249. Internal diameter of downpipe in inches. Fall in level of water in gutter. Contents discharged in cubic inches. Observed mean duration of flow in seconds. Discharge in cubic inches per second. 5 5 5 5 6" to 5" 5" to 4" 4" to 3" 3" to 2" 18,975 18,975 18,975 18,975 11-5 26-5 37-0 66-5 1650-0 716-0 512-8 285-3 5 6" to 2" 75,900 141-5 536-4 The vertical length of downpipe attached to the cesspool in the above experiments was about 31 feet 6 inches to the junction with the rain-water drain, and was 5 inches internal diameter through- out. The necessities of design in arranging for the reception and attachment of the downpipe to a column of lattice construction, and in the passing of roof and traveller girders, gave rise to about 5 bends of 45 degrees each, so that the discharge was subject to conditions not more favourable than those usually found in practice. The rapid decrease in discharge with the decrease of head over the mouth of the cesspool and downpipe will be observed, and the rate of decrease is greater than that due to theoretic loss of velocity following on loss of head. Probably the special conditions induced ROOF CONSTRUCTION IN MILD STEEL AND IRON. 283 by the shape and dimensions of cesspool, the ratio of the area of the downpipe to the area of cesspool, and the inability of the volume and height of water contained in the cesspool over the mouth of the downpipe to maintain the latter in the condition of dux? falls FIG. 250. Scale 1 inch = 1 foot. FIG. 251. Scale 1 inch = 1 foot. " full flow," are sufficient to account for the comparatively small discharge at low heads. But these are conditions common in greater or less degree to most details of guttering and rain-water disposal, hence the value of practical experiment in cases such as the above and a wide field is open for the student in the carrying out and analysis of FIG. 252. Scale 11 inch = 1 foot. FIG. 253. Scale \\ inch = 1 foot. experiments similar in kind, but covering a wider range of in- vestigation into the influence of cross-section of gutter, the best form of cesspool, and the precise value of discharging power of varying diameters of downpipe. 284 CONSTRUCTION IN MILD STEEL. The arrangement indicated in the figures and experimented upon as described above, was intended for use in buildings of large area, with numerous valley gutters, and if an attempt were FIG. 254. Scale 1^ inch = 1 foot. FIG. 255. Scale 1 inch = 1 foot. made to deduce from the above figures the maximum area of roof surface which could safely be drained by such an arrangement of gutter, cesspool, and downpipe, the calculation would include FIG. 256. Scale 1 inch = 1 foot. the following considerations. Assuming that no accidental obstruction occurs in the gutter or downpipe, such as collections of leaves, mud, etc., it will be desirable that the surface of water ROOF CONSTRUCTION IN MILD STEEL AND IRON. 285 in the gutter shall never, during the period of heaviest rainfall, be allowed to stand higher than will give a certain margin of safety FIG. 257. Scale liinch = 1 foot. to prevent overflow and flooding, especially in those cases where such an occurrence would be attended with serious annoyance and FIG. 258. Scale 1 inch = 1 foot. discomfort. In estimating this margin, it will be necessary to remember that the surface of water in the gutter flowing towards % diaT tolls '/2d* V* f To suLil *vi* bdUx 8 'long slotted Elevation orv tine A. A FIG. 275. Scale 1 inch = 1 foot. and the faces of the standard, and throw it off on to the roof covering below. Fig. 267 shows a sill piece in elevation. The ventilating louvres above referred to are of the fixed type, incapable of being closed, and the slope, dimensions, and overlap of the louvre blades have therefore to be so arranged as to give 2 9 3 CONSTRUCTION IN MILD STEEL. the greatest possible amount of watertightness, while preserving a free entrance and exit of air for ventilating purposes. A large scale detail of the blades and their attachment is given in Figs. 268 and 269, which show the means adopted to FIG. 276. Scale 1 inch = 1 foot. secure these requirements, which were successfully attained in the cases under description. A fair idea of the degree of watertightness obtainable by such an arrangement as that shown can be obtaine- by the construction %,* TS. FIG. 277. Scale 1 inch = 1 foot. of a model of two or more rows of the blades in zinc full size. Water sprinkled or poured upon the blades will collect in drops at the lower edge, and if a drop be subjected to a powerful current of air, as, for example, from the nozzle of a pair of bellows, it can ROOF CONSTRUCTION IN MILD STEEL AND IRON. 299 be ascertained whether it is possible to blow the drop over the top of the next blade below, the experiment forming a rough approxi- mation to the condition of rainfall, combined with a horizontal or _ Detail C . _ FIG. 278. Scale 1 inch = 1 foot. inclined current of air in a gale of wind blowing across the lantern. Louvre blades which warp or sag after erection present a very unsatisfactory appearance, and, in consequence the distance apart Detail ctt D . FIG. 279. Scale 1 inch = 1 foot. of louvre standards should be regulated so as to give sufficient stiffness to the blade, or the cross-section of the blade must be so designed as to give the requisite stiffness for the span to be adopted. In the cases above described the blades were capable of 3oo CONSTRUCTION IN MILD STEEL. spanning a distance up to about 7 to 8 feet, but beyond this distance an intermediate support became desirable. Eoof lanterns and ventilators usually occupy exposed positions, and all their fastenings and connections should be such as will afford due security under these conditions. ROOF CONSTRUCTION IN MILD STEEL AND IRON. 301 Eoofs of flat pitch are frequently adopted in cases where, for architectural reasons, it is ' desirable that the roof construction should be concealed behind parapet walls or other architectural 3 02 CONSTRUCTION IN MILD STEEL. feature. This condition gives rise to a class of roof truss which approximates more to the form of a lattice girder, with sloped ctb A FIG. 282. Scale 1| inch = 1 foot. Detail JR FIG. 283. Scale 1 inch = 1 foot. ROOF CONSTRUCTION IN MILD STEEL AND IRON. 303 upper flange, than to the ordinary form of roof principal usually classed under that term. An example of this type is shown in Fig. 270, which shows a FIG. 284. Scale \\ inch = 1 foot. portion of the truss nearest the wall end, the section of the wall itself with the parapet being shown, and the architectural features of the cornice and string courses being broken off for convenience. FIG. 285. Scale 1 inch = 1 foot. The roof is of flat pitch, the covering being of zinc on boarding laid with drips and falls as shown, and the slope of the upper member of the truss arranged to suit. The lower or tension 304 CONSTRUCTION IN MILD STEEL. member is curved or given a large camber for appearance sake. In Fig. 271 the centre portion of the truss is given, showing the lantern and skylight, which is glazed with ^-inch rough rolled FIG. 286. Scale \ inch = 1 foot. FIG. 287. Scale \ inch = 1 foot. plate in wood sash bars, or with one of the numerous forms of patent glazing. Ventilation is secured, as in previous examples, FIG. 288. Scale \ inch = 1 foot. FIG. 289. Scale \ inch = 1 foot. by galvanized wrought iron or mild steel louvres secured to cast- iron standards, with an additional ventilator at the ridge of the skylight framed in timber and covered with zinc. ROOF CONSTRUCTION IN MILD STEEL AND IRON. 305 The end of the truss opposite the wall rests upon a riveted steel plate girder carrying a heavy water tank, and the detail of attachment to the girder, together with the assemblage at this Rivets ctict DETAIL OF SHOE. FIG. 290. Scale 1 inch = 1 foot. point of the truss, girder, tank, gutter, and roof-covering detail, is shown in Fig. 272, with a sectional elevation of the connection of truss to girder in Fig. 273. /"ctia? ~bott DETAIL. OF IsHOE. =-- ~i' f ^ /'"ma FIG. 353. Scale | inch = 1 foot. FIG. 354. Scale 2 inch = 1 foot. girders, of which the end of one next the main girder is seen in Fig. 360, carry the decking, which consists of trough flooring plates, as shown, covered with asphalte, and supporting ballast filling upon which the sleepers of sundry lines and crossings are laid, these latter serving the purpose of railway traffic between the jetty and the mainland. As the main girder flanges are 3 feet in width, while the cylinder below is 7 feet in diameter with a capping 8 feet diameter, the curb or coping line of the jetty is brought forward, so as to be flush with the cylinder cap below, in the manner shown in Fig. 360, riveted steel brackets being attached to the box girder at intervals, supporting a capping of heavy timbers, as shown. 352 CONSTRUCTION IN MILD STEEL. The box girders are of dimensions sufficient to enable painting to be done inside, and means of access are provided. The attachment of a cross girder to the main box girder in rear of the latter is shown in Fig. 361. The attachment of the bollards in this structure is a detail of PLAN ON CAP. FIG. 355. Scale \ inch = 1 foot. importance, and is of more complex type than the single concrete foundation which can be employed under other conditions. It is shown in Figs. 359, 362, and 363, the bollard, of special section, FIG. 356. Scale | inch = 1 foot. being inserted between the webs of main box girders, as shown in Fig. 363, and carried down below the seatings of those girders into the concrete filling of the cylinder below, the pull on the bollard MILD STEEL AND IRON IN MARINE ENGINEERING. 353 being further resisted by diagonal ties carried back to the wall behind, the whole being intended to resist the pull of hawser of a heavy vessel. The cylinders are of massive construction, and are spaced, as Crane Road 11-0" rtnbrs of Rails j RMcd Sted Joist IZ* X e" in Zl' lengths FIG. 357. Scale f inch = 1 foot. before stated, about 60 feet apart, longitudinally, in a single row. The upper portion of the cylinder, 7 feet in diameter, is shown in Fig. 358, cast in complete rings, 1| inch thick, and connected by flanged joints with 1^-inch bolts through drilled holes. Cast holes are frequently used in this class of work, but holes drilled to a templet are far more satisfactory, and secure complete 2 A 354 CONSTRUCTION IN MILD STEEL. interchangeability of parts. The advantages gained in this respect in erection counterbalance the additional cost. The meeting surfaces of the flanges are machined all over, it being virtually no more costly than the machining of separate strips. Watertightness during the process of construction and sinking is thus attained, assisted by the use of canvas and red lead jointing material, or by FIG. 358. Scale 1 inch = 12 feet. the insertion of india-rubber cord flattened out by the squeeze of the bolts. Details of the cap to the column are shown in Fig. 364 in section, and in plan in Fig. 365. The outline of the cap is designed with simple and easy curves, as shown, without projecting mouldings, in order that small floating craft, such as barges, etc., may not catch their coamings or fenders on a rising tide, the cap being but a short distance above high water. The make-up length, to allow of deviations from regularity in the final level to which the cylinders are sunk, is the one immediately below the cap, as shown in Fig. 358. MILD STEEL AND IRON IN MARINE ENGINEERING. 355 The lower portion of the cylinder is shown in Fig. 366. The three lowermost rings are 10 feet in diameter, 1 J-inch metal, being This space, ta be. fiU&d, rriJtJv Iron/ Cement stem stenurneftrt- \ JilocJcs spaced, \ ^LcoKS ^^^T^^^ H ^ M'afx* c^r^s \3-6' ,2^ / I ^ // * s^itut*, ^^^^// ^//jlW^ FIG. 391. Scale \ inch = 1 foot. and arranged in tiers as shown in Figs. 388 and 390. These struts were removed as the concreting of the structure was brought up. The upper portion of the caisson was surmounted by portable steel bulwarks of -j^-inch plate stiffened with angles and strutted internally with timber, as shown in Figs. 388 and 390, this strutting being so arranged as to form a platform on top for the temporary work connected with the flotation, sinking, and con- creting of the structure. Six sluice valves, 12 inches in diameter, lined with gun metal and tested to 150 Ibs. pressure, were supplied, one to each sub- division of the end watertight compartments, Nos. 1, 2, 3, 4, 5, and 6. These valves were worked, as shown, from the upper platform, MILD STEEL AND IRON IN MARINE ENGINEERING. 379 and were for the purpose of admitting water to the end compart- ments aforesaid. Mooring rings were attached to the caisson at convenient places, and the sloping ends were provided outside the skin plating with angle irons riveted to the plating and running vertically up the slope, to form a key with the first layer of concrete blocks laid against the slope, and moulded with corresponding grooves in the blocks, to minimise the risk of the first row or rows of blocks being shifted off the face of the caisson by sea stroke until they received the full weight of the succeeding tiers. The caisson was constructed and put together in the building- yard at home, and was subsequently taken to pieces and shipped to the site of the works, there to be re-erected, riveted, and launched, completed in the water, floated out to the site of the breakwater, and sunk. Local conditions connected with the site of launching and depth of water available, made it desirable that the launching draughts should not exceed 2 feet 1^ inch forward, and 4 feet 6 inches aft, and to obtain these conditions the caisson was launched in an incomplete state, with only so much of the framework and skin plating erected as was compatible with the above conditions. The caisson was launched end on, in preference to broadside on, the bottom of the central well compartments being temporarily decked over with 4-inch planking of sufficient watertightness to serve for launching purposes. This was subsequently removed when the caisson had been towed into sufficiently deep water. A section of the launching ways is shown in Fig. 391, the ways being laid with a declivity commencing with T % mcn p er foot, and terminating with |J inch per foot at low water, the declivity of the caisson itself being fy inch per foot. A minimum depth of water of 11 feet at low water, extending outwards for about 60 feet beyond the end of the ways, with a width of 70 feet, sufficed for launching purposes, the launch being successfully effected. The subsequent process of erection and completion of the caisson in the water was but a repetition of the process of building up successive additions of steel-work in framing and skin plating, and the gradual loading up of ballast, until the entire structure, including all temporary timber work and other temporary appliances, was completed, and sunk to its final draught on an even keel of 32 feet, as designed. '. ^ ^ OF TH _ *r UNIVERSITY 3 8o CONSTRUCTION IN MILD STEEL. In view of the sea risks to be encountered during all the stages subsequent to the launch, of completion in the water, floating out OOTT 0001 006 009 OOL 009 OOS OOfr 00 002 DOT CondJZion 32 KM^J/tOM/ l^ \f UIUAAAAAJI I/ \ U f+s U l Scale for Metacentres, Gravity and Buoyancy above base. feet. 25 20 to the site, and final sinking in place, it was deemed desirable that a large amount of transverse stability when afloat should be maintained. This was secured by the ballast stowed upon the floor, and between the floor girders, of compartments 1 to 6 inclusive. This MILD STEEL AND IRON IN MARINE ENGINEERING. 381 ballast consisted for the most part of burr concrete, composed of steel "burrs" or punchings grouted in with Portland cement mortar, and supplemented with ordinary concrete ballast. By this means a large metacentric height was maintained at all stages of construction, as shown in Fig. 392, which gives the curves of centres of buoyancy and gravity, metacentres, and displacement from the launching condition to that of final flotation and draught previous to sinking. A summary of the weights at launching and at the finished draught of 32 feet is given in the following table : Launching condition. Tons. Final condition. Net steelwork Rivet and bolt heads Paint 219-87 5-34 2-37 383-66 9-31 4-14 Timber 20-68 90-06 Bolts and plates for timbers Burr concrete Ordinary concrete Sluices and mooring rings 0-34 33-00 2-89 412-50 58-70 2-99 Total weight 281-60 964-25 Draught forward Draught aft ... 2' 1J" 4' 6" 32' 0" 32' 0" V 2 The conditions of stability at the final condition (32 feet draught) were as follows : Centre of gravity Transverse metacentre Centre of buoyancy Transverse G.M. 11-12 feet above 15-60 13-80 4-48 feet. The burr concrete was about 2 feet thick over the floor, and the ordinary concrete placed above was about 9 inches thick. The burr concrete, 1 412*5 tons in weight, was composed of 370 tons of punchings and 42*5 tons of Portland cement and sand, the mixture weighing about 350 Ibs. per cubic foot. Experi- ments made on the weight of concrete used in filling the caisson gave the following results : 1 For further remarks on Burr concrete, see p. 402. 382 CONSTRUCTION IN MILD STEEL, 1 Portland cement, 1 J sand, 5 limestone broken to pass through an l|-inch ring, weighed 155 Ibs. per cubic foot = about 14| cubic feet per ton, the voids in the limestone being about 44 per cent, and those in the sand 30 per cent. A concrete of 1 Portland cement, 2 sand, and 5 broken stone, gave nearly the same results, weighing 157 Ibs. per cubic foot = say, 14J cubic feet per ton. The caisson up to this point has been considered simply as a riveted steel structure, and further reference to its subsequent history and the ultimate use to which it was put might be regarded as outside the scope of these notes, if it were not that the sub- sequent operations explain certain peculiarities in the design. These, then, will be briefly alluded to. As previously stated, the breakwater was founded upon a mound of quarried and deposited limestone rubble, in a depth of water varying from 45 to 65 feet below low water, and brought up to a level of 36 feet below low water, this being the depth at which it was considered the foundation courses of the superstructure could be laid with safety. That portion of the surface of this mound upon which the caisson was intended to rest was carefully levelled by divers and brought to a fair surface by the deposit of fine material or small stuff, care being taken that no large stones projected above the finished level. The caisson, having attained the draught before mentioned, was towed into position over the prepared site above described, and, the valves to the end chambers being opened, was sunk through the space, about 4 feet, intervening between the prepared surface of the mound and the under surface of the caisson at low water. The possibilities of bad weather and heavy seas rendered this, perhaps, the most critical juncture in the entire scheme, and the succeeding operations about to be described were planned with the view of obtaining in the shortest possible time such a pre- ponderance of dead weight over displacement as should reduce the risk of any shifting of the caisson out of its place by heavy seas to a minimum. The programme described in the following table was therefore planned and carried out as closely as circumstances permitted, and with entire success, the concreting being carried on with the utmost possible despatch, while mooring chains were used as an additional safeguard against any shift of the caisson. STEEL AND IRON TN MARINE ENGINEERING. 383 tO t^dCiOtO'MCOOOtOCOrH rH COOl>.bCOCOCO Ci Ci Ci Ci CiCiCOCOCOCOCOCOOOO O O O O OOOOOOCOtOtOtOCOCOCO rH rH rH rH rHrHrHrHrHC^- O rH CO Ci CO Ci CO CO (M 00 "* O Ci CO O CO (N CO CO CO O to to CO Oi TJH tO rH CO CO Ci CO rH GO CO t> t>- CO **T Ci CiTflCOOOCOI>t > -d CO CO rH L^ CO COOCOCOCOCOCOCOCiCSCi CN Ci CiCOCOCOtOC^t^HH^cocO rH rH rHCq FIG. 412. Scale \ inch = 1 foot. a total mass to be hauled of 1100 tons, including ballast. Two chains are employed, one on each side, each chain consisting of two links, each link having a section of 3" X " at the waist of the 2 E 4i8 CONSTRUCTION IN MILD STEEL. link. The total collective sectional area of the two chains avail- able for pull is therefore 10*5 square inches, and the chains are Steel key Z\ /4x^V-T -^~ Cast iron Wheel FIG. 413. Scale \ inch = 1 foot. FIG. 414. Scale | inch = 1 foot. MILD STEEL AND IRON IN MARINE ENGINEERING. 419 designed for a maximum working hauling power of 70 tons on the two chains. fy rod. tit top of teeth only. FIG. 415. Scale 3 inch = 1 foot. FIG. 416. Scale | inch = 1 foot. 420 CONSTRUCTION IN MILD STEEL. The chains are endless, passing over two sprocket wheels, one at the forward end of the caisson camber and one at the engine end, actuated by the engine gear. The sprocket wheels of cast iron are shown in Figs. 413, 414, 415, 416, and the massive casting supporting the outer sprocket wheel and attached to the masonry of the side of the camber is shown in Figs. 417, 418. The chains are supported for the whole of their length between the sprocket wheels by cast-iron girders, shown in Figs. 419, 420, k _ .-* -MS ELEVATION - 8-0' J FIG. 417. Scale inch = 1 foot. supported by cast-iron brackets, as shown in Fig. 421, attached to the caisson camber walls, the upper surface of the girder upon which the chains travel being machined. The chain links, pins, and nuts are of mild steel. Tests of the material employed will be found in the table of the strength of steel for special purposes, p. 46. The edges only of the links are machined, the flat sides being left with a flat surface as they come from the rolls. The holes for pins are drilled carefully to gauge, MILD STEEL AND IRON IN MARINE ENGINEERING. 421 and the pins made a close fit in the holes. The nuts are drop- forged and machined on meeting face only, made a tight fit on the screwed portion of the pin but without gripping the links, which are free to turn when revolving round with the sprocket wheels. Care is taken in shaping the teeth of the wheels to avoid any possibility of the links riding up. The whole of the chains are each tested to a proof load of 40 tons in separate lengths of from 110 to 118 feet, the tests 422 CONSTRUCTION IN MILD STEEL. being made by an hydraulic ram and the pull ascertained by a dynamometer. Upon the application of the first pull on the chain, which FIG. 419. Scale \ inch = 1 foot. involved tensile stresses gradually increasing from zero to 7*6 tons per square inch on the section of the waist of the link, a residuary TtfalFv 1 * o! - - T | fi- PLAN. FIG. 420. Scale inch = 1 foot. permanent set was always found upon the removal of the load, amounting on the average to O'OOll of the length of chain tested (about 110 to 118 feet). MILD STEEL AND IRON IN MARINE ENGINEERING. 423 When the chain was again pulled for the second and third time no further permanent set was observed, and the extensions ^ drtlUd hole* far t' STEEL , crucible, 13 , extra soft, 3 for stocks and dies, 3 graving tool, 3 , hard file, 3 , high carbon, 3 , medium, 3 razor steel, 3 turning tool, 3 , wood- working chisel, 3 Stems of caissons, 388 Stopped ends of gutters, 281, 289 Strength, tensile. See TABLES OP TESTS Struts in roof principals, 276 , strength of. See COLUMNS Sulphur, influence of, on steel, 7 , percentages of. See CHEMICAL ANALYSES , maximum percentage advisable, 8 Table No. 1, Approximate percentages of carbon and approximate ultimate tensile strength of steel for various purposes, 3 No. 2, Increases in tensile strength corresponding to percentages of man- ganese and carbon, acid steel, 11 No. 3, Increases in tensile strength corresponding to percentages of man- ganese, and carbon, basic steel, 12 No. 4, Tests on mild steel angles, 20 No. 5, Tests on mild steel tees, 24 No. 6, Tests on mild steel flats, 26 No. 7, Tests on mild Bteel channels, 29 No. 8, Test on mild steel rolled joists, 30 No. 9, Tests on mild steel zed angles, 32 No. 10, Tests on mild steel trough flooring, 33 No. 11, Tests on mild steel round bars, 33 Table No. 12, Tests on mild steel rect- angular bars, 35 No. 13, Tests on mild steel plates, 36 No. 14, Tests on mild rivet steel, 41 No. 15, Tests on mild steel for bolts and nuts, 43 No. 16, Tests on mild steel forgings and other special steels, 43 No. 17, Tests on mild steel for special purposes, 45 No. 18, Tests on wrought-iron bars, rectangular and round, 56 No. 19, Methods of annealing of steel castings, 64 No. 20, Tests on cast-steel bars, 66 No. 21, Transverse strength of cast- steel bars, 74 No. 22, Transverse strength of cast- iron bars, 77 No. 23, Mechanical elements of equal-legged angles, 85 No. 24, Mechanical elements of unequal-legged angles, 87 No. 25, Mechanical elements of ordinary tees, 91 No. 26, Mechanical elements of bulb tees, 94 No. 27, Mechanical elements of rolled joists, 97 No. 28, Mechanical elements of channels, 101 No. 29, Mechanical elements of zed angles, 104 No. 30, Weights of heads and points of mild steel rivets, 116 No. 31, Approximate total weights of overhead travelling cranes, 136 No. 32, Weights of mild steel bolts and nuts, 176 No. 33, Ultimate resistance to com- pression of wrought-iron columns, 189 No. 34, Influence of rivet pitch on the strength of columns, 193 No. 35, Results of experiments on rate of discharge of rainwater from roof gutters, 282 No. 36, Weights of timber, wet and dry, 400 No. 37, Stowage value of pig-iron and other ballast, 402 No. 38, Weights of materials and machinery in floating caissons, 403 No. 39, Observed extensions of hauling chains under tensile stress, 10- inch links, 424 No. 40, Observed extensions of hauling chains under tensile stress, 9- inch links, 425 No. 41, Weights of sliding caissons, 427 Tank plates, 161 , joints of, 165 448 INDEX. Tanks, cast iron, 157 , connections of roofing with, 161 , details of, 157 , girderwork for, 168 , pipework for, 174 , tie-rods for, 167 Tees, ordinary, 90 , , mechanical elements of, 91 , bulb, 91 , , mechanical elements of, 94 , tests of mild steel for, 24 , use of, in struts, 215 Templet system of marking off rivet holes, 111 Tension, resistance to (See TABLES), of mild steel, wrought iron, cast steel Tests. See TABLES OF Tidal levels, influence on caisson design, 393 Timber, weight of, wet and dry, 400 Transverse strength of cast-steel bars, 74 of cast-iron bars, 77 Traveller girders, examples of, 1 42 Travelling cranes, 134 , approximate weights of, 136 , clearances for, 137 , gauge of road for, 138 , headway for, 137 , loads on wheels of, 134 Trough flooring, tests of steel for, 33 Ultimate resistance to compression. See COLUMNS to tension. See TABLES to extension. See TABLES Unsaponifiable matter in boiled linseed oil. See CHEMICAL ANALYSES Valley gutters, 280, 282, 284 , cesspools to, 281 Valley gutters, details of, 280, 283 , discharge from, 282 Valves in caissons, 378, 397, 39S Ventilators in roofs, 289 Viaduct, girderwork in, 117 Vulcanized India rubber in mud scrapers, 416 W Washers or bearing plates, cast iron, 358 Water pressure on caissons, 388 tanks in caissons, 397, 398 , cast iron, 157 , rain, discharge of, 282 Weights of heads and nuts of bolts, 176 and points of rivets, 116 of floating caissons, 403 of sliding caissons, 427 of timber, wet and dry, 400 Wind pressure, 269 Wrought iron, 46, 56, 57 bars, rectangular and round, tests on, 56 Yoke girder for caissons, 425 , connection of, with hauling chains, 426 , supports of, 425 Zed angles, 102 , mechanical elements of, 104 , steel, tests of, 32 , use of, in column design, 220 Zinc roof covering, 277 THE END. PfilNTED BY WILLIAM CLOWES AND SONS, LIMITED, LONDON AND BECCLKS. OVERDUE. I 193& in 1 49? * (V