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 The Concrete House 
 
 and its 
 Construction
 
 The Concrete House 
 
 and 
 
 Its Construction 
 
 By Maurice M. Sloan 
 
 PriceJLOO 
 
 Published by 
 
 The Association of American 
 Portland Cement Manufacturers 
 
 Philadelphia, 1912
 
 COPYRIGHT, 1912, BY 
 ASSOCIATION OF AMERICAN PORTLAND CEMENT MANUFACTURERS 
 
 PRESS OF WM. F. FELL COMPANY 
 PHILADELPHIA
 
 Preface 
 
 The demand for fire-resisting, durable and sanitary construction has been 
 the dominant note in most that has been said and written on the subject 
 of architecture during the last decade. The American dwelling of the 
 best class is a model of convenience, comfort and beauty, and these 
 attributes may be found even in houses of moderate cost. But with rare 
 exceptions, three fatal defects accompany modern construction. Modern 
 houses are not fire-resisting, not durable and, to a lesser degree, not 
 sanitary. 
 
 Knowledge of these facts, coupled with that newly awakened, ir- 
 resistible demand for vastly increased economy and efficiency in the 
 nation's industrial and social development, has led American architects 
 to concentrate every effort toward the solution of the problem. They 
 found that the highest standard of fire-resisting construction was so 
 closely allied with extreme durability and sanitary excellence as to em- 
 brace these three important structural reforms under that single head. 
 Iron and steel did not, unless protected, represent fire-resisting construc- 
 tion, and in this investigation many other materials were rejected as non- 
 fireproof in themselves. 
 
 In the average house, fire starting in the cellar soon transforms the 
 building into a smoking ruin. Only the eternal vigilance of our fire 
 departments, maintained at a cost of more than $100,000,000 annually, 
 prevents the destruction of thousands of homes each year. 
 
 A study of the fire losses of this and European countries shows our 
 annual loss to be $2.51 per capita, while in the cities of the six leading 
 nations of Europe it is only 33 cents. 
 
 That fire-proof construction is the exception rather than the rule, 
 is due mainly to a mistaken idea of its cost. Fire-resisting floors and 
 
 [51
 
 roofs are not prohibitive in cost, and even though the architect be wedded 
 to concrete, brick or stone in the matter of walls, he is in favor of fire- 
 proof interior construction. 
 
 The purpose of this book is to make clear the advantages of concrete 
 in the construction of dwellings. 
 
 Experiment and research have reduced the list of available fire- 
 resisting materials to practically two products concrete and clay. Con- 
 crete is not only a superior fire-resisting material, but ranks supreme from 
 the standpoint of economy, owing to the facility with which it may be used 
 for practically every structural detail of a house. Its wide range of adapta- 
 bility has been demonstrated by such architects as McKim, Mead & 
 White, who used concrete with distinguished success in the new Pennsyl- 
 vania Terminal Station, in New York city, where it is usually mis- 
 taken for costly stone work. Carrere & Hastings chose simple concrete 
 blocks for the costly Steers mansion, near Greenwich, Conn. Mr. Gros- 
 venor Atterbury, in charge of the Sage Foundation work, achieved re- 
 markable results with concrete in seeking to better the living conditions 
 of the laboring classes by his invention of cheap houses of solid and seam- 
 less concrete, a type more durable, sanitary and fire-resisting than the 
 majority of our most costly dwellings. 
 
 In work of this kind, as well as in great engineering achievements, 
 is to be found indisputable evidence that the restricted use of concrete 
 in the construction of dwellings is not due to any defect or limitation 
 of the material itself, but chiefly because architects have failed to give 
 the subject the serious consideration it deserves. The fact that concrete 
 is a comparatively new material has also had a retarding influence, but 
 now that striking examples of its extreme utility as well as perfect 
 adaptability to artistic expression are to be found in many sections of the 
 country, there is promise that concrete houses will become the rule 
 rather than the exception. 
 
 This book does not treat of the subject in a superficial way, but goes 
 into all the details of concrete construction as applied to houses, and it 
 is published with the conviction that it will have a real and practical 
 value to the architect. 
 
 [6]
 
 McKim, .Mead and White, Architects 
 
 Pennsylvania Terminal Station. New York 
 
 Above the costly Travertine stone, imported from Italy, the interior walls 
 are faced with concrete, colored and cast in imitation of this stone. Even 
 experts have been deceived as to the point where the stone ends and the con- 
 crete begins. The economy and utility of concrete for architectural purposes 
 is strikingly exemplified in this magnificent building.
 
 Chapter I 
 
 The Advantages of Concrete for 
 House Construction
 
 Chapter I 
 
 The Advantages of Concrete for House Construction 
 
 Fireproof Qualities of Concrete. It would be difficult to plan and con- 
 struct a house that would ignite quicker or burn faster than the common 
 type of dwelling. Every architect and builder understands the danger 
 of studded partitions, wooden floor joist and outside sheathing, the close 
 proximity of timber construction to chimneys and flues, the inaccessible 
 recesses of the hollow frames into which chips and shavings have fallen, 
 the knob and tube work of electric wiring. To mention these features 
 of the ordinary house brings realization of the constant peril confronting 
 those obliged to live in them. 
 
 The antithesis of all this is found in concrete. Concrete means fire- 
 proof walls and floors at very little cost in excess of combustible con- 
 struction. Floors of concrete are non-combustible. Moreover, they 
 will confine smoke and flames to the room in which a fire may start. 
 They practically eliminate the danger of suffocation from smoke, so 
 often followed by loss of life. Concrete not only affords a sense of se- 
 curity in this respect, but so far as the building itself is concerned makes 
 insurance unnecessary. There is no instance on record where a build- 
 ing constructed of reinforced concrete throughout has been destroyed 
 by fire or conflagration. 
 
 In tests of concrete panels conducted by the U. S. Geological Sur- 
 vey, a heat of 1700 Fahr. was maintained for two hours. At the expira- 
 tion of that time paper labels on the backs of the specimens were not even 
 scorched and the concrete could be touched by the hand without dis- 
 comfort. Professor Ira H. Woolson, formerly of Columbia University, 
 now Consulting Engineer of the National Board of Fire Underwriters, 
 
 [ii]
 
 used as a test-house a structure with four-inch walls of cinder concrete 
 which, according to the last report, was intact after tests aggregating 
 twenty hours. The temperature ranged from 1700 to 1900 Fahr., which 
 is in excess of estimated conflagration temperatures. Moreover, at 
 the end of each four-hour test, and while the walls were red hot, a stream 
 of water at 60 pounds nozzle pressure was played back and forth over the 
 ceiling for ten minutes a terrific punishment but the walls remained 
 intact. All this is far in excess of anything buildings encounter in ordi- 
 nary fires. In a word, in the true concrete house, lamps might explode, 
 furnaces melt of their own heat, wires become crossed and flues over- 
 heated, or any of the hundred and one accidents occur that cause fires, 
 without the slightest danger to the building. Only the contents could be 
 destroyed. Many owners of concrete buildings carry no insurance on 
 the structures. 
 
 In every large city of a million or more inhabitants, from five to 
 ten fires start each day. Some days the list is greatly in excess of this 
 number. They are never noted by the public unless of the spectacular 
 kind, involving great loss of life or property, or attended with dramatic 
 features. But were it not for the ever-vigilant fire departments, each 
 one of these incipient fires might easily cause a conflagration. It costs 
 the country one hundred millions a year just to extinguish such fires. 
 Our total loss from fire is $450,000,000 annually. In nearly every in- 
 stance the damage is caused by the use of combustible material in build- 
 ing construction. Concrete is non-combustible. 
 
 Durability. As to the stability or strength of a concrete house, the 
 following is an example strikingly typical : Preceding the recent earth- 
 quake in Jamaica, there was a scarcity of water, and at the concrete 
 residence of Mr. Alfred Mitchell, in Port Antonio, bath-tubs were used 
 as temporary tanks or reservoirs. During the earthquake this house was 
 rocked until the water splashed over the sides of the tubs. Mr. Mitchell, 
 whose American residence is New London, Connecticut, wrote that the 
 house had passed through the ordeal without showing the least crack. 
 Other buildings in the district were utterly demolished. This remark- 
 
 [12]
 
 able strength may be obtained in the small and cheap concrete dwelling 
 as readily as in a large and costly house. In this matter of durability 
 we again encounter in concrete the very opposite of other materials. It 
 improves with age. Its known life runs into thousands of years. Wood 
 shrinks, warps, burns and decays; stone and brick units fall apart and 
 are disrupted through the action of frost and temperature changes. Con- 
 crete is improved both in quality and appearance by exposure to the 
 weather. It may be used for foundations, walls, floors, roofs, stairways 
 and chimneys, thus making a solid, seamless house throughout. 
 
 Vermin-Proof Qualities. With concrete it is possible to so build 
 walls and floors as to make them impervious to rats, mice and other ver- 
 min, too often the purveyors of disease. In a word, concrete houses may 
 be made as sanitary as they are fire-resisting. Concrete floors and walls 
 tend to prevent either the admission or accumulation of things dangerous 
 to health, many of which find protected habitat in the recesses of the 
 ordinary house. 
 
 Non-Conductivity of Concrete. The low conductivity of concrete, 
 which makes it such an admirable fire-resisting material, also retards the 
 entrance of cold. When properly made it is devoid of cracks and im- 
 perfect joinings. Settlement of walls, so common in buildings of 
 brick and stone, is not apt to occur. It is not a paradox to say that the 
 concrete house is cool in summer and warm in winter. It has been 
 found by actual experiment that a saving of 20 per cent, in the cost of 
 fuel has been obtained by substituting concrete for brick, stone or frame. 
 In the concrete house shown in Fig. 14 the temperature is 15 degrees 
 lower than the outside temperature on the hottest days of summer. 
 
 Sound-Proof Qualities of Concrete. Concrete possesses marked 
 sound-proof qualities. When concrete is used throughout a dwelling there 
 results a minimum of sound transmission, insuring the quiet and repose so 
 essential to the ideal home. Allied to this is the exceedingly desirable 
 attribute of rigidity, which in turn means non-vibrating floors. The 
 
 [15]
 
 virtue of concrete in this respect is so pronounced that in factory con- 
 struction it has come to be regarded as an economic factor of the highest 
 importance, making for increased efficiency as well as representing a 
 material saving in the wear and tear of machinery. 
 
 Low Cost of Upkeep. As stated, concrete means the elimination of 
 insurance on the building and the same thing applies to the cost of up- 
 keep or repairs. For this reason it is highly important to determine 
 whether the cheapest construction is not, after all, the most expensive. 
 At the expiration of seven or eight years, repairs become an important 
 item in the case of the average house, and this should be carefully esti- 
 mated when the first cost is considered. If the value of property is to 
 be maintained it must be kept in first-class condition and in the case of 
 ordinary construction this can only be done through constant repairs. 
 
 Walls of concrete, especially when solid and untreated as to surface 
 finish, require absolutely no repairs, and when floors and roofs are con- 
 structed of the same material the up-keep would be confined merely 
 to the painting of windows and doors. The prevailing notion that the 
 cost of a concrete house is far in excess of other materials is absolutely 
 wrong. The partial imitation of other houses in concrete that is to say, 
 a house with concrete walls may exceed slightly the cost of other types, 
 but it has frequently happened, especially where sand and stone were 
 convenient, that the cost was less. But in the true concrete house, 
 that is to say, a house of concrete throughout, its duplicate in stone or 
 brick would be prohibitive in cost. As matters stand to-day, there is 
 no fair basis of comparison, for, as stated, all that has been done up to 
 date, except in very rare cases, has been to build the usual type of house 
 with concrete walls. The trend at present, however, is toward the ab- 
 solutely fireproof and indestructible house that shall be of concrete from 
 foundation to roof. The same type of house in brick or stone, if practic- 
 able at all, would cost three times as much as the concrete house. It is 
 in looking at the concrete house from this point of view that we begin 
 to comprehend its true significance and value.
 
 Chapter II 
 
 Architectural Design and Treatment 
 of Concrete Houses
 
 Chapter II 
 Architectural Design and Treatment of Concrete Houses 
 
 The fundamental rule of all good architectural design is that the ap- 
 pearance of the building shall express the structural capabilities of the 
 materials of which it is composed. The great main divisions of archi- 
 tectural history are marked either by the adoption of new materials or 
 by improved methods of using the old ones. But as all transition in 
 architectural styles is slow and gradual, elements of previous architectural 
 design still appear in the newer styles. So it is that the columnar halls 
 of the Egyptian temple take their proportions and construction from the 
 rock temples carved in the mountain side, where gigantic pillars were left 
 to support the roof of the vault, as in modern mine workings. 
 
 The Greeks, following the precedent of the Egyptians, built with the 
 stone column and superimposed lintels until the Romans developed the 
 arch, and learned that great spans could be made by supporting an arch 
 ring of stones upon heavy buttresses. It remained, however, for those 
 masters of Gothic architecture, the medievalists, to produce a new archi- 
 tecture by balancing arch thrust with arch thrust, and supporting the 
 whole gigantic and, withal, light and wonderful structure upon isolated 
 piers, the beauty of which has never been surpassed. 
 
 The Development of a Particular Style. The difference thus seen 
 between the two great historical divisions of architecture is based on 
 the structural design. In the first instance the elements of the classic 
 orders are the lintel and the column, while in Gothic architecture the 
 design depends upon the vault, arch and buttress. All other sub-divi- 
 
 [19]
 
 sions of architectural design are purely adaptations of these, and illustrate 
 either growth or decadence. 
 
 In modern times new materials have been introduced. The use of 
 structural steel has developed designs impossible with any other material ; 
 but even with this modern material the use of the column and lintel is 
 adhered to. For the application of an entirely new principle in construc- 
 tion one must turn to reinforced concrete. This differs from all other 
 
 Fig. I. A false or strained surface treatment representing waste of time and 
 
 money. 
 
 materials heretofore used in that it is composite, using the tensile re- 
 sistance of steel to develop the compressive resistance of a monolithic 
 artificial stone, and, with it all, possessing a quality of fireproofness be- 
 yond that of any material previously employed for building purposes. 
 
 If particular styles of architecture can be developed from the column, 
 lintel and arch, it is certain that in the use of a new material such as re- 
 inforced concrete, a style of architectural design and decoration can be 
 
 [20]
 
 developed which will express truly the nature and capabilities of the 
 material. Unfortunately, it is difficult to overcome the habits of years 
 and the training of past generations, so that up to the present time the 
 architectural designer has shown, in handling reinforced concrete, the 
 influence exerted by previously used materials. 
 
 The effort of the architectural designer to imitate masonry construc- 
 tion in handling reinforced concrete is very evident in the building il- 
 lustrated in Fig. i. This shows an effort to deceive the observer into a 
 belief that the structure is built up of blocks cemented together, and, in 
 order to make the deception doubly real, the joints are boldly marked by 
 casting a bevel into the concrete to illustrate the chambered joints of 
 massive masonry construction. Not satisfied with this effort to simulate 
 masonry, the designer sometimes goes to the extent of bush-hammering 
 the center section of the blocks, after the manner of the earliest methods 
 of dressing stone. 
 
 In the design of dwelling houses the user of concrete first employed 
 hollow concrete blocks, and the early efforts were exerted in making these 
 blocks look like rock-faced ashlar. Unfortunately, all of the molds had 
 the same pattern, and instead of getting the variations of light and shade 
 which make up the life of rock-faced stonework, the entire building be- 
 came a monotonous repetition of units, with the same highlights and 
 shades. 
 
 The thoughtful designer who is about to use concrete as a struc- 
 tural and decorative material will endeavor to determine how best he can 
 use the peculiar properties of concrete and reinforced concrete to obtain 
 a true expression of the capabilities of the material and at the same time 
 to develop a structure which will be pleasing. 
 
 The essential difference in the possibility of reinforced concrete, as 
 compared with the lintel and column supports of the classic orders and 
 the vaulted arch and buttress of the later medieval construction, is that 
 it is practically a masonry material, possessing, besides the great com- 
 pressive resistance of stone, the tensile strength of the steel which can be 
 embedded in it. It is therefore possible to develop a particular style of 
 architecture in working in this material, though it can be used for the 
 
 [21]
 
 Fig. 2. One-story concrete workingman's cottage, exemplifying simple and 
 direct use of concrete. 
 
 Fig. 3. A carefully studied design, showing frank treatment of concrete walls 
 
 and surface finish. 
 
 [22]
 
 development of almost any architectural treatment, a feature which is 
 particularly valuable in house construction. 
 
 Architectural Composition of Concrete Houses. The use of con- 
 crete in monolithic construction for dwelling houses has been some- 
 what limited, although rapid advance is being made, both for houses of 
 moderate cost and pretentious residences of great cost. 
 
 Fig. 4. Buttressed porch construction in monolithic concrete. Impracticable 
 in other types of masonry. 
 
 To illustrate the wide range that concrete has already reached in 
 dwelling house construction reference is made to Figs. 2 and 3, which 
 show an interesting comparison with reference to size and cost. 
 
 In Fig. 2 there is shown a one-story concrete cottage erected at 
 Ada, Oklahoma. The design of this dwelling would probably not please 
 the aesthetic taste of the architectural designer, yet one cannot help 
 
 [23]
 
 considering how superior in architectural pretensions this small dwelling 
 is in comparison to its prototype built of wood, replete with band-sawed 
 brackets and fussy wooden finials and cornices, so familiar two decades 
 ago in houses of equal value. Fig. 3, on the other hand, shows a con- 
 crete house which has been carefully studied by a skilled architect, and 
 it is peculiarly interesting from the fact that the actual texture of the 
 concrete of which the walls are composed shows in the illustration. One 
 of the excellencies of this house is in the design of the facade. There has 
 been a very evident appreciation of the character of the material in that 
 no attempt has been made to form imitation arches over the heads of 
 the openings. The nature of the material is also expressed in the forma- 
 tion of the gables, both at the peak and the eave line, in the buttresses 
 of the chimney, corner walls, and coping and buttresses of the garden 
 wall. 
 
 One might dispute the statement that such buttresses as illustrated 
 in Fig. 4, which shows the construction of a porch of a solid concrete 
 residence built in Milwaukee, are expressive of reinforced concrete con- 
 struction. They, however, are certainly monolithic in their profile, as 
 it would be extremely difficult and impractical to build such buttresses 
 in masonry. This design is also expressive of the material on account of 
 the formation of the arched openings, which would be impractical in 
 ordinary masonry construction. The drain spouts or scuppers from the 
 porch are an ornamental detail indicative of the material when used 
 to the best advantage. 
 
 In order to illustrate a few of the structural possibilities of reinforced 
 concrete with reference to house construction, and to show how these 
 possibilities will eventually develop a new style of house architecture, 
 attention is called to Figs. 5 and 6. 
 
 In Fig. 5 an interesting example of the use of reinforced concrete is 
 shown in the projecting porch or balcony at the rear of the building, and 
 the detail illustrates the possibilities of the material for features of this 
 character. If the building had been constructed of timber, this projecting 
 porch would have been carried on unsightly posts, or insecure and unen- 
 during wooden brackets, whereas by the use of concrete a perfectly safe 
 
 [24!
 
 Fig. 5. A house showing the adaptability of concrete to the construction of 
 projecting masonry. 
 
 mini m mirmrr 
 >-.*- 
 
 ' 
 
 Fig. 6. Concrete as adapted to the requirements of English half-timber 
 design. Note monolithic corbel or shelf supporting window. 
 
 [25]
 
 and everlasting construction is accomplished. While the dwelling here 
 described is not intended to be presented as a particularly pleasing de- 
 sign, it illustrates very well the use of concrete in wall construction. 
 
 To further show the practicability of reinforced concrete in the con- 
 struction of details which could not be so well accomplished by other 
 materials, attention is called to Fig. 6, and is particularly directed to the 
 manner in which the bay-window on the side is supported by a monolithic 
 corbel or shelf. It also shows the manner in which reinforced concrete 
 walls can be decorated to meet the requirements of the English half- 
 timber house design. All of the walls of this house are of solid concrete, 
 the surface being finished by bush-hammering. 
 
 A consistent and interesting detail is also shown in the porch and 
 open promenade connected with the house, this work being really ex- 
 cellently designed, massive and simple, and altogether pleasingly ex- 
 pressive of the capabilities of the material. 
 
 To further show the beginning of the designer's appreciation of 
 the possibilities of solid concrete for house construction, attention is 
 directed to Fig. 7. It shows the long spans possible for such details as 
 porch construction. It must be remembered that such spans are ob- 
 tained without any danger of settlement due to deflection or the shrink- 
 age of timber. They typify the material, and will become, as the archi- 
 tectural designer attains skill in the handling of the material, more and 
 more prominent in reinforced concrete house construction. Again, the 
 peculiar adaptation of the material in forming the base or ledge support 
 for the bay window is illustrated in this example, and the possibilities of 
 reinforced concrete are also shown in overhanging pent-roofs at the eave 
 line. These are unique since they are constructed of concrete, which is 
 admirably suited to the purpose. 
 
 The illustration which is the subject of these remarks is a twelve- 
 roomed house constructed at Winthrop, Mass. This house when partially 
 completed was instrumental in stopping the sweep of a serious conflagra- 
 tion. At the time of the fire the outside walls were up to the second 
 story, and while the wood window-frames were burned away, the concrete 
 was not damaged, and the construction was resumed. The floors of this 
 
 [26]
 
 dwelling are of concrete construction, and the example may be studied for 
 possibilities in the design of concrete dwellings of similar size. 
 
 Solid concrete construction lends itself admirably to designs in 
 which simplicity predominates both in plan and in elevations. Con- 
 crete is never more interesting than when in flat wall surfaces it 
 shows to advantage the proportion and placing of the window and door 
 
 Fig. 7. A porch illustrating the practicability of long span construction in 
 
 concrete. 
 
 openings, and when the gray walls are made beautiful and interesting by 
 the high lights and shadows of a bright sunlight. 
 
 An example of the consistent use of concrete in house construction is 
 illustrated by Fig. 8, which shows a concrete house of the utmost sim- 
 plicity; one extremely beautiful in this quality. A study of the per- 
 spective shows that the structure is entirely devoid of appliqued orna- 
 mentation, and, in fact, the only attempt at a purely architectural orna- 
 
 [27]
 
 mentation is found in the molded architrave over the main entrance 
 doorway. The cornice is beautiful because it expresses the material, 
 and no attempt has been made to copy classic details in dentil courses, 
 mutuals and frieze moldings. Certainly, the use of such ornament in a 
 building of this character would have been frivolous and misplaced, and 
 particularly unfortunate because of the probably unsatisfactory results 
 which would have been unavoidable. 
 
 Fig. 8. A beautiful house in which concrete has been consistently treated 
 
 throughout. 
 
 The illustration under discussion shows conclusively that the success 
 of a concrete building architecturally, depends more upon the proportion 
 of the mass, the arrangement of the voids, or window and door openings, 
 and in the true expression of the material used than upon any features 
 which may be denominated as architectural ornamentation. How suc- 
 cessful this house is when built of concrete can be better understood by 
 
 [28]
 
 attempting to consider it when constructed of any other material. For 
 instance, the imagination could not see any beauty in a building of this 
 design if made of wood, in which the walls were of weather-boarding or 
 shingles. If constructed of squared ashlar, it would certainly have the 
 formidable appearance of a fortification, and as a dwelling house would 
 be still more undesirable if made of rubble masonry. It is certain that 
 
 Fig. 9. A small house of simple design expressive of monolithic construction. 
 
 no more successful use of concrete could have been made for a house of 
 these proportions and surroundings. 
 
 That concrete is as adaptable to the construction of smaller houses, 
 and can be used with success from an architectural standpoint for a 
 house of entirely different design and surroundings from that which 
 was described above, is shown in Fig. 9. This house is fortunate 
 in the design of the porch, and the entire structure has been handled 
 
 [29]
 
 with a simplicity which is pleasing, and expressive of monolithic con- 
 struction. 
 
 A very excellent expression, also, of the best that has been done in 
 monolithic construction for housework is shown in Fig. 10, and while this 
 conception has not the simplicity of the two residences previously de- 
 scribed, it shows in the long sweep of the span over the porch entrance, 
 
 Fig. 10. A second example of the adaptability of concrete to long span con- 
 struction. Note porch. 
 
 and in the simplicity of the steps and balustrades of the porch, an ex- 
 cellent use of the material. While one feels that there is a restlessness in 
 the spacing and proportions of the window openings, and in the topping 
 out of the porch posts with the somewhat conventional ornamentation, 
 yet, in general, this dwelling has a far better appearance than some of the 
 accepted best work of houses built of wood and stone. 
 
 Another example of concrete house construction which has much 
 
 [30]
 
 to commend it is illustrated in Fig. n. One cannot help but feel that 
 a mistake has been made so far as the architectural design is concerned 
 in using the evidently wooden beams and porch rails at the roof of the 
 porch, and also that the roof and dormer are hardly consistent in wood 
 with the monolithic and massive lower portion of the house. At the 
 same time the simplicity and general mass and proportion of voids to wall 
 
 Fig. II. A house of commendable simplicity, but inconsistent in its timber 
 
 accessories. 
 
 surface is most excellent, and would be still more appreciated if the photo- 
 graph showed the deeper shadows which would occur with bright sunlight. 
 If there is one style of architecture with which monolithic concrete 
 construction fits better than another, it is the California or Mexican 
 "Mission," as expressed in the low rambling buildings with the deep re- 
 cessed porches and Spanish tiled roofs so favorably known and extensively 
 used in California.
 
 A costly and interesting example of residence construction of this 
 type is shown in Fig. 12. Everything in the design is indicative of the 
 strength and monolithic possibilities of the material. One will notice 
 upon close examination that the face of the porch wall near the base of 
 the piers sweeps out in a radius, and that the base of the bay window on 
 the side is also strengthened and made interesting by a sweeping and 
 
 Fig. 12. Typical California or "Mission" house. A type admirably adapted 
 to concrete construction. 
 
 broadening curve toward the foundation. The formation or outline 
 of the gable walls could only be expressed properly in a material like 
 concrete, which could be molded to the required form. One feels that 
 the color scheme is expressive of harmony, a pleasing combination of 
 flowers, tropical foliage, and red-tiled roof, all emphasized by the deep 
 shadows and bright sunshine of a semi-tropical land. 
 
 [32]
 
 While monolithic concrete for house construction is possible of great 
 development in the way of particular and pleasing styles of architecture, 
 it has, in the hands of skilled designers, attained beautiful and picturesque 
 results when used with other materials in following the older types of 
 country house construction. In Fig. 13 is shown how reinforced con- 
 crete may be successfully used in the construction of a "Colonial" country 
 
 Fig. 13. Attractive use of concrete as adapted to familiar types of the country 
 
 house. 
 
 house. The entire effect of this residence is one of repose and dignity, 
 and its proportions and details are such as to class it with the suburban 
 architecture of best Colonial type. 
 
 The use of concrete in the construction of a modern suburban 
 
 home in which the effort has been only to follow the most recent style 
 
 of suburban house architecture without any special emphasis of the 
 
 character of the material, is shown in the very successful design illustrated 
 
 3 [33]
 
 in Fig. 14. This house was built with monolithic walls, and is extremely 
 pleasing in the accomplished simplicity and interesting details of the 
 front and side of the building shown in the perspective. 
 
 Concrete has been considerably used in combination with other 
 materials, and the success of the combination can be seen in Fig. 15. 
 Here the two ends of the structure, which is a twelve-roomed country 
 house, are made interesting by the rubble work indicating the chimney- 
 breast and chimney, and the use of boulders to bring out and enhance 
 the appearance of the plain concrete wall must be commended. The 
 entire design, with the rubble entrance posts supporting the open timber 
 trestle, together with the tile roof and wide-extending eaves, makes a 
 picturesque and, on the whole, pleasing and homelike concrete house 
 composition. 
 
 Architectural Details of Monolithic Concrete. While the best archi- 
 tectural effects have been obtained in those houses which have been con- 
 structed entirely of concrete, by a careful study of the proportions of 
 the building and the arrangement and location of the window and door 
 openings, and arches and supports of porch construction, yet it is fre- 
 quently desired both by the owner and the architect that concrete dwell- 
 ings should have some ornamentation. It is hardly necessary, nor does 
 it lend to the app'earance of the building, to attempt to ornament concrete 
 houses located in the country, or in truly suburban districts. In the 
 construction, however, of villas, and of houses located in the more pre- 
 tentious parts of provincial towns and cities, there is probably some ex- 
 cuse for the use of ornamentation and embellishment of concrete ex- 
 teriors. 
 
 A study of architectural details for reinforced concrete house con- 
 struction will certainly show that the finer details of the classic, or a full 
 revival of the classic or Renaissance architecture, are not suitable when 
 applied to the decoration of dwellings of concrete. For instance, such a 
 detail as that shown in Fig. 1 6 is of a degree of fineness incompatible with 
 its being made of cement or concrete and used in conjunction with mono- 
 lithic walls for house decoration. On the other hand, a detail like that 
 
 [34l
 
 Fig. 14. A handsome house showing successful use of concrete, but without 
 emphasizing its character. 
 
 Fig. 15. Interesting example of the combined use of concrete and rubble work. 
 
 (35)
 
 Fig. 1 6. Concrete should be translated into simple and original forms as 
 opposed to the elaborate detail shown above.
 
 illustrated in Fig. 17 is consistent with the nature of the material, and em- 
 
 
 bellishes by its simplicity the monolithic construction of which it is a part. 
 
 If the architectural details or ornamentations are to be cast 
 monolithic with the walls, they should be simple and bold in their out- 
 line, and of such a contour that the forms can be made at a minimum 
 expense, and at the same time the perfection of detail insured and left 
 undamaged by the removal of the forms. The purpose of ornamental 
 moldings, band courses and decorative features is to furnish, by the de- 
 
 Fig. 17. Restrained embellishment, consistent with the simplicity of concrete. 
 
 marcation of the lights and shades of their several surfaces, a relief and 
 interest to the otherwise bare and box-like form of the building produced 
 by the plain walls. It is not necessary that moldings, especially in con- 
 crete houses, should be curved after the fashion of the crown and other 
 moldings in classic architecture. They are equally effective for the 
 purpose if made with simple intersecting planes, as illustrated in Fig. 18 
 at (a), (b), and (c). 
 
 [371
 
 Upon comparing details suitable for cut stone, and those adaptable 
 to concrete construction, it is interesting to note in Fig. 19 how the 
 natures of the two materials are expressed in the profiles and forms of the 
 
 Fig. 1 8. Profiles suitable for concrete detail. 
 
 window-sills herewith shown. In the figure at (a) is a consistent detail for 
 a cut stone sill, such as would be used in Colonial work when made of 
 
 Fig. 19. The more simple of the two would be effective in concrete. 
 
 marble or limestone. This expresses the curved lines of the classic, 
 while the detail shown at (b), though probably lacking in the beauty 
 
 [38]
 
 of the classic curves, expresses boldly and efficiently a monolithic 
 material, and is so formed that it can be successfully used in such 
 construction. 
 
 In concrete house design the most interesting part of the facade is the 
 porch and main entrance, and owing to the nature of the material such 
 details as those illustrated in Figs. 20 and 21 are always interesting and 
 good. When the designer confines himself to these simple forms, the 
 
 l''\g. 20. Facade of simple design more appropriate than elaborate ornamen- 
 tation. 
 
 general effect of the dwelling amply repays in simplicity for the omission 
 of more elaborate ornamentation. 
 
 To say that concrete construction as applied to dwellings should 
 be developed along original and simple lines does not mean that elaborate 
 or highly ornamented work is impracticable. On the contrary, the most 
 complex and intricate patterns can be reproduced by the use of glue 
 molds if the architect finds it necessary to embellish his building with a 
 multitude of detail, including even undercut work. This can be done 
 at far less cost than would be the case if the design were carved in 
 
 [391
 
 stone, and, moreover, once the molds are made, a casting may be re- 
 peated indefinitely. 
 
 Architectural Details of Molded and Cast Concrete. It is desirable 
 in some instances to incorporate in the design of concrete houses decora- 
 tive features in the nature of spot ornamentation, cartouches, medallions, 
 
 Fig. 21. A porch and entrance representing direct and simple treatment of 
 
 concrete. 
 
 and entablature decorations over doors and windows. It is seldom 
 practical to cast as a part of monolithic concrete, decorative features in 
 the nature of modeled work, which includes figures, foliage and work in 
 bas-relief. 
 
 There are two reasons why decorative features should not be made 
 monolithic with the structure. One is, that if these ornamentations are 
 
 [40]
 
 repeated it is necessary to have a considerable number of forms and 
 molds, which increases the expense, and another and very excellent 
 reason exists in the fact that it is difficult to produce such work in 
 concrete without liability of having it spoiled in the process of cast- 
 ing or during the construction of the building. It is, therefore, best 
 to make such ornamentations in cement or artificial stone and either 
 set them in recesses left in the walls or else set them when the walls are 
 being cast. 
 
 If such a detail as is indicated in Fig. 22 is required as a decorative 
 feature of a concrete dwell- 
 ing, the color and texture of 
 the material of which the 
 cartouche or ornamentation 
 is made should be carefully 
 studied with reference to that 
 of the wall. The best work 
 that has been done in the 
 way of molded and cast 
 cement or artificial stone 
 ornamentation is that in 
 which the work has, after 
 being cast, been gone over 
 by hand and properly chased 
 and undercut. It is only in 
 this way that character can 
 
 be given to the material, and, when this is done, the work compares very 
 favorably with the best work in carved stone. 
 
 It is by the use of separately molded panels and decorative features 
 cast of cement that suitable character and an element of decoration can 
 be given to concrete dwellings. The use of such ornamentation lends to 
 the dignity of the structure from the fact that it harmonizes in color, and 
 when properly modeled and executed gives the peculiar interest always 
 in evidence where carved work is used. 
 
 Some suggestions of the possibilities in the way of decorative orna- 
 
 [41] 
 
 Fig. 22. A decorative detail that compares 
 favorably with costly carved stone work.
 
 ment cast of cement or made of artificial stone may be observed in Figs. 
 23 and 24, and a skilled designer can use such details, when cast separately 
 from the building, with an assurance that they will be perfect upon the 
 completion of the structure. 
 
 Architectural Decoration in Color. One of the first means of decorat- 
 ing concrete structures was to introduce band courses and spot ornamen- 
 tation made up of colored tile set or embedded in the concrete, in more 
 
 or less pleasing color har- 
 mony or contrast. For this 
 purpose tiles of different 
 manufacturers were used, 
 but from experience it has 
 been found that tiles of 
 uniform color and texture 
 throughout were more satis- 
 factory than those which had 
 been slip-glazed, or in which 
 the color was only in the 
 form of an enamel. While 
 the latter is approved for 
 interior decoration, such as 
 around fireplaces, it has 
 not weathered as well as it 
 should when used on the 
 
 exterior of buildings. It has crazed, and in some cases the entire enameled 
 surface has disappeared from the tile. 
 
 Therefore, a good rule to observe in the use of colored tile for decora- 
 tive schemes in concrete houses is to employ only tile of natural color 
 throughout. Such tile should be selected with reference to its color 
 permanency. 
 
 In the use of tile mosaic and similar surface color decoration the 
 best effects are obtained by using such ornamentation sparingly. The 
 design should be carefully studied with reference to color and the ar- 
 
 [ 42 1 
 
 Fig. 23. A fine example of separately cast con- 
 crete detail.
 
 rangcment of the tile, and must be placed with absolute accuracy, as 
 otherwise the entire effect of the ornament would be lost, and it would 
 become, instead of an in- 
 teresting detail, a blemish. 
 This is best understood by 
 referring to Fig. 25, which 
 shows a carefully studied 
 doorway with mosaic inlay 
 on the two main piers. 
 These are so near the eye 
 that they are subjected to 
 close scrutiny, and if they 
 were not placed exactly cen- 
 tral, plumb and level, the 
 appearance of this beautiful 
 detail would be spoiled. This 
 doorway is a very interesting 
 example of what can be done 
 with monolithic concrete 
 properly proportioned and 
 studied. 
 
 Instead of using tiles 
 and mosaics for color effect, 
 very elaborate and rich orna- 
 mentation of polychrome 
 terra-cotta can be w r orked 
 out and has been successfully 
 used. There are great dec- 
 orative possibilities in the 
 proper use of this material, 
 
 from the fact that any shade 
 
 it , , , Fig. 24. Pedestal showing the adaptability of 
 
 and color can be produced concrete to elaborate undercut work. ' 
 
 upon the most richly molded 
 
 surface. Where bold ornamentation is required for cartouches, brackets, 
 
 l43l
 
 and panels in colors, nothing is as admirably adapted to the beautifying 
 of concrete surfaces as terra-cotta, either in glazed or dull colors. 
 
 Color effects can also be obtained for the decoration of freize courses 
 and flat medallions or panels, by using for such local or spot ornamenta- 
 tion, colored aggregates, which may be cast in slabs separately and set in 
 place, or, in some instances, could, by the arrangement of the forms, be 
 cast monolithic with the walls. This form of ornamentation will hardly 
 appeal to the architectural designer except for interior decoration, for 
 such features as fireplaces, panels in vestibules, and work of this character. 
 
 The Decorative Features of Timber Construction for Concrete Houses. 
 It must not be considered that reinforced concrete is not generally 
 adaptable to other than the peculiar style of structure to which it seems 
 to lend itself so admirably. There has been and still is a considerable 
 demand for what is known as the "English half-timber" country house, 
 ana reinforced concrete walls worked up with wood half-timber construc- 
 tion securely fastened in place, or embedded in the concrete, give a much 
 more permanent and substantial construction than the usual half-timber 
 work consisting of batten boards with metal lathe and cement plaster 
 between them. In the hands of a skilful designer reinforced concrete 
 can be used very successfully with half-timber construction, and an ex- 
 cellent example of it so applied is shown in Fig. 26. 
 
 Nor is the use of wood in connection with concrete walls confined to 
 the "half-timber" construction, but may readily be used as illustrated 
 in Fig. 27, which shows the entrance to a residence built of concrete with 
 monolithic walls. Further possibilities of wood and timber construction 
 in connection with the monolithic concrete are shown in the picture of 
 the front porch of the same house. The neatly profiled projecting ends 
 of the porch timber, resting upon the beautifully molded pillars, can but 
 give interest and attraction to this well-designed suburban residence. 
 Even the porch rail, though of wood, is of such simplicity as to harmonize 
 well with the clean outline and dignified plainness of the porch walls and 
 outside construction. 
 
 Interior Decoration and Details. Reinforced concrete interior 
 
 [44]
 
 bo 

 
 b/J 
 

 
 Fig. 2". Porch showing combination ol timber and monolithic construction. 
 
 [47]
 
 details must necessarily be plain and simple in their profiles, though if 
 artificial stone or cast cement is used, decorative features for fireplaces 
 can be replete with ornamentation. To illustrate some of the best in- 
 terior details in concrete, the attention is called to the fireplace shown in 
 Fig. 28. This fireplace is refined in the extreme, and is a relief when com- 
 pared with the stock mill- 
 constructed affairs so often 
 seen in the modern house. 
 
 Even more plain, but 
 quite effective, is the fire- 
 place shown in Fig. 29. This 
 substantial design conveys 
 the sense of security and 
 durability always desirable 
 in a fireplace. The rough 
 lintel is in pleasing contrast 
 with the smoother surface, 
 and the work throughout is 
 simple and direct, showing 
 how effective concrete work 
 can be made. 
 
 Somewhat more elabor- 
 ate, but still interesting, are 
 the fireplaces shown in Figs. 
 30 and 31. That in the former 
 illustrates how monotony in 
 design may be relieved by the 
 introduction of figures or de- 
 signs in low or high relief. 
 
 Where beam and slab construction is used for the floors in houses of 
 larger size, the concrete beams and girders make admirable beamed ceil- 
 ing effects. Usually it is customary to plaster the concrete with a white 
 coat, but a good decorator could finish the rough concrete so as to give 
 rich effects by means of carefully studied color schemes and stencilled 
 
 [48] 
 
 Fig. 28. Concrete fireplace with plain and sim- 
 ple profile.
 
 Fig. 29. Effective concrete work expressed in dignified design. 
 
 Fig. 30. Example of smooth and rough textures in surface finish. 
 4 [49]
 
 Fig. 31. Elaborate but interesting treatment of concrete. 
 
 Fig. 32. Example of beautiful and dignified interior construction. 
 
 [50]
 
 a 
 rt 
 
 c
 
 ornament. To illustrate how beautiful and dignified an interior of this 
 construction can be the attention is called to Fig. 32. It only requires, 
 in constructions of this kind, for the best effect obtainable, to have the 
 beams go central over points of support, and to study the panelling of the 
 beams and girders of the ceiling so as to obtain symmetry and equality 
 of spacing. 
 
 There are possibilities in concrete for the most interesting stair con- 
 structions. Concrete is adaptable to such a variety of forms, and when 
 properly reinforced, so self-supporting, that the lines of the usual con- 
 ventional stairs or steps can be departed from radically. Spiral or flying 
 stairways, with graceful, sweeping horses and rails, are entirely practical 
 and possible at a minimum cost in concrete construction. 
 
 The possibilities of this material for both the construction of the 
 stair and the rail are shown in Fig. 33, and whether the entire stairway 
 and rail are of monolithic construction, as illustrated in this photograph, 
 or whether other materials are used for embellishment, it is certain that 
 for interest, simplicity, and beauty there are few rivals to that shown in 
 the figure.
 
 Chapter III 
 Details of Construction
 
 A doorway showing the adaptability of concrete to either plain or ornamental 
 work. Note the great contrast between the elaborate undercut floral 
 decoration and the simple units comprising the structural features. 
 
 t54l
 
 Chapter III 
 Details of Construction 
 
 Types of Floor Construction. In building construction there are practi- 
 cally four types of floor construction, when classified as to their structural 
 formation. These are the flat slab, the beam and girder, the hollow tile 
 and concrete joist construction, and what is known as panel construction. 
 
 The simplest form is the flat slab of concrete, supported by walls or 
 partitions, and of sufficient thickness and reinforcement to span the 
 intervening space between the walls. 
 
 \''^f- 
 l^-.' 
 
 
 J 
 
 > "**'. p v''-> " '** v. *> ">; Kp.^ ^j^lai 
 
 r . r" r> ?: y o y. . .^. R .p- .- . p g.' \s 
 
 Beam 
 
 Fig. 34. Slab and beam construction. 
 
 Girder 
 
 3 
 
 Where the spans are too great for a flat slab, it is then usual to sup- 
 port the concrete slab on concrete beams and girders which are monolithic 
 with the slab, and which have the general appearance indicated in Fig. 34. 
 
 In buildings where the floor loads are comparatively light, a type 
 of construction known as the concrete joist construction has been exten- 
 sively used. A section through such a floor is illustrated in Fig. 35 at 
 (a) and (6). In each of these sections it will be noticed that both of 
 the main supports of the floor are concrete joists, reinforced with steel 
 rods, and the intervening space between the joists is filled in with hollow 
 
 [551
 
 terra-cotta tile. The illustration at (a) shows this type of construction 
 for floors where the load is very light, and where the rectangular joists 
 are strong enough to carry their portion of the load from center to center 
 of the adjacent tile. In Fig. 35 (b) is illustrated a construction which 
 is stronger than that shown at (a), from the fact that several inches of 
 concrete are placed upon the top of the tile, and being monolithic with the 
 concrete joists, additional compressive area is provided, thus insuring the 
 capability of the floor for carrying greater loads. The purpose of the 
 
 ;*<>"** '#' 
 ***. .".** 
 
 p p. p 
 
 ^i^L 
 
 :V 
 
 lit 1 
 
 ai*. 
 
 l?: P. 
 
 Tr^ 
 
 sr 
 
 (a) 
 
 
 p. 
 
 
 1 
 
 
 ! '&'?$$*; 
 
 
 .' 6 -J'-.">-: ; :?i:-;?. 
 
 
 <''. 
 
 
 : (?. 
 
 ''!.t.- l-i-O- 
 
 v'-.v^* ..-. 
 
 Fig. 35. Floor sections, showing arrangement of concrete and hollow tile of 
 
 concrete. 
 
 hollow tile in this floor construction is purely to fill in the space between 
 the joists, and to form sides into which the concrete can be poured. The 
 tile also provides a plastering surface to form a flat ceiling. 
 
 The advocates of the hollow tile and concrete joist floor constructions 
 claim that the adherence of the concrete to the sides of the hollow tile 
 insures greater strength in the floor construction because the upper one 
 or two inches of the tile adds to the compressive resistance of the concrete, 
 
 [56]
 
 or, at least, extends the area of compression in the upper part of the 
 system. 
 
 There are several varieties of the hollow tile and concrete joist con- 
 struction, and one of the most recent of these types, known as the " Hin- 
 ton" system, is illustrated in Fig. 36. Upon examination of this illus- 
 tration it will be seen that instead of forming the hollow tile blocks with 
 vertical sides, the sides are splayed in such a manner as to make the con- 
 crete joists wide at the top and narrow where reinforced with the steel. 
 By the use of such a block the compressive area of the concrete is increased, 
 and less concrete is used, as it is saved where not required, namely, below 
 the neutral axis. A third merit claimed is that the tiles almost meet at 
 the bottom and form a uniform material for plastering. This is of some 
 
 Fig. 36. Arrangement of concrete and hollow splayed tile. 
 
 advantage where the ceiling is to be painted or decorated, as the possi- 
 bility of different markings or discolorations by the two materials is 
 avoided. 
 
 The panel construction differs little from the flat slab construction, 
 except the slab is supported upon beams on all four sides without inter- 
 mediate beams, and the slab is usually reinforced in two directions. Some- 
 times the flat slab is simply supported upon posts or columns of concrete 
 which are spread at the top. This relieves the slab for some distance 
 out from the column, thus reducing the stresses. To such systems the 
 name of "mushroom" has been given, though there are three or more 
 similar systems variously known. These systems have not as yet been 
 
 [571
 
 much used in house construction, though they could well be employed in 
 more pretentious work. 
 
 Methods and Types of Steel Reinforcement. In reinforcing con- 
 crete, plain round bars have been used successfully, and buildings which 
 have been so reinforced have withstood all stresses and vibrations. There 
 is, however, a general preference for some type of bar or reinforcing rod 
 which gives a greater bond in the concrete; that is, the bar is rolled, or 
 
 formed with projections, so 
 that when embedded in the 
 concrete it would require a 
 greater force to withdraw it 
 than a plain bar. Bars which 
 have been specially rolled or 
 formed for reinforcing concrete 
 are known as "deformed" 
 bars. There are so many 
 I types of these bars that it is 
 impossible to illustrate them 
 all, and consequently only a 
 few of the older and more 
 usual forms are given. These 
 bars are shown in Fig. 37, at 
 (a), (b), (c), and (d). 
 (if) The figure at (a) repre- 
 
 FijJ. 37- Types of reinforcement. sents a " square twisted " steel 
 
 bar. This type of bar is ex- 
 tensively used, as there is no patent on it, and the additional cost of the 
 twisting is slight. It is probably more used than all of the rest of the 
 reinforcing bars on the market. 
 
 In the figure at (6) there is illustrated what is known as the "cor- 
 rugated " bar. This is one of the first deformed bars put on the market, 
 and gives a maximum cross section, and a good deformation with a 
 minimum increase in weight. 
 
 [58]
 
 The bar at (c) is known as the Kahn bar, in which the deformation is 
 practically obtained by shearing the stirrups and bending them directly 
 from the rolled fins on the sides of the bar. This bar is made in many 
 sizes and several different sections. 
 
 While there have been many different types of deformed bars placed 
 on the market, those shown may be considered as representative, and are 
 quite commonly used. 
 
 In the reinforcement of slabs in house construction expanded metal 
 or woven wire may be conveniently and cheaply employed. The latter 
 is particularly good from the fact that it is woven with large wires in one 
 
 :.''.. -' '-'.. '- ' :'. V' < ."' 
 
 Fig. 38. Example of fabricated reinforcement. 
 
 direction and small wires in the other, making it economical for slabs of 
 rectangular shape reinforced in two directions. This reinforcement is 
 shown at (d) in the figure. 
 
 As reinforced concrete construction was developed there were a 
 number of types of steel reinforcement placed on the market in the nature 
 of fabricated material, in which the several reinforcing rods and bars, 
 together with the stirrups, were held together in a frame or unit. In 
 general practice, however, there seems to be a preference among con- 
 tractors to use what is known as the "loose bar" system, illustrated in 
 Fig. 38. Here the several straight bars and trussed bars are cut to length, 
 bent either in the shop or at the building, and are placed in the form 
 
 (59]
 
 separately. Sometimes they are supported from the bottom of the forms 
 by means of small cast blocks of cement, or else are tied together with 
 sheet iron or bar iron supporters, and are held in place by wiring, or sup- 
 ported on the stirrups which rest upon the top of the centering. The 
 stirrups are sometimes wired to the steel reinforcing bars, and are held 
 at the proper distance apart by a rod, to which they are secured by 
 wire. 
 
 While the loose bar system causes additional work in the field, 
 it is a question whether any of the patented systems of fabricated frames 
 can compete in cost, from the fact that there is royalty to pay, additional 
 care in handling, and sometimes additional freight rates, due to a differ- 
 ent freight classification. 
 
 Fig. 39- 
 
 One of the best fabricated systems of steel reinforcement is that 
 illustrated in Fig. 39. This system is very practical, and from the fact 
 that it can be shipped in a flat condition and pulled into shape, is very 
 conveniently handled, and can probably be purchased in the shop for less 
 cost than most of the fabricated systems on the market. 
 
 Another system of girder frame that can be used particularly in 
 house construction is what is known as the electric welded frame, il- 
 lustrated in Fig. 40. In this frame the stirrups are welded to the rein- 
 forcing bars. By this arrangement the proper amount of the steel re- 
 inforcement for any beam or girder is insured, and the number and spac- 
 ing of the stirrups fixed. It is also in a very convenient form for ship- 
 ment. 
 
 [60]
 
 Methods of Finishing Floors. Reinforced concrete floor slabs may 
 be finished upon the top with any material, and in house construction 
 it is probable that wood floors are the most desirable. Some houses 
 have been built with concrete floors, especially apartment houses. The 
 concrete finish can be placed directly upon the reinforced concrete slab 
 
 5firrup Welded Jo 3sr 
 
 ~<5ect/on of Bar Showing 
 
 Fig. 40. Electrically welded frame reinforcement. 
 
 at the time it is put in place, or, if this is not practical, the slab can be 
 swept clean, washed with dilute muriatic acid, the acid thoroughly re- 
 moved by washing with water, and the top coat worked on. This method 
 is successful when care is used in the application and workmanship of 
 the top finish. A section of a floor so constructed is illustrated in Fig. 
 41. Usually the finish is i inch in thickness, and sometimes in house 
 
 Fig. 41. Concrete floor slab with top 
 coat. 
 
 Fig. 42. A wooden floor on concrete 
 slab. 
 
 work brass sockets are inserted at or near the corners of rooms so that the 
 rugs may be secured in place. 
 
 Another method of applying a concrete finish is to place on top of 
 the concrete slab, some time after it has been poured, two inches of cinder 
 concrete, and finish with the one-inch top coat as described above. It 
 is usual to use a cinder concrete mixture consisting of one part of Portland 
 
 [61 1
 
 cement, two parts of sand or gravel, and six parts of clean boiler cinders. 
 In the top coat use one part Portland cement, one part sand, and one 
 part crushed stone or granite grits. 
 
 When a wood floor is desired, and this would ordinarily be used in 
 house construction, it is best to use the construction illustrated in Fig. 42. 
 Here 2" x 3" sleepers are laid, 16 inches center to center, upon the con- 
 crete. Sometimes nails are driven in the side of the sleeper and the 
 space between is filled with cinder concrete, this being made level with the 
 top of the sleepers. Either a rough floor to receive a fine hardwood 
 floor, or the finished floor, is laid directly upon the sleepers. It would be 
 best in house construction, if the finished floor is to be laid directly upon 
 the sleepers, to paint the back of the flooring, so that any moisture that 
 may remain in the sleepers or in the cinder concrete will not warp and 
 twist the flooring. 
 
 Roof Construction. The roofs of concrete houses should necessarily 
 be entirely fireproof, and consequently the roof covering should be sup- 
 ported upon a construction which will not ignite and burn. A house, 
 however, differs from the manufacturing building or warehouse with re- 
 gard to the roof construction in that it is not likely to be subject to the 
 shock and weight from falling walls, or the debris from adjacent structures 
 on fire. It can therefore be of lighter construction than is usually re- 
 quired for fireproof commercial buildings of reinforced concrete. It must 
 also be considered that the roof of a house, in its slopes, intersections, and 
 skylines, has much to do with the architectural appearance of the build- 
 ing. The construction is, therefore, considerably influenced by the gen- 
 eral formation of the roof, that is to say, whether it is flat or sloped. 
 The degree of slope also influences the roof covering. 
 
 In buildings which are designed on classic lines, having square para- 
 I>ets and flat roofs, there is probably no better construction than a rein- 
 forced roof slab. This slab is carried upon beams and girders in the same 
 manner as the floor construction, and may be built either with a slope or 
 flat. To drain the flat roof, build up the cinder concrete as indicated in 
 Fig. 43. The advantage of constructing the roof in this manner is that 
 
 [62!
 
 A frank and direct use of concrete designed with reference to economy, utility, and 
 
 minimum cost for up-keep. 
 
 64
 
 quite frequently the forms used for the floor construction can be used for 
 the roof forms. The additional thickness of the cinder concrete gives 
 insulation against temperature changes. 
 
 The proper covering for a flat concrete house roof, which does not 
 appear in the perspective or elevations of the building, is either some 
 form of prepared roofing or else 4-ply slag and gravel roof. Many 
 of these roofs are guaranteed for a period of ten years, and are entirely 
 serviceable and satisfactory. 
 
 In placing such a roof it is the usual practice to smooth over the top 
 of the cinder concrete forming the slope of the roof with cement mortar, 
 so as not to have any projecting stones or edges of aggregates, which are 
 likely to cut through felt. Then the first layer of felt is well secured to 
 
 Roof Slab- 
 
 Fig. 43. Flat slab roof with cinder concrete top coat sloped for drainage. 
 
 the concrete with hot pitch. This has always been sufficient to hold the 
 roofing in place. It is good practice to build up gussets around all the 
 parapet walls, and run the felt up and under some form of coping tile, 
 or else in cheaper work, fasten it under a cleat which is secured to nailing 
 strips left in the concrete. These two forms of construction are shown 
 at (a) and (6) in Fig. 44. 
 
 The extent of flat roofs in house construction is such that it is entirely 
 safe to make a concrete roof slab and cover it with a top coat of a damp- 
 proof cement mixture, thus doing without any roofing material. Shrinkage 
 or settlement cracks may occur, however, and the integrity of the roof is, 
 of course, destroyed if it does crack. 
 
 This danger of concrete cracking is reduced to a minimum where the 
 5 [65]
 
 areas of the roof are small, such as would he the case in house construc- 
 tion, and could be entirely obviated by dividing the roof up in sections 
 and putting in expansion joints, as illustrated in Fig. 45. In this con- 
 struction a V-shaped piece of copper is placed on the forms or centering, 
 and embedded in the concrete slab, the joint being afterward raked out 
 and filled with asphalt or mastic cement. In using asphaltic prepara- 
 tions for filling a joint of this kind the best result is obtained by heating 
 the crevice with a torch before the asphalt is poured in. 
 
 . 
 
 Cement Coping 
 
 Roof in a 
 
 ' V 
 
 Cinder Concrete 
 
 p- V.-- " i 
 
 >>:*;>.; 
 
 mm 
 
 (a) 
 I'ig. 44. Two types of concrete roof construction combined with felt covering. 
 
 Where the roof of a concrete house is flat, and where the item of 
 i o>t is not a consideration, one of the best roof coverings is flat or prom- 
 enade tile, laid in bitumastic cement. Such roofs are very desirable 
 where it is proposed to use the roof as a roof-garden or observatory. A 
 somewhat cheaper way of accomplishing the same result is to cover the 
 concrete roof slab, after it has been smoothed off with cement, with a 
 prepared or felt roof covering, and then placing on this covering a thick 
 concrete finish for a wearing surface at least I ^ inches thick marked 
 off in blocks for appearance. 
 
 [661
 
 Cement 
 
 Fig. 45. Method of constructing expansion 
 joints and applying filler. 
 
 As the roofs of houses are subjected to extremely light loads, they can 
 be economically constructed with rectangular concrete beams, either cast 
 in place or cast on the ground and used as joists, and then covered w r ith 
 some material such as trussed metal lath, or ferro-inclave, the former 
 being illustrated at (a), Fig. 46, and the latter at (6). The advantage of using 
 these is due to the fact that no 
 centering is required. They are 
 arranged to plaster with cement 
 mortar on both sides, and a re- 
 inforced slab is thus obtained 
 sufficiently strong for any roof 
 construction. Such construc- 
 tion can sometimes be used at 
 less cost than a monolithic slab. 
 
 In the use of such materials, wires or other means of fastening 
 ^hould be left in the joist, so that the metal reinforcing sheets can be 
 secured to them. If the building is built with concrete walls, light steel 
 beams can be used for framing the roof, and the slab construction secured 
 
 to them, though the use of such steel 
 beams is attended by a diminution 
 of the fireproof properties, provided 
 they are not in turn protected by a 
 covering of at least a 1 3^-inch thick- 
 ness of concrete. 
 
 If it is desired that the roof of 
 a concrete house should be covered 
 with slate, or with flat, corrugated, 
 or special interlocking tile or asbestos 
 shingles, and if the roof is sloping and 
 
 of concrete construction, it is necessary to provide some means by which 
 the slate or tile may be secured to it. Quite frequently the roof is con- 
 structed with cinder concrete, which is sufficiently porous to allow the 
 nailing of furring strips to the top of the roof, so that the slate or tile 
 may be fastened to them. The best practice would be to imbed in the 
 
 [67] 
 
 (a) 
 
 
 Fig. 46. Metal lath and fcrro-inclave re- 
 inforcement in light roof construction.
 
 concrete nailing strips, and cross-furr the roof as indicated in Fig. 47, thus 
 providing a secure nailing for the slate or tile. The spacing of the furring 
 strips is regulated by the character of the roof covering. The strips to 
 which the furring strips are fastened should be nailed to them with solid 
 copper or copper-sheathed nails. 
 
 The construction of roofs for concrete buildings, as to gutters and 
 eaves, varies little from buildings constructed of other materials. Con- 
 crete, however, has an advantage in that overhanging cornices and stop 
 gutters are readily constructed and molded, and may be flashed in any 
 
 manner by using furring strips 
 and nailing blocks embedded 
 in the concrete. 
 
 Concrete is a material of 
 such great durability and per- 
 manency that in designing the 
 eaves or cornices of building% 
 an effort should be made to 
 avoid the use of hanging gut- 
 ters of metal. The best results 
 are obtained by casting stop 
 gutters or recessed gutters 
 
 Furrin 
 
 fietel Lafh 
 
 Fig 47. Details of roof construction where slate 
 
 directly in the concrete, and 
 
 or tile is to be used. 
 
 making these damp-proof by 
 
 means of carefully graded aggregates, thus obtaining a dense concrete, or 
 by painting with waterproof cement paints, or by lining them with metal. 
 
 Tin is not a good material for the formation of eave boxes and the 
 lining of gutters of concrete, from the fact that placed next to concrete it 
 does not seem to be as durable as when used in conjunction with wood 
 construction. Copper or lead should always be used where the use of 
 metal flashings or gutter linings is unavoidable or desirable. 
 
 Some suggestions for the construction of the gutters and eaves of 
 concrete dwellings may be seen in Figs. 48, 49, and 50. In the first men- 
 tioned figure there is shown the detail at the eaves of a building con- 
 structed with concrete walls and roof slab, and having for the roof cover- 
 
 [68]
 
 ing one of the many excellent forms of interlocking tile roofs. Here the 
 gutter is cast directly in the concrete of the cornice, and is flashed with 
 copper. It is interesting to note the manner in which the copper flashing 
 is secured in this detail. 
 
 Wide projecting eaves are admirably adapted to the design of con- 
 crete houses. The detail shown in Fig. 49 is suggestive of the manner in 
 which the gutters for such roofs could be arranged so as to secure per- 
 
 Fig. 48. Fig. 49. 
 
 Figs. 48 and 49. Suggestions for the construction of gutters and eaves for concrete 
 
 dwellings. 
 
 manency, and thus avoid the trouble so likely to arise with galvanized 
 iron or copper hanging gutters. As the'gutter in this detail is well out- 
 side of the building wall, no very great care need be used to have it es- 
 pecially water-tight, so that the metal flashing may be omitted, and the 
 gutter may be finished with a cement mortar coating made waterproof 
 by the use of properly graded aggregates; or, since it is not within the 
 range of vision, it could be coated with a waterproof paint. 
 
 A gutter inexpensive to construct is shown in Fig. 50, and this gutter 
 
 [69]
 
 may be formed in a variety of ways. It also acts as a good snow-guard, 
 is efficient, and excellent in appearance. 
 
 All of these concrete gutters and cornices are enduring, and have the 
 advantage of requiring no repair expense, an item very frequent with the 
 same features of frame houses and those of masonry or brick having the 
 usual wooden roofs. 
 
 Window and Door Frame Construction. Since concrete is a mono- 
 lithic material, there is no real necessity for arching window or door open- 
 
 Fig. 50. Another suggestion for the construction of gutters and eaves for concrete 
 
 dwellings. 
 
 ings, and it is surely very inconsistent to accentuate the hoods of such 
 openings by showing arch rings marked in joinings to simulate voussoirs. 
 In consequence, the window and door openings are made either with a 
 square head, or, if the architectural design requires, are formed on the 
 curves, either segmental or three-centered, though such arches have little 
 structural significance, especially where the concrete is reinforced with 
 steel rods or bars. 
 
 In masonry and in brick structures it has been the usual practice to
 
 Entrance of Albert Kahn's residence, Detroit, Mich. Doorway and steps 
 cast in solid concrete. A striking example of the economy of concrete as 
 compared with cut stone.
 
 build up window or door frames as the masonry or brickwork progressed. 
 While this can be done with concrete construction, it is not the best prac- 
 tice. In pouring the wet concrete and in working the formwork around 
 the openings the millwork is not benefited, as any excess of water in the 
 concrete is apt to buckle and warp the millwork. The best practice is 
 to place the door and window frames after the wall, with its openings, 
 has been cast. 
 
 In the setting of all door and window frames the primary requisite 
 is to obtain a weatherproof joint between the frame and wall construction, 
 both at the jambs, sill and head. The best practice in window construc- 
 tion where a reveal frame is used is to rebate the wall as indicated in Fig. 
 51, and in constructing the window 
 frame to make it of such a size that 
 it can readily be placed from the back. 
 The inside face of the frame is ex- 
 tended to scribe to the opening, as 
 indicated at a, and by this means 
 the frame can be secured in place to 
 wooden nailing blocks set in the con- 
 crete, or else by plugging the wall 
 after the concrete has set. 
 
 A finish is secured on the outside 
 by the reveal molding, as at &, and 
 
 the construction made further weatherproof by the casing, as shown at c. 
 The head of such a frame can be designed as shown in Fig. 52, both the 
 reveal molding and the inside trim being around the head of the frame, 
 and a rebate being formed in the concrete at the head, as was done on the 
 jambs. 
 
 While concrete sills can be molded monolithic with the walls, it is 
 far better to mold the sills separately and set them in place, constructing 
 the sill of the window frame as shown in detail in Fig. 53. In this figure 
 the molded treatment or artificial stone sill is shown at a, the wood sill of 
 the frame at 6, while the inside trim and apron are indicated at c. 
 
 In the best work an effort is always made to insure a weatherproof 
 
 l73l 
 
 Fig. 51. Detail of weatherproof joint 
 between frame and wall construction.
 
 joint between the wood sill and the 
 cement sill, and the best practice is 
 to insert a weatherstop, as shown at 
 d. This weatherstop consists of a 
 3/g" x i" galvanized strip, which 
 breaks the joint between the wood 
 and cement sills by entering grooves 
 formed in each, thus preventing the 
 entrance of moisture. 
 
 What was said with reference to 
 the jamb and hood construction for 
 window frames applies equally to 
 door frames, though it is sometimes 
 best to construct door frames with- 
 out a rebated jamb, and depend 
 upon some other means to make a 
 weatherproof joint between the wood 
 
 frame and the concrete. Such a detail is illustrated in Fig. 54, and the 
 security of the joint between the wood frame and the concrete is obtained 
 
 Plaster 
 
 Trim 
 
 Door 
 
 Fig. 52. Detail of window construction. 
 Reveal molding and inside trim 
 placed around head of frame. 
 
 'itf- 53- Separately molded sill set in 
 place. 
 
 [74 
 
 Fig. 54. Detail of construction for door 
 frames in concrete houses.
 
 pr t n 
 
 by casting a groove in the concrete, and by extending the outside casing 
 into the groove. This construction is shown in the figure at a. The door 
 frame is still further secured and made tight in place by plugging the jamb 
 and nailing under the stop bead, as shown at b. 
 
 An interesting detail of another type of construction for a door 
 frame is that illustrated in Fig. 55, which shows a plank front frame 
 arranged in a rebate. 
 
 It is best in the construction of concrete houses to eliminate cut- 
 stone work as much as possible, and to form the sills monolithic with the 
 wall or cast them separately. It is 
 best not to depend for the threshold 
 upon a projection formed of concrete, 
 as when worn it is difficult to replace. 
 A metal or hardwood threshold is 
 superior. In the best work this 
 threshold would be of cast brass, 
 properly secured to the cement sill. 
 Of course there is no reason why 
 bluestone, granite or specially cast 
 concrete stone sills should not be set 
 
 on the concrete walls, and be introduced for the sills of door openings 
 where there is apt to be excessive wear. 
 
 Concrete Wall Construction. In house construction, concrete walls, 
 and especially those reinforced with steel rods or bars in two directions, 
 have some advantages over walls built of stone or brick. 
 
 In the first place, concrete walls may be made only two-thirds the 
 thickness of brick and masonry walls and still be of equal or greater 
 strength. Since such walls are monolithic, they are less liable to buckle, 
 and the junctions at corners are stronger; besides, the work over the 
 heads of window and door openings is more secure, as there is no tendency 
 for arches to loosen and drop, and joints, as those between the voussoirs, 
 to crack. 
 
 Concrete walls are good non-conductors, and make warm winter 
 
 [751 
 
 Fig- 55- Plank frame for door ar- 
 ranged in a rebate.
 
 and cool summer houses; particularly are they excellent in retaining heat 
 from the fact that there is less likelihood of leakage through cracks such 
 as is the rule rather than the exception in brick and masonry walls. Walls 
 of concrete are, when properly constructed, much more likely to be water 
 and weatherproof, and in this respect are an improvement over brick and 
 stone walls of rubble masonry, as such walls are ordinarily constructed. 
 In this fact there also exists one marked point of superiority of concrete 
 for wall construction as compared with masonry or brick walls, which 
 is that from the very nature of the material a concrete wall must be solid 
 and free from the structural defects that are so evident in walls of masonry 
 where the workmanship is bad or even fair. 
 
 Strength of Concrete Walls. There is no doubt of the great strength 
 of reinforced concrete walls, but careful consideration has been given to 
 this part of reinforced concrete construction in framing the building laws 
 for cities of the first class, and these are interesting, as they indicate 
 the best practice, which may well be adhered to in the construction of 
 country houses. 
 
 The New York city regulations governing the use of reinforced 
 concrete contain the following interesting and instructive paragraph : 
 
 "Exterior and interior bearing and enclosure walls of reinforced 
 concrete supporting floor and roof loads shall be securely anchored 
 at all floors, and of such thickness that the compressive stress shall 
 not exceed 250 pounds per square inch, but in no case shall the 
 walls be less than 8 inches in thickness. The thickness of such 
 walls shall not in any instance be less than ^V f the unsupported 
 height." 
 
 And further in reference to the reinforcement of concrete walls the 
 law states: 
 
 "Steel reinforcement shall be placed near both faces of the wall, 
 running both horizontally and vertically, and weighing not less 
 than Yi pound per square foot of wall." 
 
 Method of Supporting Floors. The best practice in concrete house 
 construction is to use, in conjunction with the concrete walls, fire-proof 
 
 176]
 
 Typical sectional form for concrete wall construction. 
 
 Method of securing window frames during wall construction. 
 [771
 
 Wall recesses for timber joist. 
 
 Pouring concrete into a column form. 
 I 78]
 
 floors, ordinarily also of reinforced concrete construction. When such 
 floors are used they become monolithic with the walls, and a very rigid 
 and secure building is obtained by allowing the reinforcing rods of the 
 beams to interlace with those of the walls. 
 
 Should wood construction be used for the floors in dwellings where 
 the walls are of concrete, as is sometimes done in the smaller houses, the 
 
 Fig. 56. Two methods of setting wooden joist in concrete walls. 
 
 joist may be set and cast in place, or else be supported in the ways il- 
 lustrated in Fig. 56 at (a) and (6). 
 
 The objection found to the method of supporting the ends of the 
 joists or floor timbers by setting them and casting them in place is that 
 when the ends of the timbers are thus confined the wood is liable to decay. 
 They should always set in a pocket somewhat larger than their dimen- 
 sions, so that the air may get to the wood and prevent dry rot. 
 
 The manner of supporting the joists or floor beams shown in Fig. 56 
 
 [791
 
 at (a), is good, from the fact that the wall may be run up several stories 
 and the floors rapidly constructed after the centering for the walls has 
 been removed. By arranging the iron ties and embedding their ends in 
 the concrete, every fourth or fifth joist may be used to tie the building 
 together, or if so desired, every joist may be tied in. One advantage 
 exists here in that the ledge makes an excellent bearing for the joist, and 
 is also very convenient for sizing the joists and bringing them to a level. 
 Joists or floor beams may also be supported in a very secure and effi- 
 
 (a) 
 
 F'g- 57- Hollow walls fastened together with copper, galvanized iron, or concrete ties. 
 
 cient manner by using wall hangers, as shown in the figure at (&). These 
 hangers are known as "Duplex Concrete Hangers," and are made for 
 2", 3" and 4" joists, especially for concrete construction, though any 
 hanger of suitable design could as well be used. 
 
 Both of the methods shown in the figure permit all of the ends of the 
 joists or floor timbers to be well ventilated. 
 
 Hollow Concrete Walls. As any dead air space in a wall or floor 
 of any material is most excellent on account of the insulation it provides 
 in case of either heat or cold, as well as sound, and also because a drier 
 interior wall surface is obtained, concrete walls so cast have some ad- 
 vantages over solid concrete walls. The best construction is to make 
 the two walls as distinct as possible and to provide as few connections 
 
 [80]
 
 between the two walls as is practical to insure the stability of both. 
 In fact it is far better to unite the two walls with only copper or galvan- 
 ized iron ties, as shown in Fig. 57 at (a), than to tie them together with 
 cross walls of concrete as illustrated at (6). Such walls as the latter are 
 costly, and somewhat difficult to construct unless special or patented 
 forms or centerings are used. Generally the air space desired may be 
 obtained by some other means, such as a veneer lining or furring, at a 
 considerably less cost and, withal, greater efficiency. 
 
 Veneered, Lined and Furred Walls. In order to insure against 
 dampness, and more especially to prevent the possibility of condensation 
 on the inside of walls of concrete, a condition which is hardly likely to 
 occur except under extraordinary conditions of exterior cold and great 
 
 Fig. 58. Furring inside concrete walls with hollow brick, plaster block, or tile. 
 
 interior humidity, and also to provide greater insulation, it is best where 
 the expense is not a factor in the problem of dwelling house construction 
 to veneer, line or furr the walls on the inside. 
 
 A good practice is to veneer or line the inside walls with hollow 
 brick, plaster block, or tile, as shown in Fig. 58. A method equally 
 efficient is to furr the walls on the inside with metal lath and furring 
 strips. In either case the desired air space is obtained without in any 
 way destroying the fireproof properties of the construction. An ex- 
 cellent lining for concrete walls is found in a layer of cork, which may be 
 stuck to the walls with cement, and which readily takes plaster. 
 
 Concrete walls 8 inches in thickness, painted on the inside with a 
 damp-proof paint proper for covering concrete, will answer every purpose. 
 
 81
 
 Chapter IV 
 Operations in the Field
 
 \Vorkingman' s Cottage, Sage Foundation Homes Co. 
 
 Crosrenor Alterbury, Architect 
 
 The huge cored slabs for walls, floors, roof and partitions and even stairways 
 are precast and assembled in manner shown. 
 
 84
 
 Chapter IV 
 Operations in the Field 
 
 With the structure satisfactorily designed, successful construction of 
 a building of any material is dependent upon the careful selection of the 
 component materials and a working knowledge of how to combine them 
 properly. The wide distribution of sand, rock and gravel (known as 
 the aggregate) and the extensive use of concrete have increased general 
 knowledge as to what constitutes good materials and the ability to do 
 good work. Such results have been brought about by following definite 
 methods which have now become common practice. 
 
 Selection of Materials. In selecting Portland cement always secure a 
 brand guaranteed to meet the requirements of the standard specifica- 
 tions of the United States Government or those of the American Society 
 for Testing Materials. Portland cement may be had in cloth sacks, 
 paper bags or wooden barrels. More commonly it is shipped in cloth 
 sacks with an allowed rebate for the return of empty bags in good con- 
 dition. Each bag of cement weighs 94 pounds net and four bags con- 
 stitute a barrel of 376 pounds. One bag of loose cement is practically 
 equivalent to one cubic foot. On account of its sensitiveness to moisture, 
 Portland cement must be carefully protected from dampness at all times, 
 even when piled at the site of the work. 
 
 Sand for concrete should be had hard and clean and should have 
 grains grading in size from % inch down. Pit and stream sands are 
 generally of good quality, but drift sand is usually too fine of grain to 
 make good concrete. The presence of dirt can easily be ascertained by 
 pouring a small quantity of sand into a pail of clear water or by rubbing 
 a portion between the palms of the hands. A practical test may be made 
 
 [8 5 1
 
 by placing a four-inch depth of sand in a fruit-jar, and by adding water 
 until the jar is within one inch of full and by shaking the contents vigor- 
 ously. If, after the water has again become clear, there is a layer of mud 
 more than one-fourth inch in thickness, the sand should not be used 
 without first washing. 
 
 The most suitable stone for crushed rock is one which is clean, hard, 
 breaks with sharp angles and to which mortar easily adheres. Trap, 
 granite and hard limestone are among the best. The use of shale, slate, 
 and very soft limestones and sandstones should be avoided. The crushed 
 rock should be screened only sufficiently to remove the fine dust. The 
 maximum size of stone allowable is often dependent upon the thickness 
 of the object to be molded. It is common practice to fix the extreme 
 limit at i% inch in diameter. 
 
 Bank-run gravel, just as dug from the pit or taken from the stream 
 bed, seldom runs even and rarely has the proper proportions of sand and 
 pebbles for making the best concrete. An ideal pit gravel is 40 per cent, 
 sand. Since there is generally too much sand in proportion to the 
 pebbles, it is advisable and economical to screen the sand from the peb- 
 bles and then to remix them in the correct proportions. As a general 
 rule, pebbles larger than I % mcn in diameter are discarded ; all material 
 smaller than l / inch is considered sand. Gravel should contain no 
 rotten stone and should be clean. 
 
 Depending on the character of the particles, sand, crushed rock and 
 gravel vary in weight from 100 to no pounds per cubic foot. 
 
 For fire-proofing and for various other purposes requiring low 
 stresses, cinder concrete is frequently used. The cinder should consist 
 of hard, clean, vitreous clinker free from sulphides, unburned coal and 
 ashes. A clean cinder will not discolor the palms of the hands when 
 rubbed between them. 
 
 The water used in mixing the concrete should be clean and free 
 from oil, alkali and vegetable matter. 
 
 Proportioning and Mixing. The proper proportion for combining 
 the Portland cement and the aggregate is dependent upon the quantity and 
 
 [861
 
 character of the materials and the purpose for which the resulting con- 
 crete is intended. For reinforced and damp-proof concrete that propor- 
 tion is desirable which produces the densest concrete possible. Under other 
 conditions only sufficient cement is used to develop the strength required 
 of the concrete. For reinforced and damp-proof concrete, a I .'2:4 mix is 
 commonly employed. Where compressive strength alone is a requisite, 
 the concrete is frequently proportioned 1:2^:5. For massive founda- 
 tions, a 1:3:6 concrete may be used. In such proportions, the first 
 numerical term refers to the parts of Portland cement, the second to 
 the parts of sand and the third to the parts of crushed rock, screened 
 gravel, or other coarse aggregate. The proportions are based on meas- 
 urements by volume in which a bag of cement is considered one cubic 
 foot. If pit gravel is used, although the saving in cement will usually 
 more than compensate the cost of screening and remixing, similar pro- 
 portions are adopted in which the second or sand term is dropped. Such 
 proportions then read I 4, 1 :5 and 1 :6. Cinder concrete is usually made 
 in the proportion I part cement to 2\ parts sand to 5 parts cinders. 
 Oh large work, and where the determination of the exactly correct pro- 
 portions is expedient, the voids in the sand and stone are determined by 
 saturation with water or by specific gravity. With the proportion of 
 voids thus carefully ascertained, there is generally used an excess of 5 
 to 10 per cent, of cement over the voids in the sand and a 5 per cent, 
 excess of sand over the voids in the stone. 
 
 In making a batch of concrete the amount of each material required 
 should be actually measured by volume, otherwise concrete entirely 
 homogeneous in texture and appearance can not well be produced. 
 Since a bag of Portland cement (loose) is equivalent to one cubic foot, for 
 convenience all measurements should be based on the cubic foot as the 
 unit. As a means of measuring, a bottomless box, or a device equally 
 exact, should be employed. The sizes of measuring boxes are depend- 
 ent upon the amount of concrete to be mixed in each batch. 
 
 The materials can be thoroughly mixed into concrete either by hand 
 or by machine. The method selected is dependent entirely upon con- 
 ditions. W T here the work is of such a character and size as to war- 
 
 [89]
 
 rant the investment, much faster progress can be made by using a ma- 
 chine mixer. The machine should be of such a type as to insure uni- 
 form mixing of the materials throughout the mass of concrete. There 
 are many such machines on the market and the merits of each, as adapted 
 to the user's particular needs, should be carefully studied. 
 
 For work of moderate magnitude, measuring boxes of convenient 
 size are specified in Table i. 
 
 TABLE 1. SHOWING QUANTITIES OF MATERIALS AND APPROXIMATE RESULTING 
 AMOUNT OF CONCRETE FOR TWO-BAG BATCH, USING SAND AND STONE 
 
 
 Propor- 
 
 
 
 tions by 
 
 Two-bag Batch 
 
 
 Parts 
 
 
 Kind of Concrete 
 Mixture 
 
 8 
 
 
 1 
 
 t. 
 
 t> 
 
 Materials 
 
 Con- 
 crete* 
 
 Size of Measuring 
 Boxes. Inside 
 Measurements 
 
 Water in 
 Gallons 
 for Med- 
 ium Wet 
 
 a 
 
 1 
 
 H 
 
 a | 
 
 
 Stone 
 
 
 | 
 
 a 
 
 K 
 
 
 CO 
 
 2^5 
 
 
 Sand 
 
 or 
 
 Mixture 
 
 
 ^ 
 
 co 
 
 CO 
 
 
 
 
 
 
 Gravel 
 
 
 
 
 
 
 
 Cubic 
 
 Cubic 
 
 Cubic 
 
 
 
 
 
 
 
 
 Bags 
 
 Feet 
 
 Feet 
 
 Feet 
 
 
 
 Gallons 
 
 1:2:4 concrete. . . . 
 
 I 
 
 2 
 
 4 
 
 2 
 
 VA 
 
 lY* 
 
 %Y* 
 
 2'X2' 
 
 <>' v *' 
 2 X 4 
 
 IO 
 
 1:2^:5 concrete.. 
 
 I 
 
 2K 
 
 5 
 
 2 
 
 4 3 A 
 
 9 1 A 
 
 IO 
 
 2' X 2>' 
 
 2' x 5' 
 
 12>/, 
 
 1:3: 6 concrete. . . . 
 
 I 
 
 3 
 
 6 
 
 2 
 
 ^ 
 
 \\Y* 
 
 12 
 
 2' x 3 ; 
 
 2' X 6' 
 
 .3* 
 
 There are several slightly different and entirely satisfactory meth- 
 ods of mixing concrete by hand. When sand as a fine aggregate is 
 used with a coarse aggregate (such as crushed rock, screened gravel, 
 cinders, etc.), the sand is carefully measured and the entire quantity 
 required for one batch of concrete is spread out in a thin, oblong shape 
 upon a smooth, tightly jointed mixing board. Upon the sand is scattered 
 evenly the full amount of Portland cement needed. The two materials 
 are then mixed dry by shoveling, with the laborers working opposite 
 
 * Amount of concrete resulting is only roughly approximate. In estimating quan- 
 tities use Table 2, page 92. 
 
 (90]
 
 each other in pairs. They turn the cement and sand with a dragging 
 stroke which is very effective in mixing the materials. During this 
 operation a helper aids the mixing by using a garden-rake. The turning 
 continues until the cement and sand no longer show in streaks and the 
 mass has a uniform color. 
 
 The mixture is again spread out in its original oblong shape and the 
 measured full amount of stone or other coarse aggregate is scattered 
 evenly over it. About one-half to two-thirds of the required amount of 
 water is sprinkled over the stone, after which the mass is turned. The 
 concrete is thrown into a ridge, is cut open to a crater shape, and the 
 remainder of the water is added. Turning is continued, and a little 
 water added to the dry spots until the mass is thoroughly mixed. 
 
 For bank-run gravel (or other material in which the fine and coarse 
 aggregate are not separated) the method of mixing is slightly different. 
 One-half of the total aggregate required is spread out in oblong shape, 
 the full amount of Portland cement is scattered over it, and the remainder 
 of the aggregate is added. The materials are turned dry until they are 
 thoroughly mixed, when the mass is cut open and water added in the 
 same manner as described above when sand and crushed rock are used. 
 
 The amount of water necessary to a batch of concrete is dependent 
 upon the character and condition of the aggregate and the consistency 
 required of the concrete for the purpose and for the manner in which 
 it is to be used. When possible, and especially for reinforced construction, 
 it is advisable to use that consistency commonly known as mushy, in 
 which state the concrete is sufficiently wet that, when being transported 
 from the mixer to the work in buckets or in wheelbarrows, its surface 
 naturally becomes smooth and level. With all things equal, mushy 
 wet concrete is most dependable for completely filling all space in the 
 forms, for securing a perfect bond with the metal reinforcing, and for 
 producing a very dense concrete. 
 
 For certain effective surface treatments and for detailed ornamental 
 castings a dry concrete is frequently used. The amount of moisture 
 required is a variable quantity. At least sufficient water should be used 
 to give the material the plasticity common to molding sand. For mas- 
 
 (91]
 
 sive work dry concrete should be wet enough to flush mortar slightly to 
 the surface under heavy tamping. Dry concrete attains a working 
 strength more quickly than wet concrete, and the forms may be removed 
 sooner, but ultimately the wet mix surpasses it in strength. 
 
 In casting ornamental concrete, and for other purposes, a mortar is 
 frequently required. Sand is generally chosen as the fine aggregate, though 
 stone screenings of various kinds are often used. The proportions are de- 
 pendent upon the sizes of the particles in the aggregate. In general I part 
 of cement is used to i| or 2 parts of fine aggregate. Mortars too rich in 
 cement are liable to check and thus injure the appearance of the surface. 
 
 At the greatest, not more than thirty minutes should elapse between 
 the mixing of the concrete and the depositing of it into permanent posi- 
 tion. The methods of handling the concrete between the mixer and the 
 forms vary with the size of the work. On large construction, hoists are 
 used in connection with distributing spouts. For smaller structures 
 derricks, wheelbarrows, and buckets are the usual means of conveyance. 
 
 Estimating Quantities of Materials Needed. For estimating the 
 quantities of materials needed for any structure, Tables 2 and 3 will be 
 of considerable service. In making up the estimate, compute the total 
 cubic feet of mortar or concrete required and, for the barrels of cement 
 and cubic yards of sand and stone, multiply this total by the decimal 
 figure under each respective heading. These tables are based on ordi- 
 nary sand and on average conditions of 45 per cent, voids in broken stone 
 with the dust screened out. 
 
 TABLE 2. ESTIMATING QUANTITIES OF MATERIALS FOR MORTAR 
 
 Mixture 
 
 Quantities of Materials in One Cubic 
 Foot of Mortar 
 
 Cement 
 
 Sand 
 
 i \% 
 
 Barrel 
 0.1481 
 0.1239 
 0.1052 
 
 Cubic Yard 
 0.0311 
 0.0344 
 0.0370 
 
 12 
 
 I 2.K 
 
 
 92
 
 TABLE 3. ESTIMATING QUANTITIES OF MATERIALS FOR CONCRETE 
 
 Mixture 
 
 Quantities of Materials in One Cubic Foot of 
 Concrete 
 
 Cement 
 
 Sand 
 
 Stone or Gravel 
 
 1:2:4 concrete 
 
 Barrel 
 0.058 
 0.048 
 0.041 
 
 Cubic Yard 
 0.0163 
 0.0170 
 0.0174 
 
 Cubic Yard 
 
 0.0326 
 0.0341 
 0.0348 
 
 i : 2]/2 : 5 concrete 
 
 1:3:6 concrete 
 
 
 To illustrate the manner of using these tables, assume that 25 cubic 
 feet of i : 2 mortar and 850 cubic feet of concrete are required for a bunga- 
 low. Of this concrete, 90 cubic feet of a 1 :2^:5 mix are needed for the 
 footings and foundations and the remaining 760 cubic feet of a 1 :2 4 mix 
 for cellar and house walls, etc. 
 
 ESTIMATE FOR BUNGALOW 
 
 Cement for 1:2 mortar 25 X 0.1239 3.10 bbls. 
 
 Sand for i : 2 mortar 25 X 0.0344 -86 cu. yds. 
 
 Cement for 1 : 2^2: 5 concrete 90 X 0.048 4.32 bbls. 
 
 Sand for 1 : 2^2: 5 concrete 90 X 0.0170 1.53 cu. yds. 
 
 Stone for i : 2>: 5 concrete 90 X 0.0341 3.07 cu. yds. 
 
 Cement for 1:2:4 concrete 760 X 0.058 44.08 bbls. 
 
 Sand for 1:2:4 concrete 760 X 0.0163 12.39 cu. yds. 
 
 Stone for 1:2:4 concrete 760 X 0.0326 24.78 cu. yds. 
 
 Formwork and Centering. The formwork and centering for reinforced 
 concrete construction, while it is purely falsework, which is taken down, 
 removed and is no part of the finished structure, enters considerably into 
 the cost of any concrete building. 
 
 To illustrate the great percentage to the cost of construction the form 
 work and centering bear to the finished structure, it might be stated that 
 reinforced concrete for house construction in place is worth about $21.00 
 a cubic yard for the usual wall and floor construction. This cost is, 
 roughly, divided equally between the concrete, the steel, and the form and 
 centering, the cost of each being, approximately, $7.00 for every cubic 
 yard of concrete poured. 
 
 This cost shows how important it is that the formwork and centering 
 should be of such a design that it may be economically constructed, and, 
 
 [93]
 
 at the same time, produce well molded work. It is not sufficient that 
 the formwork shall be smooth, for unless care is taken in its construction 
 and support the finished work will show sagged floor slabs, beams and 
 girders, posts and piers out of plumb, and floor members twisted and 
 warped. 
 
 The strength 'and accuracy with which form construction must be 
 designed and executed cannot be too forcibly brought to mind, especially 
 where cast concrete is a feature of exterior treatment and architectural 
 decoration of a building. Nothing can look worse than brackets, mutuals 
 or pilaster caps which, while otherwise well wrought, are placed out of 
 plumb due to carelessness in placing the forms and in supporting them. 
 
 Concrete constructors, realizing the importance of cheap forms, 
 have devised and patented many particular ideas of more or less merit. 
 In form and centering construction, however, like other structural evolu- 
 tions, there has been a "survival of the fittest," and in nearly all instances 
 the patented forms, due to their costliness and lack of adaptability to 
 particular operations of construction, have not been generally used. 
 Forms of simple design, so arranged as to be readily put together and 
 taken down, have been almost standardized where concrete construc- 
 tion has been carried on extensively. 
 
 Built-up Form Construction for Floors. The several types of form 
 construction may be generally classified according to the manner in which 
 they are built, as "built-up," "unit panel construction," and "constructive 
 formwork." 
 
 In the first type, the beams and girders of the floor construction are 
 formed in the concrete by building up wooden troughs having the size 
 and shape of the beams and girders, properly supporting these upon 
 suitable uprights well braced, and covering the spaces between the beams 
 and girders with battened panel sections supported upon joists or ribs 
 resting upon ledger boards nailed to the sides of the beam and girder 
 form. 
 
 This type of form construction for concrete floors, where beams, 
 girders and slabs occur, has come into common use, and a working draw- 
 
 l94l
 
 ing giving the usual sizes of the pieces used in the construction of these 
 forms is given in Fig. 59. 
 
 Unit Panel Construction. In the second type, the unit panel con- 
 struction, the panel formed by the beams and girders is made up in the 
 form of a box, which, when inverted and properly supported upon the 
 
 Fig- 59- Details of forms used in built up-construction. 
 
 bottom boards of the beams and girders, makes up the side forms for 
 these structural members, and also provides a centering for the slabs. 
 
 These panel forms are sometimes made in sections, so as to be col- 
 lapsible, as shown in Fig. 60. The operation of the form is explained by 
 the note in the illustration. 
 
 [951
 
 As the unit type of form construction is used especially where there 
 are a great number of unit panels of the same size, they would not be so 
 practical for individual house construction, though they could well be 
 used if a number of houses of the same plan were to be built, as in an 
 operation. 
 
 Constructive Forms. In the third type of form construction an 
 effort is made to minimize the cost of centering by incorporating in the 
 
 t> 
 
 Piece H/rJaea in place ., when 
 
 knocked down 
 form may Ae 
 
 Fig. 60. Unit panel forms made in collapsible sections. 
 
 actual concrete construction a means by which the sides of the beams and 
 girders, or supporting members, can be formed, the space filled, and a 
 saving in more costly material accomplished. 
 
 This type of form construction is emphasized in what is known as 
 "Hollow-Tile" and "Joist Construction," and in such constructions 
 as "Ferro-Dome" and "Corr-Tile." In the Ferro-Dome construction 
 the stamped steel boxes, when properly spaced upon supports, with flat 
 boards for the bottom of the intersecting beams, form a mold for the sides 
 of the beams, as shown in Fig. 61. Sometimes, as in the Corr-tile con- 
 
 [96]
 
 struction shown in Fig. 62, instead of these metal forms, square blocks 
 of terra-cotta are used, with flanges and channel tile, making a complete 
 form for intersecting beams; thus all that is needed .for constructing the 
 work is a flat centering properly supported on studding. 
 
 Fig. 61. Example of Ferro-Domc construction. 
 
 Various kinds of patented forms have been devised which are sup- 
 posed to have the economical advantage of being adjustable to any length 
 of span, and so arranged that by spreading them, different widths of beam 
 could be obtained. It is considered that by the use of such forms their 
 cost was practically made up 
 on the first job for which 
 they were used, and that the 
 cost of the form construction 
 on subsequent work was re- 
 duced to the mere expense 
 of hauling the forms to the 
 site and placing them upon 
 
 the proper centering, with a small percentage of loss due to deterioration. 
 Such form work for floor construction in house work is hardly practical. 
 
 Forms for Wall Construction. In the construction of concrete walls 
 two kinds of wooden forms are used namely, those which are constructed 
 7 [97] 
 
 Fig. 62. Example of Corr-tile construction.
 
 to cast an entire story height of wall, and those which are arranged to build 
 the wall in sections of two, three, four, or five feet in height. 
 
 The former method requires, of course, the most lumber and car- 
 pentry labor, but it is the most expeditious, while by the use of the latter, 
 or sectional forms, the cost of the form construction is reduced to a 
 minimum, but the work proceeds much more slowly. 
 
 Besides those forms of lumber made up by carpenters on the job, 
 there are several types of patented forms which are usually of the sec- 
 
 Fig. 63. Typical example of form work in one-story wall construction. 
 
 tional type, and are so arranged with units of different lengths and corner 
 units, as to allow a wall of any length or plan to be built. 
 
 Forms for the Construction of a Story Height of Wall. The arrange- 
 ment and construction of the formwork, where a story height of wall 
 is to be placed at one time, is shown in Fig. 63. With this type of form- 
 work for molding concrete walls, the one side of the form, as at a a, must
 
 be built first, either upright or on the ground and raised, and then se- 
 curely braced to hold the side plumb and true. The uprights, as at 
 b b, may be 3" x 4", or preferably 2" x 6" yellow pine, spaced not further 
 apart than 24 inches from center to center. The sheathing nailed to the 
 uprights may be either x 2*/" face tongued and grooved yellow pine 
 flooring, or else i" x 12" sap-pine boards dressed on one side. It is not 
 necessary that the back braces, at c c, be of any more strength than enough 
 to hold the form in position and secure it against wind pressure, because 
 both sides of the form must be tied together to resist the pressure of the 
 
 Ap 
 
 cers 
 
 Fig. 64. Spacers for reinforcement. 
 
 wet concrete. It would not be practicable or economical to provide 
 sufficient back braces to resist the bulging or buckling effects due to this 
 cause. 
 
 When one side of the form has been constructed in this manner, 
 the other side may be built and placed, being braced in position; before 
 the sheeting boards are put on, the steel reinforcement should be put 
 in position and secured to the side of the form first erected. The best 
 way to fasten and place the steel is to provide looped spacers, as shown 
 in Fig. 64, through which the vertical rods may be passed, and which 
 
 [991
 
 are so arranged as to be secured to the back form with staples. These 
 also form a bearing or support to which the horizontal reinforcement 
 can be wired. 
 
 Method of Tying and Separating the Sides of Forms. The braces 
 shown in Fig. 63 are only intended to hold the two sides of the forms 
 vertical and the mass of the wet concrete contained between them in a 
 plumb and secure manner until the concrete has set. It is never con- 
 sidered good practice to attempt to brace both sides of the forms for a 
 wall so strongly and at such frequent intervals as to exclude the necessity 
 
 of other ties between the two sides. 
 Usually wire ties or bolts are used 
 to hold in the sides of the forms 
 and prevent them from bulging 
 on account of the hydrostatic 
 pressure of the wet concrete. 
 When the ties or bolts are 
 drawn up it is difficult to regu- 
 late the tension so that the forms 
 will not be either bulged or pulled 
 in and otherwise warped and dis- 
 torted. To avoid this trouble 
 
 Fig. 65. A common method of bracing and 
 tying wall forms. 
 
 some means is employed to keep 
 the sides of .the wall forms at the 
 same distance apart when the 
 bolts or wire ties are drawn up. 
 
 The usual methods of tying the sides of the forms together, and ar- 
 rangements for separating them at proper distances, are shown in Figs. 
 65, 66, and 67. 
 
 In Fig. 65 is .shown a method which meets with much favor on 
 account of its cheapness and the convenience with which the materials 
 may be obtained. The separator a consists of a small stick of wood 
 smoothed and accurately cut to length, while close to it is placed the wire 
 tie &, of No. 1 8 gauge soft iron. This is formed. in U-shape, passed around
 
 the upright c, through holes in the forms, and twisted around the upright 
 d. The proper tension is obtained by twisting the wires with a bar, as 
 at e. Sometimes, owing to the fact that the wire cuts into the wood of 
 the uprights, a small metal plate or another stick of wood is inserted be- 
 tween the wire tie and the upright. 
 
 When wooden separators of this kind are used they are generally 
 pushed through the concrete while the work is still "green"; or, at least, 
 before it has set hard. When the forms are removed the ends of the wire 
 
 Fig. 66. The use of the hook bolt as a substitute for wire ties. 
 
 ties are cut off and the work is finished by filling the holes left in the con- 
 crete when the wooden separators are driven out. 
 
 One of the disadvantages of using the wire ties and cutting them off 
 in this manner is due to the fact that some of the ends will be exposed, 
 will rust, and this iron rust running down the surface of the wall will 
 cause unsightly stains. 
 
 This difficulty can be obviated by the use of a hooked bolt, illustrated 
 in Fig. 66. The bolt a is formed with a hooked end to fit over the 
 upright as at b; it passes through the two forms and is brought to the 
 
 [101 ]
 
 proper tension by the use of a bar, an iron plate washer and a wrench nut, 
 as shown at c. In this construction the bolt is withdrawn before the con- 
 crete has completely hardened, though the bolts may be loosened by 
 partially removing them, or by turning them while the concrete is setting 
 up. In this way they may be more readily withdrawn when the forms 
 are taken down. Sometimes instead of the wooden separator, an iron 
 pipe separator is slipped over the bolts and left in the concrete wall. 
 
 t|/// 4 - '. 4 ... 
 
 Fig. 67. A practical type of wall form separator. 
 
 These pipe separators are, however, costly, and have the same objection 
 as the wire ties with regard to rusting at the ends. 
 
 A good wall form separator is that known as the "McCarty Con- 
 crete Separator." This is simply a spool or cylinder of concrete with a 
 hole through the center for the tie-bolt, molded to the length required for 
 the thickness of the wall and left embedded in the concrete. Being ce- 
 ment, it becomes incorporated with the concrete of the wall, and is not 
 subject to the objection found in metal separators. This separator with 
 the tie-bolt is illustrated in Fig. 67.
 
 Fig. 68. A clever device used in connection with 
 wire ties 
 
 A clever device which can be used with wire ties, and by which the 
 
 ends of the wire ties can be 
 
 covered with the concrete on 
 
 the surface of the wall after 
 
 the forms have been removed, 
 
 is illustrated in Fig. 68. This 
 
 device is clearly shown in the 
 
 figure, and its use in conjunc- 
 tion with the wire tie, or with 
 
 a rod tie with hooked ends, 
 
 is shown in the illustration. 
 
 When the forms are to be 
 
 taken down the wedge at d is 
 
 knocked out and the forms removed; then the device may be released 
 
 from the wire or hooked tie by knocking over the end of the hooked lever, 
 
 as at b, thus releasing the de- 
 vice from the tie. In this way 
 the ends of the tie do not come 
 closer to the surface than one- 
 half or three-quarters of an 
 inch, and are covered by the 
 concrete. The hole left in the 
 surface of the wall by the re- 
 moval of the device can be 
 filled by plastering or grouting. 
 
 Panel or Sectional Wall 
 Forms. Where the wall is 
 to be constructed in sections 
 three or four feet high, the 
 formwork becomes compara- 
 tively simple. A good arrange- 
 ment for the construction of 
 
 concrete walls in sections is to use battened panels, as at a a in Fig. 69, 
 
 [ 103) 
 
 Fig. 69. Panel or sectional wall forms.
 
 supported and braced by the uprights b b, made up of two pieces of 
 2" x 6" timber, held together by separators at the end, as at c c; when 
 braces of this kind are used bolts can be placed in any position, and the sep- 
 arator at the top holds the braces together as a yoke. The braces are suffi- 
 ciently long to grip that portion of the wall already constructed, and in 
 this way the form construction for the portion of the wall to be built 
 is held plumb and secure over the finished wall. The tie-bolts may be 
 
 Fig. 70. "Sullivan Pressed Steel Plank-Holders. 
 
 oiled or soaped so that they can be more readily withdrawn from the 
 concrete. 
 
 Where there is much wall to construct, or where the contractor can 
 use the braces for a number of operations, they may be made of channel 
 or angle irons placed back to back, held together with separator plates 
 and rivets. These are much more costly, of course, than the wooden 
 braces, and somewhat heavier to handle. 
 
 Another method of constructing concrete walls in sections is illus- 
 trated in Fig. 70, which shows the use of what is known as the "Sullivan 
 
 I 104 ]
 
 Pressed Steel Plank-Holders." By means of these the form-boards are 
 interlocked at the corner and together, and they also act as a washer and 
 grip for the tie-bolts; wire ties may be used with them as well as bolts. 
 
 Forms for Hollow Wall Construction. Hollow walls built of concrete 
 have been used for house construction to some extent. The advantage of 
 a hollow concrete wall consists in the dead-air space contained between the 
 inside and the outside wall, which insulates the building, tending to make 
 it cool in summer, and allowing it to retain the heat in winter. Concrete 
 
 
 
 
 
 
 
 
 SI 
 
 V 
 
 
 / 1 
 
 
 
 
 
 
 ' '; 
 
 1 
 
 
 
 ^ 5 
 
 j 
 
 u 
 
 
 
 ! 
 
 i 
 
 
 
 
 
 
 
 i 
 
 i-^i 
 
 ^ 
 
 Fig. 71. Wooden forms for hollow wall construction. 
 
 is, however, such an excellent non-conductor, and solid concrete walls are 
 so much superior to brick and stone walls with regard to their ability to 
 prevent radiation, that the additional expense required to build hollow 
 walls of concrete is hardly warranted. 
 
 Forms for the casting of hollow concrete walls are necessarily com- 
 plicated, and are particularly so when attempts are made to construct 
 them with wooden forms. It is only possible to construct hollow walls 
 by means of sectional forms arranged to cast two or three feet of the wall 
 at a time. Fig. 71 illustrates a type of wooden form construction that 
 
 [105]
 
 can be used where a hollow wall is desired. The outside forms are of the 
 usual battened type, braced by the slotted wooden braces yoked at the 
 top, as shown at a a. The bars, at b b, which support a wooden core box, 
 rest upon the top of the battened forms for molding the outside of the 
 wall. This core box is so arranged that it can be wedged out to the 
 required width by means of cleats or wedges, and after the concrete has 
 been cast these cleats or wedges are released and the core box is slightly 
 collapsed, thus allowing it to be withdrawn. 
 
 Many devices can be gotten up which will permit the collapsing or 
 slight reduction in size of the core box, arranged to operate by the use of 
 wedges or keys driven into place, or released by a blow from a hammer. 
 
 Good results at reasonable cost in the construction of hollow concrete 
 walls can only be obtained by spending much care and thought upon the 
 construction of the core box, and where there is much work of this kind 
 to be done it would be better to use specially designed metal forms for 
 the construction of hollow walls. There are several types of patented 
 hollow-wall forms on the market which can be used economically where 
 several buildings are to be built. 
 
 Patented Steel Forms. Steel forms made up in units, with special 
 devices for clamping the several units together, have been developed 
 and used to a considerable extent. It is impossible here to describe 
 at length the several types of patented sectional steel and steel-lined 
 forms. One of the most recent types of steel forms for wall work is illus- 
 trated in Figs. 72 and 73. The former shows in detail the unit sections 
 of the forms and the method of clamping them together at the junction 
 of the units, while the latter shows their use in the construction of an 
 all-concrete dwelling. In general, the units are 24" square, and are 
 made of No. 16 galvanized sheet iron, reinforced around all four sides 
 by i" x i" x i/g" steel angles; the units are arranged with two clamps on 
 the right hand edge, so that when these clamps are turned into posi- 
 tion they tie the adjacent edges of the units together. Besides these 
 clamps, dowel-pins are provided on each plate which fit into correspond- 
 ing holes in the adjoining unit. In the use of these unit forms the window 
 
 [ 106 ]
 
 Patent steel forms used in concrete wall construction. 
 
 Patented steel forms in use. 
 
 107
 
 and door frames are set in conjunction with the forms, and are cast in 
 place. In order to make the construction as adjustable as possible to 
 any dimensions, other widths of units may be had in increments of two 
 inches, and three-inch plates are used in order to get odd sizes. The units 
 are tied together by wire ties which pass through holes in the angles, and a 
 detail of the clamping device previously described is shown in Fig. 72. 
 
 Remarks Regarding Forms and Their Construction. It is an ac- 
 cepted fact by those who have had much experience in concrete con- 
 struction that it is not economical to use poor grade lumber for forms. 
 The cost of using old lumber, because of the work required to patch it, 
 extract the nails, and prepare it so as to give results in any way satis- 
 factory, is greater than to purchase new. 
 
 All lumber for form work should be either white pine, yellow pine 
 or spruce; hemlock should not be used ordinarily for exposed work. 
 When the lumber is delivered it should be carefully piled, with spaces be- 
 tween the boards, with the top layer pitched to shed water, and where 
 possible, it should be protected from the sun. It is vital that the boards 
 for form construction shall not be badly warped or twisted, and any care 
 that can be given to prevent this amply repays for the trouble. 
 
 The joints in form construction should be close especially where a 
 wet mixture of concrete is used, though the best results are not always 
 obtained by using matched boards. The moisture sometimes causes the 
 wood to swell, and when they are driven up tight there is a tendency to 
 buckle which sometimes results in poor work. 
 
 It is of the utmost importance that the bottom of floor forms when 
 in place shall be clean of all shavings, sawdust and chips before the con- 
 crete is placed, and the same precaution must be used with reference to 
 wall forms. 
 
 In winter time all form work must of course be clear of ice or snow 
 before the concrete is placed. In summer time, or hot weather, form 
 work should be kept well wetted in order that the lumber may not shrink 
 and leave large cracks through which a wet mixture of concrete will run, 
 and by which unsightly fins or markings are left upon the concrete. 
 
 [ 108]
 
 c. 
 o 
 
 -/ 
 
 c
 
 S 
 
 . "rt 
 
 
 t O 
 
 *e w
 
 It is not well in house construction to oil the forms. In the first 
 place, it is apt to leave the concrete discolored and stained on the outside. 
 It is also likely to cause trouble where the concrete is plastered on the 
 inside, by the oil coming out in the finished plaster work. There seems 
 to be no real necessity for or advantage to be gained in oiling either wall 
 or floor forms in the construction of dwelling houses. 
 
 Selection and Care of Steel Reinforcement. It is generally conceded 
 that any type of deformed steel bar is superior to plain round rods for 
 the purpose of reinforcing concrete. In the selection of the type of de- 
 formed bar the constructor should be governed by the pattern of bar which 
 is most available in the locality of the proposed building site. If 
 there is an operation contemplated, which would require a great 
 amount of steel reinforcement, then prices can be obtained on several 
 types of deformed bars, with the idea of getting the best possible quota- 
 tion. It will generally be found that the most available deformed rein- 
 forcing bar is the square twisted bar, and that this bar fulfills every re- 
 quirement of a uniform net section, as well as a deformation without an 
 increase in the weight of the bar. 
 
 The only advantage of plain round bars is that they are less costly 
 than any type of deformed bar, and can be obtained from the stock of 
 any local dealer in sufficient quantity for the construction <*f a concrete 
 house of ordinary dimensions. 
 
 Where reinforcing steel is sent from the mill, or even from a distant 
 wholesale dealer or broker, it is usually shipped in open freight cars, and 
 generally it is necessary to haul the steel from the siding or freight sta- 
 tion. It is best, if possible, to haul it in wagons of sufficient length to 
 prevent it from trailing on the ground. 
 
 In any construction work annoyance and loss of time are saved by 
 exercising care in the disposal of the materials, and the manner of taking 
 care of steel reinforcement is not an exception to this rule. The steel, 
 upon delivery, should be sorted out with reference to the position it oc- 
 cupies in the building, and with regard to sizes. In a very large operation 
 of concrete houses the steel should be placed in racks and checked off as 
 
 [in ]
 
 used. It some system is not adopted in taking care of the steel reinforc- 
 ing bars.it will be found that some of the longer bars will be used in places 
 for which shorter bars were ordered, and that the short bars left over will 
 not meet the requirements of the conditions for which the longer bars 
 were needed. 
 
 All steel reinforcing bars before being placed in position should be 
 cleaned of loose scale by using a wire brush. They should, of course, 
 never be painted, and should be free from oil, clay, or dirt. Material of 
 this kind on the steel will destroy its bond in the concrete. 
 
 While the ordinary steel reinforcement will stand a great amount 
 of rough handling, yet it is best not to attempt to bend suddenly or other- 
 wise subject the steel to severe shocks, especially where high carbon steel 
 is being used, as sometimes the steel rods will be broken off. Accidents 
 of this kind are more likely to occur in cold weather. 
 
 Kinds of Steel Used for Reinforcing. Two grades of steel are used 
 in the manufacture of reinforcing rods or bars, generally known as "high 
 carbon" and "low carbon '*" steel. Such terms are probably mislead- 
 ing, as usually so-called "high carbon" steel is made by the Bessemer 
 process, and has an ultimate tensile strength of between 80,000 and 90,- 
 ooo pounds, while the steel commonly denominated as "low carbon" is 
 made by the open-hearth process, and has a tensile strength of from 60,000 
 to 70,000 pounds. There is also what is known as "re-rolled " steel, which 
 is a term applied to reinforcing bars which have been rolled from dis- 
 carded railroad rails, these being split up and the heads or bulbs of 
 the rails being rolled into reinforcing bars. The re-rolled material is gen- 
 erally about 10 cents per cwt. less costly than the newly manufactured 
 stock. 
 
 Square reinforcing bars arc frequently designated as "cold-twisted" 
 or "hot-twisted," these terms being applied to square twisted bars which 
 have been deformed by being twisted cold or hot respectively. 
 
 Selection of Kind of Steel. There is considerable diversity of opin- 
 ion among engineers as to the best kind of steel to use for reinforcing 
 
 [112]
 
 bars. The high carbon steel gives the greater tensile resistance and also 
 a greater elastic limit, but it is also less ductile and can be bent with less 
 surety than the low carbon steel. 
 
 In concrete dwellings the floor loads are never great, and the labor 
 is less likely to be skilled in the fabrication of the steel, so that it would 
 seem best to use steel with low tensile strength, and having the capability 
 of being bent cold at any angle without sign of fracture or the likelihood 
 of developing flaws. 
 
 Among the best reinforcements for dwellings are woven-wire fabrics. 
 In such materials the wires possess great tensile strength from the fact 
 of their having been drawn through dies. They are admirably adapted 
 to concrete construction because they can be bought in rolls of any length, 
 and being a fabric, there is no danger of misplacement of the reinforce- 
 ment. The lighter cross wires supply without any care or attention the 
 necessary shrinkage rod. 
 
 Price and Manner in which Steel Reinforcement is Sold. All steel 
 rods and bars are sold from what is known as a "base price." This base 
 price is for all rods or bars of %-inch in diameter or over. If the bars 
 are less in size than %-inch there is what is called a "size differential," 
 which is a fractional part of one cent a pound above the "base price." 
 The present differential for sizes is given in the following table: 
 
 | -inch Bar. Base. 
 H " $ -05 per cwt. 
 
 1 " " Tr . " 
 
 Y .IO 
 
 7 ' on " " 
 
 TtT - 2O 
 
 3 " ~~ " 
 
 -g - 2 
 
 5 - c <' '< 
 
 Ttf -35 
 
 t -50 ' 
 
 This schedule of size differentials is based on plain material. Usually 
 deformed bars cost $2.00 or more a ton extra, while either cold or hot 
 twisting adds about a tenth of a cent a pound, or $2.00 per ton, to the 
 
 8 [113]
 
 cos't of plain bars. In buying reinforcing steel it must also be under- 
 stood that there is what is known as a "shearing differential," and 
 also a "quantity differential"; the former is a cost of .05 of a cent 
 a pound on all bars less than 5 feet in length, while the latter is a 
 charge of .15 of a cent a pound for shipments from the mill of less 
 than two thousand pounds. 
 
 To all of these prices must be added the freight rate from the mill 
 to the point of delivery, and also the cost of hauling, before the actual 
 
 cost per pound delivered at 
 the site can be determined. 
 
 * 
 Use of Expanded Metal 
 
 and Woven Wire Fabrics. 
 Both expanded metal and 
 woven wire fabrics must be 
 handled intelligently in the 
 field. 
 
 Expanded metal is fur- 
 nished in gauges from 4 to 18, 
 in sheets 6, 8, and 12 feet in 
 length, and in widths of from 
 i to 6 feet. The usual way of 
 shipping expanded metal is in 
 flat bundles containing five or 
 six sheets wired together. 
 
 In using expanded metal 
 the long diagonal of the mesh 
 
 must always be parallel with the span of the slab, as otherwise the full 
 tensile strength of the material is not obtained. Expanded metal should 
 be lapped on the ends at least 6 inches, and such laps should occur over 
 points of support. 
 
 In using wire fabrics it is well to interlace them, or join them, at the 
 longitudinal edges. They may be wired together, or lock- woven wire 
 fabric may be secured along the edges, as illustrated in Fig. 74. Some- 
 
 [114] 
 
 Fig. 74. Attaching the edges of wire reinforce- 
 ment.
 
 times, however, merely a short piece of wire hooked at both ends is used 
 for securing the edges of the fabric. 
 
 Methods of Bending, Fabricating, Securing and Placing Reinforce- 
 ment. The most economical practice in working and fabricating steel 
 reinforcement is to make careful bills of material, and have the rein- 
 forcing rods or bars of the required length sent to the site of the operation, 
 and to do the bending and fabricating of the steel on the operation. 
 
 Fig- 75- Hand shear for cutting reinforcement. 
 
 There is always some cutting to do, and it will be found economical to 
 provide on the job a hand-shear, of the design shown in Fig. 75. With 
 this shear rods up to I inch square can be cut without much difficulty, 
 especially if the shear is securely mounted and an extension is made to 
 the lever by means of a piece of pipe. Where truss or other rods are to 
 be bent, diagrams should be made and the bars bent according to such 
 diagrams. 
 
 [115]
 
 There are a number of simple devices that can be arranged to facili- 
 tate the bending of rods or bars to the required angle. One of the 
 simplest of these consists of a strongly constructed table, made up of at 
 least 8" x 8" pieces securely braced and fastened, and arranged with a 
 cast or wrought iron plate which has secured to it an iron block and a 
 movable block which can be set in such a manner as to clamp the steel, 
 either by means of wedges or by clamping devices, as illustrated in Fig. 76. 
 
 Stirrups may be bent by machine and sent directly from the shop, 
 delivered in the required form, or else they may be bent in a heavy ma- 
 chinist's vise, such a vise being very useful when securely mounted, for 
 working steel reinforcement. 
 
 Fig. 76. Reinforcement bending table. 
 
 It is very seldom in house construction that large-sized reinforcing 
 rods would be used, and rods up to I inch in diameter can readily be bent 
 cold. Reinforcing rods larger than this are generally heated in a small 
 portable forge, and bent while hot. 
 
 For fastening reinforcing rods and bars together, and for securing 
 the stirrups, as well as for fastening cross-bars in wall reinforcement, and 
 slab rods, no better method has been found than that of wiring them 
 together. This, of course, can be done with pliers, but where there is 
 much to do the device illustrated in Fig. 76 has been used success- 
 fully, and with a resultant saving in time. This device is known as 
 
 [116]
 
 the "Curry Tyer," and the illustrations show clearly the method of 
 operating. By the use of this tool the wire is given a uniform number of 
 twists, and the rods or bars are secured much more positively than can 
 be done with an ordinary plier. It is also claimed that much time is 
 saved in cold weather by the use of this device, as with ordinary pliers 
 the work is necessarily slow from the fact that the workmen's hands 
 become numb. 
 
 Protection of Work. During the hardening period, concrete should 
 be protected from sun, wind, and frost. In house construction much of 
 this protection is afforded by the forms. 
 
 Intense heat of the sun in midsummer and high, dry winds tend to 
 evaporate water from the surface of green concrete and thus injure its 
 appearance. This is easily prevented by such means as enclosing and 
 shading the concrete with canvas. Freshly placed concrete, even though 
 protected, should be sprinkled with water as soon as this can be done 
 without pitting the surface. It may then be covered with sand, if expe- 
 dient, and thereafter wet as often as necessary. When possible, the ex- 
 posed surface of concrete should be safeguarded from sun and wind until 
 the concrete has attained an age of thirty-six hours. 
 
 Alternate freezing and thawing of concrete which has not had oppor- 
 tunity to set, seriously injure it. Consequently it has been customary, 
 and is still usual practice, to conclude all concrete work in early winter 
 as soon as there is danger of freezing. Within recent years, methods have 
 been adopted by means of which urgent concrete work is done even in 
 the dead of winter. Such results are secured either by lowering the 
 freezing-point of the concrete or by heating the materials entering into 
 its composition and by protecting the concrete after it has been placed. 
 
 Ordinary salt is the cheapest means of lowering the freezing-point of 
 concrete. It is common practice to dissolve in the mixing water a quan- 
 tity of salt equivalent to one per cent, (by weight) of the water used for 
 each degree of drop in temperature below the freezing-point, 32 Fahr. 
 However, not more than ten per cent, of salt should be used, as a greater 
 quantity may seriously injure the concrete. Consequently this preven- 
 
 [117]
 
 Fig- 77- ''Curry Tyer. " 
 
 A convenient method for wiring reinforcement 
 together. 
 
 [118]
 
 C ' 
 
 8 C 
 
 a 
 
 rt 
 
 o 
 
 rt
 
 u 
 
 a 
 o
 
 tive is not usable for temperatures lower than 22 Fahr. Calcium 
 chloride is also employed for the same purpose. These salts should not 
 be used in concrete when the appearance of the surface is a matter of 
 consideration, as they are likely to show in spots in the form of white 
 efflorescence. Also in reinforced construction there is probability of salt 
 causing the steel to corrode. 
 
 For concreting in cold weather more satisfactory results are procured 
 by heating the aggregate and the water and by keeping the concrete 
 warm until the cement has set. An elaborate and expensive plant is not 
 necessary. The aggregate may be heated by heaping it over steam pipes 
 or coils or by piling it over a make-shift furnace consisting of an old 
 boiler, a metal tube, a semi-circular form, or other simple devices. Like- 
 wise water for mixing may be heated in barrels or tanks by steam coils 
 or pipes or in tanks by a furnace. Frequently it is drawn directly from a 
 boiler used to generate steam for other purposes. 
 
 Often, even when the temperature of the air is above the freezing- 
 point, green concrete is injured by the use of frosty aggregate. Especi- 
 ally in early spring must sand, stone, and gravel be carefully inspected 
 to see that they contain no frost. In such case the materials must be 
 heated as in freezing w r eather. Sometimes a stream of water from the 
 well or hydrant is sufficiently warm to dispel the frost when played on the 
 aggregate. 
 
 After the concrete is placed in the forms, it is sometimes necessary 
 to prevent it from freezing. Often the forms supply adequate protection 
 for all except exposed surfaces, which should be covered with a tarpaulin, 
 boards, or building paper, freely supported a couple of inches above the 
 concrete. Sand and clean straw are also used. In severe weather simi- 
 lar additional protection is given the concrete in the forms and often a jet 
 of steam is introduced under the tarpaulin covering. For green concrete 
 floors and inside work, all window and door openings are tightly closed and 
 the interior heated by salamanders, sheet-iron stoves, or furnaces. 
 
 Concrete amply protected in freezing weather for forty-eight hours 
 after it has been placed is out of danger of frost. 
 
 Details of ornamentation must be carefully shielded until the entire 
 
 [121 ]
 
 structure is completed. Sharp corners can be protected from chipping and 
 spalling by placing wooden pieces as buffers on each side. Ornaments 
 cast as independent units must not be set until the latest time permissible. 
 Such ornaments, as well as those cast in place, should be crated and en- 
 closed with canvas to protect them from falling debris and sticky mortar. 
 
 To the exterior faces of tiles 
 paper is glued to prevent the 
 chance adhesion of cement mor- 
 tar and is later removed by the 
 application of water. Concrete 
 and tile ornaments can be 
 cleaned with a w r eak solution of 
 acids, as described under "Sur- 
 face Treatment" on page 129. 
 
 Treatment of Concrete Sur- 
 faces. As in the design of a 
 house, the treatment of a con- 
 crete surface is purely a matter 
 of individual taste. The only 
 thing uponwhich there is unanim- 
 ity of opinion is that a surface 
 should not be of the forbidding 
 color and texture sometimes 
 found in sidewalks a surface 
 perfectly smooth and cold and 
 leaden in hue. Some architects 
 have designed attractive houses 
 in which the walls were left 
 
 just as they appeared when the forms were removed. Others have 
 adopted this plan as to texture of surface, following with a wash in white 
 or color. In many cases walls are scrubbed when green, resulting in the 
 removal of the cement film and exposure of aggregates. The outer coat- 
 ing has sometimes been removed by sand-blasting, and again by bush- 
 
 Fig. 78. Tamper for getting mortar face.
 
 hammering. The nature of concrete is such that it affords great oppor- 
 tunity for the architect to exercise his ingenuity and taste in producing 
 satisfactory results. Various methods of treating surfaces are described 
 below. 
 
 Mortar Facings and Untreated Surfaces. Where utility is the prin- 
 cipal point of consideration, a surface sufficiently pleasing for the purpose 
 may be obtained by using a moderately wet mixture (well tamped) and 
 tightly and neatly built forms. 
 With such a concrete, a thin film 
 of mortar usually settles against 
 the sides of the forms. Frequently, 
 due to carelessness and the bridg- 
 ing of the coarser aggregates, 
 small pockets appear when the 
 forms are removed. Such an 
 objectionable feature is easily 
 avoided, either by spading or by 
 the use of facing boards (Figs. 78 
 and 79). 
 
 As the name suggests, spad- 
 ing is accomplished by means of a 
 straight garden spade or a special 
 tool of similiar shape, which is 
 forced down and worked to and fro 
 between the concrete and the form 
 
 in order to force back the coarser aggregate and to permit the flow of wet 
 mortar against the forms. In this manner a surface can be produced which 
 will be as smooth and regular as that of the forms. Since this kind of sur- 
 face treatment requires close supervision to see that the workmen do not 
 neglect to use the spading tool, there has been developed a more depend- 
 able method which secures the same effect by means of a device called a 
 facing board. The facing board consists of a short length, usually 5 
 feet, of y\-inch sheet-metal plate, 10 to 12 inches wide, with the top 3 
 
 [123] 
 
 Fig. 79. Facing board.
 
 inches bent to an outward flare. To the inner face of this plate, near each 
 end and at the middle, are riveted short vertical lengths of one-inch angle 
 irons and simple loop lifting handles. In operation the boards are set 
 ends abutting, with the angle spacers against the inner face of the outside 
 wall form. The ordinary concrete is placed between the inside wall form 
 and the facing board, while the one-inch space between the facing board 
 and the outer form is filled with a mushy wet mortar. The facing board 
 is then carefully worked up, almost out of the concrete, which is 
 again tamped lightly so as to insure a good bond between the ordinary 
 concrete and the facing mortar. This operation is repeated as the work 
 progresses. 
 
 By using the original method of a dry mix and tamping, there has 
 come into use a surface finish which in boldness, beauty, and execution 
 of detail has the charming appearance of free-hand sketches. Suitability 
 of design and careful construction of forms are primary requisites of this 
 remarkable treatment. By using a concrete fairly lean in Portland 
 cement and somewhat short in proportion of fine aggregate, and by tamp- 
 ing the concrete thoroughly, there is produced a surface which brings out 
 the sharpness of detail without displaying the minor irregularities and 
 imperfections frequently discernible in the ordinary mortar finish. 
 The surface obtained has all the charm, warmth, and softness of a coarse- 
 grained stone. Its face is rough and deeply pitted, consequently such 
 work is often mistaken for weathered stone. Exposure to the elements 
 for several years has brought forth no evidence of injury from frost and 
 no efflorescent discoloration of surfaces so treated (Fig. 80). 
 
 For such untreated surfaces the concrete is usually proportioned I 
 part cement to I ^ parts sand to 4^ parts crushed limestone screenings, 
 which must pass a J^-inch mesh and be retained on a 34-inch screen. 
 Such a small amount of water is used that, when the concrete is tamped 
 into place, no mortar flushes to the surface. 
 
 Abrased and Tooled Surfaces. Plain mortar-facing finishes, al- 
 though productive of a smooth surface, are not always satisfactory for 
 every design. To erase form marks and to produce uniform color, tex- 
 
 [ 124]
 
 ture and appearance, such surfaces are frequently ahrased or tooled. 
 Three forms of abrasion are in good practice brushing, scrubbing, and 
 sand-blasting. 
 
 Brushing. Simple character is given an ordinary mortar-faced sur- 
 face by brushing the green concrete with a stiff fiber or wire brush. 
 Special brushes of slitted sheet metal may be purchased on the market or 
 can be made by clamping together strips of wire cloth or ordinary fly 
 screen. For a plain brush finish it is advisable that the facing mortar be 
 
 Fig. 80. Concrete surface that corresponds to coarse-grained building stone. 
 
 free of coarse aggregate. The concrete should be brushed while it is still 
 green, but not so soon as to remove granular particles and to give the 
 surface a pitted appearance. The length of time between the placing of 
 the concrete and the removal of the forms for this finish is dependant 
 upon weather conditions and the amount of concrete placed. In summer 
 the forms should usually be taken down on the day following the placing: 
 in cooler weather greater time must be allowed. The older the concrete, 
 
 [ 125 1
 
 the more the labor required to produce the desired effect. Often the 
 forms must be planned and built in sections so as to permit early removal 
 and to facilitate this attractive treatment. (See Fig. 81.) 
 
 Scrubbing. Where the forms can not be removed quickly enough to 
 permit of brushing, similar effects are obtained by scrubbing the concrete. 
 Scrubbing is done by means of a concrete brick, soft limestone, or a car- 
 borundum stone. As soon as the forms can be removed, the concrete 
 is flushed with water and rubbed vigorously with a number 16 stone. 
 After the roughness and the cement skin have been removed, the lathered 
 surface is washed down, dusted with the i :2 dry mixture of cement and 
 sand, and the scrubbing is completed with a number 30 stone. When the 
 desired effect is obtained, the surplus cement grout is carefully washed 
 from the concrete face. This treatment produces a surface lighter in ap- 
 pearance than that of ordinary troweling, and, by filling the pores with 
 cement grouting, yields a surface at least as entirely waterproof as the 
 original. In case it is desired to treat concrete of considerable age, there 
 may be required the acid treatment described under "Exposed Selected 
 Aggregates," page 129. (See Fig. 82.) 
 
 Sand-Blasting. By means of an air compressor, a small gasoline 
 engine, and a hose with a nozzle, sand can be so forcibly driven against 
 concrete surface as to remove the cement film. Several days previous 
 to such treatment all imperfections of surface should be touched up with 
 mortar or removed by tooling as may be required. Otherwise in at- 
 tempting to get rid of these irregularities, the surface will be little im- 
 proved in appearance. If it is desired to preserve sharp lines of archi- 
 tectural detail, these should be protected by covering with heavy paper or 
 wooden strips. Like means should be used in preventing over-treatment 
 and in obtaining homogeneous appearance and invisible boundary lines 
 where two separately applied treatments on adjoining sections merge. 
 For blasting purposes a clean, sharp, hard silica sand or crushed quartz 
 is most effective. The size and shape of the nozzle are dependent upon 
 the power in the compressor, the range, and the size of the blasting aggre- 
 gate. For materials passing a number 8 and a number 12 screen, a \ 
 inch and a */g inch nozzle are respectively used. Likewise correct nozzle 
 
 [126]
 
 Fig. 81. 
 
 Fig. 82.
 
 pressure is also a variable quantity. Usually for concrete thirty days 
 old, a working pressure of 60 pounds is adequate. Older concrete may 
 require as much as 80 pounds pressure. The surface resulting from such 
 treatment also has the imprint of age and is very similiar to that pro- 
 duced by scrubbing. For work of considerable size this process is very 
 rapid and inexpensive. (See Fig. 83.) 
 
 Tooling. The lack of character in the ordinary mortar finish may 
 be got rid of by picking the surface with pointed tools. Such treatment 
 chips off the mortar on the outside of the structure, and by roughening 
 the surface changes it from a monotonous plane to a wall of lively and 
 pleasing texture. Ordinary hand-picks and stone-axes have been used 
 to a considerable extent, but the most satisfactory results have been ob- 
 tained by means of the hand and air-operated bush-hammer. 
 
 When the surface is to be bush-hammered, the concrete, during con- 
 struction, should be faced with materials suitable for rendering the 
 finished results desired. Sand mortars, when bush-hammered, yield a 
 surface of very uniform appearance. Where the surface contains coarse 
 aggregate, a greater variety in appearance is obtained. In order to pre- 
 vent scaling of mortar and dislodging of coarse aggregate, the concrete 
 should attain considerable age before being treated. Usually such treat- 
 ment is applied when the structure is one or two months old. In three 
 months the cement generally becomes as hard as the aggregate, and such 
 a surface, while requiring more labor, yields greater individuality. 
 
 The size and pointing of tools for hammering are matters of personal 
 opinion. Excellent work has been done with a 9-pound hammer with 32 
 points on one end and 25 on the other, and also with a hammer of the 
 same weight with 16 an<^ 25 points. The points are merely small pyra- 
 mids spaced about two-thirds of an inch. On large construction, pneu- 
 matic tools facilitate the work and cheapen the cost. Variation in ap- 
 pearance of the surface may be effected by the manner in which the stroke 
 is made. Perpendicular blows merely roughen, while glancing strokes 
 produce lineal markings. Tooling is a simple and effective means of 
 dispelling the coldness of plain concrete surfaces. (See Fig. 84.) 
 
 Displayed Selected Aggregates. For decorative effect and variety in 
 9 [ 129 1
 
 color and composition no treatment offers the architect a wider field 
 than that of exposed selected aggregates. A wealth of color is everywhere 
 at hand in the various marbles, burnt clays, gravels and granites, from 
 which he may make his selection of crushed aggregates (one or several) 
 and combine them on the mixing board in much the same manner as the 
 artist mixes his paints. Placed in the wall and treated so as to display 
 the beauty of the composition, very attractive and pleasing results are 
 
 Fig. 84. 
 
 obtained. On account of the great range of possibility in this field 
 definite instruction cannot be given as to the selection, size, grading and 
 proportioning of the various aggregates. Such details depend on the 
 subject and the treatment proposed. After these factors have been de- 
 termined upon, the matter reduces itself to the ordinary problem of con- 
 crete construction. If two or more coarse aggregates are used they 
 should be thoroughly blended before being mixed with the sand and 
 
 [130]
 
 A window in the residence of Albert Mover. South Orange, N. J. Tracy & Swarlout. Architects, N. Y 
 
 Fig. 85. -Wall showing beauty of displayed selected aggregates. Also a 
 striking example of the harmony of concrete and tiles or mosaics in 
 rather bold relief.
 
 cement to form a wet concrete. For such treatment a rich mixture, such 
 as a 1:2:4 or a I:2 ^ : 5 mix > is usually desirable. If it is advisable to 
 economize in the matter of selected aggregates, this may be accom- 
 plished by the use of facing boards (sec page 123) and by backing up 
 the outside layer of selected aggregates with concrete made of ordinary 
 materials. 
 
 Several methods are practised for removing the cement film and for 
 displaying the color of the concrete. The forms may be taken down while 
 the concrete is yet green and the face scrubbed or brushed. Likewise at 
 the proper age the surface may be tooled. After the film of cement has 
 been removed to brighten up the colors of the aggregate, the walls should 
 be treated to one or more applications of a wash composed of I part 
 commercial hydrochloric (muriatic) acid mixed with 5 to 10 parts of clear 
 water, with an interval of several minutes between the applications. 
 When the desired effects have been obtained, usually within half an hour, 
 the walls are scrubbed down with a fiber brush and are afterward flushed 
 with water to remove the acid thoroughly. Such treatment yields a 
 surface rough in appearance and pleasing in color. (See Fig. 85.) 
 
 If a smooth surface is preferable to the rough appearance, a terrazzo 
 effect may be obtained by dressing the surface with a carborundum stone, 
 as described under "Abrased and Tooled Surfaces." By such means 
 not only the outside cement film is removed, but the aggregates are also 
 ground down smooth and given a polish. Light, portable, power grinding 
 machines are now on the market which quickly and economically accom- 
 plish this work. The grinding and polishing bring out the beauty of each 
 particle of aggregate and enhance the effect by leaving it in a setting of 
 cement. 
 
 Colored Surfaces. For decorative effect it is often desirable to pro- 
 duce a concrete of a shade which will harmonize with some general color 
 scheme. This may be accomplished either by the use of mineral coloring 
 matter or by selected aggregates of such a color that, when made into 
 concrete, the desired results will be produced. 
 
 Artificial Colors. The use of artificial colors in concrete is a matter 
 which should be entered into only after careful and thorough experimen- 
 
 [133]
 
 tation or upon advice of persons familiar with all factors in the case. 
 Only mineral pigment should be used. For various reasons it is best to 
 use a color facing-mortar only and to apply it by means of facing boards. 
 Mix the colors dry with the cement, and in making concrete use this mix- 
 ture in the usual way. Sometimes the coloring matter is added to the 
 water. To produce even effects, it is essential to measure exactly and 
 carefully mix every ingredient, including the water. Likewise it should 
 be remembered that mortar when wet appears several shades darker 
 than when it is dried out. By mixing 5 pounds of coloring matter with 
 each bag of cement in an ordinary 1 :2 sand mortar, the following colors 
 will be approximately secured : brown roasted iron oxide ; buff to yellow 
 yellow ochre; blue ultramarine; gray to dark slate lampblack or 
 carbon black; black manganese oxide, eleven pounds per bag. By in- 
 creasing or decreasing the proportion of coloring matter, various hues 
 may be obtained. 
 
 Natural Colors. Through the use of many natural materials, such 
 as marbles, granites, sandstones, gravels, burnt clays, corals and sands, 
 results far preferable to artificial colors can be obtained. These materials 
 are crushed fine and are made into concrete in the customary manner. 
 The surface coloring is brought out by exactly the same method used for 
 displayed selected aggregates. For example, beautiful pinks may be 
 obtained with red marble dust ; a terrazzo effect may be obtained by in- 
 corporating with the red marble dust a few black and white marble chips; 
 or a slightly different effect secured by using black and white marble 
 screenings alone. Crushed granite or feldspar will give glitter to a surface, 
 and so on an infinite number of effects may be produced. 
 
 Mosaic Decoration. One of the most popular effects is obtained by 
 ornamenting a concrete surface with colored tiles. In working out orna- 
 mentation two general methods of treatment are possible: the simple 
 Roman plan of using tesserae, in which the design is formed from square 
 or nearly square pieces, or the more modern way of cutting the clay into 
 units of sundry shapes to conform to the potter's process and to delineate 
 the design. This latter method is comparable to that used in stained- 
 
 !i34l

 
 glass windows. The cement joints correspond to the lead in the stained 
 glass. Either plan is practicable. 
 
 Several methods of setting tiles are in use. In general, careful at- 
 tention must be given to the correct lay-out of the design and to a means 
 of fixing it securely until held permanently by the concrete. In walks 
 and floors this is simply a matter of exact location. For walls and ceilings 
 the entire figure is often molded complete or in sections in a concrete slab 
 of the same texture as that of the wall proper and later set in place. With 
 this and similiar schemes, a piece of heavy paper or felt is placed between 
 the form and the face of the tiles to prevent them from being stained by 
 liquid cement. Special adhesive substances can be bought or made by 
 means of which the tiling can be glued in exact location on the forms and 
 securely held there until backed up and fixed by the concrete. (See Fig. 
 86.) Later the application of water dissolves the glue and leaves the 
 decorations permanently in place. Likewise space may be left for insert- 
 ing the decorations later by lightly nailing to the inside of the form blocks 
 of wood cut to the shape of the units composing the design. When the 
 forms are removed, the concrete retains the wooden block, which should 
 be left in position until the concrete surface has been given the desired 
 finish. The block can then be removed and the ornament set in place 
 with good cement mortar. 
 
 136
 
 Chapter V 
 
 Calculations for Determining the Strength and Design of 
 Reinforced Concrete in House Construction
 
 5 
 
 "C 
 BJ 
 
 be
 
 Chapter V 
 
 Calculations for Determining the Strength and Design of 
 Reinforced Concrete in House Construction 
 
 Principles of Reinforced Concrete. Concrete, which usually consists of 
 broken stone embedded in or cemented together with a mortar con- 
 sisting of Portland cement mixed with gravel or sand, partakes of the 
 nature of an artificial stone, and becomes monolithic upon the harden- 
 ing of the cement. The broken stone is used as a filling material to 
 save the cost of the more expensive cement, and is known as the 
 "aggregate," while the cementing material is usually designated as the 
 "matrix." 
 
 Concrete has great compressive resistance, but is deficient in tensile 
 strength. The great discrepancy between the compressive resistance 
 and tensile strength of concrete is as the ratio of I to 10 that is, plain 
 concrete of the usual mixture used in construction work has for its 
 compressive strength 10 times its strength under tension. When sub- 
 jected to tensile stresses it is still further weakened and made unreliable 
 by the possibility of cracks or flaws occurring on account of the shrinkage 
 of the material. These defects, which sometimes are due to the pouring 
 and setting of the concrete, would not decrease the compressive strength, 
 from the fact that should such cracks or flaws occur they would, under 
 a direct compressive stress, be brought together, and the two blocks would 
 have, in spite of the defect, a perfect bearing one upon the other. 
 
 The Purpose of Steel Reinforcement in Concrete. Any beam 
 which is supported at its ends, and sustains weight either uniformly dis- 
 tributed or concentrated, is subjected to bending, and transverse stresses 
 
 [ i39l
 
 are created. The transverse stresses in a beam consist of compressive 
 stresses and tensile stresses. In the upper portion of the section of a 
 simple beam, as shown in Fig. 87, the fibers are in compression, while in 
 the lower portion the material is subjected to tension. An imaginary 
 plane separating these two directly opposite kinds of stresses is always 
 denominated the "neutral axis." 
 
 Since concrete has approximately ten times as much compressive 
 resistance as tensile strength, it is quite evident that if a beam was made 
 of plain concrete, the full value of the material in compression could 
 never be developed, from the fact that it has such a low value in tension 
 
 Fig. 87. A concrete beam without reinforcement and stressed beyond elastic 
 limit would fail as shown. 
 
 in that portion of the section below the neutral axis. In order to develop 
 the full compressive resistance of concrete in the section of a beam above 
 the neutral axis steel rods or bars are embedded in the concrete near the 
 lower edge or soffit of the beam. Such a beam is said to be "reinforced," 
 and is economically designed when sufficient steel is embedded in the 
 concrete to develop the full compressive resistance of the concrete in the 
 beam section above the neutral axis. 
 
 Steel reinforcement is also used in the construction of columns or 
 posts of concrete to prevent these members from buckling or bending 
 on account of their slender proportions, for all columns over 10 diameters 
 are liable to transverse stresses corresponding with those created in the 
 
 [ 140 ]
 
 beam. These stresses are developed by inequalities in the strength in 
 the section or by eccentric loading. The steel reinforcing rods in a 
 column also prevent the column from shearing along an oblique line, as 
 the type of failure indicated in Fig. 88 is quite usual when reinforced 
 concrete columns are tested to failure. 
 
 The Use of Shrinkage Rods and Bars. Another reason for using 
 steel embedded in concrete is for the purpose of tying the mass of 
 concrete together so as to prevent any cracking from setting. Many 
 materials are subjected to a reduction in sixe in 
 setting or hardening, and such changes in the 
 mass are apt, where other parts are held, to pro- 
 duce cracks. By binding together the mass of 
 concrete, whether it be a column or floor slab, 
 with steel rods at intervals, such shrinkage cracks 
 are prevented. 
 
 The rods or bars placed in the concrete for 
 this purpose are usually designated as "shrinkage 
 rods." It is customary to introduce shrinkage 
 
 rods in floor slabs and walls. 
 
 L ^ 
 
 l\emforcinf Kbcfs 
 
 Fig. 88. Line of failure 
 in a concrete column 
 when stressed beyond 
 elastic limit. 
 
 Secondary Reinforcement. There is also used 
 in both columns and beams what is designated 
 as "secondary reinforcement. " In beams, vertical 
 or oblique stirrups, as illustrated in Fig. 89, are 
 
 usually introduced. These stirrups are primarily used to transmit the 
 stresses from the main reinforcing rods or bars to the concrete in the 
 upper section of the beam. They also prevent the beam from cracking 
 along oblique lines, as illustrated in the figure. Such cracks are called 
 "diagonal tension cracks." 
 
 It will be noticed from the illustration that these stirrups cross 
 such lines of defects, and prevent them by giving additional tensile 
 strength at right angles to the plane of these faults. In columns, the 
 vertical rods, as illustrated in Fig. 90, are tied at intervals with light 
 
 [141]
 
 iron, looped wires, or other means, in much the same manner as the floor 
 systems tie in the columns of a building. The purpose of the secondary 
 
 Fig. 89. Arrangement of reinforcement in beams. 
 
 reinforcement in columns is to prevent the long longitudinal rods or bars 
 from buckling under stress, and splitting or spalling the concrete of the 
 column, as well as to tie together the mass of con- 
 crete in the column. 
 
 
 
 \ 
 
 i 
 
 \ 
 
 
 
 
 ^t 
 
 % 
 
 w-?V ;I 
 ii teraSy 
 
 U ^f^S: 
 
 Fig. 90. Position of 
 reinforcement in 
 columns. 
 
 Arrangement of Primary and Secondary Rein- 
 forcement. There is illustrated in Fig. 91 a typical 
 system of slab, beam, girder, and column construction 
 of reinforced concrete. The rods or bars marked "a" 
 in the figure are the main reinforcing rods, and it will 
 be noticed that several of these rods or bars arc bent 
 up at the ends, and extend to the top of the beam 
 near the points of support. This is done in order 
 that there shall be additional resistance to longitu- 
 dinal shear, and also to prevent the diagonal tension 
 cracks near the abutments. Another reason for 
 [142]
 
 bending some of the rods up in this manner is to provide tensile resist- 
 ance at the top of the beam near the point of support, so as to resist 
 what is called the "negative moment." 
 
 The negative moment, or contraflexture, is simply the changing of 
 the stresses to opposite kinds where the ends of a beam are fixed, or held 
 rigidly. When these bent-up rods lap over the points of support they 
 tie the construction together, and give the beam the advantage of con- 
 tinuity. This reduces the bending moment considerably, although it is 
 seldom taken into account in the design of concrete beams and girders. 
 
 Fig. 91. Arrangement of primary and secondary reinforcement. 
 
 At b b in the figure is shown the "secondary reinforcement." This 
 secondary reinforcement consists of stirrups usually of light bar iron, 
 i/g" x i", or l /i" or 3/8 " round, bent in the form of U-shaped stirrups, 
 which interlace with the main reinforcing bars and project into the upper 
 part of the beam. When there is a slab, monolithic with the beam, 
 these stirrups are carried to the upper part of the slab. The number of 
 stirrups required and the proper spacing is given on page 187. 
 
 The rods or bars indicated at c c are known as the "slab rods," 
 
 [i43l
 
 and extend at right angles to the beams, thus reinforcing the concrete 
 slab. These bars are usually from }/' to Y^' square or round, being 
 spaced from 3" to 8" on centers, depending upon the amount of resistance 
 necessary for the particular spans and loads. 
 
 It is usual in all slab reinforcement to provide shrinkage rods or 
 bars, which are shown in the illustration at d d. These rods are generally 
 very light bars, about }/" square or round, and it is the usual practice 
 to place them about 24" center to center. 
 
 Besides the slab reinforcement and shrinkage bars, it is considered 
 good practice to provide what is known as "shear bars" over all main 
 girders "girders" being understood as the concrete supporting members 
 which sustain the ends of the beams. These shear rods are intended to 
 increase the resistance of the slab over the top of the girder, and are 
 quite frequently made of the same-sized bars as the slab reinforcement. 
 They are generally 5' in length, and spaced 12" center to center. 
 
 "Lap-rods" or "tie-bars" are placed over the junction of all beams 
 and girders where the main reinforcing rods do not lap. Such tie-rods 
 are made, as a rule, %" square or round, and generally about 5' in length. 
 Sometimes two such rods are placed over the junction of girders, and one 
 rod over the junction of beams. These rods are indicated in the illus- 
 tration at e. 
 
 The longitudinal rods in columns are not, as a rule, decided upon 
 with regard to their number and area by any fixed formula. The general 
 practice is to put in enough steel to equal in area I to I ^2% of the sec- 
 tional area of the concrete. Longitudinal column rods are shown in the 
 figure at/, and it is never good practice to make these rods less than J^" 
 in diameter. It is customary to extend these rods above the floor con- 
 struction, so that the rods of superimposed columns may lap with them, 
 the lap usually being made about 2' 6" in length. 
 
 The longitudinal rods of columns are always tied together at inter- 
 vals with either J<" round ties, or else held in position with wire ties, 
 or ties of bar iron punched so as to allow the rods to pass through. The 
 practice is to make these ties a distance apart equal to the diameter of 
 the column, never, however, exceeding an 18" pitch or spacing. 
 
 [144]
 
 10
 
 Strength of Concrete. The concrete used in building construc- 
 tion is usually composed of a 1-2-4 mixture that is, one part 
 Portland cement, two parts sand or fine gravel, and four parts broken 
 stone. Sometimes broken slag or clean boiler cinders are substituted 
 for the broken stone, in which case the concrete is known as "slag" or 
 "cinder" concrete, respectively. It is poor practice, however, to use 
 either of these two for reinforced concrete for building construction, 
 although cinder concrete is sometimes used for floor slabs supported on 
 steel beams. 
 
 The contractor is not particularly interested in the ultimate strength 
 of concrete, but he is interested in the allowable unit working stresses. 
 These allowable unit stresses are different in the several cities, and are 
 fixed by the building laws. Outside of the jurisdiction of the cities 
 the judgment of the designer is the governing factor in deciding upon 
 these values. 
 
 In all instances where allowable unit stresses are given, it is under- 
 stood to mean the stress in pounds per square inch, which is allowed as 
 a basis in figuring the safe working strength of the material! The 
 following table gives the allowable compressive, shear, tensile and bond 
 stresses for concrete and steel used by the best conservative practice in 
 the design of reinforced concrete structures: 
 
 TABLE 4. ALLOWABLE WORKING STRESSES FOR CONCRETE WHEN 
 
 REINFORCED 
 (STRESSES ARE IN POUNDS PER SQUARE INCH) 
 
 Mixture 
 1-2-4 
 
 Compression 
 under 
 Transverse 
 Stress 
 
 Compression 
 under 
 Direct 
 Stress 
 
 Shearing 
 Stress 
 
 Bond or 
 Adhesive 
 Stress 
 
 Stone Concrete 
 
 600 
 
 500 
 
 75 
 
 50 
 
 Slag Concrete 
 
 400 
 
 300 
 
 50 
 
 40 
 
 Cinder Concrete 
 
 250 
 
 150 
 
 25 
 
 15 
 
 The most important values in the table are the direct compressive 
 values of reinforced concrete, used in figuring the strength of columns, 
 
 [147]
 
 and also the unit compressive strength of concrete allowable in figuring 
 the strength of beams and girders. The values of shear are of some use 
 in figuring the shearing resistance of beams at their points of support. 
 It is necessary sometimes to determine the adhesive strength of a steel 
 bar or rod embedded in the concrete, and here the bonding stress or the 
 grip of the concrete upon the steel is important. 
 
 These values will be used in some of the examples in design given 
 in the following pages. 
 
 Strength of Beams and Girders. There are shown in Fig. 92 
 at (a) and (6), diagrammatical figures which show the distribution of 
 the stresses in reinforced concrete beams, based on usual assumptions 
 
 employed by engineers in deter- 
 mining their strength. These 
 _ assumptions are as follows : 
 
 / Concrete than* Vrevl^l^A^ First: That the steel takes 
 
 all of the tensile stress, while the 
 
 /^B| Fbsit/on of Jr'ee/. -+M 
 
 concrete takes all of the com- 
 pressive stress. 
 
 Second: That the relative 
 
 ofJfosxy m Concrete 
 
 C*) 
 
 Fig. 92. Diagram showing distribution of 
 stresses in reinforced concrete beam. 
 
 amounts of the stresses upon 
 
 the steel and concrete are in direct proportion to their ratio of moduli 
 of elasticity. 
 
 Third : That the total compressive resistance of the concrete above 
 the neutral axis must equal the total tensile resistance of the steel. 
 
 Fourth: That the stresses on the concrete vary directly from zero 
 at the neutral axis, to maximum at the extreme fiber; thus the variation 
 of stress in the section above the neutral axis is indicated by a triangle. 
 
 From the above it will be seen that reinforced concrete beams, 
 being a composite material, differ from beam sections of a single material, 
 for in the latter the neutral axis passes through the center of gravity of 
 the section, whereas in reinforced concrete beams the neutral axis is 
 constantly shifted by changes of the relative percentage of the steel and 
 concrete in the section, and raises or lowers in order to adjust the direct 
 
 [148]
 
 stresses above and below the neutral axis to comply with their differences 
 in their relative stresses and strains. The one important thing, there- 
 fore, to determine before the strength of a beam section can be ascer- 
 tained, is the position of the neutral axis. 
 
 Formula for Determining the Position of the Neutral Axis. The 
 location of the neutral axis in any reinforced concrete beam varies 
 with the relative percentage of steel, with the quantity of the con- 
 crete, and with the quality of the concrete. 
 
 The formula for determining the position of the neutral axis is 
 applicable to both rectangular beams and beams of T-section. This is 
 true for all practical purposes because in beams of T-section the neutral axis 
 lies so close to the bottom of the slab that the T-section may be considered 
 as a rectangular beam of a width equal to the available extent of the slab 
 in compression. This will be explained in conjunction with T-sections. 
 
 The formula for determining the distance k, or the percentage of the 
 depth which the neutral axis is below the top of the beam, is as follows: 
 
 k = \/(pn) 2 +2 pn pn 
 
 The values in this formula are best understood by referring to Fig. 
 93 and the following notation : 
 
 k = Ratio of the depth of the neutral axis from the top of the beam 
 to the effective depth d. 
 
 p = Ratio of the area of the steel to the area of the concrete in the 
 portion of the beam above the center of action of the steel. This 
 is true because the 2 or 3 inches of concrete below the steel is 
 considered merely as fireproofing. 
 
 n= Ratio of the moduli of elasticity of the steel to the moduli of 
 elasticity of the concrete. In the best practice this value for 
 stone concrete is 12, and the values for slag and cinder con- 
 crete are, respectively, 15 and 30, though sometimes different 
 values for these are used. 
 
 The formula given above is the basic formula for all reinforced 
 concrete design, and as illustrating its application the following example 
 is interesting: 
 
 [ 149 1
 
 Example: At what percentage of the distance from the top to the 
 center of action of the steel reinforcement is the neutral 
 axis located, providing the beam is of rectangular section 
 and is reinforced with T 6 7 of one per cent, or .006 of 
 steel? The ratio of the moduli of elasticity of the two 
 materials is I to 12. 
 
 Solution: Referring to the formula k = V / (pn) 2 + 2 pnpn the values 
 of p and n are respectively .006 and 12; then, by substi- 
 tution the value of 
 
 k=V(\oo6 X i2) 2 +2 X .006 X i2-.oo6 X 12 
 or, k= V.OO5I84+.I44 .072 =.314. Answer. 
 
 It is customary not to work out these formulas every time the 
 distance k is desired for any particular percentage of steel reinforce- 
 ment, but to refer to a table giving these 
 values. Such a table is given on page 
 
 a/ &f 
 
 Fig. 93- 
 
 Determination of the Distance Jd. 
 The necessity for obtaining the distance 
 from the top of a reinforced concrete 
 beam to the neutral axis is to locate 
 the center of gravity of the compressive 
 stresses in the concrete above the neutral 
 axis. 
 
 Referring to Fig. 93, it will be seen that the stress in the concrete 
 varies from zero at the neutral axis to maximum at the extreme upper 
 edge of the beam. As this variation is uniform under working stresses, 
 the variation in the compressive stresses can be represented as a triangle. 
 The center of action of the compressive stresses is, therefore, at the 
 center of gravity of this triangle, and is consequently located at one- 
 third of the altitude of the triangle from the base, or is equal to , 
 when kd is the distance of the neutral axis from the top of the beam, and 
 the lever arm with which the concrete and steel reacts can be designated 
 as jd, and can be determined directly, when the neutral axis has been 
 located. The value j varies, of course, with the variation in the value of 
 
 [150]
 
 k. The value of k is determined by the ratio of the steel reinforcement 
 and the ratios of the moduli of elasticity. Consequently, a table which 
 gives the value of j, referring to Fig. 93, in ratio of the distance d, 
 is valuable, as it gives the lever arm which determines the resisting 
 moment of the steel reinforcing rods or bars used in the beam. 
 
 The values of j for different ratios of steel reinforcement and for 
 different values of n, or the ratios of the moduli of elasticity of the 
 steel and concrete, are given in the following table: 
 
 TABLE 5 
 
 Values 
 ofp 
 
 N = io 
 Values of k and j 
 
 Values of k and j Values of k and j 
 
 .001 
 
 k = .i32 
 
 J=-956 
 
 k = .i43 
 
 j=.952 k = .is8 
 
 i=-947 
 
 .002 
 
 k = .i8l 
 
 j=.940 
 
 k = .i96 
 
 j = -935 
 
 k = .2i5 
 
 j=. 9 28 
 
 .003 
 
 k = .2i7 
 
 j=. 9 2 7 k = .236 
 
 j=.922 
 
 k = .2 5 8 
 
 j = .9H 
 
 .004 
 
 k = .246 
 
 j=.9i8 k = .266 
 
 j=.9ii 
 
 k = .29i 
 
 = .903 
 
 .005 
 
 k = .27O 
 
 j = .9io k = .29i 
 
 j=-903 
 
 k = .3i9 
 
 = .894 
 
 .006 
 
 k = .2g2 
 
 j=. 9 o3 k = .3i4 
 
 j = .8 9 6 
 
 k = -343 
 
 = 885 
 
 .007 
 
 k = .3ii 
 
 j=.8g6 
 
 k = -334 
 
 j=.88 9 
 
 k = . 3 66 
 
 = .878 
 
 .008 
 
 k = . 3 28 
 
 j=.8 9 i k = . 3 52 
 
 j=.88 3 
 
 k = . 3 8 4 
 
 = .872 
 
 .009 k = .344 
 
 j=.88 5 
 
 k = . 3 70 
 
 J=-877 
 
 k = .4Oi 
 
 j = .866 
 
 .010 k = .358 
 
 j=.88l 
 
 k = . 3 8 4 
 
 j=.8 7 2 
 
 k = . 4 i7 
 
 j=.86i 
 
 .012 
 
 k = . 3 8 4 
 
 j=.8 7 2 
 
 k = 4ii 
 
 j=.86 3 
 
 k = .444 
 
 J=-852 
 
 .014 
 
 k = . 4 o7 
 
 j=.864 
 
 k = -435 
 
 J=-855 
 
 k = .470 
 
 J=-843 
 
 .016 
 
 k = .428 
 
 J=-857 
 
 k = . 45 6 
 
 j=.8 4 8 
 
 k = 492 
 
 j=.8 3 6 
 
 .018 
 
 k = .446 
 
 j=-85i 
 
 k = . 47 6 
 
 j=.8 4 i 
 
 k = -5i3 
 
 j=.82 9 
 
 .020 
 
 k = .463 
 
 j = .844 k = .493 
 
 j = .8 3 6 k = . 53 o 
 
 J=-823 
 
 030 
 
 k = -53i 
 
 j = .823 k = .56i 
 
 j=.8i3 k = .6oo 
 
 j =.8oo 
 
 .040 
 
 k = .58o 
 
 j=.8o7 
 
 k = .6io 
 
 j=. 79 6 k = .6so 
 
 j=. 7 8 4 
 
 .050 
 
 k = .6i8 
 
 J=-794 
 
 k = .650 
 
 j=. 7 83 k = .686 
 
 j=-77i 
 
 Resisting Moment of Rectangular Beams (Considering the Steel). 
 In order to determine the resisting moment of a reinforced con- 
 crete beam it is only necessary to find what percentage the area of the 
 steel bears to the area of the concrete in the beam section, and select 
 from the above, Table 5, the value of j. The product of the value j, 
 the distance from the center of action of the steel to the top of the beam 
 (d), and the total safe working stress of the steel (a s), will give the resist- 
 ing moment of the beam. This can best be expressed by the formula 
 
 MI =j d a s 
 
 [151]
 
 In this formula 
 
 MI = the resisting moment of the beam in inch-pounds; 
 
 d =the distance from the center of action of steel reinforcement 
 
 to the top of the beam ; 
 
 a = the total area of the steel reinforcing rods, and 
 s =the safe unit tensile stress of the steel, which is generally taken 
 
 at 16,000 pounds. 
 
 In determining the ratio of the steel, in order to obtain the 
 corresponding value j in the table, the area of the concrete is always 
 
 considered as the width of the 
 beam multiplied by the dis- 
 tance from the top of the 
 beam to the center of action 
 of the steel, as the concrete 
 below the reinforcing rods or 
 bars is not a part of the theo- 
 retical beam, and acts only as 
 fireproofing for the steel rein- 
 forcing rods. 
 
 Example: Determine the re- 
 sisting moment 
 of the rectangu- 
 lar reinforced 
 concrete beam 
 Fig. 94. illustrated in Fig. 
 
 94- 
 
 Solution: The total area of the concrete from the center of action 
 of the steel to the top edge is 10" x 20" = 200 square 
 inches. As the reinforcing rods or bars are %" square, 
 the sectional area of one rod is .5625, and 2 rods or bars 
 will have a sectional area of 1.125; hence the ratio of 
 steel reinforcement in the section of the beam is 
 1.125-^ 200 =.0056 
 
 Assume that N=I2. 
 
 From Table 5 it will be seen that the ratio of the lever 
 [152]
 
 Detail of residence of Mrs. Gaston Daus, Ocean City, N. J. Grant M. Simon, Architect, Phila, 
 
 Porch return constructed of solid concrete, which means elimination of 
 cost for up-keep. Note untreated surface of house walls.
 
 ft, 
 
 - "O 
 
 E S 
 
 o c 
 - o 
 2 o 
 
 -= c
 
 arm, or j, for the ratio of steel reinforcement, or .006, is 
 .896, so that in inches the lever arm with which the steel 
 acts about the center of compression is 
 
 20 X .896 = 17.9 inches = jd. 
 
 The resisting moment of the reinforced concrete beam can be found 
 by substitution in the formula Mi = j d a s, so that 
 
 Mi = l7.9 X 1.125 X 16,000 = 322,200 inch-pounds. 
 
 Resisting Moment of a Rectangular Beam Section, Considering 
 the Concrete. In reinforced concrete beams of rectangular section 
 the strength of the two materials must be considered that is, the 
 resisting moment of the steel reinforcement must be found, and if there 
 is any doubt about the concrete in compression when stressed to its 
 maximum working stress at the extreme fiber, then its resistance must 
 be determined as well, and the least resisting moment considered as the 
 one limiting the strength of the beam section. 
 
 In all reinforced concrete beams when the percentage of steel is 
 such that the concrete and steel are of equal resistance, and both are 
 fully stressed to their allowable unit working stresses when the beam 
 section is developing its maximum allowable resistance, the beam is 
 said to be reinforced with a critical percentage of steel. This critical 
 percentage of steel is always the same for fixed unit stresses and moduli 
 of elasticity, so that if the steel reinforcement is below the critical per- 
 centage, the strength of the concrete need not be questioned, and the 
 resistance of the steel alone is considered. 
 
 The resisting moment of the concrete above the neutral axis may 
 be found as simply in a rectangular beam as the resisting moment of the 
 steel reinforcement, when once the neutral axis has been determined for 
 the percentage of steel used as reinforcement. 
 
 In a rectangular reinforced concrete beam the intensity of stress at 
 the neutral axis is zero, while at the extreme fiber it may be as high as the 
 maximum allowable compressive stress for concrete in compression when 
 subjected to transverse stress. The average is therefore one-half of the 
 
 ti55]
 
 maximum stress, so that if the maximum unit compressive strength of 
 the concrete is taken at 600 pounds, the average stress will be 600 + 2 = 300 
 pounds per square inch. In order therefore to determine the resistance 
 of the concrete above the neutral axis all that is necessary to do is to 
 multiply the area of the cross-section of the beam above the neutral axis 
 by the average unit compressive resistance of the concrete, the product, 
 in turn, being multiplied by the distance from the center of action of the 
 steel reinforcement to the center of action of the compressive area of the 
 concrete. 
 
 As previously stated, the location of the center of the compressive 
 area is one-third of the distance from the top of the beam to the neutral 
 axis, or , and the lever arm with which the concrete acts about the 
 steel reinforcement is j d, so that the resisting moment of the beam 
 section, with regard to the compressive resistance of the concrete, may 
 be found by the following formula: 
 
 M c = kj d 2 bc 
 
 2 
 
 in which 
 
 M c = the resisting moment with regard to the compressive re- 
 sistance of the concrete. 
 
 k = ratio of the distance from the top of the beam to the 
 neutral axis to the distance d. 
 
 j = ratio of the distance between the center of compression 
 in the concrete and the center of action of the steel, to the 
 distance d. 
 
 d =the distance from the center of action of the steel to the 
 top of the beam. 
 
 b =the width of the beam. 
 
 c =the maximum unit allowable compressive resistance of 
 the concrete. 
 
 Example: Determine the resisting moment of the reinforced con- 
 crete beam shown in Fig. 94, considering the concrete. 
 
 Solution: As found in the previous example, the ratio j = .896; 
 and from Fig. 94 = d = 2o"; b also is determined from 
 the figure as being 10"; while k = .3i4, as also deter- 
 mined from Table 5. In this instance the allowable 
 
 [156]
 
 compressive resistance of the concrete will be taken as 
 600 Ibs. Therefore, by substitution in the formula 
 
 M c = 
 
 .314 X .896 X 20 X 20 X 10 X 600 
 
 = 337,612 inch-pounds. 
 
 Beams of T-section. Where reinforced concrete beams or girders 
 support and are monolithic with a concrete floor slab, in analyzing 
 the strength of the beam or girder it is considered as a T-section. The 
 form of the beam section thus considered is shown in Fig. 95, and it will 
 be seen that by the adoption of this section the available amount of the 
 concrete in compression is greatly increased over that which would exist 
 in a simple rectangular beam. 
 
 In the analysis of a beam of T-section to determine its strength or 
 
 Fig. 95. Increased area over which compressive stress acts when beam and 
 slab are molded as a monolith. 
 
 resisting moment, it is a question as to what width of slab can be consid- 
 ered as acting homogeneously with the beam. A conservative rule is 
 that the width of the T-section shall not be over 20 times the thickness 
 of the slab. For instance, if the slab is 4" in thickness, the width of the 
 slab incorporated in the T-section would be 80 inches, provided, of course, 
 that this distance does not extend the slab past the middle of the distance 
 between the two beams. Where the beams are closer together than 20 
 times the thickness of the slab, the flange of the T-section is considered 
 to extend a distance on each side of the beam equal to one-half the dis- 
 tance to the next beam. 
 
 In the recently prepared Building Laws of the city of New York 
 
 [i57l
 
 the width of the slab to be incorporated with the beam in forming the 
 T-section is limited to one-sixth the span of the beam, but is not to be 
 greater than six times the thickness of the slab on either side of the beam. 
 The important factor to determine in the analysis of a beam of 
 T-section is, as with rectangular beams, the location of the neutral axis; 
 but the extreme strength of a reinforced concrete beam of T-section can 
 be very simply found by making an assumption, which is seldom much 
 in error, and is consequently sufficiently safe for practical purposes, 
 especially when it is realized that because of the assumptions made in 
 calculating the bending moments, reinforced concrete construction has 
 
 an actual factor of safety far 
 above that used. 
 
 Approximate Determination 
 of the Strength of the T-Sec- 
 tion. To determine approxi- 
 mately the resisting moment of 
 a reinforced concrete beam of 
 T-section, reference is made to 
 Fig. 96. As previously stated, 
 
 the reinforced concrete beam, being composed of two materials of 
 different strength, it is necessary to find the resistance of each under 
 the stresses due to the load, and to limit the load on the beam so that 
 the allowable strength of the weaker material will not be exceeded. 
 Nearly always in reinforced concrete beams of T-section and it would 
 be especially so in house construction there is ample concrete in compres- 
 sion, and the steel is the limiting factor. Another assumption that is 
 to be made in determining the approximate strength of T-sections is 
 the location of the center of action of compression in the slab, and one 
 which is, on an average, nearly always safe to make, is to assume the 
 center of action to be at the center of the slab. When this assumption is 
 made, the resisting moment of the steel may be expressed by the follow- 
 ing formula: 
 
 M s = a s D 
 [158] 
 
 
 
 
 */ 
 
 
 ~ 
 
 
 '-'.>"./*' 
 
 'i >.'* 
 
 
 
 v.'iV ."' * '*-) 
 
 i 
 
 2 
 
 " 
 
 
 % 
 
 1 
 
 1 
 
 
 _ 
 
 Fig. 96.
 
 In this formula 
 
 M s = the resisting moment of the beam section in inch-pounds, 
 considering the steel. 
 
 a = the total area of the steel reinforcement. 
 
 s =the safe unit fiber stress to which the steel is to be subjected. 
 
 D =the distance from the center of action of the steel reinforce- 
 ment to the center of the slab. 
 
 Example: Assume that the beam section shown in Fig. 96 is rein- 
 forced with four i" square twisted bars, and that a safe 
 unit stress on the steel of 16,000 pounds is to be considered 
 as the working stress. What will be the resisting moment, 
 and what load, including weight of beam and slab, will the 
 beam carry providing it has a span of 20 feet? 
 
 Solution : By substitution in the above formula 
 
 M s = 4 X 16,000 X 20 = 1,280,000 inch-pounds. 
 
 If this is the resisting moment in inch-pounds, and the 
 bending moment of any simple beam uniformly loaded is 
 equal to M = I }/ W L, where W is the total load per 
 square foot and L is the span in feet, the total load 
 that the beam will support can readily be found by the 
 formula 
 
 Ms 1,280,000 
 
 W= T ,r or W= T i v , n =42,666 pounds. Answer. 
 
 I J 1 . 1 2 /N ^O 
 
 To Determine Whether there is Sufficient Concrete in Compression, 
 Approximately. In conservative practice in the design of reinforced 
 concrete work it is usual to stress the extreme fiber, or upper 
 edge of the section in compression under transverse stress, to a 
 working stress of 600 pounds. It is also understood that the stress in 
 the concrete at the neutral axis is zero. In determining the approximate 
 resistance of a T-section considering the steel reinforcement, as explained 
 on page 158, the position of the center of action of the concrete in com- 
 pression was assumed as at the center of the slab. This assumption 
 makes the neutral axis pass through the web of the beam at a distance 
 below the slab equal to one-half the thickness of the slab. The variation 
 of the compressive stresses in the concrete is uniform from the neutral 
 
 [i59l
 
 axis to the extreme upper edge of the slab, so that the safe allowable 
 unit stress at the bottom of the slab would be one-third of the maximum 
 allowable, or 200 pounds, and the average allowable stress in the slab 
 section would be equal to 
 
 600+200 
 , or 400 pounds. 
 
 One of the first principles of engineering is that, for every force 
 acting in one direction in a body in equilibrium there must be a corre- 
 sponding and equal force acting in the opposite direction; therefore the 
 total resistance of the concrete must at least be equal to the total resis- 
 tance of the steel. To determine, then, approximately, whether the 
 beam has sufficient concrete in compression in a slab, all that is necessary 
 to do is to compare the strength of the steel reinforcement with the 
 direct resistance of the portion of the concrete considered as being in 
 compression, or more directly, the average stress in the concrete must 
 not exceed 400, so that the results obtained by the following formula 
 
 must be within this limit: c = -, ; 
 
 b t 
 
 in which b = the width of the slab in compression; 
 t =the thickness. 
 
 Example : Determine whether the concrete in the slab section shown 
 in Fig. 96 is sufficient to give the full resistance of the 
 steel at 16,000 pounds. 
 
 Solution: The total area of the steel is 4 square inches, and the 
 fiber stress, or safe unit tensile resistance, is 16,000 pounds. 
 As the slab is 4 inches in thickness, the available width 
 of slab is 4 X 20, or 80 inches. These values having been 
 obtained, substitution can be made in the above formula 
 as follows: 
 
 4 x 16,000 
 : 80 X 4 =20 P unds : 
 
 showing that the concrete is only stressed up to one-half 
 of its allowable compressive resistance and is perfectly 
 safe. 
 
 [ 160]
 
 ! 1
 
 Example of the adaptability and economy of concrete in stairway con- 
 struction.
 
 More Accurate Method of Determining the Resisting Moment of T- 
 sections (Considering the Steel). In order to accurately determine 
 the resisting moment of reinforced concrete beams of T-section, the loca- 
 tion of the neutral axis x x, Fig. 96, must be determined. 
 
 It is a generally accepted practice in locating the neutral axis for 
 beams of T-section, to consider that the beam is a rectangular beam, as 
 included within the lines a, b, c, d. There is very little chance of error in 
 this assumption, for the reason that the neutral axis quite frequently falls 
 within the slab, and even though it should fall below the bottom of the 
 slab, the small section of the concrete represented by the shaded areas can 
 be practically included. The chance of error is particularly reduced 
 because the portion of the concrete below the neutral axis is never taken 
 into account in determining the strength factors of the section. 
 
 In finding the location of the neutral axis xx, or the distance kd, the 
 same formula as that applied for the determination of the same distance 
 in rectangular beams is used, namely: 
 
 k = \/(p n) 2 +2 p n p n. 
 
 Before applying this formula it will be necessary to determine upon 
 the values p and n. If the T-section illustrated in Fig. 97 is taken as an 
 
 Q 
 
 example, the value p is equal to g r^ = .00454; the value of n is 
 ordinarily taken, for stone concrete, at 12, so that by substitution in the 
 formula 
 
 54 X 1 2Y- + 2 X^00454 x'i2 -00454 X i2 = .28oi 
 
 As the distance d, Fig. 96, is 22 inches, the actual distance from the top 
 of the slab to the neutral axis, or the line x x, is 
 
 .2801 X 22 = 5.16 inches, 
 
 showing that the neutral axis is a little over if\ inches below the bottom 
 of the slab. The center of action of the concrete is always taken at 
 one-third of the distance kd from the top, so this brings the center of the 
 compressive area one-third of 5.16, or 1.72 inches from the top, and makes 
 the distance = 20.28 inches. 
 
 [163]
 
 In order to determine the resisting moment of the beam with refer- 
 ence to the steel reinforcement, the formula 
 
 Ms = a s D 
 is used, and by substitution 
 
 Ms = 2O.28 X 8 X 16,000 = 2 594,840 inch-pounds. 
 
 More Accurate Method of Determining the Resistance of Concrete 
 to Compression in a T-section. After the neutral axis has been 
 located in a T-section, as illustrated in Fig. 97, it is known that the 
 minimum stress in the section is zero at the neutral axis, and maxi- 
 
 mum at the extreme top surface of the slab. The entire resistance of the 
 portion of the concrete of the beam section in compression may then be 
 found by taking the area, which is stippled in the figure, at the average 
 stress of 300 pounds, and by taking the two side sections of the T, which 
 are shown in the figure by the cross-section lining, at the average stress 
 which exists in these sections. This average stress is greater than 300 
 pounds if the neutral axis falls below the bottom of the slab, and is equal 
 to 300 pounds if the neutral axis coincides with the line of the bottom 
 of the slab. Therefore, where the neutral axis falls below the bottom 
 of the slab it is necessary to determine the average stress in the two side 
 
 [164]
 
 sections of the T. The allowable maximum compression at the top of 
 the slab is 600 pounds per square inch, and the total allowable compres- 
 sion at any section of the slab is in direct proportion as its distance varies 
 from the top of the slab toward the neutral axis; so that the maximum 
 allowable stress on any line between the neutral axis and the top of the 
 slab may be determined by the proportion expressed in the following 
 equation : 
 
 Cl = k k' c 
 
 in which Ci = the unit stress at any line above the neutral axis. 
 
 ki = the ratio of the distance between the neutral axis and the 
 
 line at which it is desired to obtain the stress, to the total 
 
 depth of the beam. 
 k = the ratio of depth of neutral axis to effective depth of the 
 
 beam, 
 c =the allowable unit stress at the extreme top edge of the 
 
 beam. 
 
 From this the average stress, 'or ca, for the two side sections of the 
 T can be obtained by the formula 
 
 c k +c 
 
 2 
 
 To illustrate the method by which it is determined whether there is 
 sufficient concrete in compression, the following example is given: 
 
 Example : Determine whether there is sufficient concrete in compres- 
 sion, at the allowable unit stress of 600 pounds, in the 
 beam section illustrated in Fig. 97, to equal the resistance 
 of the steel when stressed to 16,000 pounds. 
 
 Solution: The conditions of the problem are illustrated in Fig. 97; 
 the total compressive resistance of the portion of the 
 rectangular section shown dotted above the neutral axis 
 is equal to 
 
 5.16 X 12 X 300= 18,576 pounds; 
 [ 165 ]
 
 The average stress in the two side sections of the T, 
 applying the above formula 
 
 ki, 
 
 c+c 
 
 which by substitution becomes 
 1.16 
 
 600 -7 +6OO 
 c a = ~ = 367 pounds. 
 
 The area of the two sections is 68 X 4, or 272 square 
 inches, and their total resistance to compression is 272 X 
 367=109,824 pounds; then, by adding together the 
 resistance of the portion of the rectangular section shown 
 dotted, and the resistance of the two side sections shown 
 cross-section, the total resistance of the concrete in com- 
 pression when stressed up to the maximum of 600 pounds 
 at the extreme top edge, is equal to 109,824+18,576, or 
 128,400 pounds. 
 
 Comparing this resistance to direct stress in compression, with the 
 allowable resistance of the steel, it will- be seen that the 8 square inches 
 of steel at 16,000 pounds has a resistance of 128,000 pounds, so that the 
 concrete in compression is more than sufficient, and no further attention 
 need be given to these portions of the problem. 
 
 It is usual in the design of reinforced concrete to have available 
 tables which give the resisting moment of beams and girders of different 
 depths, reinforced with different areas of steel, and monolithic with 
 slabs of different thicknesses. From such tables it is very convenient 
 to select a beam section which will give the required resistance. This 
 can be done by inspection, and no calculation is required except to deter- 
 mine the bending moment on the beam. It is usual in such tables to 
 show by a line running through the table the demarcation between the 
 portion of the table wherein the resisting moments are limited by the 
 steel from those values in the table which are limited by the concrete in 
 compression. Still more convenient and desirable in the design of con- 
 crete houses are tables giving the resisting moments of slabs of different 
 thicknesses, reinforced with bars and rods of different sizes and spacings. 
 
 1 166]
 
 Plan 
 
 Such tables and the accompanying explanations regarding their 
 use are given on page 192. 
 
 Resistance of Concrete Posts or Columns. From extensive experi- 
 ments upon full-sized sections of reinforced concrete posts or columns it 
 has been found that the use of longitudinal rein- 
 forcing rods properly tied in with wire ties add 
 materially to the strength of the concrete, so that, 
 while plain concrete in posts up to 15 diameters in 
 length could not be considered as capable of sup- 
 porting safely more than 350 pounds to the square 
 inch, conservative practice concedes that rein- 
 forced concrete columns can safely sustain 500 
 pounds to the square inch of section. 
 
 In the several first-class cities the values 
 allowed upon reinforced concrete columns vary 
 considerably, but conservative prac- 
 tice allows the use of 500 pounds to 4~ ^4- "5 
 the square inch when columns are re- 
 inforced with steel the area of which is 
 from i to 1 1 /2% of the area of the con- 
 crete for the longitudinal rods or bars /rv/7 Loop ties 
 for columns whose length does not ex- 
 ceed 15 diameters. It is seldom that 
 concrete columns are used in building 
 construction where the proportion of 
 length is greater than this. If it 
 should be, the safe strength per square 
 inch should be reduced in proportion Fl(=>v^f/nn 
 
 as the length exceeds the diameter of Fig Q8 ._Method of tying together 
 15 to i. 
 
 <" 
 
 or 
 
 column reinforcing. 
 
 vertical 
 
 Example: Assume that it is desired to support a load of 80,000 
 pounds on a reinforced concrete column. 
 [167]
 
 Solution: The safe unit stress is 500 pounds; therefore the area of 
 column required equals 
 
 80,000-^-500, or 1 60 square inches; 
 
 A column 13" square would have a sectional area of 156 
 square inches, which is sufficiently close to the required 
 result to be used. 
 
 To. reinforce this column with i% of steel would require a total 
 sectional area of steel rods for longitudinal reinforcement equal to 1.56 
 square inches, which divided among 4 rods would give for the area of 
 each rod or bar .39 square inch. The sectional area of a ^-inch round 
 rod is .45; therefore four rods of this size could be used and should be 
 placed and tied together as indicated in Fig. 98. 
 
 In order that the strength of reinforced columns of any size may be 
 conveniently found, the following table is given. This table gives the 
 strength of the several sized columns for the allowable unit compressive 
 stresses on reinforced concrete columns. 
 
 TABLE 6. SAFE LOADS IN POUNDS FOR DIFFERENT UNIT STRESSES 
 ON SQUARE REINFORCED CONCRETE COLUMNS 
 
 
 
 
 
 
 
 A rea of Steel in 
 
 
 Area in 
 
 350 pounds 
 
 500 pounds 
 
 650 pounds 
 
 750 pounds 
 
 sq. inches 
 
 Size 
 
 Sq. Inches 
 
 per sq. inch 
 
 per sq. inch 
 
 per sq. inch 
 
 per sq. inch 
 
 
 
 of Column 
 
 Load 
 
 Load 
 
 Load 
 
 Load 
 
 1% 
 
 I\% 
 
 8x 8 
 
 64 
 
 22,400 
 
 32,000 
 
 41,200 48,000 
 
 .64 
 
 .96 
 
 9x 9 
 
 81 
 
 28,400 
 
 40,500 
 
 52,700 61,000 
 
 .81 
 
 1. 21 
 
 IO X IO 
 
 IOO 
 
 35.000 
 
 50,000 
 
 65,000 75,000 
 
 I.OO 
 
 1.50 
 
 II X II 
 
 121 
 
 42,400 
 
 60,500 
 
 78,700 
 
 91,000 
 
 1. 21 
 
 1.81 
 
 12 X 12 
 
 144 
 
 50,400 
 
 72,000 
 
 93,600 108,000 
 
 1.44 
 
 2.16 
 
 13X13 
 
 169 
 
 59,200 
 
 84,500 
 
 109,900 126,000 
 
 1.69 
 
 2-53 
 
 I4x 14 
 
 196 
 
 68,600 
 
 98,000 
 
 127,400 147,000 
 
 1.96 
 
 2.94 
 
 15x15 
 
 225 
 
 78.800 
 
 112,500 
 
 146,500 
 
 169,000 
 
 2.25 
 
 3-37 
 
 16 x 16 
 
 2 5 6 
 
 89,600 
 
 128,000 
 
 166,400 192,000 
 
 ' 2. 5 6 
 
 3-84 
 
 17x17 
 
 289 
 
 101,200 
 
 144,500 
 
 187,900 216,000 
 
 2.89 
 
 4-33 
 
 i8x 18 
 
 324 
 
 113,400 
 
 162,000 
 
 210,600 243,000 
 
 3-24 
 
 4.86 
 
 19 x 19 
 
 361 
 
 126,400 
 
 180,500 234,700 271,000 
 
 3-61 
 
 540 
 
 2O X 20 
 
 400 
 
 140,000 
 
 200,000 260,000 300,000 4.00 
 
 6.00 
 
 21 X 21 
 
 441 
 
 154,400 
 
 220,500 286,700 337,ooo 4.41 
 
 6.61 
 
 22 X 22 
 
 484 
 
 169,400 242,000 
 
 314,600 
 
 363,000 4.84 
 
 7.26 
 
 Strength of Steel Columns Considering the Resistance of the 
 Reinforcement. In some sections of the country it is the practice to 
 
 168
 
 5 
 
 o 
 
 RJ
 
 include in the calculations for determining the strength of reinforced 
 concrete posts the strength of the steel in the longitudinal rods. Such 
 formulas are based on the assumption that the steel is subjected to 
 the corresponding stress due to its proportional deformation, fixed by 
 the deformation of the concrete under its safe stress. 
 
 The relative strains and stresses for the two materials are expressed 
 by the ratios of the moduli of elasticity, which for stone concrete is taken 
 at from 12 to 15. The formula for the strength of columns on these 
 assumptions is then as follows: 
 
 P = c (A a)+a n c 
 In this formula 
 
 P = safe bearing strength of the column. 
 
 A = area of column section. 
 
 a = sectional area of all of the longitudinal reinforcing bars. 
 
 c = safe compressive strength of the concrete. 
 
 n = ratio of the moduli of the elasticity. 
 
 It is safe in using such a formula to take n at 12, and c at 500 pounds. 
 
 Example: Assume that it is desired to find the safe strength of a 
 reinforced concrete column 14 inches square, reinforced 
 with 4 i -inch round bars. 
 
 Solution: The total area of the column section is 14" x 14", or 196 
 sq. in., and the total area of the steel reinforcement is 
 .78 X 4, or 3.12; by substitution in the above formula 
 P = 5OO (196 3.12) +3.12 X 12 X 500 = 115,160 pounds. Answer. 
 
 Live and Dead Loads. In all buildings, whether dwelling houses or 
 those of larger and heavier construction, the design of the floors and 
 walls depends upon the weights or loads they will bs required to sustain. 
 
 In dwelling houses walls of ordinary construction are generally of 
 ample strength to carry the weight or load usually imposed. In the 
 matter of floors and roofs, these can be directly proportioned and re- 
 inforced to their w r eights and the loads they are required to sustain. 
 
 The architectural designer has to do with two kinds of weights or 
 loads, namely, the weight of the materials composing the structure
 
 itself, and the weight or load applied or superimposed upon the floors. 
 These two loads are designated as the dead and live loads respectively. 
 
 Dead Load. The weight of the materials composing a floor or roof 
 makes up the dead load, and it is generally the practice to reduce both the 
 dead and live loads to the weight in pounds distributed over a square 
 foot of surface, so that when either a ' 'dead " or " live " load is mentioned 
 it is understood to be the weight in pounds per square foot of floor area. 
 There would, of course, be an exception where one was considering a 
 load upon a column or post, in which case the aggregate dead and live 
 loads might be meant. 
 
 In order to accurately determine the dead load the designer must 
 know the weights of the materials entering into the construction, and 
 these, for dwellings of reinforced concrete, would be as follows: 
 
 TABLE 7. WEIGHT OF BUILDING MATERIALS 
 
 REINFORCED CONCRETE WEIGHS 150 POUNDS PER CUBIC FOOT 
 CINDER CONCRETE WEIGHS 90 POUNDS PER CUBIC FOOT 
 
 Reinforced Concrete Slab 
 
 Miscellaneous Material 
 
 Tkicknessin ,*, ^^pSSST 
 
 Material 
 
 Weight in Pounds per 
 Square Foot 
 
 
 
 2 Inch Cinder Concrete 
 
 
 3 
 
 37 1 A 
 
 with Sleepers 
 
 14 
 
 3M 
 
 43% 
 
 2 Inch Cement Top 
 Coat 
 
 13 
 
 4 
 
 50 
 
 j Yellow Pine Flooring 
 
 3 
 
 4H 
 
 56^ 
 
 I Hardwood Flooring 
 
 4 
 
 5 
 
 62 K 
 
 Slag Roof 
 
 6 
 
 
 
 Slate Roof 
 
 8 to 10 
 
 
 
 Metallic Lath and 
 
 
 
 
 Cement Plaster 
 
 10 
 
 
 
 Sheet Copper Roofing 
 
 2 
 
 
 
 Interlocking Tile 
 
 18 
 
 
 
 Flat Promenade Tile 16 
 
 It is usually safe in house construction, where there are reinforced 
 concrete beams and girders, to take the dead load of the floor construc- 
 tion at from 90 to 100 pounds per square foot, and for hollow terra-cotta 
 
 [172]
 
 tile and concrete joist construction, to take the live load at from 75 to 
 80 pounds. 
 
 Live Load. The live load in any building is an assumed weight 
 per square foot of floor area which is considered to be the extreme possible 
 limit of the superimposed floor loading, such as the weight of the people, 
 furniture and merchandise, and, in some cases, even partitions, if there 
 is a possibility that the location of these may be changed to suit the 
 requirements of tenants. 
 
 In dwelling-houses the live load per square foot of floor surface is 
 very little probably not actually amounting, under ordinary conditions, 
 to more than 10 or 15 pounds per square foot. In all dwelling-houses, 
 however, there is the possibility of a great number of people being 
 assembled on the floors, and consequently in the larger cities a live load 
 of 70 Ibs. is generally stipulated in building laws as being the proper 
 superimposed weight for designing the floor construction. This load 
 is rarely, if ever, realized and a load of 40 pounds per square foot is 
 ample for the design of concrete houses not subjected to the requirement 
 of municipal building laws. 
 
 The combination of the live and dead loads gives the total load per 
 square foot of floor area. The average total floor load for a dwelling- 
 house, considering a live load of 40 pounds, would seldom be over 120 
 to 130 pounds per square foot. 
 
 Roof Loads. In modern structures of considerable size it is some- 
 times considered essential, in designing the roofs, to make allowance for 
 snow and wind loads. Generally in the design of smaller buildings, 
 which classification would include dwellings, even pretentious types, 
 it is usual to combine the snow and wind loads, and to use a superim- 
 posed load on the roof of from 25 to 30 pounds per square foot. This 
 load added to the weight of the roof construction gives the total roof 
 load per square foot. 
 
 In climates comparatively temperate the load of 25 to 30 pounds 
 could be reduced to from 15 to 20 pounds unless it was proposed to use 
 
 [ i73l
 
 the roof as a promenade, when it would be safer to use a somewhat 
 heavier superimposed load. Roofs that are very steep have, of course, 
 little snow load, but on the other hand the wind pressure increases. 
 
 Weights on Floor Slabs, Beams, Girders, etc. In the planning 
 of floors the floor slab, if of concrete, must be designed first. The dead 
 load of the floor slab alone is not as great as the dead load of the entire 
 floor construction, so that in order to get a total load per square foot on 
 a floor slab the live load is added to the actual weight of the floor slab 
 and the finished floor, whatever that may be. 
 
 The total load per square foot upon a beam or girder must take into 
 account the weight of the beam or girder itself, distributed over the 
 floor area which it supports, and this dead load is, of course, somewhat 
 more than the dead load of the slab itself. The total weight that a beam 
 or girder supports is equal to the area of floor carried by it multiplied by 
 the total floor load, which includes the dead and live loads, and in the 
 same manner we calculate the load carried by a column or post, with 
 the exception that if it carries more than one floor the aggregated weight 
 from all floors which the column supports must be taken. 
 
 Usually the area supported by a beam or girder is equal to the span 
 multiplied by the distance from center to center of these structural 
 members, and where a girder supports a number of reinforced concrete 
 beams it is usual to figure the girder as being uniformly loaded rather 
 than as supporting a number of concentrated loads. This is owing to 
 the monolithic character of the construction, the weight from the beams 
 being well distributed over the girder. 
 
 [i74l
 
 Chapter VI 
 
 Calculating the Bending Moments for Reinforced 
 Concrete Beams and Slabs, and the Determina- 
 tion of Size and Reinforcement
 
 Chapter VI 
 
 Calculating the Bending Moments for Reinforced Concrete 
 
 Beams and Slabs, and the Determination of Size 
 
 and Reinforcement 
 
 Theory of Bending Moments. The loads on a beam produce trans- 
 verse stress on the material composing the beam. The loads and 
 the reaction at the supports act about any point in the length of the beam 
 through lever arms equal to the perpendicular distance from the line of 
 action of the load or the reaction, and both the loads and the reactions 
 produce moments about any point. These moments are either positive 
 or negative, as they act together or in opposition to each other. It is 
 evident, therefore, that the moments which act in the same direction 
 may be added together, and that those which are opposed may be deducted 
 from the sum. In this way the algebraic sum of the moments about any 
 point in the length of a beam may be obtained, and the resultant moment 
 is called the bending moment. This bending moment is resisted by the 
 strength of the material of which the beam is composed, so that in order 
 to determine whether a beam is of sufficient section to resist the action 
 of the loads and the reactions, it is necessary to find the maximum or 
 greatest bending moment to which the beam is subjected. 
 
 Formulas for Greatest Bending Moments on Simple Beams. 
 The greatest bending moment on any simple beam may be determined 
 by finding the algebraic sum of the moments about the point at which 
 the greatest bending moment occurs. 
 
 For convenience it is customary to use simple formulas, arranged 
 in terms of the weight and span, for finding the bending moment on 
 
 12 [ 177 ]
 
 beams loaded with a uniformly distributed load, a load concentrated at 
 the center, or a triangular shaped load such as the weight of brickwork 
 on a lintel over an opening. 
 
 In the following tabulation a simple beam is considered as one 
 supported at both ends, while a cantilever is a projecting beam or one 
 supported at one end only. In the formulas the bending moment, M, 
 is determined in inch-pounds, the weight, W, is taken in pounds, and the 
 span in feet or inches as designated L or 1, respectively. 
 
 FORMULAS FOR BENDING MOMENTS 
 
 Wl 
 Simple Beam, Uniform Load M = o " or 1.5 WL 
 
 Wl 
 Simple Beam, Load Concentrated at the Center M = ~~ or 3 WL 
 
 Wl 
 
 Simple Beam, Triangular Load, Apex at the Center M = -7- or 2 WL 
 
 Wl 
 Simple Beam, Uniform Load; Ends of Beam Fixed M =~~ or 1.2 WL 
 
 Wl 
 Cantilever Beam, Uniform Load M = or 6 WL 
 
 Cantilever Beam, Load Concentrated at End M =W1 or 12 WL 
 
 Example: What will be the greatest bending moment of a rein- 
 forced concrete floor beam which has a span of 20 feet, 
 and where the distance from center to center of beam is 
 6 feet, and the total load 140 pounds per square foot? 
 
 Solution: The area of floor supported is equal to 6X20, or 120 
 square feet, and the total load on the beam consequently 
 equals 120 X 140, or 16,800 pounds. Considering that 
 the beam will be taken as fixed at the ends, the formula 
 for a uniform load with the ends fixed will be applied. 
 This formula gives the value of 
 
 Wl 
 
 M= , or 1.2 WL, 
 
 so that by the substitution of the values in the formula 
 M = i.2 X 16,800 X 20 = 403,200 inch-pounds. 
 
 Application of Formulas to Reinforced Concrete Beams. The 
 factor of safety used for reinforced concrete is large that is to say,
 
 while in figuring the resistance of the material it is customary to use 
 factors of safety of four, for the steel and concrete, there are certain 
 assumptions made with reference to the method of figuring the bending 
 moments which are so far within the safe limits that under any ordinary 
 conditions of fair design and workmanship the actual bending moment 
 is so reduced as to give a much greater factor of safety than is usual in 
 
 
 
 
 i-. ft-\a'^>. A A *^ 
 
 A-A^J| 
 
 -. .'A* . ' ^ ^ 
 
 A :b.'\A.' A ' 
 
 
 
 
 >:>.'^. & . 
 
 
 V/* '* A 'i 
 
 
 $$ 
 
 
 
 ;<..f A'r^a; 
 
 
 ^^^.' 
 
 :*.,>. . >. 
 
 
 /y/ 
 
 Fig. 99. 
 
 
 
 
 
 ^^^^ 
 
 c..-.- -.: 
 
 .. #k .- A 
 
 Z 
 
 Fig. 100. 
 
 structures subjected to static loads. The principal reason for the 
 increase in the factor of safety in reinforced concrete construction lies 
 in the fact that the entire system of beams and girders, together with the 
 floor slab, is usually monolithic, and the girders and beams, besides being 
 continuous over several supports, act mutually in two directions, thus 
 adding greatly to the strength of the floor system. (See Fig. 99.) 
 
 [ 179]
 
 The conservative practice in the design of reinforced concrete floor 
 slabs is to figure the bending moment by the formula when the loads 
 and spans are considered as acting over a distance equal to the distance 
 from center to center of beams, and to use the formula - when the 
 
 o 
 
 clear span of the slab, or the distance from face to face of beam, is taken 
 as the span, and the distance over which the load is distributed. These 
 two assumptions are illustrated in Fig. 100. There is generally some 
 economy gained by using the first formula, but when this formula 
 is used, the reinforcing rods should be brought to the top of the slab 
 over the beam bearings. 
 
 In the design of beams and girders it is undoubtedly safe to consider 
 them as fixed at the ends, and to therefore figure the bending moment 
 upon them by the formula . Where this formula is used the span of 
 the beam and girder should always be taken as the distance from center 
 to center of supports, even though only the load which would be supported 
 by the clear span is considered. 
 
 As in slab construction, the beams and girders should never be 
 considered as fixed at the ends unless they are monolithic at the points 
 of support with the floor construction, or else are securely built into the 
 walls, and then only when the reinforcing rods are bent up toward the 
 supports to form reinforcement for the change in the bending moment 
 which takes place in continuous beams over supports. The method of 
 figuring bending moments for slabs, beams, and girders, and the partic- 
 ular formula which may be used, is usually regulated by the building 
 laws in cities of the first class. Outside of the scope of such laws the 
 designer can use such modifications of these formulas as his judgment 
 and experience may dictate. Where the material and workmanship are 
 of first quality, the designer can certainly afford to use those assumptions 
 which will give him the most economical results, and still be assured of 
 having a secure and safe building, for the reasons stated above. 
 
 Minimum Depths of Slabs, Beams, and Girders. In the 
 design of reinforced concrete structures there are certain minimum 
 thicknesses for slabs, and depths for beams and girders, which are uni- 
 
 I 180!
 
 a 
 
 T3 
 C 
 
 a 
 v 
 
 "a. 
 S
 
 versally adhered to. For instance, it is considered impractical to build 
 a reinforced concrete slab between beams of less than 3 inches in total 
 thickness, and it is best, in any case, not to make the slab less in thick- 
 ness than two-fifths of an inch for each foot in span. For example, assume 
 that the span of a slab between beams is 8 feet: if two-fifths of an inch 
 is allowed for each foot of span, and the span is 8 feet, this would give a 
 thickness of sixteen-fifths, which is 3! inches, and the slab would be 
 made 3^/2 inches in thickness. 
 
 It is customary in designing beams and girders to confine the mini- 
 mum depth of the beam or girder, counting from the under side of the 
 slab to the bottom of the member, as three-fifths of an inch for each foot 
 in span. To illustrate, assume that a beam has a span of 20 feet; allow- 
 ing three-fifths of an inch for each foot in span would make the minimum 
 depth of the beam sixty-fifths, or 12 inches, which would be shallow 
 enough for a beam of this span supporting any kind of a load. 
 
 In deciding on the depth of beams and girders the commercial width 
 of lumber from which the forms are to be made should be taken into 
 account, unless it is proposed to saw and work stock boards to the 
 necessary width. It is only by such care that the best economy is 
 attained in the construction of concrete dwellings. 
 
 The Minimum Width of Beams and Girders. There are three 
 factors which regulate the width of beams and girders of reinforced 
 concrete : 
 
 First: The minimum space into which reinforcing rods can be 
 placed and into which concrete may be poured and spaded 
 or tamped. 
 
 Second: The minimum width that will allow the steel to be suffi- 
 ciently fireproofed. 
 
 Third: The minimum amount of concrete around the reinforcing 
 rods or bars that will develop their resistance. 
 
 It is seldom practical to make reinforced concrete beams less than 
 6 inches in width, and they may be as much wider as is needed to 
 meet the requirements above stated, or as may be necessary for archi- 
 
 [183]
 
 tectural appearances. In all instances there should be at least ij^ inches 
 of concrete outside of the steel reinforcement on both sides and bottom 
 of the beam to give the necessary protection in the way of fireproofing, 
 and it is also considered good practice to allow a distance from center 
 to center of the reinforcing rods or bars of at least 2}/ times the diameter 
 of the rod or bar. 
 
 Determining the Bending Moment on Square Slabs. In figur- 
 ing the bending moments on slabs, whether they span from wall 
 to wall unsupported by beams, or are incorporated with beams and, 
 being monolithic with them, form a T-section, it is always customary in 
 figuring the load and the bending moment to consider a portion of the 
 slab i foot in width. 
 
 The difference between slabs and beams and girders, with reference 
 to the bending moment, exists in the fact that the slabs may be supported 
 on four sides and be reinforced in two directions. Where it is possible 
 to reinforce a slab in two directions, considerable economy can be exer- 
 cised from the fact that the bending moment in either direction is mate- 
 rially reduced, and consequently the slab need not be so thick, and sup- 
 porting beams may be omitted. Where the slab is square, and is sup- 
 ported on all four sides in a secure and fixed manner, then the bending 
 moment on the slab may be found by the following formula: 
 
 WL 
 
 M (foot-pounds) 2Q 
 
 or, if the span is in feet and the resulting bending moment is in inch- 
 pounds, 
 
 3WL 
 
 M (inch-pounds) = I 
 o 
 
 To illustrate the application of this formula, assume that it is 
 desired to find the bending moment created in a floor slab 12 feet square, 
 and supporting a total uniformly distributed load of 125 pounds. The 
 load on a portion of the slab I foot in width is equal to 12 X 125, or 1500 
 
 pounds. Applying the above formula, and substituting, 
 
 i 
 
 3\VL 3X1500X12 
 
 M = - = - = 10,800 inch-pounds. 
 o 
 
 [I8 4 ]
 
 By referring to Table 9 it will be observed that a slab with a total thick- 
 ness of 5 inches, reinforced with ^-inch square twisted bars, spaced 
 4 inches center to center, will give the required resistance; the reinforce- 
 ment must, of course, extend in both directions. 
 
 Double Reinforcement in Rectangular Slabs. Floor slabs which 
 are supported on four sides, but which are rectangular instead of 
 square, may be reinforced lengthwise and crosswise; the reinforce- 
 ment running crosswise of the beam must be heavier than that running 
 lengthwise, from the fact that the greater proportion of the load will be 
 carried by the short span. This is best explained by the fact that the 
 stress in steel or concrete, or in fact any material, is, within working 
 stresses, always proportional to the amount of strain or deformation pro- 
 duced in the material. It is consequently evident that the greatest strain 
 will be produced in the reinforcement running the short way of the slab 
 when subjected to the same deflection, as the reinforcement running length- 
 wise. In rectangular slabs, therefore, it is necessary to figure the amount of 
 reinforcement required in both directions, by figuring the bending moment 
 created in the slab, with regard to both short and long span. 
 
 TABLE 8. PROPORTION OF LOAD CARRIED IN BOTH DIRECTIONS 
 BY RECTANGULAR FLOOR SLABS 
 
 Ratio oj 
 Slab tc 
 
 ' Length of 
 Breadth 
 
 i 
 
 Proportion of Load Carried 
 by Reinforcement of 
 Short Span 
 .5 . 
 
 Proportion of Load 
 Carried by Long 
 Span 
 .5 
 
 [ i 
 
 . .6 
 
 .4 
 
 .2 
 
 67 
 
 33 
 
 .7 
 
 .74. . 
 
 26 
 
 .4. 
 
 7Q. . 
 
 21 
 
 c 
 
 .8-*. . 
 
 17 
 
 .6 
 
 .87 
 
 .11 
 
 7 
 
 .80 
 
 II 
 
 .8 
 
 91 
 
 O9 
 
 .O 
 
 . .QT . . 
 
 O7 
 
 ! . 
 
 . .04. .. 
 
 . .06 
 
 The proportionate part of the total load on a rectangular floor slab 
 which will be carried by the reinforcement extending the short way of 
 the slab, can be found by the following formula: 
 
 I 4 
 
 L P~I-W< 
 
 [185]
 
 In this formula 
 
 Lp = the proportion of the load resisted by the reinforcement placed 
 
 the short way of the slab. 
 1 = the length of the slab. 
 w = the breadth of the slab. 
 
 the value Lp is the proportional part of the total load per square foot. 
 In order to save calculation, the various values of Lp, or the proportional 
 part of the load carried by the reinforcement extending the short way of 
 the beam, may be determined from Table 8, which has been worked 
 out for proportional parts of length to breadth, varying by tenths, from 
 square slabs to rectangular slabs having a length equal to twice their 
 breadth. 
 
 In order to explain the use of Table 8 and the method of calculating 
 the amount of reinforcement required in a rectangular slab reinforced in 
 two directions, the following example is given: 
 
 Example: Determine the amount of reinforcement required both 
 crosswise and lengthwise, for a reinforced concrete slab, 
 supported on four sides, having a width of 10 feet and a 
 length of 12 feet. 
 
 Solution : The ratio of the length to the breadth is as 
 
 Referring to the above table, it will be found that the 
 proportional part of the load carried by the reinforcement 
 extending across the slab is .67; if therefore, the total 
 load is 130 pounds per square foot, the proportional part 
 of this load carried by the short span will equal 130 X 
 .67 = 87 pounds per square foot. In figuring the bending 
 moment in rectangular slabs, after the proportional part 
 of the load is found for each span, the bending moment 
 is figured by the formula 
 
 M = - 
 
 WL 
 
 therefore the bending moment in this instance will equal 
 
 870 X 10 
 - =870 foot-pounds, or 10,440 inch-pounds. 
 
 [186]
 
 By referring to Table 9, a 4-inch slab with square bars, it will be 
 found that f-inch square bars spaced 5-inch centers will give a resisting 
 moment of 10,650 pounds, which is only slightly in excess of the require- 
 ments, and is the correct size to use. 
 
 Stirrups. All concrete beams, whether rectangular or T-sec- 
 tion, should have secondary reinforcement in the form of stirrups, which 
 extend from the main reinforcing rods or bars, vertically or diago- 
 nally, through the web of the beam to the top. These stirrups have several 
 uses, namely, they help to transmit the stress in the reinforcing rods to 
 the portion of the concrete in compression by resisting the horizontal 
 shear; their greatest use, however, is to prevent what is known as 
 diagonal tension cracks near the abutments, or points of support. 
 
 There are various formulas by which the number of stirrups can be 
 figured, but designing engineers do not, as a rule, apply them in practice, 
 and such formulas would be particularly useless in the design of concrete 
 dwellings, where the loads are light. A very excellent rule, and one which 
 is used almost universally by designing engineers of considerable experi- 
 ence, is to place in the beam or girder stirrups equal in number to the 
 span in feet. As the stirrups are primarily shear members, and as the 
 shear increases toward the points of support and is zero at the center 
 of the span of a beam uniformly loaded, it is customary to place the 
 stirrups close together at the abutments, and farther apart toward the 
 center of the span. An excellent rule is to space the stirrups at the 
 abutments according to the following tabulation : 
 
 First three stirrups @ 4-inch center to center. 
 
 Next two stirrups . @ 6-inch center to center. 
 
 Next stirrup @ 12-inch center to center. 
 
 Next stirrup @ 1 8-inch center to center. 
 
 The maximum distance for stirrups should not be over three feet apart 
 at the center of the span. 
 
 Stirrups used as the secondary reinforcement for concrete beams 
 and girders in house construction may be of %-inch diameter round rods, 
 and this size of stirrup is sufficient if spaced according to the above 
 schedule. 
 
 [187]
 
 Chapter VII 
 
 Tables for Designing Reinforced Con- 
 crete Construction and Their Use
 
 Chapter VII 
 
 Tables for Designing Reinforced Concrete Construction and 
 
 their Use 
 
 The several formulas which have been given for finding the location 
 of the neutral axis and the resistance of reinforced concrete beams, 
 involve more or less lengthy calculations, so that it is usual to employ 
 tables which give the results of many calculations based on the formulas. 
 
 One of the most valuable of these tables gives the resistance, or 
 resisting moment, of reinforced concrete slabs. The resisting moments 
 of reinforced concrete slabs one foot in width are given in inch-pounds 
 in Table 9. The resisting moment selected from the table must equal 
 the maximum bending moment due to the load on the slab taken in inch- 
 pounds. An examination of this table shows that it gives the resisting 
 moments for slabs from 3 inches to 6 inches in thickness, varying by the 
 one-half inch, and reinforced with both square and round bars, ranging 
 from 34 inch to % inch, and spaced from 2 inches to 12 inches center to 
 center. 
 
 It will be observed that an irregular line passes through these 
 tables. This line separates the values which are limited by the steel 
 reinforcement from those values that are limited by the resistance of 
 the concrete to compression. The values above the line are regulated 
 by the strength of the steel reinforcement, while those below the line 
 are determined by the resistance of the concrete. 
 
 The nearer the values approach the line, the more nearly are both 
 the steel and the concrete subjected to their maximum w r orking stresses. 
 
 A study of the table w r ill show the values of the resisting moments 
 below the line increasing in a much less ratio than the amount of steel 
 used for the reinforcement, thus showing a loss of economy. 
 
 [191]
 
 The values in the following table are based upon the strength values 
 of stone concrete, composed of one part of Portland cement, two parts 
 of clean gravel or sand, and four parts of good hard broken stone. The 
 allowable working stress of the steel is taken at 16,000 pounds per 
 square inch, and the allowable compressive stress on the concrete at the 
 extreme fiber is 600 pounds per square inch. The ratio of the moduli 
 of elasticity of the materials is taken at 12. Attention is also called to 
 the fact that the fractional values in the first column of the table are the 
 figures denoting the size of the bars either the diameter of the round 
 rods or the side of the square bars. The figures at the top over each 
 column is the spacing of the rods in inches, or, as it is sometimes called, 
 the "pitch." 
 
 It must be borne in mind in selecting values from the tables that 
 the nearest value within 5% above or below the bending moment may 
 be used, and it is generally considered best not to use the bars in sixteenth 
 sizes, but rather to use those in the eighth size, such as ^, 3/g, 1^, and Y%. 
 It is good practice to use the same sized rods or bars throughout a job, 
 and rather to use small bars at a reasonable spacing than the larger 
 bars at 8", 9", or 10" pitch. 
 
 TABLE 9. RESISTING MOMENTS IN INCH-POUNDS. IN EVERY CASE 
 
 CENTER OF STEEL IS ONE INCH FROM BOTTOM OF SLAB 
 [Figured for stone concrete 1-2-4 mixture 16,000 pounds on steel 600 pounds on 
 concrete Phila. Law. Below line, steel is in excess of critical percentage and concrete 
 is limiting factor.] 
 
 THREE-INCH CONCRETE SLABS. 
 ROUND RODS SPACED CENTER TO CENTER. 
 
 Diameter of Rods 
 
 2 
 ins. 
 
 3 
 
 ins. 
 
 4 
 ins. 
 
 5 
 ins. 
 
 6 
 ins. 
 
 7 
 ins. 
 
 8 
 ins. 
 
 9 
 ins. 
 
 10 
 
 ins. 
 
 // 
 
 ins. 
 
 12 
 
 ins. 
 
 J<4 inch 
 
 5155 
 
 45<>7 
 
 4078 
 
 338o 
 
 2818 
 
 2396 
 
 2112 
 
 1880 
 
 1690 
 
 1535 
 
 1409 
 
 iff 
 
 5870 
 
 5222 
 
 4776 
 
 441 1 
 
 4133 
 
 3742 
 
 330 
 
 2927 
 
 2640 
 
 2400 
 
 2 2OO 
 
 $ " 
 
 6432 
 
 5803 
 
 5332 
 
 4973 
 
 4709 
 
 4430 
 
 4262 
 
 4075 
 
 3802 
 
 3452 
 
 3168 
 
 T 7 ff " 
 
 
 6288 
 
 5817 
 
 5467 
 
 5189 
 
 49 1O 
 
 4718 
 
 4541 
 
 4177 
 
 4.176 
 
 !4Il8 
 
 y, " 
 
 
 6696 
 
 6265 
 
 sooo 
 
 5606 
 
 574.2 
 
 CI CQ 
 
 4.060 
 
 4810 
 
 46^1 
 
 4. CQO 
 
 " . 
 
 
 
 6620 
 
 6280 
 
 5980 
 
 57 1O 
 
 5520 
 
 5112 
 
 5175 
 
 501 1 
 
 4.80 s 
 
 i " . 
 
 
 
 
 6605 
 
 6l2O 
 
 6058 
 
 5870 
 
 5671 
 
 55OO 
 
 5142 
 
 S222 
 
 H " 
 
 
 
 
 
 6615 
 
 6^6O 
 
 6172 
 
 so8o 
 
 5822 
 
 5664 
 
 CC2O 
 
 % " - 
 
 
 
 
 
 
 6615 
 
 64-12 
 
 6265 
 
 6086 
 
 C017 
 
 5801 
 
 
 
 
 
 
 
 
 
 
 
 
 
 192
 
 THREE-INCH CONCRETE SLABS. 
 SQUARE BARS SPACED CENTER TO CENTER. 
 
 inch 
 
 T7 
 x'2 
 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 ,0 
 
 // 
 
 12 
 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ms. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 
 5532 
 
 4900 
 
 4425 
 
 4105 
 
 3587 
 
 3050 
 
 2600 
 
 2382 
 
 2152 
 
 1955 
 
 1794 
 
 
 6260 
 
 5600 
 
 5HO 
 
 4800 
 
 4493 
 
 4264 
 
 4066 
 
 3734 
 
 336o 
 
 3053 
 
 2800 
 
 
 6800 
 
 6187 
 6658 
 
 5730 
 6225 
 
 536o 
 5865 
 
 5065 
 5568 
 
 4840 
 
 5?O4 
 
 4637 
 
 5IOS 
 
 443" 
 
 4-Q^O 
 
 4286 
 4766 
 
 4138 
 4600 
 
 4008 
 4460 
 
 
 
 
 6630 
 
 62Q ^ 
 
 CQQO 
 
 564. s 
 
 CC-JJ. 
 
 C7J.2 
 
 ^ 1 80 
 
 CQ 1 6 
 
 4QOO 
 
 
 
 
 
 6648 
 
 6365 
 
 61 10 
 
 5918 
 
 5726 
 
 SCSI 
 
 54.00 
 
 C265 
 
 
 
 
 
 
 6686 
 
 6437 
 
 6260 
 
 6058 
 
 50OO 
 
 57 5O 
 
 5606 
 
 
 
 
 
 
 
 6710 
 
 654O 
 
 6^S 
 
 6206 
 
 6038 
 
 cq 1 1 
 
 
 
 
 
 
 
 
 68OO 
 
 66^0 
 
 6460 
 
 6"*2O 
 
 6190 
 
 
 
 
 
 
 
 
 
 
 
 
 
 THREE AND ONE-HALF INCH CONCRETE SLABS. 
 ROUND RODS SPACED CENTER TO CENTER. 
 
 inch 
 
 If/- of Rods 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 10 
 
 11 
 
 12 
 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 
 7515 
 
 6525 
 
 5284 
 
 4226 
 
 3525 
 
 2995 
 
 2640 
 
 2350 
 
 2115 
 
 1920 
 
 1760 
 
 
 8.S93 
 
 7620 
 
 6880 
 
 6320 
 
 15505 
 
 4680 
 
 4 I2 5 
 
 3660 
 
 3300 
 
 3000 
 
 2751 
 
 
 95io 
 
 8490 
 
 7770 
 
 7250 
 
 6810 
 
 6410 
 
 594 
 
 5280 
 
 4755 
 
 4315 
 
 3960 
 
 
 10260 
 
 9270 
 
 8540 
 
 7990 
 
 7570 
 
 7150 
 
 6840 
 
 6580 
 
 6315 
 
 5876 
 
 5390 
 
 
 
 00 V) 
 
 Q22S 
 
 8660 
 
 8210 
 
 77QO 
 
 7?I c 
 
 721 S 
 
 6Q4.O 
 
 67 ^s 
 
 6S25 
 
 
 
 1 0490 
 
 982O 
 
 9260 
 
 8805 
 
 8^85 
 
 8085 
 
 777O 
 
 754-O 
 
 7^00 
 
 7O7O 
 
 
 
 
 IO1-U) 
 
 07QO 
 
 Q^"U> 
 
 80^5 
 
 8SQS 
 
 82QS 
 
 80 SS 
 
 7800 
 
 7620 
 
 
 
 
 
 1 0^20 
 
 9800 
 
 Q7QO 
 
 9100 
 
 87QO 
 
 8mo 
 
 8^80 
 
 8O75 
 
 
 
 
 
 10650 
 
 1 02 1 5 
 
 o8ts 
 
 QSIO 
 
 822 = 
 
 8C)7() 
 
 8720 
 
 s s< >o 
 
 
 
 
 
 
 
 
 
 
 
 
 
 THREE AND ONE-HALF INCH CONCRETE SLABS. 
 SQUARE BARS SPACED CENTER TO CENTER. 
 
 inch 
 
 ter of Rods 
 
 2 
 ins. 
 
 3 
 
 ins. 
 
 4 
 ins. 
 
 5 
 ins. 
 
 6 
 ins. 
 
 7 
 ins. 
 
 8 
 ins. 
 
 9 
 ins. 
 
 10 
 ins. 
 
 11 
 
 ins. 
 
 12 
 
 ins. 
 
 
 8110 
 
 7090 
 
 6410 
 
 538o 
 
 4485 
 
 38i5 
 
 3360 
 
 2975 
 
 2690 
 
 2445 
 
 2240 
 
 
 9210 
 
 8200 
 
 7500 
 
 6920 
 
 6505 
 
 5950 
 
 5250 
 
 466.5 
 
 4200 
 
 3810 
 
 3500 
 
 
 1 0095 
 
 91 10 
 
 3.S 
 
 782,5 
 
 739 
 
 6975 
 
 6/05 
 
 6410 
 
 6052 
 
 5500 
 
 5045 
 
 
 
 0870 
 
 9 1 60 
 
 8595 
 
 8160 
 
 77ic 
 
 74 SO 
 
 71 5O 
 
 6880 
 
 6675 
 
 6465 
 
 
 
 10500 
 
 98-15 
 
 Q27O 
 
 8815 
 
 84O 5. 
 
 8l IO 
 
 77QO 
 
 7670 
 
 7-iOS 
 
 7OQO 
 
 
 
 
 10380 
 
 9860 
 
 O4OO 
 
 OO5O 
 
 8680 
 
 8-185 
 
 8140 
 
 
 76QO 
 
 
 
 
 
 10^60 
 
 on I 5 
 
 qsio 
 
 9"MO 
 
 802 s 
 
 86so 
 
 8410 
 
 82OO 
 
 
 
 
 
 
 10775 
 
 0080 
 
 o6uo 
 
 Q1OO 
 
 QI 1C 
 
 8895 
 
 8670 
 
 
 
 
 
 
 
 10400 
 
 IOOQ5 
 
 u.S^5 
 
 OS6o 
 
 031 5 
 
 01 IO 
 
 
 
 
 
 
 
 
 
 
 
 
 
 13 
 
 193 ]
 
 FOUR-INCH CONCRETE SLABS. 
 ROUND RODS SPACED CENTER TO CENTER. 
 
 Diameter of Rods 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 10 11 
 
 12 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 2820 
 4390 
 6330 
 8610 
 
 ins. 
 
 ins. 
 
 ins. 
 
 % inch 
 
 10130 
 11750 
 
 13055 
 14160 
 
 8453 
 
 6430 
 
 5070 
 
 7925 
 
 4225 
 6600 
 
 3590 
 5610 
 
 8080 
 
 3165 
 4950 
 
 7 1 oo 
 
 2535 
 3960 
 5680 
 
 7750 
 
 2300 
 3600 
 5120 
 6975 
 
 2115 
 3300 
 4735 
 6457 
 8440 
 
 5 " 
 YJJ 
 
 10290 
 11600 
 12700 
 13640 
 14460 
 15190 
 
 9320 
 10580 
 11700 
 12610 
 13460 
 14220 
 14880 
 
 I " 
 
 A " 
 
 9785 
 10900 
 11810 
 12680 
 13400 
 
 I4H5 
 14646 
 
 9170 
 
 IO200 
 III7O 
 I2OOO 
 12770 
 13455 
 14095 
 
 9700 
 10620 
 11430 
 12215 
 12875 
 13500 
 
 9230 
 10130 
 11030 
 H750 
 12420 
 
 13055 
 
 Yi " 
 
 9850 
 10590 
 11300 
 11970 
 12635 
 
 9400 9070 
 10190 9860 
 10960 10570 
 11630 11245 
 12235 i J 89o 
 
 9 <* 
 
 
 9590 
 10290 
 
 10995 
 1 1600 
 
 * '* 
 
 
 li " 
 
 
 M " 
 
 
 
 
 
 
 FOUR-INCH SLABS. 
 SQUARE BARS SPACED CENTER TO CENTER. 
 
 Diameter of Rods 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 10 
 
 11 
 
 12 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ^4 inch 
 
 11030 
 12610 
 13920 
 15000 
 
 9612 
 11150 
 12450 
 13590 
 14500 
 I53io 
 
 6070 
 
 6460 
 
 538o 
 8500 
 
 4575 
 7140 
 
 4033 
 6300 
 
 3570 
 5600 
 8070 
 
 3230 
 5040 
 7260 
 
 2930 
 4580 
 6600 
 8990 
 
 2690 
 4200 
 6025 
 
 8240 
 
 f\ " 
 
 IOIOO 
 
 11390 
 12540 
 13480 
 14320 
 15030 
 
 9370 
 10650 
 11750 
 12700 
 13540 
 14270 
 14940 
 
 3 " 
 jj 
 
 9970 
 11080 
 
 I2OOO 
 I29OO 
 13630 
 I43IO 
 H9I5 
 
 9440 9018 
 10530 10100 
 11430 11030 
 12290 11850 
 13060 12610 
 
 13730 13300 
 14340 13920 
 
 T V " 
 
 958o 
 10600 
 11390 
 12190 
 12870 
 13480 
 
 9300 
 
 10200 
 II050 
 IISOO 
 12500 
 I3I30 
 
 YV. " 
 
 9880 
 10740 
 11430 
 12130 
 12770 
 
 9610 
 10440 
 11150 
 11830 
 12450 
 
 9 << 
 
 
 5 " 
 
 
 U " 
 
 
 
 V&. " 
 
 
 
 
 
 
 FOUR AND ONE-HALF INCH CONCRETE SLABS. 
 ROUND RODS SPACED CENTER TO CENTER. 
 
 Diameter of Rods 
 ' 
 
 2 
 ins. 
 
 I3I35 
 15230 
 17010 
 18510 
 19770 
 20874 
 
 3 
 
 ins. 
 
 4 
 ins. 
 
 5 
 ins. 
 
 6 
 ins. 
 
 7 
 ins. 
 
 8 
 ins. 
 
 9 
 ins. 
 
 10 
 ins. 
 
 11 
 ins. 
 
 12 
 ins. 
 
 \i inch . . 
 
 9864 
 
 7400 
 
 "557 
 
 5916 
 9246 
 
 4932 
 7704 
 1 1090 
 
 4194 
 6550 
 9427 
 
 3700 
 
 5775 
 8317 
 11320 
 
 3290 
 5123 
 7393 
 10065 
 
 2960 
 4620 
 
 6655 
 9060 
 
 II833 
 
 2687 
 4200 
 6042 
 8225 
 10750 
 
 2465 
 3850 
 5545 
 756o 
 9860 
 
 A " 
 
 13320 
 15040 
 16510 
 17845 
 19035 
 19980 
 20874 
 
 f " 
 
 13625 
 15125 
 16405 
 17580 
 18595 
 1950S 
 20345 
 
 12600 
 14070 
 15300 
 16480 
 17520 
 
 18435 
 19300 
 
 T^J " 
 
 13215 
 14495 
 15555 
 16625 
 17580 
 18405 
 
 12435 
 13655 
 14860 
 
 15845 
 16745 
 17655 
 
 X " 
 " 
 
 13125 
 14260 
 15230 
 
 16155 
 17010 
 
 12555 
 
 13625 13185 
 14700 14200 
 15550 15080 
 16405 15935 
 
 12715 
 13655 
 14635 
 15405 
 
 12320 
 13320 
 
 M235 
 15040 
 
 " 
 
 U " . . . 
 
 V\ " 
 
 
 
 194]
 
 FOUR AND ONE-HALF INCH CONCRETE SLABS. 
 SQUARE BARS SPACED CENTER TO CENTER. 
 
 Diameter of Rods 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 10 
 
 // 12 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 3420 
 
 5345 
 7700 
 
 10475 
 
 ins. 
 
 % inch 
 
 H275 
 16360 
 18200 
 19800 
 
 12350 
 
 H465 
 16195 
 
 17745 
 19050 
 20140 
 
 9415 
 
 7535 
 11760 
 
 6280 
 9805 
 
 5340 
 8330 
 
 I2OOO 
 
 4705 
 7350 
 10590 
 
 4170 
 6535 
 9415 
 
 3765 
 
 5880 
 
 8475 
 "535 
 
 3HO 
 4900 
 7060 
 9610 
 
 5 " 
 
 H " 
 
 13100 
 
 H855 
 16330 
 17655 
 18755 
 19740 
 20640 
 
 13700 
 15205 
 16510 
 17700 
 18685 
 
 19595 
 20420 
 
 12890 
 14360 
 15605 
 16780 
 17830 
 18740 
 19565 
 
 ^ " .- 
 *A " 
 
 9 " 
 
 13540 
 14880 
 
 15995 
 I70IO 
 
 17950 
 18800 
 
 12995 
 H275 
 15345 
 16360 
 
 17345 
 18200 
 
 12435 
 13640 
 14860 
 15846 
 16745 
 17655 
 
 13215 
 14330 
 15265 
 16230 
 17110 
 
 12745 
 13800 
 14920 
 15790 
 16625 
 
 12350 
 13420 
 
 14465 
 15330 
 16195 
 
 5 A " 
 
 
 1' " 
 
 
 
 % " 
 
 
 
 
 
 
 
 FIVE-INCH CONCRETE SLABS. 
 ROUND RODS SPACED CENTER TO CENTER. 
 
 Diameter of Rods 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 10 
 
 11 12 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 338o 
 5280 
 7605 
 10355 
 13523 
 
 ins. 
 
 ins. 
 
 J4 inch 
 
 16310 
 19085 
 21330 
 
 23345 
 25056 
 26495 
 
 11273 
 
 8455 
 13207 
 
 6762 
 10567 
 15210 
 
 5637 
 8805 
 12674 
 
 4793 
 7485 
 10774 
 14665 
 
 4225 
 6600 
 
 9505 
 12938 
 
 376o 
 5854 
 8450 
 
 H503 
 15020 
 
 3070 
 4800 
 6905 
 9402 
 12283 
 15550 
 
 2818 
 4400 
 
 6337 
 8627 
 11267 
 14264 
 
 T 5 -v " 
 
 16550 
 18815 
 20755 
 22465 
 23925 
 25285 
 
 26455 
 
 H " 
 
 17050 
 18950 
 20485 
 22080 
 23480 
 24690 
 25730 
 
 T^ " 
 
 17530 
 19260 
 20700 
 
 22OOO 
 23250 
 24345 
 
 16435 
 18010 
 
 19585 
 20890 
 22080 
 23215 
 
 a " 
 
 I 5 
 
 17090 
 18565 
 19835 
 21045 
 
 22155 
 
 16300 
 17685 
 19085 
 
 2020O 
 21330 
 
 17050 
 18315 
 19545 
 20620 
 
 16370 
 17605 
 18875 
 19335 
 
 
 17105 
 18220 
 19390 
 
 16550 
 17665 
 18815 
 
 if " 
 
 
 p " 
 
 
 
 
 
 FIVE-INCH CONCRETE SLABS. 
 SQUARE BARS SPACED CENTER TO CENTER. 
 
 2 
 Diameter of Rods 
 ins. 
 
 3 
 
 ins. 
 
 4 
 ins. 
 
 5 
 ins. 
 
 6 
 ins. 
 
 7 
 ins. 
 
 8 
 
 ins. 
 
 9 
 ins. 
 
 10 
 ins. 
 
 11 
 ins. 
 
 12 
 ins. 
 
 % inch 17720 
 
 14350 
 
 10763 
 
 8610 
 13445 
 
 7175 
 11205 
 
 6100 
 9520 
 13720 
 
 538o 
 8400 
 12105 
 
 4764 
 7470 
 10760 
 14650 
 
 4305 
 6720 
 9685 
 13185 
 
 3910 
 6110 
 8800 
 
 H975 
 1 5640 
 
 3590 
 56oo 
 8070 
 10905 
 14350 
 
 A " 20565 
 
 17970 
 20255 
 22270 
 23960 
 25460 
 26745 
 
 16260 
 
 18545 
 20410 
 22140 
 23675 
 25035 
 26150 
 27225 
 
 % 22945 
 
 17165 
 19065 
 
 20755 
 22115 
 
 23575 
 24805 
 
 25845 
 
 16030 
 
 17855 
 19605 
 21060 
 22425 
 23645 
 24750 
 
 A " 24900 
 
 16935 
 18585 
 19985 
 21330 
 22580 
 23710 
 
 16145 
 17720 
 
 19295 
 20565 
 21770 
 22925 
 
 *A " 26515 
 
 17090 
 
 18545 
 19815 
 21045 
 22140 
 
 16415 
 18000 
 19200 
 20315 
 21445 
 
 T V " 
 
 17300 16740 
 18595 17990 
 19755 19275 
 20890 20255 
 
 & A " 
 
 '' " 
 
 % " 
 
 
 
 195
 
 FIVE AND ONE-HALF INCH CONCRETE SLABS. 
 ROUND RODS SPACED CENTER TO CENTER. 
 
 inch 
 
 TS 
 
 H 
 A 
 
 9 
 Tri 
 
 44 
 
 ter of Rods 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 10 
 
 // 
 
 12 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 7606 
 11880 
 17110 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 
 19024 
 
 12680 
 19810 
 
 95io 
 14850 
 
 6340 
 9900 
 14260 
 19400 
 
 5390 
 8400 
 
 I2I2O 
 1 6500 
 
 4750 
 7425 
 10700 
 
 14550 
 19000 
 
 4230 
 6590 
 9500 
 12940 
 17000 
 
 3800 
 5940 
 8550 
 11650 
 15210 
 19250 
 
 3455 
 5400 
 7770 
 10589 
 13820 
 17500 
 
 3170 
 4950 
 7125 
 9700 
 12680 
 16050 
 19810 
 
 
 23160 
 26080 
 28575 
 30705 
 32560 
 
 34215 
 
 
 22795 
 25260 
 
 27385 
 29380 
 31055 
 32540 
 33900 
 
 20630 
 22990 
 25120 
 27000 
 
 28745 
 30255 
 31710 
 
 
 21285 
 23400 
 
 25175 
 26875 
 28480 
 29890 
 
 
 21990 
 
 23815 
 25420 
 26975 
 28455 
 
 2O68O 
 
 22455 
 242OO 
 
 25635 
 27045 
 
 
 21555 
 23160 
 
 24740 
 26075 
 
 20630 
 22235 
 23790 
 25120 
 
 
 21480 
 22865 
 24350 
 
 20705 
 22160 
 23570 
 
 
 21555 
 22795 
 
 
 
 
 
 FIVE AND ONE-HALF INCH SLABS. 
 SQUARE BARS SPACED CENTER TO CENTER. 
 
 Diameter of Rods 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 w 
 
 // 
 
 12 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 % inch 
 
 21630 
 25030 
 27800 
 30570 
 32670 
 34500 
 
 16150 
 
 I2IIO 
 18900 
 
 9700 
 15110 
 
 8075 
 12600 
 18160 
 
 6870 
 10720 
 15430 
 
 6050 
 9460 
 13620 
 18540 
 
 5360 
 8400 
 
 I2IIO 
 16470 
 
 4840 
 756o 
 10890 
 14830 
 19390 
 
 4390 
 6870 
 9900 
 I336o 
 17600 
 
 4040 
 6300 
 9080 
 12360 
 1 6 1 50 
 
 it ii 
 
 Ttf 
 % " 
 
 21920 
 24810 
 27240 
 29430 
 31300 
 32930 
 34500 
 
 22430 
 24930 
 
 27045 
 29OIO 
 30670 
 32150 
 33560 
 
 20770 
 23130 
 25240 
 27170 
 28920 
 30400 
 31860 
 
 & " 
 4 " 
 
 21770 
 23760 
 25640 
 27290 
 28970 
 30330 
 
 20510 
 22500 
 24470 
 26100 
 27630 
 29060 
 
 21630 
 23470 
 25030 
 26610 
 27945 
 
 2O680 
 22430 
 242OO 
 25635 
 27045 
 
 9 " 
 
 21700 
 23350 
 24860 
 26270 
 
 20920 
 22525 
 24100 
 25420 
 
 20290 
 21920 
 
 23425 
 24810 
 
 Y* " 
 
 1 1 " 
 
 
 VA. " 
 
 
 
 
 
 SIX-INCH CONCRETE SLABS. 
 ROUND RODS SPACED CENTER TO CENTER. 
 
 Diameter of Rods 
 
 2 
 . ins. 
 
 3 
 
 ins. 
 
 4 
 
 ins. 
 
 5 
 ins. 
 
 6 
 ins. 
 
 7 
 ins. 
 
 8 
 ins. 
 
 5275 
 8250 
 11880 
 16150 
 
 2 1 no 
 
 9 
 ins. 
 
 4700 
 7320 
 10550 
 14230 
 18770 
 23770 
 
 10 
 ins. 
 
 11 
 
 ins. 
 
 12 
 ins. 
 
 % inrh 
 
 21 140 
 
 14100 
 
 22000 
 
 10570 
 16500 
 23760 
 
 8450 
 13210 
 19010 
 
 7050 
 
 IIOOO 
 
 15800 
 21520 
 
 5990 
 9330 
 13470 
 18330 
 23940 
 
 4230 
 6600 
 95io 
 12930 
 16900 
 21380 
 
 3840 
 6000 
 8610 
 11750 
 I536o 
 19380 
 24000 
 
 3520 
 5500 
 7900 
 10760 
 14090 
 17830 
 
 22000 
 
 .1 
 
 } ,y 
 
 27540 
 
 31110 
 34200 
 36900 
 
 39240 
 41280 
 
 y s " 
 
 27240 
 30270 
 32850 
 35220 
 37260 
 39240 
 40830 
 
 , 7 , f " 
 
 27390 
 30060 
 32340 
 3438o 
 36360 
 38040 
 
 25290 
 27750 
 30165 
 32190 
 34050 
 35850 
 
 K " 
 
 26190 
 28300 
 
 30470 
 32310 
 33900 
 
 9 " 
 
 26840 
 28860 
 30690 
 32430 
 
 25590 
 27540 
 29430 
 31125 
 
 % " 
 
 26500 
 28230 
 30060 
 
 25485 
 27300 
 29010 
 
 1,'. " 
 
 26400 
 27990 
 
 2556<) 
 2/240 
 
 % " 
 
 
 
 
 196
 
 SIX-INCH CONCRETE SLAHS. 
 SQUARE BARS SPACED CENTER TO CENTER. 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 10 11 
 
 12 
 
 J ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 4480 
 
 10090 
 13730 
 17940 
 22700 
 
 1 i inch . 25650 
 
 17940 
 26040 
 29580 
 32640 
 3528o 
 37530 
 39660 
 41520 
 
 13450 
 
 2IOIO 
 26820 
 29800 
 32430 
 34710 
 36780 
 38760 
 40380 
 
 10770 
 16800 
 
 242CX) 
 
 8970 
 14000 
 20180 
 
 7625 
 11910 
 17150 
 23350 
 
 6720 
 10500 
 15140 
 20600 
 
 5950 
 9330 
 13450 
 18300 
 2^900 
 
 539 
 8400 
 
 I2IOO 
 16480 
 21525 
 
 4880 
 7640 
 
 IIOOO 
 
 14840 
 19550 
 24750 
 
 j r> ,, " 30000 
 
 H " 3354 
 
 fa " 36690 
 
 27540 
 30270 
 32560 
 34590 
 36540 
 38250 
 
 25830 
 28350 
 30750 
 32790 
 34710 
 36480 
 
 l /2 " 3933 
 
 2(,,SS(. 
 29130 
 
 31440 
 33060 
 34800 
 
 25650 
 27810 
 30000 
 31740 
 335io 
 
 & " 41550 
 
 26820 
 28830 
 30690 
 32430 
 
 25770 
 27700 
 29670 
 31230 
 
 YK " 
 
 26900 
 28710 
 30480 
 
 26040 
 27780 
 29580 
 
 if " 
 
 
 
 
 To illustrate the use of Table 9, attention is called to the following 
 example in which the slab is supported on two sides only: 
 
 Example: What size of slab and what reinforcement will be neces- 
 sary for the reinforced concrete construction over a 
 living-room in an all-concrete house? It is the intention 
 to reinforce the concrete slab in one direction only and 
 it is considered that the ends of the concrete slab are 
 fixed. The distance between the concrete beams is 8 
 feet, and the live or superimposed load, exclusive of the 
 weight of the construction, is 70 pounds per square foot. 
 The floor is to be finished with a wood floor secured to 
 sleepers embedded in 2 inches of cinder concrete. 
 
 Solution: The assumption is that a 4-inch slab will be sufficiently 
 thick, so that the total floor load per square foot of slab 
 will be made up as follows: 
 
 Live Load 70 |xninds 
 
 Weight of Slab 50 pounds 
 
 Weight of Flooring 4 pounds 
 
 Weight of Cinder Concrete 15 pounds 
 
 139 pounds per square foot. 
 
 Considering a portion of the slab I foot in width, the 
 total load on such a portion is equal to weight per square 
 foot by the span of the slab in feet, or 
 
 139 X 8 = 1,112 pounds. 
 [197]
 
 The bending moment of the slab may be figured by the 
 
 formula 
 
 WL 
 10 
 
 or, if the span is taken in feet and the result is desired in 
 
 inch-pounds: 
 
 M = i.2 WL. 
 
 If the weight W= 1,112 pounds, and the span in feet, or 
 L = 8, then by substitution 
 
 M = 1.2 X 1,112 X 8 = 10,675 inch-pounds. 
 Assuming that it is desired to use square twisted bars, 
 refer to the portion of Table 9 relating to 4-inch slabs. 
 It will be seen that ^g-inch square bars, spaced 5 inches 
 from center to center, have a resistance of 10,650 
 inch-pounds, which is sufficiently close for practical 
 purposes. 
 
 In order to illustrate further the use of Table 9, the following prob- 
 lem in the design of a rectangular slab supported on all four sides is 
 
 given : 
 
 Example : 
 
 Solution 
 
 A floor slab in a dwelling-house is supported on all four 
 sides by outside and partition walls. The length of the 
 slab is 14 feet, and the width is 10 feet, while the total 
 load, including the weight of the slab, is 120 pounds per 
 square foot. Determine the thickness and the reinforce- 
 ment necessary for reinforcing the slab in both directions. 
 
 It is first necessary to find the ratio of the length of the 
 slab to the breadth (as explained on page 185). This 
 ratio, or 
 
 then, from Table 8, the proportion of the load carried 
 by the short and the long span is found for the value 
 of 1.4 to be .79 and .21 respectively. The load in pounds, 
 therefore, to be carried by the short span would be 
 .79 X 120 = 94.80 pounds per sq. foot, 
 
 while for the long span the weight producing the bending 
 moment would equal 
 
 .21 X 120 = 25.20 pounds per sq. foot; 
 [198]
 
 the next thing to find is the proportionate weight on the 
 slab both ways for a strip of slab i foot in width, and 
 these weights are as follows: 
 
 Wb=io X 94.80 = 948 pounds, 
 \Vi = i4 X 25.20 = 353 pounds; 
 
 as the span and load are taken from center to center of 
 supports the bending moment both the short way and 
 the long way of the slab is then calculated by the formula 
 
 WL 
 M= 10 ' 
 
 or, using L in feet, and obtaining the results in inch- 
 pounds, 
 
 M = i.2 WL. 
 
 This calculation is as follows: 
 
 Bending Moment 
 
 Short Way of Slab =1.2 X 948 X 10=11,376 
 
 in. Ibs. 
 Bending Moment 
 
 Long Way of Slab=i.2 X 352 X 14 = 5,914 
 in. Ibs. 
 
 Table 9 may now be used for determining what slab and 
 what reinforcement will be necessary to give the required 
 resistance. 
 
 NOTE. It is best in making selections from the table, where rectan- 
 gular slabs are concerned, to use first the bending moment short way of 
 the slab. 
 
 In above example the bending moment the short way of 
 the slab is 11,376 inch-pounds. Referring to Table 9 
 it will be observed that a 4,V-mch slab, reinforced with 
 %-inch square twisted bars placed 7 inches from center 
 to center, has a resistance of 12,000 inch-pounds, and that 
 if }4-inch square twisted bars spaced 6 inches on centers 
 are used the long way of the slab, the resistance will be 
 6,280 inch-pounds, which is in excess of the bending 
 moment of 5,913 inch-pounds created in the slab length- 
 wise.
 
 Resisting Moments of Rectangular Beams. While the resist- 
 ing moment of rectangular reinforced concrete beams may be found 
 with little trouble when the percentage of the steel reinforcement and 
 the location of the neutral axis have been found, nevertheless when the 
 bending moment has to be calculated it is much more convenient to 
 determine the actual size and reinforcement needed directly from a 
 table giving resisting moments for rectangular beams of different depths 
 and reinforced with different percentages of steel reinforcement. Con- 
 sequently, the resisting moments in inch-pounds are given in Table 10. 
 The values in this table are limited by an allowable unit fiber stress on 
 the steel of 16,000 pounds, and an allowable unit compressive stress on 
 the concrete at the extreme edge of 600 pounds, and a ratio of 12. 
 
 Referring to the table it will be observed that the resisting moments 
 are given for beams reinforced with y\ of one percent to I percent of 
 steel, varying by one-tenth of one percent, and also for beams from 
 6 inches to 36^/2 inches in depth. The large values in the columns are 
 the resisting moments in inch-pounds for each inch in width of the beam, 
 while the decimal values are the areas of the steel reinforcement required 
 in square inches for each inch in width of the beam. It will also be 
 noticed from the figure accompanying the table that the depth, or the 
 distance d given in the column to the extreme left, is the distance from the 
 center of action of the steel to the top of the beam, and is not the total 
 depth of the beam. 
 
 The following example illustrates the use of the above table: 
 
 Example: A rectangular reinforced concrete beam supported on the 
 columns of a portico, supports a tile roof which imposes 
 a total load of 500 pounds per running foot; the span of 
 the beam is 20 feet. Determine the size of the beam 
 and the amount of reinforcement necessary to carry the 
 weight. 
 
 Solution: The total load on the beam is 20 X 250, or 5,000 pounds, 
 and as the beams are not fastened at the ends, the bend- 
 ing moment in inch-pounds is found by the formula 
 
 M = , or, aWL.
 
 TABLE 10. RESISTING MOMENTS IN INCH-POUNDS OF RECTANGULAR 
 
 REINFORCED CONCRETE BEAMS. (PER INCH IN WIDTH OF BEAM.) 
 
 Ratio of Steel Reinforcement. 
 
 d 
 
 .005 .006 
 
 .007 
 
 .mis 
 
 
 .<><l!> 
 
 .01 
 
 6 
 
 2601 
 
 030 3036 .036 
 
 3214 
 
 .042 
 
 3365 
 
 .048 
 
 3505 -054 
 
 3616 
 
 .060 
 
 VA 
 
 3052 
 
 033 3563 -039 
 
 3772 
 
 .046 
 
 3949 
 
 .052 
 
 4 i 02 .059 
 
 4244 
 
 .065 
 
 7 
 
 3540 
 
 .035 4132 .042 
 
 4374 
 
 .049 
 
 4580 
 
 .056 
 
 4757 -063 
 
 4922 
 
 .070 
 
 7 1 A 
 
 4064 
 
 038 4743 -045 
 
 5022 
 
 .052 
 
 5257 
 
 .060 
 
 5461 .068 
 
 5651 
 
 075 
 
 8 
 
 4623 
 
 040 5397 -048 
 
 57H 
 
 .056 
 
 5982 
 
 .064 
 
 6213 .072 
 
 6429 
 
 .080 
 
 8^ 
 
 5219 
 
 043 6093 .051 
 
 6450 
 
 .060 
 
 6753 
 
 .068 
 
 7014 .077 
 
 7258 
 
 .085 
 
 9 
 
 5851 
 
 .045 6831 .054 
 
 7231 
 
 .063 
 
 7571 
 
 .072 
 
 7864 .081 
 
 8137 
 
 .090 
 
 9^ 
 
 6520 
 
 .048 7611 .057 
 
 8057 
 
 .067 
 
 8435 
 
 .076 
 
 8762 .086 
 
 9066 
 
 095 
 
 10 
 
 7224 
 
 050 8433 .060 
 
 8927 
 
 .070 
 
 9347 
 
 .080 
 
 9708 .090 10045 
 
 .100 
 
 ioy 2 
 
 7965 
 
 053 9298 .063 
 
 9842 
 
 .074 
 
 10305 
 
 .084 
 
 10704 .0951 11075 
 
 .105 
 
 ii 
 
 8741 
 
 .055 10104 -66 
 
 10802 
 
 .077 
 
 11309 
 
 .088 
 
 11747 .099 
 
 12155 
 
 .no 
 
 n l A 
 
 9554 
 
 .058 11153 .069 
 
 11806 
 
 .081 
 
 12361 
 
 .092 
 
 12839 .104 
 
 13285 
 
 .115 
 
 12 
 
 10403 
 
 .060 12144 -72 
 
 12855 
 
 .084 
 
 J3459 
 
 .096 
 
 13980 .108 
 
 14465 
 
 .120 
 
 I2M 
 
 11288 
 
 .063 13177 .075 
 
 13949 
 
 .088 
 
 14604 
 
 .100 
 
 15169 .113 
 
 15696 
 
 .125 
 
 13 
 
 12209 
 
 .065 14252 .078 
 
 15087 
 
 .091 
 
 15796 
 
 .104 
 
 16407 .117 
 
 16978 
 
 .130 
 
 i3 l A 
 
 13166 .068 15370 .081 
 
 16270 
 
 095 
 
 17034 
 
 .108 
 
 17694 .122 
 
 18308 
 
 .135 
 
 14 
 
 14159 .070 16530 .084 
 
 17498 
 
 .098 
 
 18319 
 
 .112 
 
 I9O28 .126 
 
 19689 
 
 .140 
 
 i4 l A 
 
 15189 1.073 17732 .087 
 
 18780 
 
 .102 
 
 19651 
 
 .116 
 
 20412 .131 2II20 
 
 .145 
 
 15 
 
 16254 .075 18976 .090 
 
 20087 
 
 .105 
 
 21032 
 
 .120 
 
 21844 .135 22602 
 
 .150 
 
 isH 
 
 !7355 -078 20262 .093 
 
 21448 
 
 .109 
 
 22455 
 
 .124 
 
 23324 .140 24134 
 
 .155 
 
 16 
 
 18493 .080 21590 .096 
 
 22854 
 
 .112 
 
 24127 
 
 .128 
 
 24854 .144 
 
 25716 
 
 .160 
 
 i6> 
 
 19667 .083 22960 .099 
 
 24305 
 
 .116 
 
 25446 
 
 .132 
 
 26431 .149 
 
 27349 
 
 .165 
 
 17 
 
 20877 .085 24373 .102 
 
 25800 
 
 .119 
 
 27011 
 
 .136 
 
 28057 .153 
 
 29031 
 
 .170 
 
 171^22124 .088 25828 .105 
 
 2/340 
 
 .123 
 
 28624 
 
 .140 
 
 29732 .158 
 
 30764 
 
 .175 
 
 18 123406 .090! 27325 .108 
 
 28925 
 
 .126 
 
 30283 
 
 .144 
 
 31455 .162 
 
 32547 
 
 .180 
 
 18^24724 
 
 .093 28864 .in 
 
 30554 
 
 .130 
 
 31988 
 
 .148 
 
 33227 .16- 
 
 34380 
 
 .185 
 
 19 26079 
 
 095 30445 -114 
 
 32228 
 
 133 
 
 33741 
 
 .152 
 
 35047 .171 
 
 36264 
 
 .190 
 
 19^27469 
 
 .098 32069 .117 
 
 33946 
 
 .138 
 
 35540 
 
 .156 
 
 36916 .176 
 
 38198 
 
 .195 
 
 20 28896 
 
 .IOO' 33740 .120 
 
 357io 
 
 .140 
 
 37386 
 
 .l6O 
 
 38834 .180 
 
 40182 
 
 .200 
 
 20^30359 
 
 103 35443 -123 
 
 37517 
 
 .144 
 
 39279 
 
 .164 
 
 40800 .185 
 
 42216 
 
 .205 
 
 21 31758 
 
 105 37J93 -126 
 
 39370 
 
 .147 
 
 41218 
 
 .168 
 
 42814 .189 
 
 44300 
 
 .210 
 
 2 1 Ji 33493 
 
 .108 38985 .129 
 
 41267 
 
 .151 
 
 43204 
 
 .172 
 
 44877 .194 
 
 46435 
 
 .215 
 
 22 34964 
 
 .110 40819 .132 
 
 43209 
 
 154 
 
 45237 
 
 .176 
 
 46989 .198 
 
 48620 
 
 .220 
 
 22^36572 
 
 .113; 42696 .135 
 
 45195 
 
 .158 
 
 47317 
 
 .180 
 
 49149 .203 
 
 50855 
 
 .225 
 
 23 '38215 
 
 .115 44614 .138 
 
 47226 
 
 .161 
 
 49443 
 
 .184 
 
 51357 -207 
 
 53140 
 
 .230 
 
 23^ 39895 
 
 .118 46575 .141 
 
 49302 
 
 .165 
 
 51616 
 
 .188 
 
 53615 .212 
 
 55476 
 
 235 
 
 24 41610 
 
 .120 48578 .144 
 
 51422 
 
 .168 
 
 53836 
 
 .192 
 
 56II5 .216 
 
 57862 
 
 .240 
 
 24^43362 
 
 .123 50623 .147 53587 
 
 .172 
 
 56102 
 
 .196 58275 .221 
 
 60298 
 
 245 
 
 25 45150 
 
 .125 52711 .150 55796 
 
 175 
 
 58416 
 
 .2OO 60678 .225 
 
 62784 
 
 .250 
 
 25 1 A 4 6 974 
 
 .128 54840 .153 58050 
 
 179 
 
 60777 
 
 .204 63129 .230 
 
 65320 
 
 255 
 
 26 
 
 48834 
 
 .130 57011 .156 60349 
 
 .182 
 
 63182 
 
 .208 65639 .234 
 
 67907 
 
 .260 
 
 26^50731 
 
 133 59226 .159 62693 
 
 .186 
 
 65636 
 
 .212 68177 .239 
 
 70544 
 
 .265 
 
 27 152663 
 
 .135 61482 .162 65081 
 
 .189 
 
 68136 
 
 .216 70774 .243 
 
 73232 
 
 .270 
 
 27^54632 
 
 138 63779 -165 67513 
 
 193 
 
 70683 
 
 .220 73420 .248 
 
 75968 
 
 275 
 
 28 56636 
 
 .140 66120 .168 69990 
 
 .196 
 
 73277 
 
 .224 76II4 .252 
 
 78756 
 
 .280 
 
 28>6 58677 
 
 143 68503 .171 72513 
 
 .200 
 
 75917 
 
 .228 78856 .257 
 
 81594 
 
 .285 
 
 29 (60754 
 
 .145 70928 .174 75079 
 
 .203 
 
 78604 
 
 .232 81648 .261 
 
 84482 
 
 .290 
 
 29^62867 
 
 148! 73395 -177 77691 
 
 .207 
 
 81338 
 
 .236 
 
 84487 .266 
 
 87420 
 
 295 
 
 30 165016 
 
 150 75903 -180 80347 
 
 .2IO 
 
 84119 
 
 .240 
 
 87376 .270 
 
 90409 
 
 .300 
 
 30^67201 
 
 153 78454 -183 83047 
 
 .214 
 
 86946 
 
 .244 
 
 90312 .275 
 
 93447 
 
 .305 
 
 3i 69423 
 
 .155 81048 .186 85792 
 
 .217 
 
 89820 
 
 .248 
 
 93299 .279 
 
 96536 
 
 310 
 
 31^ 71680 
 
 .158 83683 .189 88582 
 
 .221 
 
 92740 
 
 .252 96332 .284 
 
 99676 
 
 .315 
 
 32 73974 
 
 .160 86361 .192 91418 
 
 .224 
 
 95708 
 
 .256 994H .288 
 
 102865 
 
 320 
 
 32^76314 
 
 .163 89081 .195 94296 
 
 .228 
 
 98722 
 
 .260 102545 -293 
 
 106105 
 
 .325 
 
 33 78669 
 
 .165 91843 .198^ 97220 
 
 .231 
 
 101783 
 
 .264 105724 .297 
 
 109394 
 
 33 
 
 33^81071 
 
 .l68 ; 94647 .201 100188 
 
 235 
 
 104891 
 
 .268 108953 -32 
 
 "2735 
 
 335 
 
 34 83509 
 
 .170 97494 .204 103200 
 
 .238 
 
 108046 
 
 .272 112229 .306 
 
 116125 
 
 340 
 
 34^85984 (.173 100382 .207 106258 
 
 .241 
 
 111247 
 
 276 H5554 -3" 
 
 "9565 
 
 345 
 
 35 88494 .175, 103313 .210 109360 
 
 245 
 
 H4495 
 
 .280 118928 .315 
 
 123056 
 
 350 
 
 35^91040 .178 106286 .213 112508 
 
 249 
 
 117790 
 
 .284 122350 .320 
 
 126597 
 
 355 
 
 36 93623 .180 109300 .216 115700 
 
 .252 
 
 121130 
 
 .288 125821 .324 
 
 130188 
 
 .^60 
 
 36^96243 .183 112362 .219 118930 
 
 .256 
 
 124513 
 
 .292 129335 .329 
 
 133825 
 
 365
 
 so that by substitution 
 
 M = i3 X 5,ooo X 20 = 150,000 inch-pounds. 
 
 The width of rectangular beams is generally determined 
 either by an architectural or structural requirement. 
 The minimum width of beams on account of practicability 
 of construction is usually 6 inches, and in house construc- 
 tion the maximum width would seldom exceed 12 inches. 
 Assume that a beam 10 inches in width is to be used, the 
 resistance for each inch in width would equal 
 
 150,000^- 10, or 15,000 inch-pounds; 
 
 referring to Table 10, the column headed ".006," it will 
 be seen that a beam from 13^2 inches to 14 inches in 
 depth will answer, and that the total area of steel 
 reinforcement will equal 
 
 .081 X io=.8i square inch. 
 
 Therefore two -^g-inch square twisted bars will be nearly 
 enough, and two %-inch much more than is required for 
 reinforcing the beam. 
 
 If the beam is designed as a rectangular section supporting the floor 
 slab, the depth of the beam is considered from the top of the slab to the 
 center of reinforcing in the beam. This must leave at least \^/i inches of 
 concrete under the steel, to act as fireproofing. 
 
 [ 202 ]
 
 Chapter VIII 
 Concrete Block Houses
 
 Chapter VIII 
 Concrete Block Houses 
 
 The demand for better homes, for more sanitary, permanent and fireproof 
 houses of moderate cost, led to the enthusiastic reception accorded the 
 concrete building block. In skilled, intelligent hands, many remarkably 
 beautiful and satisfactory dwellings have been and are being built of 
 this cement product. On the other hand, especially in the earlier days 
 of the industry, not a few unsightly and unsatisfactory structures re- 
 sulted. The fact that little or nothing is said of success, while great 
 publicity is given to failure, has led many to believe that good houses 
 cannot be built of concrete blocks. Such is far from the case: many of 
 the best architects in the country have designed and built residences of 
 concrete blocks, some of which have cost more than one hundred thousand 
 dollars. From the smallest cottage to the palatial mansion, these struc- 
 tures are satisfactory in every detail the combination of tasteful design 
 with good workmanship. 
 
 Designing the Block. With regard to the size and proportional 
 dimensions of the block or blocks, little can be said other than that these 
 details should be in perfect keeping with the general architectural style 
 of the structure. The same holds true in the matter of surface finish 
 of the block. Concrete, as concrete, has sufficient beauty in itself to 
 make imitation of other materials not only unnecessary, but even repre- 
 hensible. Too frequently mechanics have designed and marketed block 
 molds perfect mechanically but so bad esthetically that architects have 
 often rightfully refused to use the product. With a simple mold of plain 
 design, an artisan can produce a block of wonderful beauty and utility. 
 To bring out the beauty of the concrete, the exterior of the block is 
 
 [205]
 
 finished in accordance with any of the several methods given under 
 "Surface Treatment," page 122. 
 
 Making the Block. The selection, proportioning and mixing of 
 the aggregate for concrete blocks are governed in general by the informa- 
 tion covering these subjects on preceding pages. On account of the 
 narrowness of the spaces of molds, the maximum size of stone permissible 
 in a well-graded aggregate is usually J^ to % inch in diameter. The 
 Portland cement, sand and crushed rock should be combined in such 
 proportions as to form a dense, damp-proof block. This correct pro- 
 portion is determined by methods previously described. For average 
 conditions, with sand grading uniformly from o to 34 mcn an d stone from 
 3/s to }/2 inch, the concrete is generally proportioned I part cement to 
 i V^. parts sand to 3 parts crushed rock or I part cement to 2 parts sand 
 to 4 parts crushed rock. With clean, well-graded, crusher-run stone 
 screenings or bank-run gravel, the proportions are most frequently I to 3 
 or i to 4. When sand alone is used, more cement is required. Such 
 concrete is most often proportioned I to 2 or I to 3. In order to produce 
 blocks similar in quality and appearance, all materials, including the 
 water, should be accurately measured by volume. 
 
 It is highly important that an abundance of water be used in the 
 concrete for blocks. The cement requires it, and in no other way can 
 dense, damp-proof blocks be made. The quantity of water necessary 
 to a given amount of dry materials varies. If the block is made by tamp- 
 ing, there should be at least sufficient water that liquid cement will flush 
 to the surface when the concrete is rammed into the block mold. Fre- 
 quently block manufacturers, in their efforts to turn out quantities of 
 blocks with a minimum number of molds, have made the very serious 
 mistake of mixing the concrete too dry, so that the blocks might be 
 stripped of the molds more quickly. No amount of tamping will pro- 
 duce density in a concrete lacking sufficient water. Concrete for poured 
 blocks is usually of the consistency known as "mushy" or "quaking." 
 
 Curing Cement Products. To cure concrete products rapidly 
 
 [206]
 
 :.S 
 
 = 5 
 
 ^- 
 
 C t_ Js 
 
 111 
 
 s E 
 
 rt tx
 
 . 
 
 -, rt so 
 
 see 
 
 a a o 
 
 a M-O 
 
 a bio c 
 
 
 O rt 
 
 a a 
 rt 
 
 3 O 
 to 
 
 , 
 otc 
 
 s ^ 
 
 S-o 
 o.= 
 
 "a- 2 
 
 S l 
 
 
 
 u .c 
 
 en -M 
 
 ^ ,r 
 
 O C. 
 I- O 
 CJ 1- 
 
 '3 
 
 S 
 = 
 
 ^ 
 
 "3 
 
 (A
 
 and with the best results, heat and moisture are essential. A thorough 
 understanding and practice of these requirements enable the manu- 
 facturer not only to market his product sooner, but also to produce a 
 superior article. 
 
 Sufficient water must be incorporated with the concrete previous 
 to molding and must be conserved in the product until it is thoroughly 
 cured. After the block is molded, precautions must be taken to protect 
 it from sun, wind and frost until the cement has thoroughly set. (See 
 instructions for protection of freshly placed concrete, page 117.) Open- 
 ings to the curing room are closed by doors or canvas, so as to cut off 
 all drafts, which tend to remove moisture from the concrete product. 
 Moreover, as soon as possible without pitting the surface, the freshly 
 molded units are sprinkled with water and the operation repeated 
 at intervals of four to twenty-four hours for five to seven days. 
 When seven days old, blocks may be piled in the open air. Even then 
 an occasional wetting is beneficial. Ordinarily cured blocks should not 
 be placed in the wall until they have attained the age of at least thirty 
 days, as freshly made concrete contracts slightly until the cement has 
 attained its full set, and small shrinkage cracks might appear at the 
 mortar joints. 
 
 Portland cement sets up more quickly in warm weather than in 
 cold. Within recent years many cement products manufacturers have 
 been taking advantage of this characteristic of cement by installing 
 steam-curing plants. With steam even at atmospheric pressure, it 
 has been found that in a steam-tight kiln the concrete becomes suffici- 
 ently hard in the course of a few days to permit the shipping of the 
 product. 
 
 $ Exhaustive tests made by the United States Bureau of Standards 
 have deduced the fact that a compressivc strength of concrete consider- 
 ably in excess of that obtained normally after aging for six months can 
 be obtained in two days by subjecting the product to steam under 
 considerable pressure. Moreover, steam-cured products are lighter in 
 color and much more uniform in appearance than concrete of the same 
 aggregate cured by ordinary methods. 
 14 (209!
 
 Advantage of Block Construction. The concrete block is the 
 simplest form of unit construction. Since it is a factory product, the 
 same mold is used many times for many different structures, with a 
 resulting small charge for forms. Each unit can be carefully inspected 
 for quality and uniformity of appeal ance previous to erection in the house 
 wall and all faulty pieces rejected. A concrete block house presents no 
 unusual difficulties of construction. Masons of ordinary skill can build 
 a residence with concrete blocks much more quickly and cheaply than 
 with ordinary stone or brick. The floors and interior finish are the same 
 as those usually given masonry structures. 
 
 The architect interested in concrete blocks may obtain them from 
 manufacturers who make a standard pattern, or, if these are not satis- 
 factory, he may select his own aggregates and surface finish, even to the 
 extent of having special face molds made for machines used in the manu- 
 facture of ordinary blocks. This was done in the case of the Steers' 
 residence, shown on another page. This large and costly dwelling was 
 built of blocks cast in plain form on a machine of simple pattern, but with 
 aggregates selected and mixed to give the required color and texture. 
 This dwelling is an excellent example of the utility of the concrete block 
 when in competent hands, as it represents the combined efforts of prom- 
 inent architects and engineers. 
 
 Where the architect selects the block made by the manufacturer, 
 he should make certain that it is of the very best quality as to density 
 and strength. In the matter of porosity, however, it may be said that 
 blocks which admit moisture when first erected sometimes become 
 thoroughly water tight. 
 
 The concrete block is especially valuable in localities scarce in timber, 
 where the cost of forms for poured or cast houses might be excessive. 
 In some countries the block has taken piecedence over reinforced con- 
 crete for house wall construction, notably in England, Scotland and Ire- 
 land. These countries have surpassed the United States in attractive 
 block buildings, especially of the cottage type. They are usually con- 
 structed of the severely plain block, such as is shown in the accompanying 
 illustrations. There has been no attempt at fantastic shapes or orna- 
 
 [210]
 
 mentation, merely the substitution of the concrete block for plain, 
 dressed stone. 
 
 The several illustrations of block houses show the attractive char- 
 acter of the material when used in the most direct and unpretentious 
 manner. 
 
 The design of reinforced concrete buildings requires an understand- 
 ing of at least such elementary principles of engineering as will insure 
 safety to the structure, but with blocks the builder may, generally speaking, 
 proceed as with brick or stone. As is the case with all materials used 
 in unit construction, however, each requires special treatment, but the 
 laying up of a block wall is not more difficult or complicated than the 
 construction of a wall of brick or stone. In brief, the block is an excellent 
 substitute for these materials, whether applied to dwellings or buildings 
 of larger size. 
 
 [213
 
 *. 
 
 fc 
 
 I * 
 
 ! I 
 
 I b 
 
 (A 
 >, 
 
 =: .i 
 
 II 
 
 !
 
 Administration Building, Washington Park, Chicago. 
 
 An especially interesting example of untreated surface. 
 (See pages 123 and 124.)
 
 Alphabetical List of Architects, Engineers and 
 
 Builders Whose Work is Represented in the 
 
 Illustrations Contained in this Book* 
 
 ARCHITECTS 
 
 PAGE 
 
 Atterbury, Grosvenor, New York 10, 84 
 
 Bcatty, C. N., Hot Springs, Ark 176 
 
 Blake & Butler, New York 208 
 
 Buchanan, C. W., Pasadena, Cal 35 
 
 Carrere & Hastings, New York 208 
 
 Chapman & Frazer, Boston 13 
 
 Clark, C. C., Altadena, Cal 169 
 
 Covell, William S., New York 170 
 
 Elzner & Anderson, Cincinnati 25 
 
 Fernekes & Cramer, Milwaukee 22, 23, 64 
 
 Kahn, Albert, Detroit (Frontispiece) 71 
 
 Lord & Hewlett, New York 207 
 
 McKean, R. W., Riverside, Cal 190 
 
 McKim, Mead & White, New York 7 
 
 Parrish, W. H., Carnegie, Pa 120, 181, 182 
 
 Parry, Oliver Randolph, Philadelphia 35, 218 
 
 Plack, W. L., Philadelphia 25 
 
 Purdon, James, Boston 33 
 
 Putnam & Cox, Boston 78 
 
 Read & Morrill, Brooklyn 109 
 
 Richards, H. H., Chicago 204 
 
 Rocking, F. L., Pasadena, Cal 32 
 
 Rotier, H. J., Milwaukee 212 
 
 Shaw, Howard V., Chicago 132, 211 
 
 Simon, Grant M., Philadelphia 14, 145, 153, 154 
 
 Smith, John J., Winthrop, Mass 27 
 
 Thorne, Harry E., Ottumwa, Iowa 1 10 
 
 Tracy & Swartout, New York 131, 161 
 
 Warren & Wetmore, New York 162 
 
 Wilby, Ernest, Detroit Frontispiece 
 
 ENGINEERS 
 
 Aberthaw Construction Company, Boston 119 
 
 Howes, Benjamin A., New York 48,49,50,51, 125, 138, 170,214,215 
 
 Simpson Bros., Boston 220 
 
 Turner Construction Co., New York 162 
 
 BUILDERS 
 
 Bosworth, P. H., San Francisco 18, 135 
 
 Carey & Reed, Philadelphia 14, 72, 87, 145, 153, 154 
 
 Knapp, C. R., Albany -77 
 
 Riley, W. H., Riverside, Cal . . 188 
 
 * In a few cases it was impossible to obtain names of architects and 
 omissions were, therefore, unavoidable. 
 
 [217]
 
 Church Window, Lynn, Mass. 
 
 Simpson Bros., Engineers. Boston 
 
 Architectural detail cast in concrete. Equals stone in strength and appearance 
 
 and costs much less.
 
 Index
 
 Index 
 
 Abrascd and tooled surfaces, 124 
 
 Adaptability of concrete, 6 
 
 Advantages of concrete for house con- 
 struction, 1 1 
 
 Aggregates, 85, 86, 89, 129 
 
 Architectural composition, 23 
 
 Architectural decoration in color, 42 
 
 Architectural design and treatment, 19 
 
 Architectural details of molded and cast 
 concrete, 40 
 
 Architectural details of monolithic con- 
 struction, 34 
 
 Artificial colors, 133 
 
 Bars plain, corrugated and deformed, 
 
 58,59 
 
 Beams and girders, 148, 178 
 Beams and slabs (illustration), 55 
 Bending moments, 177, 184 
 Bending reinforcement, 115 
 Blocks, 205 
 
 Blocks, advantage of, 210 
 Blocks, curing of, 206 
 Blocks, design and manufacture of, 205, 
 
 206 
 
 Brushing surfaces, 125 
 Built-up form construction, 94 
 Buttress construction (illustration), 23 
 
 Calculating bending moments, 177 to 187 
 
 inclusive 
 Calculations for reinforced concrete, 139 
 
 to 171 inclusive 
 Centering, 93 
 
 Cinder concrete, 67, 86, 89 
 Collapsible forms, 96 
 Colonial types (illustration), 33 
 Color decoration, 42 
 Colored surfaces, 133, 134 
 Columns, 78, 167, 168 
 Concrete blocks, 205 
 Concrete in compression, 159, 164 
 Concrete copings, 66 
 
 Concrete form separator, 102 
 Concrete residence of costly type (fron- 
 tispiece) 
 
 Concrete and rubble work (illustration), 35 
 Concrete wall construction, 75, 76 
 Conductivity, resistance to, 15 
 Conflagration test of concrete, 26 
 Consistency in design (illustration), 28 
 Constructive forms, 96 
 Copings, 66 
 
 Cored slabs (illustration), 84 
 Core tile construction, 97 
 Cost of steel for reinforcing, 113 
 Country houses, 33 
 "Curry Tyer, " 118 
 
 Dead loads, 171 
 
 Decoration in color, 42 
 
 Decoration with mosaic inlay (illustra- 
 tion), 45, 131, 161 
 
 Decoration with tile inlay, 42 
 
 Decorative details (illustration), 41 
 
 Decorative features of timber construc- 
 tion, 44 
 
 Density of concrete, 89 
 
 Designing reinforcement, 191 
 
 Details of construction, 55 
 
 Development of particular style, 19 
 
 Displayed selected aggregates, 129 
 
 Door frames, 70, 74, 75 
 
 Doorways (illustrations), 36, 37, 45, 54, 71 
 
 Double reinforcement, 185 
 
 Dry mixed concrete, 91 
 
 Durability, 12, 70 
 
 Earthquake, resistance to (illustration), 
 
 13 
 
 Eaves, 68, 69, 70 
 Elaboration of design, 39 
 Entablatures, 40 
 
 Estimates, a practical example, 93 
 Estimating quantities of materials, 92 
 
 [221]
 
 Expanded metal, 59, 114 
 Expansion joints, 66, 67 
 Exterior finish (illustration), 88 
 Exterior surface decoration (illustration). 
 18 
 
 Fabricated reinforcement, 50, 60 
 
 Fabricating reinforcement, 115 
 
 Facade design, proper treatment of (illus- 
 tration), 39 
 
 False treatment (illustration), 20 
 
 False work, 93 
 
 Felt roof coverings, 65, 66 
 
 Ferro-Dome construction, 97 
 
 Ferro-Inclave, 67 
 
 Fire losses, 5 
 
 Fireplaces (illustrations), 48, 49, 50, 145 
 
 Fireproof qualities, n 
 
 Flashing, 66, 68, 69 
 
 Flat roofs, 62, 65 
 
 Floor construction, 55, 61, 76 
 
 Floor covering of wood, 62 
 
 Floor finish, 61 
 
 Floor loads, 174 
 
 Floors of terra cotta tile, 56, 57 
 
 Flower boxes (illustration), 72 
 
 Form holders, 104 
 
 Forms, 77, 78, 94 to 1 1 1 inclusive 
 
 Forms for one-story stages, 98 
 
 Forms for wall construction, 97 
 
 Form work and centering, 93 
 
 Fountain, 72 
 
 Frank treatment of concrete (illustration), 
 14, 22, 73, 87, 153, 154 
 
 Frieze, 44 
 
 Furred walls, 81 
 
 Girders, 55 
 
 Glue molds, use of in intricate design, 39 
 
 Gravel, 86, 89 
 
 Gutter construction, 68, 69, 70 
 
 Half-timber design (illustrations), 25, 46 
 
 Hand mixing, 90 
 
 Heating materials in cold weather, 121 
 
 Hinton floor system, 57 
 
 Hollow concrete walls, 80, 105 
 
 Hook bolts for forms, 101 
 
 Interior construction (illustrations), 7, 72 
 Interior decoration and details, 44, 48, 52 
 Interior treatment (illustrations), 48, 49, 
 50, 51 
 
 [222 ] 
 
 Joining frame and wall construction, 73 
 
 Joints, 66 
 
 Joists, 55, 78, 79 
 
 Joists, methods of supporting, 78, 79 
 
 Kahn bar, 59 
 
 Lever arm determination, 150 
 
 Lined walls, 81 
 
 Live and dead loads, 171 
 
 Loads, 168, 171, 172, 173, 174 
 
 Long span construction (illustrations), 27, 
 
 30 
 Low cost of up- keep, 16 
 
 Machine mixing, 89 
 
 Mantels (illustrations), 49, 50 
 
 Materials, 85, 86, 92 
 
 Measuring boxes, 90 
 
 Measuring ingredients, 89, 90 
 
 Metal lath, 67 
 
 Method of supporting floors, 76 
 
 Methods and types of steel reinforcement, 
 58 
 
 Methods of finishing floors, 6l 
 
 Mission style (illustration), 32 
 
 Mixing, 86, 89, 90, 91 
 
 Modulus of elasticity, 149 
 
 Molded and cast details, 40 
 
 Monolithic concrete, architectural details 
 of, 34 . 
 
 Monolithic construction expressed in de- 
 sign (illustration), 29 
 
 Mortar facings, 123 
 
 Mosaic decoration, 134 
 
 Mosaic inlay for surface decoration 
 (illustration), 45 
 
 Mushroom system, 57 
 
 Neutral axis, formulas for determining. 
 
 149 
 Non-conductivity, 15, 75 
 
 Operations in the field, 85 
 
 Ornamental details (illustrations), 41, 54 
 
 Ornament expressed in color, 42 
 
 Ornamental mosaic (illustration), 45 
 
 Ornament, precast, 44 
 
 Ornamental tile, 42 
 
 Paneling in concrete, 44 
 
 Panel or sectional wall form, 103 
 
 Pedestal of concrete (illustration), 43
 
 Placing reinforcement, 115 
 
 Porch construction (illustrations), 23, 27, 
 
 29. 30, 31, 35- 40. 47, 72, 87, 153, 154 
 Portland cement, 85 
 Posts, 167 
 
 Pouring concrete, 78 
 Precast concrete construction, 84 
 Precast detail (illustrations), 41, 42, 43 
 Primary and secondary reinforcement, 142 
 Principles of reinforced concrete, 139 
 Profiles suitable for detail (illustration), 38 
 Projecting masonry (illustration), 25 
 Proportioning and mixing, 86, 89 
 Protection of work, 117, 121 
 Reinforcing bars, 58, 59, 60, 61, in, 112 
 Reinforcing, calculations for, 177 to 199 
 
 inclusive 
 
 Reinforcing steel, kinds of, 112 
 Reinforcing stirrups, 59, 61 
 Reinforcement, 139 to 171 inclusive 
 Reinforcement of joists, 55 
 Reinforcement of roofs, 67 
 Repairs, avoidance of, 16, 70 
 Residence in Jamaica (illustration), 13 
 Resisting moment, 151, 155, 200, 201, 202 
 Roof construction, 62, 65, 66, 67, 68, 69, 
 
 70 
 
 Roof coverings, 65, 66, 67, 68, 69 
 Roof gardens, 66 
 Roof gardens (illustration), 63 
 Roof gutters, 68, 69, 70 
 Roof loads, 173 
 Rubble work as an accessory (illustration), 
 
 35 
 
 Safe loads on columns, 168 
 
 Salt, protection from freezing by, 117 
 
 Sand, 85 
 
 Sand blasting, 126 
 
 Sand blasting (illustration), 128 
 
 Sanitary construction (illustration), 138 
 
 Scrubbed surfaces, 126 
 
 Seashore house of concrete (illustrations), 
 14,87 
 
 Secondary reinforcement, 141 
 
 Sectional forms, 77 
 
 Sectional wall forms, 103 
 
 Securing reinforcement, 115 
 
 Selected aggregates, 129 
 
 Selected and displayed aggregates (illus- 
 trations), 131, 161 
 
 Selection and care of steel reinforcement, 
 in 
 
 Selection of materials, 85 
 
 Separately cast details (illustrations), 41, 
 42, 43 
 
 Separately cast ornament, 44 
 
 Separately molded members (illustration), 
 
 84 
 
 Shingles, 67 
 
 Shrinkage rods and bars, 141 
 Sills, 74, 75 
 Simplicity, 27 
 Simplicity in design (illustrations), 31, -57, 
 
 ..4 
 Single story construction (illustration), 22 
 
 Slab reinforcement, 185 
 
 Slabs and beams (illustrations), 55, 84 
 
 Sloping roofs, 67 
 
 Small houses (illustrations), 22, 29, 120, 
 181 
 
 Solid walls (illustration), 87 
 
 Sound-proof properties, 15 
 
 Spacers for reinforcement, 99 
 
 Spading concrete, 123 
 
 Stairways, 52 
 
 Stairways (illustrations), 51, 84 
 
 Standard specifications for Portland ce- 
 ment, 85 
 
 Steel forms, 106 
 
 Steps (illustration), 71 
 
 Stirrups, 59, 61, 187 
 
 Stone, 86 
 
 Strength of concrete, 147, 159, 164 
 
 Strength of concrete walls, 76 
 
 Successful use of concrete (illustration), 35 
 
 Surface finish (illustrations), 7, 14, 87. 
 125, 127, 130, 131, 145, 153, 161 
 
 Surface treatment, 122 to 136 inclusive 
 
 Tables for designing reinforcement, 191 
 
 to 197 inclusive 
 Tamping concrete, 124 
 T-beams, 157, 158, 163, 164 
 Terra cotta tile, 56, 57 
 Texture smooth and rough (illustrations), 
 
 48, 49, 50 
 
 Tile for mosaic inlay (illustration), 45 
 Tile roofing, 67 
 Tile, their use as a decorative medium. 
 
 42, 134 
 
 Timber combined with concrete, 44 
 
 Timber combined with concrete (illus- 
 tration), 47 
 
 Tooled surfaces, 124, 129 
 
 Top coat for floors, 6 1 
 
 Treatment of concrete surfaces, 122 
 
 Tying reinforcement, 118 
 
 Tying and separating sides of forms, 100 
 
 Types of floor construction, 55 
 
 Undercut design in ornament (illustra- 
 tions), 41, 42, 43 
 Unit panel construction, 94, 95 
 
 [223]
 
 Untreated exterior surfaces, 123 
 Untreated surfaces (illustrations), 14, 87, 
 
 153. 188 
 Up-keep, low cost of (illustration), 64 
 
 Veneered, lined and furred walls, 81 
 Vermin-proof qualities, 15 
 Vertical column reinforcement, 167 
 
 Wall construction, 75, 76, 77, 78. 80, 81 
 
 Wall forms, 77 
 
 Walls (illustration), 87 
 
 Water, 86 
 
 Waterproof joints, 73 
 
 Waterproof qualities of concrete (illustra- 
 tion), 72 
 
 Weatherproof concrete, 76 
 Welded frames, 60, 61 
 Window construction, 70, 73 
 Window and door frame construction, 70, 
 
 73. 74 
 
 Wire form ties, 100 
 Wiring reinforcement, 118 
 Wooden floor covering, 62 
 W'orkingman's cottage (illustration), 10 
 Working stresses, 147 
 Woven wire, 59, 114 
 
 [224!
 
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