THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA LOS ANGELES GIFT OF John S.Prell i JOHfl S. PRELL Civil & Mechanical Engineer. SAN FRANCISCO, CAJU SKELETON CONSTRUCTION IN BUILDINGS. NUMEROUS PRACTICAL ILLUSTRATIONS OF HIGH BUILDINGS. BY WILLIAM H. BIRKMIRE, Author of "Architectural Iron and Steel" and ' Compound Riveted Girders as Applied in the Construction of Buildings? FOURTH EDITION. NEW YORK: JOHN WILEY & SONS. LONDON: CHAPMAN & HALL, LIMITED. 1905 COPYRIGHT, 1893, BY WILLIAM H. BIRKMIRE. BOBERT DRUMMOND, ELECTROTYPER AND PRINTER, NEW YORK. Library lilt PREFACE. THE author has endeavored in this volume to describe and illustrate the method of skeleton-constructed buildings ; a new type of structure, which calls for principles entirely differ- ent from the old system of cast-iron fronts and cast-dowelled columns with wooden girders. He has been induced to prepare it from the fact that the improvements in modern iron construction, especially in high buildings, has been so rapid during the past few 'years that no work, however recent, meets the latest requirements. Notwithstanding the fact that the subject of the strength of columns has been ably treated of again and again, tables of tests of various-shaped columns are given, and in a few chap- ters especial stress has been laid upon the advantages and dis- advantages of different shapes of iron and steel in columns for making rigid connections with the floor beams, curtain-wall girders and with each other a necessary requirement, indis- pensable to good construction. Other chapters are devoted to the details and calculations attending the erection of high build- ings using the skeleton construction, the system of wind-brac- ing, curtain-wall supports, and foundations. WM. H. BIRKMIRE. NEW YORK, April, 1893. 713847 TABLE OF CONTENTS. CHAPTER I. GENERAL AND DESCRIPTIVE. PAGE Development of the Skeleton Construction I The Skeleton Construction and how Composed 2 Conditions imposed by the New York Building Law upon the Use of Cur- tain Walls 2 Variations of the Skeleton Construction 2 Representative Chicago High Buildings 3 The Woman's Christian Temperance Union Building, Chicago 4 The Owings Building, Chicago 5 The German Opera House, Chicago 6 The Masonic Temple, Chicago 8 Representative New York High Buildings 9 New Netherlands, N. Y 9 The World Building, N. Y 12 The Manhattan Life Insurance Building, N. Y 14 New York Sun Building 10 New York Building Law in Relation to Skeleton Construction 13 CHAPTER II. COLUMNS. Buildings of New York in which Cast-iron Columns are Used 20 " " Chicago " " " " " 20 " New York " " Wrought-iron and Steel Columns are Used. 20 The Height of Buildings Using Cast-iron compared with those Using Wrought-iron and Steel Columns , 21 Cast-iron Columns 21 Wrought-iron and Steel Columns 22 The Advantages and Disadvantages of Different Shapes of Compound Sec- tions 24 Cost of Columns 24 Availability of Material for Columns 25 The Advantages of Different Shapes of Columns for Connections 25 VI TABLE OF CONTENTS. PAGE The New York Building Law Relating to the Strength of Columns 26 Strength of Cast-iron Columns 28 Factors of Safety for Cast-iron Columns 31 Strength of Wrought-iron and Steel Columns 32 Tests of Phoenix Columns. Table 33 " "Latticed " " 34 " "Z-bar " " 34 " " Wrought-iron Box Columns. Table 35 Strength of Steel Column 35 Ultimate Strength of Wrought-iron Columns. Table 36 Elements of Z-bar Columns. Tables 37 Safe Load on " " 391045 Safe Load for Phcenix " " 46 Dimensions of " " " 47 CHAPTER III. COLUMN CONNECTIONS. Cast-iron Column with Wooden Girders 49 " Connection in the Skeleton Frame 52 Z-Bar Column Connection. . . , 53 Phcenix " " 56 Connection of Column Sections made up of Angles and Plates 58 Rivet Spacing in Column Connections 61 CHAPTER IV. FLOOR LOADS AND FLOOR FRAMING. Dead Loads 63 Live Loads , 63 New York Building Law of 1892 in Relation to Floor Loads 63 Chicago Practice Relating to the Calculation of the Dead and Live Load upon Floors 64 Floor Framing 66 To Determine Coefficient for Beams 67 Properties of Wrought iron I-Beams 68 Deflection 68 Coefficient for Steel Beams 69 Properties of Steel I-beams 69 " Wrought-iron Channels /o " " Steel Channels 71 Beam Connections 72 New York Building Law Relating to Beam Connections 73 Floor Arches 77 Brick Arches 78 TABLE OF CONTENTS. Vll PAGE Porous Terra-cotta Arches 78 Concrete Arches 80 Weight of Porous Terra-cotta Blocks 80 Corrugated Iron and Steel Arches 8r The Gustavino Tile Arch 81 Tie-rods . 82 CHAPTER V. EXAMPLES OF HIGH BUILDINGS. The Home Life Insurance Building Floor Plan 86 Beam " 86 Curtain Walls. 89 Columns and Girders go Table of Material in the Steel Column with Loads 92 " " " " " " Girders 94 SPECIFICATION. General 95 Quality of Steel 96 Rivet Steel 97 Workmanship 97 Framing of Top Story and Spire 98 Painting at the Works 98 Anchors 98 Painting at the Building 99 Cast Iron IOI Lintels 101 Base for Wrought-iron Smoke Flue 101 Plates 101 Door to Flue 101 Frame to Ash-lift 101 Vault Lights 101 Curved Skylight 102 Coal-hole Covers '. 102 Sills to Doors to Roof 102 Bronze Saddles 102 Cast-iron Mullion 102 Columns to Elevator Shaft 103 Sills " " " 103 Stairs 103 Guards to Elevator Shaft 104 Vlll TABLE OF CONTENTS. PAGE Electro-plating 104 Partition to Cellar Stairs 105 Main Entrance Doors , 105 Wrought-iron Boiler Flue 105 Furring. 106 Floors beneath Elevators . . . . 106 Skylight over Main Office and Elevators 106 Glass under Skylight 106 Skylights in Top Story 107 Floor Lights 107 Window Guards 107 Grating Doors over Ash-lift 107 Platform over Elevators 107 Clamps 108 General 108 CHAPTER VI. THE HAVEMEYER BUILDING. Floor Plan no Beam " in Column Detail, Sway-bracing 116 Table of Materials in the Columns with Loads 118 SPECIFICATION. Conditions itg Time of Completion 120 Payments 121 Sub-contract , 122 Materials and Workmanship 122 Delivery and Storage 122 Wrought Iron 123 Steel 124 Cast Iron 124 Tests f 124 Construction of Works 1 24 Setting I2 g Painting 129 Beams and Channel-bars < 129 Girders 131 Box Girders 131 Tie-rods 131 Anchors, Straps, Clamps, etc 132 Tie-rods 134 Sway -braces 134 TABLE OF CONTENTS. IX PAGE Lintels of Cast Iron 135 Pillars of Wrought Iron 136 Posts 157 Cast-iron Base-plates 137 Roofs 138 Staircases 138 Ladders 140 Railings 141 Gates 141 Guards 142 Grille-work 142 Gratings 142 Partitions, Enclosures, Floors, etc 142 Iron Shutters 144 Iron Doors 145 Posts for Doors 145 Light Cast-iron Work 145 Deck and Tank House 146 Patent Lights 146 Boiler Flue 148 Elevator Fronts 149, Sidewalk Elevator 150 Miscellaneous -. 151 CHAPTER VII. THE JACKSON BUILDING. Floor Beam Spacing 152 Calculation for Floor Weights 153 Column Connections 153 CHAPTER VIII. THE NEW NETHERLAND, NEW YORK. Floor Plan 158 Beam Plan 158 Columns 161 Foundation for Columns 163 Wall Thicknesses 163 Table of Columns 165 The Waldorf, N. Y 166 Floor Plan 166 Beam Plan 169 The Postal Telegraph Building, N. Y 170 X TABLE OF CONTENTS. CHAPTER IX. WIND-BRACING. PAGB Wind-pressure 174 Wind-bracing in the Venetian Building, Chicago 174 Curtain-walls 178 Curtai n-wall Supports 179 CHAPTER X. THE OLD COLONY BUILDING, CHICAGO, ILL. The Loads used in Calculations for the Building 190 Chicago Building Law relating to Steel or Iron Beams in Foundations. . . . 192 Wind-bracing Portal Arches 195 CHAPTER XI. THE MANHATTAN LIFE INSURANCE BUILDING, N. Y. Office Arrangement 210 Arrangement of Beams and Girders 210 Cast-iron Columns 214 Steel Columns 216 Riveting 218 Cast-iron Lintels 219 Framing in Fire-proof Block Partitions 219 Anchoring of Walls 219 Arcade at Fifteenth and Sixteenth Stories 220 Tower and Dome 220 Foundations by the Pneumatic Process 222 Caisson Detail 227 Cantilever Construction 229 To Determine the Nature of the Soil 233 Foundations on Rock 233 Foundations upon Clay 234 " " Sand 234 " P'les 234 " " Steel Rails and T-beams 236 LIST OF ILLUSTRATIONS. CHAPTER I. PAGE Fig. I. The Woman's Christian Temperance Union Building, Chicago, 111. 4 2. The Owings Building, Chicago, 111 5 3. The German Op'era House, Chicago, 111 6 4. The Masonic Building, Chicago, 111 8 5. The Proposed New York Sun Building 10 6. The World Building, N. Y 12 7. Manhattan Life Insurance Building, N. Y 14 CHAPTER II. 8. Cast iron H-Column with Open Web 21 9- 10. n. 12. 13- ' Closed" 21 Rectangular Column Section 21 21 Double 21 Circular " 21 14. Z-Bar Column Section 22 15. " " " with Cover Plates 22 16. " " " " " " 22 17. Z-Bar Column Section Used in Venetian Building, Chicago 22 18. Column Section of Angles and Plates 22 19. " " " " with Web and Cover Plates 22 20. Box Column Section 22 21. " " " 22 22. Phrenix Column Section 23 23. Rectangular Wrought-iron or Steel Column Sections 23 24- " " " " " 23 25- " 23 26. Octagons " 23 27. Channel Column Section 23 28. " Latticed " 23 29. Box Column with Plates and Latticing 23 30. Plate and Box Column Section showing Notation as Used in the Calculation for the Moment of Inertia 36 xi Xll LIST OF ILLUSTRATIONS. CHAPTER III. PAGE Fig- 3 1 * 3 2 - Cast-iron Column Connections; with Wooden Girders 49, 50 33. " Iron Girders 51 34. in the Skeleton Frame 52 35. 36. Z-bar Column Connections 54, 55 37. Phoenix " " 57 38. Wrought-iron or Steel Box Column Connections 58 39. Wrought-iron or Steel Column Connections made up of Plates and Angles 59 CHAPTER IV. 40. Beam Connections 76 41. Porous Terra-cotta Arches and Ceilings 79 42. 43. Corrugated Arches 82 CHAPTER V. 45. Home Life Insurance Building, New York, Front Elevation 84 46. Beam Plan as Constructed 87 47. Floor Plan as originally Started 88 48. Beam " " " " 88 49. Section and Part Elevation of Rear Wall showing Mullions and Facias 90 50. Transverse Section of Masonry, Elevations of Columns and Floor Girders 91 51. Transverse Section 97 52. Longitudinal " 100 CHAPTER VI. 53. Havemeyer Building. i(X) 54. Typical Floor Plan in 55. Beam Plan 112 56. Roof Plan , 113 57. Foundation Plan 113 58. Transverse Section 115 59. Detail of Sway Braces 115 60. Column and Base-plate Detail 117 61. Boiler Flue 1 1 8 CHAPTER VII. 62. Front Elevation, Jackson Building 151 63. Typical Floor Plan 152 64. Column Connections 153 LIST OF ILLUSTRATIONS. Xlll PAGE Fig. 65. Double Beam Girder Connection with Cast Column 154 66. Detail of Top of Column showing Girder Supporting Upper Walls. 154 CHAPTER VIII. 67. The New Netherland, New York 157 68. Floor Plan 159 69. Beam Plan 160 70. Column Detail 162 71. Section of Court Wall 164 72. Wall Section above the Eighth Story 164 73. below " " " 164 74. The Waldorf, New York 167 75. Floor Plan 168 76. Beam Plan over Dining Room 169 77. Postal Telegraph Building, New York 171 CHAPTER IX. 78. Venetian Building, Chicago, 111 173 79. Typical Floor Plan of Venetian Building 175 80. Part Transverse Section of " " ... 176 81. Wind-strain Diagram of " " 176 82. Section of Curtain Wall supported by two I Beams 179 83. " " " " " " Plate Girder 179 84. " " " " " " two Channels 180 85. " " " " " " Plate Girder 180 86. " " Spandrel Support in Venetian Building, Chicago 181 87. " " " " " Ashland Block, Chicago 181 88. " " " " " " " 182 89. " " " " " the Fair Building, " 182 90. Plan and Elevation of a Steel-rail Foundation o 186 CHAPTER X. 90. The Old Colony Building, Chicago, 111 184 91. Typical Floor-plan of the Old Colony Building 186 92. Beam-plan of the Old Colony Building 189 93. Foundation-plan of the Old Colony Building 191 94. Vertical Section through Foundation showing Cantilever Construc- tion 193 95. Transverse Section showing Portal Arches 196 96. General Elevation of Portal Arches 199 97. Detail of Portal Arch 200 XIV LIST OF ILLUSTRATIONS. PAGE pig. 98. Detail of Column Connection 202 99. Construction of Corner Bays 204 100. Section of Bay 205 CHAPTER XI. 101. The Manhattan Life Insurance Building, New York 207 102. Typical Floor-plan 211 103. Typical Beam and Girder Plan 212 104. Section of New Street and Side Walls 214 105. Cast-iron Column-joint Detail , 215 106. Steel Column-joint Detail 217 107. Trusses supporting Recessed Front at Fifteenth Floor 220 108. Section showing Manner of Excavating in Caissons 223 109. Plan of Caissons and Arrangement of Column Bases 226 1 10. Sectional View and Top View of Caisson 228 in. Caisson Sections 228 112. Transverse Section of Foundations and Cantilever Girder 229 113. Cantilever Girder Detail 230 114. Steel-rail Foundation - 236 JOHN S. PRELL Civil & Mechanical Engineer. 0AN FKAN CISCO, CAJU SKELETON CONSTRUCTION IN BUILDINGS. CHAPTER I. GENERAL AND DESCRIPTIVE. THE method of skeleton construction has been developed by the use of iron and steel in the erection of fire-proof build- ings, and it seems to have solved the problem of economizing space in the lower floors of high and narrow buildings. In the ordinary methods of building, the higher the wall the thicker it must be at its lower parts, but the lower stones are the most valuable ; yet it is in these that the greatest area of a valuable lot must be surrendered to enormously thick walls. Therefore, every foot gained on the inside measurements increases the availibility of the structure. In the buildings where the skeleton construction is used throughout, heavy masonry walls are not known, and what appears to be such in the finished state is simply a veneer of some fire-proof material, yet the frame of the building is not a mere heap of beams and columns ; but as one example after another is erected we find that the details and connections are being carefuly studied, and the whole braced and anchored so completely that the metal construction may be raised hun- dreds of feet from foundation to roof without the aid of any masonry a great metal structure, strong in its own strength, not only to carry the direct loads which may be placed upon 2 SKELETON CONSTRUCTION IN BUILDINGS. it, but also to resist all lateral strains to which it may be sub- jected. The architectural appearance of our large cities is being rapidly altered by this new system. It imposes no new con- ditions on the architect, except as to the engineering of the metal frame ; and in a few years, with the skill already dis- played in treating these problems, many new designs will be brought forth, notwithstanding the great height to which they are built. The skeleton construction consists in the use of cast-iron, wrought-iron, or wrought-steel columns in the side-walls, con- nected longitudinally at the floor levels with beams, lattice or compound riveted girders supporting the thin curtain walls 12 to 20 inches in thickness; in addition the weight of the floors are transmitted to the longitudinal girders and columns, so that the latter support the entire building. The thin curtain walls are generally built of brick, and extend from the top of any wall girder to the underside of the next story girders, extending a sufficient distance outside to cover the girders and columns with masonry, and continue in this manner to the top of the building. The New York building law imposes certain conditions upon the use of the curtain walls, in that the curtain walls of the lower stories shall be built thicker. Why this is so the author has not been able to determine, as a 1 2-inch wall from foundation to roof resting upon these wall girders would seem sufficient for all purposes. There are some variations in the use of the skeleton frame which will also be fully illustrated and described in the pages to follow. In some cases the frame work of columns and girders are carried up to within four or five stories of the roof ; then continuous girders are placed upon the top of columns to support the upper stories of masonry walls. In some cases the columns begin at the base course on stone, iron, or steel beams. GENERAL AND DESCRIPTIVE. 3 In others from the top of foundation-walls level with the sidewalk or curb level. Another variation is where the walls and columns are sep- arated, the walls built heavy enough to carry their own weight, and the columns support the floor and their loads. Then again the longitudinal girders may be placed in every second floor, and the walls are made 20 to 24 inches in thick- ness below the fourth or fifth tier. When the first examples of the skeleton construction were completed many questions were raised, and no doubt there exists in the minds of many at the present time that the greater expansion of one material over another might work some trouble. Events have proven that the temperature of this climate from the greatest cold to the greatest heat exerts no appreciable effect, especially while the metal is covered with masonry or some fire-proof material. Representative Chicago High Buildings. Very many journals have been devoting much space to descriptions of the steel skeleton type of buildings, more especially those of Chi- cago, and the majority of writers call it the " Chicago Steel Skeleton Construction." There can be no doubt that Chicago's business districts has undergone a remarkable transformation within a few years, as any one who visits that city to-day would scarcely believe that, something like eight years ago, the tallest buildings were not ever eight stories high. Immediately after the Great Fire that totally ruined the business district, the city was built up hurriedly ; many hand- some buildings were erected, and these have been torn down to give way to very high structures, which command much admiration throughout the country. One of the first of the many tall buildings erected was the Montauk Block, which stands on Monroe Street, just west of Dearborn. It was built about eight years ago, and is ten 4 SKELETON CONSTRUCTION IN BUILDINGS. stories high. When contrasted with some of the latest struct- ures it is comparatively insignificant. The Woman's Christian Temperance Union Building, as shown in the above engraving, Fig. i, popularly called the FIG. i. Woman's Temple, because it was built by the ladies of that organization from contributions raised in small sums in all parts of the country, is perhaps the handsomest big building in Chicago. Its lines are so proportioned that its enormous height rarely elicits comment. GENERAL AND DESCRIPTIVE, 5 Then, again, the Owing's Building, Fig. 2, situated on Dearborn and Adams Streets, on account of its immense height, as contrasted with its slim frontage, is one of the nota- ble structures of Chicago. The German Opera House, Fig. 3, is another of the striking buildings in that city. Chicago may FIG. 2. THE OWING'S BUILDING, CHICAGO. not count more tall buildings than in other cities, but she has, no doubt, a greater number at present of " sky-scrapers " as they are called in the West, within a given area. The Masonic Temple is regarded as one of the greatest achievements of high building construction and engineering SKELETON CONSTRUCTION IN BUILDINGS, PIG 3. GERMAN OPERA HOUSE, CHICAGO, ILL. ADLER & SUIXIVSN, ARCHITECTS. GENERAL AND DESCRIPTIVE. 7 (see perspective, Fig. 4).* It is situated at the corner of State and Randolph Streets, and designed by Messrs. Burnham and Root, architects of Chicago. The building extends 170 feet on State Street to a 40 feet alley, and 113 feet on Randolph Street to a 25 feet alley. The height from the sidewalk to the top of coping is 274 feet. The building is 20 stories, and contains 5,436,000 cubic feet exclusive of the court. The street fronts are of dressed granite up to the sills of the fourth-story windows ; above that of terra cotta and brick, of a gray and mottled color to match the granite. There are fourteen passenger elevators arranged in a circular curve at the rear of the main entrance.- There are also freight elevators. All balconies have floors and soffits of marble and mosaic. Hall columns in the court are covered with alabaster. All interior metal is of bronze finish, highly ornamented. The inside court is lined of marble throughout. On the roof is a promenade deck, 100 X 120 feet, covered with a skylight and enclosed with glass. To the top of this skylight from the sidewalk is 302' i" '. All piers have steel columns inside which carry all the floor loads. With the exception of six piers the whole building above the fourth floor is carried on the col- umns. Two systems of vertical bracing run through the nar- row way of the building from top to bottom, one each side of the elevators. These rods run through two floors and cross one column. Each of the above columns or pair of columns, as mentioned, are provided with independent footings, which reduces and distributes the pressure uniformly on the soft and treacherous soil. The architects of Chicago probably have to deal with the most unfavorable conditions for securing a good foundation for these heavy buildings. The soil under the business district consists of a black loamy clay, which is somewhat firm at the surface, but a few feet below the surface the soil becomes quite soft, growing * For a fuller description, see the Engineering Record, Jan. 21, 1893. 8 SKELETON CONSTRUCTION IN BUILDINGS. more so the deeper the excavation is carried. The first of the large structures were built with continuous foundation walls with wide footings. This method did not prove suc- FIG. 4. MASONIC TEMPLE, CHICAGO, ILL. BURNHAM & ROOT, ARCHITECTS. (From Architecture and Building.) cessful. After many experiments, the foundations were divided into isolated piers, the footing being carefully proportioned, according to the load upon it, so that all should settle at exactly the same rate, without any detriment to the superstructure. GENERAL AND DESCRIPTIVE. 9 The footings of the piers in the Masonic Building, as in the majority of Chicago buildings, are built of steel rails and con- crete, and crossed three or four times, thus insuring a great spreading in a small height. Under a single column of the Masonic Building the con- crete is 15' 2" X 15' 2". On top of this 1 8 steel rails were laid; then 1 8 at right angles to these; then 10 parallel to the lower 18 and 10 parallel to the upper 18, making a total of 56 pieces. The old Board of Trade Building, at the corner of La Salle and Dearborn Streets, lately remodelled, presents a front re- markable even in the city of tall buildings. From a seven- story structure of rather inferior design it has been remodelled into a fourteen-story palace. Down on Dearborn Street the Manhattan Block is an im- mense structure, eighteen stories high. The Tacoma Building at Madison and La Salle, was considered a high building a few years ago ; it is now overshadowed by a number of much taller buildings. Representative New York High Buildings. Consider- ing the present rapid development of the skeleton construc- tion and this necessity for high buildings, New York City takes its place at the head, not only in the designs, but in the details of the construction. And where other cities have con- fined their high structures within narrow limits, it is not so in New York ; they are scattered along the principal thorough- fares from the Battery to Central Park, where high buildings are quite common. Among the many notable and handsome structures adjoin- ing the Park are the New Netherlands, a hotel built in 1892, by W. W. Astor. It occupies a site 100 feet by 125, on the corner of Fifth Avenue and Fifty-ninth Street, and has a cellar and basement below the street level, and seventeen stories above, the four upper stories being in the picturesque high roof. Nine hundred steel columns and about 4500 steel beams were used in the construction of this building, the 10 SKELETON CONSTRUCTION IN BUILDINGS. details of which, and other parts of the building construction are further explained and illustrated in Chapter VIII of this FIG. 5. PROPOSED OFFICE BUILDING FOR THE N. Y. SUN, PARK Row. volume. The Savoy is another of the tall buildings in the same locality, situated at the southeast corner of Fifth Avenue GENERAL AND DESCRIPTIVE. II and Fifty-ninth Street, used as a hotel. It measures 75 X 150 feet, and has an extension of 100 feet more at the rear. It is an eleven-story steel frame structure, faced with Indiana lime- stone, in the Italian Renaissance style of architecture. It was opened in 1892. The Plaza Hotel, directly opposite the Savoy, faces the Plaza at the Fifth Avenue and Fifty-ninth Street entrance to Central Park, overlooking the main Park entrance. The Hotel Majestic is another of these high and elegant hotels built in this locality. There are also a number of lofty and extensive apartment houses in the vicinity of Central Park. One of the largest is the Dakota, at Central Park West and Seventy-second Street. It is a many-gabled building, in the style of a French chateau. Then in Fifty-ninth Street near Seventh Avenue, south side of the Park, are the Central Park or Navarro Flats, which include several independent houses constructed as a single building. The different houses in the group are known as the Madrid, Granada, Lisbon, Cordova, Barcelona, Valencia, Sala- manca, and Tolosa, all combined, with numerous balconies and facades, in the Spanish style. The Osborne, Seventh Avenue and Fifty-eighth Street, is another tall structure of the above class. At the extreme southern part of the city the greatest number of high buildings are used as offices. One of the finest and largest is the Washington Building, at the foot of Broadway, overlooking Battery Park and the Harbor. The Washington Building was completed in 1884. It covers 17,000 square feet of land, and is thirteen stories in height, the two upper stories being in the mansard roof. Between the central and lower portions of the city a few of the highest buildings erected and about to be erected are shown by a few plates, such as the World Building. Fig. 6, erected in 1889-90, is the tallest office building known, reach- ing 309 feet from sidewalk to lantern ; or 375^ feet from the 12 SKELETON CONSTRUCTION IN BUILDINGS. FIG. 6. THE WORLD BUILDING, PARK Row, FACING CITY HALL PARK, N. Y George B. Post, Architect. GENERAL AND DESCRIPTIVE. 1 3 bottom of foundation to the top of the flagstaff. It has a huge skeleton of iron and steel sustaining its twenty-six stories. The Manhattan Life Insurance Company is preparing to erect a building at Nos. 64 and 68, Broadway, which will sur- pass the World Building in height a view of which is shown in Fig. 7. The building is sixteen stories above the sidewalk. Then comes the seventeenth story, 14 feet ; the eighteenth, 26 feet ; the nineteenth, 23 feet ; the twentieth, at the floor of the lantern, 27 feet, making a total of 326 feet from the sidewalk. In style it will be a valuable contribution to the architecture of lower Broadway, and will make an imposing appearance among its stately neighbors ; the Standard Oil Company, the Columbia Building, Aldrich Court, the Consolidated Stock and Petroleum Exchange, the Union Trust Company, and even the tall spire of the Trinity Church will be thrown in the shade. The proposed office building of the New York Sun, sit- uated on Park Row opposite City Hall Park, as designed by Bruce Price, architect, and shown by the sketch Fig. 5> con- templates a building thirty-two stories in height, and if carried out as the architect intends will, no doubt, take its place as one of the handsomest office structures in existence. All the above buildings are not, strictly speaking, of the skeleton type ; but a number of the principal ones using this style of construction are further described and detailed in the following pages, such as the Havemeyer Building, Postal Tele- graph, the Home Life Insurance Company, the Waldorf, the Western Union Annex, etc. New York Building Law in Relation to Skeleton Con- struction. For the skeleton construction, the existing law, passed April, 1892, makes some provision : " Curtain walls of brick built in between iron or steel columns, and supported wholly or in part on iron or steel girders, shall not be less than twelve inches thick for fifty feet of the uppermost height SKELETON CONSTRUCTION IN BUILDINGS, FIG. 7. MANHATTAN LIFE INS. Co. BUILDING, 64 & 68 BROADWAY, N. Y. Kimball & Thompson, Architects. GENERAL AND DESCRIPTIVE. 15 thereof, or to the nearest tiers of beams to that measurement in any building so constructed ; and every lower section of fifty feet or to the nearest tier of beams to such vertical meas- urement, or part thereof, shall have a thickness of four inches more than is required for the section next above it down to the tier of beams nearest to the curb-level ; and thence downwardly the thickness of walls shall increase in the ratio prescribed in section 474 of this title for the thickness of foundation-walls. Curtain-walls may be four inches less in thickness than is specified respectively for walls of dwellings and buildings, but no curtain-wall shall be less than twelve inches thick. Section 474. Foundation walls shall be construed to in- clude all walls and piers built below the curb-level or nearest tier of beams to the curb, to serve as supports for walls, piers, columns, girders, posts, or beams. Foundation-walls shall be of stone or brick. If built of stone they shall be at least eight inches thicker than the wall next above them to a depth of twelve feet below the curb-level ; and for every additional ter feet or part thereof deeper, they shall be increased four inches in thickness. If built of brick they shall be at least four inches thicker than the wall next above them to a depth of twelve feet below the curb-level, and for every additional ten feet, or part thereof deeper, they shall be increased four inches in thickness. The footing or base course shall be of stone or concrete or both, or of concrete and stepped up brick-work, of sufficient thickness and area to safely bear the weight to be imposed thereon ; if the footing or base course be of concrete, the con- crete shall not be less than twelve inches thick; if of stone, the stones shall not be less than two by three feejt, and at least eight inches in thickness for walls and at least 'twelve inches wider than the bottom width of said walls, and not less than ten inches in thickness if under piers, columns, or posts, and at 1 6 SKELETON CONSTRUCTION IN BUILDINGS. least twelve inches wider on all sides than the bottom width of said piers, columns, or posts. Section 485. Where columns are used to support iron or steel girders carrying curtain-walls, the said columns shall be of cast-iron, wrought-iron, or rolled steel, and on their exposed outer and inner surfaces be constructed to resist fire by having a casing of brick-work not less than four inches in thickness and bonded into the brick-work of the curtain-walls, or the inside surfaces of the said columns may be covered with an outer shell of iron having an air space between ; and the ex- posed sides of the iron or steel girders shall also be similarly covered in and tied and bonded. When the thickness of the curtain-walls is twelve inches, the girders for the support of same shall be placed at the floor line of each story, commencing at the line where the thickness of twelve inches starts from, and when the thickness of such walls is sixteen inches the girders shall be placed not farther apart than every other story, at the floor line commencing at the line where the thickness of sixteen inches starts from, provided that at the intermediate floor line a suitable tie of iron or steel shall rigidly connect the columns together hori- zontally, and that the ends of the floor-beams do not rest upon the said sixteen-inch walls. When the curtain-walls are twenty inches or more in thick- ness and rest directly on the foundation-walls, the ends of the floor-beams may be placed directly thereon, but at or near the floor line of each story ties of iron or steel encased in the brick-work shall rigidly connect the columns together hori- zontally. CHAPTER II. COLUMNS. Columns. The first examples of the skeleton construc- tion in buildings were those erected with cast-iron columns. Cast-iron at the time of their erection, and no doubt is at the present time, produced more quickly and cheaper than- wrought-iron or steel columns, and these were two very im- portant factors in the problem. The constructors and producers of cast-iron advocate its use only as the material for the columns inclosed in the walls. They claim also that the oxide of iron paint so commonly used for coating iron soon dries out, leaving a coating of dry, broken scale or powder. Between the columns and the outer air are only a few inches of brick or some fire-proof material, through which dampness soon finds its way. In wrought-iron, they claim that rust honeycombs and eats entirely through the metal Mild steel rusts faster than wrought-iron at first, then slower. Cast-iron, on the contrary, slowly oxidizes in damp situations ; rust does not scale from it, and the oxidation when formed is of much less dangerous kind, extending only a little way into the metal to about the thickness of a knife- blade, and then stops for good. Cast-iron of goodly thickness offers a far better resistance to fire, or fire and water combined, than wrought-iron or steel. The experiments undertaken by Prof. Bauschinger, of 1 8 SKELETON CONSTRUCTION IN BUILDINGS. Munich, in reference to the safety of cast-iron columns when exposed to the action of great heat are quoted. " Having arranged some cast and wrought iron columns heavily loaded, exactly as they would be if supporting a building, had them gradually heated ; first, to three hundred degrees, next to six hundred, and finally to red heat, then suddenly cooling them by a jet of water, just as might happen when water is applied to extinguish a fire. " The experiment showed that the cast-iron columns, al- though they were bent by the extreme heat and exhibited transverse cracks when cold water was applied, yet they sup- ported the weight resting on them ; while the wrought-iron columns were bent before arriving at the red heat, and were afterwards so much distorted by the water that the restraight- ening them was out of the question ; in fact, if supporting a real building, they would no doubt have utterly collapsed under the weight they had to sustain." If the brick- work or fire-proofing which surrounds the wall or interior columns can be depended upon as a protection for the metal against the effects of fire and water, the above ex- periment would lose its weight against the use of wrought- iron or steel. The objection to wrought-iron or steel on account of rust- ing may seem more real, and yet we have seen pieces of wrought-iron beams, anchors, etc., taken from very old walls unharmed by rust. There is, however, considerable distrust of cast-iron in high and narroiv building, especially in relation to the connections with the floor and wall girders. Brackets and lugs are apt to break suddenly and completely, but with wrought-iron and steel will bend a great deal without breaking, and that rivets are stronger than bolts. To this objection it can be said that the brackets and lugs, instead of being cast with the columns, can be put on with angle-knee connections, drilled holes in the columns and with any number of bolts, which in a great many COLUMNS. 19 of our high buildings has proven entirely satisfactory, where lateral bracing is not required. The advocates of wrought-iron and steel columns claim that cast-iron is rigid and unyielding, and that its coefficient of elasticity is much lower than that of wrought-iron or steel, and the cast-iron column is not as stiff as the others, and will not on the whole produce as rigid and unyielding a structure, Where high and narrow buildings are concerned, much at- tention is given to the bracing against wind forces that is, in the stiffness of the joints and the stability of the structure upon the foundation, and when the bracing is a portion of the frame construction, the difficulty of doing it properly with cast-iron columns is very great, but with wrought-iron or steel these difficulties are largely removed. It is not the intention of the author to enter into any dis- cussion on the question of which should be adopted, but to confine the subject to what has already been done, and illus- trate the practices of the present time, especially the build- ings he has closely followed in having charge of the con- structive details at the Architectural Iron Works. We have very many handsome buildings constructed where cast-iron, wrought-iron, and steel columns have been exclusively adopted, each system will no doubt be copied for years to come unless some radical change will turn the tide into an- other channel. But we are entering on an age of steel. Rolling mills pro- duce it quicker and cheaper than any other metal, and the change from cast-iron to steel for columns, beams, and girders, especially in our large buildings, has been generally adopted by the prominent architects throughout the country. One after another the advocates of cast-iron have fallen into line in favor of wrought-iron and steel in high and narrow buildings, but for buildings with a large base cast-iron will continue to be popular. Cast-iron columns have been used, and are still extensively 2O SKELETON CONSTRUCTION IN BUILDINGS. adopted, in some of our noted buildings. In New York we have in course of construction, together with those already built : Postal Telegraph Building D., L. &. W. R. R. Building Decker Bros. Building The Western Union Annex The Waldorf Lincoln Building Jackson Building Mclntyre Building Scott & Bowne Building Mutual Life Annex (wall col's). In Chicago cast-iron columns have been used in such build- ings as The Rookery The Auditorium Home Insurance Building The Chamber of Commerce The Monon Block Manhattan Building Western Bank Note Bldg. Unity Building Tacoma Building Owens Building. Cold Storage Building Wrought-iron and steel columns have been used in New York in the following buildings : The New Netherlands Home Life Ins. Co. Building Havemeyer Building Hotel Majestic Lancashire Building Mail and Express World Building Mutual Reserve Fund Building etc. etc. In Chicago a few of the noted wrought-iron and steel struc- tures are : Rand McNally Building Masonic Temple The Ashland Block German Theatre Venetian Building The Pontiac The Kearsarge Northern Hotel The Fair Woman's Temple, etc Many noted buildings in all the other large cities have used each system. The heights of buildings using in cast-iron compare favor- COLUMNS. 21 ably with those using wrought-iron and steel a few of which are compared below : CAST-IRON STRUCTURES. STEEL STRUCTURES. Feet. Stories. Feet. Stories Chicago, Rookery 164 12 Chicago, Northern Hotel, 168 14 N. Y., Postal Telegraph . 14 " Masonic Temple, 254 20 Chicago, Unity Building... 210 17 N. Y., New Netherlands, 217 17 " Tacoma Building, 165 13 " Home Life " Manhattan 210 16 " Havemeyer 175 15 Cast-iron Columns are usually made hollow round, Fig. 13, or when built in walls, as in the skeleton frame, hollow square, Fig. 10. Some of the variations brought about by the skeleton frame are shown, as Fig. 8, or what is called the |-|- shape, with an open web, and Fig. 9, similar to Fig. 8, but with a solid web. Then again we have the modification of the square column, as in Fig. 11. The side or back adjoining the party wall is FIG. 8. FIG. 9. FIG. 10. FIG. n. FIG. 12. FIG. 13. moved nearer the axis of the column, so that a greater dis- tance could be had for fire-proofing the body of the columns. This section was used in the Mclntyre Building, Broadway and Eighteenth Street, New York, and changed from the shape Fig. 10 to this by the architect, and approved by the Building Department. The square column encased with a shell, as Fig. 12, was used in one of the first buildings adopting the skeleton frame. In making a selection from the different shapes for the skeleton structure, it is very important to adopt the form that presents the smoothest or unbroken surface for connections with the floor and curtain-wall girders. It is also important that the masonry should be built 22 SKELETON CONSTRUCTION IN BUILDINGS. solidly around the columns. The H- sect ions, Figs. 8 and 9, are no doubt better adapted for this purpose than the rectangular shapes, Figs. 10, II, and 12. The hollow circular column, Fig. 13, is the least desirable for building in with the walls, more difficult to fire-proof, but in connecting with the girders that portion of the column can be cast square. Wrought-iron and Steel Columns as used for the skele- ton frame are various, and when a compound column section is required ; very many rolled shapes can be riveted together to make up the required section. Those made up of Z-bars and a single web plate, as Fig. 14, are about the simplest form of riveted columns. FIG. 14. FIG. 15. FIG. 16. FIG. 17. FIG. 18. FIG. 19. FIG. 20. FIG. 2r. The section is increased by the use of cover plates riveted to the outer leg of the Z's and shown at Fig. 15. Then again, we have the rectangular section of Z's, Fig. 16. The section shown by Fig. 17 is a Z-bar column used in the Venetian Building, Chicago, a twelve-story structure ; the additional required area being made up of plates and angles. The col- umn is 1 3^" X 21" X 27'. 1 1" long. It is a well-known fact that metal near the neutral axis of a column is good for little, and that the capacity of equal areas varies as the metal is removed from the neutral axis. It seems, therefore, that a better proportioned column COL UMNS. could be adopted for the requirement of the case. In Fig. 18 the column section is made up of four angles and a single web, and in Fig. 19 a single plate is added or a number of plates to make up the required section. Then the rectangular shape, Fig. 20, made up of angles and plates, requiring eight lines of rivets. The author has not been able to find a section like that of Fig. 21, used in any skeleton frame. It is made up of the cheapest rolled sections that is, angles and plates, and has many advantages for fire-proofing and building in with the ma- sonry. Then again, the greatest amount of metal is farthest from the neutral axis. This column section has been exten- sively used by the P. R. R. Co. in all their outside work. For strength and accessibility for painting, it seems to have no superior. FIG. 22. FIG. 23. FIG. 24. FIG. 25. FIG. 26. FIG. 27. FIG. 28. FIG. 29. There is another shape which is more or less used, such as that shown at Fig. 22, the Phoenix column, and other new commercial shapes, such as could be conveniently rolled, as Figs. 23, 24, 25, and 26. Fig. 27 may be either of plates and channels or latticed channels, as in Fig. 28. In Fig. 29 angles are used at each corner; two sides may be latticed and the other sides solid plates, or all sides may be latticed. 24 SKELETON CONSTRUCTION IN BUILDINGS. Any of these sections, if used in the ordinary buildings, will carry the load usually placed upon them, with the unit strain required by the building laws, providing the columns are well made, with the loads symmetrically applied, as is usual in the side walls of the skeleton frame, where three of the four sides of the columns connect with the structure. Almost all of the above sections will be fully explained in detail in the examples of actually constructed buildings in the following pages, and the preference can be given to that shape which will best serve the purpose of the building to be erected. The Advantages and Disadvantages of Different Shapes of Compound Sections. There are many points of advantage and disadvantage to each shape which must be carefully considered before deciding the proper column to use i e : I. Cost. The cost of the column when in its finished state, which means the shapes used in the section and the num- ber of holes to be punched and riveted. In the Z-bar column, Fig. 14, there are five different members, but only two lines of rivet-holes. Fig. 18 of plates and angles has the same number of members and rivet-holes. Z-bars and angles are probably as easy sections to roll as any commercial shapes. These col- umns have the advantage in only requiring two lines of rivet- holes to be punched and riveted. But if a heavier section is required, plates are placed on the outside, then six lines of holes and rivets are required. Then they become more ex- pensive, and in Fig. 15 all the material inside the square is theoretically lost. The column section, Fig. 19, is used in some of our noted buildings, and when not exceeding six lines of rivets is as sat- isfactory as Z-bar columns. In Fig. 21 the same simple shapes are used as in Fig. 20, and is to be preferred in cost to Fig. 17. Figs. 17 and 20 have eight lines of rivets. Fig. 21 has ten lines. The Phoenix column, Fig. 22, is a patented shape, and COLUMNS, 25 only rolled by one rolling mill, but it has its advantages in having only four lines of rivets in its smallest section ; but the area can be increased by simply placing fillers between the segments, and it still only requires four lines. They are also made in eight sections. The same remarks might apply to the sections in Figs. 23, 24, 25, and 26, although the author is not aware that Figs. 23 and 24 are in the market. Figs. 27, 28, and 29 are made up of ordinary commercial shapes that can be bought at any rolling mill. These sections require four and eight lines of rivets. 2. Availability of Material. It is best to make up the column sections of shapes manufactured by all the rolling mills, and not those patented and only available from special places. Z-bars are at the present manufactured generally through- out the country, and all rolling mills make angles, plates, channels, and beams. Fig. 22 is only manufactured by the Phoenix Iron Works, of Phoenixville, Pa. ; Fig. 26 by Carnegie, Phipps & Co., of Pitts- burg, Pa. 3. The Advantages of Different Shape Columns for Connections. It is an important question, and no doubt a serious one, to select the best column which will make the strongest and stiffest connections with the wall and floor girders. When there is only one beam or girder at the same level and on opposite sides, a satisfactory detail can be made for almost any of the above sections ; but when arrangements of the beams and girders are irregular, both as to position and to height, those columns which present the plainest and least irregular surfaces are the ones which should be selected. By glancing at the details of column connections and the various examples, the force of the above remarks will become evi- dent. 26 SKELETON CONSTRUCTION IN BUILDINGS. Z-bar and plate columns, as Figs. 14 to 21, are the best depending, of course, upon the size of columns and size of girders forming the connection. The Phoenix columns presented very many difficulties in their early use; but those points seem to have been remedied, so that the form of connections are very much improved. By means of cross-pintle connections, as explained further under column connections, it is possible to make a continuous column from the basement to the roof, in which the joints are stronger laterally than the body of the column, and the con- nections are practically 25$ less in weight than the usual form of plate and brackets. The New York Building Law Relating to the Strength of Columns. "The strength of all columns and posts shall be computed according to Gordon's formula,* and the crush- ing-weights in pounds per square inch of section, for the fol- lowing-named materials shall be taken as coefficients in said formula, viz. Cast iron, 80,000 ; wrought or rolled iron, 40,000 ; rolled steel, 40,000. The factors of safety shall be as I to 4 for all posts, columns, and other vertical supports when of wrought iron or rolled steel. * Gordon's formula for the ultimate strength of columns: P S Fixed ends. = - TS A area, d least side in inches, / = length in feet, P load, 5 = total com- pression; unit stress, 80,000 Ibs. for cast-iron, 40,000 for rolled-iron or steel. J y i ff for cast-iron; K = -$$015 wrought-iron or steel. The quantity A' cannot be determined theoretically; its value varies with the form of cross-section as well as with the kind of material and the arrangement of the ends of the columns. The values of S are in pounds per square inch, while those of K are in ab- stract numbers. COL UMNS. 27 All cast-iron, wrought iron, or rolled steel columns shall be made true and smooth at both ends, and shall rest on iron or steel bed-plates, and have iron or steel cap-plates, which shall also be made true. In all buildings hereafter erected or altered, where any iron or steel column or columns are used to support a wall or part thereof, excepting a wall fronting on a street, and columns lo- cated below the level of the sidewalk which are used to support exterior walls or arches over vaults, the said column or columns snail be constructed double that is, an outer and inner column. The inner column alone to be of sufficient strength to sustain safely the weight to be imposed thereon, or such other iron or steel columns of sufficient strength and so constructed as to secure resistance to fire, may be used as may be approved by the superintendent of buildings. | Cast-iron posts or columns which are to be used for the sup- port of wooden or iron girders or brick walls, not cast with one open side or back, before being set in place, shall have a f-inch hole drilled in the shaft of each post or column by the manufacturer or contractor furnishing the same, to exhibit the thickness of the castings ; and any other similar-sized hole or holes the superintendent of buildings or his duly authorized representatives may require shall be drilled in the said posts or columns by the said manufacturer or contractor at his own ex- pense. Iron posts or columns cast with one or more open sides and backs shall have solid iron plates on top of each, to prevent the passage of smoke or fire through them from one story to an- other, excepting where pierced for the passage of pipes. No cast-iron post or column shall be used in any building of a less average thickness of shaft than of an inch ; nor shall it have an unsupported length of more than 20 times its least lateral dimensions or diameter. No wrought-iron or rolled-steel column shall have an unsup- 28 SKELETON CONSTRUCTION IN BUILDINGS. ported length of more than 30 times its least lateral dimensions or diameter ; nor shall its metal be less than \ of an inch in thickness. All cast-iron, wrought-iron, and steel columns shall have their bearings faced smooth and at right angles to the axis of the column, and when one column rests upon another column they shall be securely bolted together. Strength of Cast-iron Columns. We owe our knowledge of the strength of cast-iron columns chiefly to the experiments of Mr. Eaton Hodgkinson, in the year 1840. These were very numerous and to a certain degree comprehensive, embracing over two hundred examples. As deduced from these experiments it was found that where cylindrical cast-iron columns were shorter than thirty external diameters, the weight required to break them by bending is so great that the crushing force becomes sensible, and the column yields to the combined effect of the forces. But in a long col- umn (where the length exceeds thirty external diameters), although the pressure contributes to break it by crushing as well as by flexure or bending, yet the column yields from bending with a weight which is insufficient to sensibly affect it by crushing alone. It was found that when the pressure on the column exceeded one fourth of the breaking weight, a change or derangement of the metal took place. Therefore one fifth the crushing weight is as great a pressure as can be put upon cast-iron columns without having their ultimate strength decreased by incipient crushing ; provided the thickness of metal in column is uniform, with turned ends, secured top and bottom and bolted through flanges. If the column is secured by an uncertain method, it is safer to use one sixth the crushing weight. It is obvious, therefore, that it will not do to take the table on page 30 as a guide, unless the columns are of uniform thick- ness throughout, of good metal, with cores made in one piece, COLUMNS. 29 castings reasonably perfect and straight, the ends turned off true in a lath in planes at right angles with their axis, and set up perpendicularly in the building. Mr. Hodgkinson, in his experiments, found that columns with rounded ends can sustain only about one third the weight of those with flat ends carefully fitted, with the ends at right angles to the axis of the column. In the ordinary mode of chipping off (cutting with a chisel) the ends of a column in an unfinished state, the inequalities of the bearing surfaces cause the weight to rest on a few points on the ends, and it is almost impossible that the ends shall be at right angles with the axis. The safe weight a column can sustain in such cases is consid- ered to be about tivo thirds of one turned true. A few experiments were also made on columns with rounded ends, and other forms than cylindrical. Square columns had an average breaking weight about 58 per cent greater than cylindrical columns of diameters equal to the sides of the squares. A pillar of the section -p, 9-75 inches long, 3 inches across, and the ribs 0.48 inch thick, had a breaking weight 63 per cent greater than the computed breaking weight of a solid cylindrical column of the same weight and length. A hollow cylindrical column of the same weight and length, and of an external diameter equal to the width of the -p, has a computed breaking weight about double that found by experiment for the form p . A pillar of the section H, 3 inches in height and 2.5 inches in width, of the same length and nearly the same sectional area as the preceding, had a breaking weight about 2.6 times the computed breaking weight of a solid cylindrical pillar of the same weight and length. A hollow pillar, 3 inches in external diameter and of the same weight and length, has a computed breaking weight about 19 per cent greater than was found by experiment for the H-section. The H-section being built solidly in the brick 3O SKELETON CONSTRUCTION IN BUILDINGS. work, the result would no doubt be quite different from Mr. Hodgkinson's tests. The results would be nearly those of the square and circular columns. Table Giving the Strength of Hollow Cast Columns. In computing the weight to be sustained by a column, it is not sufficient to consider only the weight appropriate to that particular use for which it is intended ; but the weight should be estimated for any use to which the building may be applied, with full allowance for floors and the weights to be placed thereon. It is not safe to take the average weight sustained on each column, as some columns will have more or less on them than the average, and will be loaded more on one 'side than the other ; besides, they are subject to concussions from bodies falling on a floor above, or may receive a lateral blow from goods falling against them in transmission. Great allowance should also be made for columns that are subject to vibrations caused by machinery, etc. The following table gives the ultimate strength of round and square cast-iron columns, in pounds per square inch of sectional area. The numbers in column -j = the length di- vided by the least diameter each taken in inches. / d Round. Square. / d Round. Square. 5 75-300 76,200 17 46,444 50,700 6 73.400 74.630 18 44,200 48,540 7 71,270 72,860 19 42,100 46,460 8 68,970 70,920 20 40.000 44,450 9 66,530 68,850 21 38,100 42,510 10 64,000 66,670 22 36,200 40,650 ii 61,420 64,410 23 34,460 38,8-0 12 58,820 62,110 24 32,790 37,175 13 56,240 59,890 25 31,220 35.560 14 53,86o 57,470 26 29,740 34,010 15 51,200 55,170 27 28,340 32,550 16 48,780 52,910 28 27,030 3LI50 COLUMNS, 31 Factors of Safety for Cast-iron Columns. (a) If column is accurately turned to a true plane and its bearing surfaces are perfectly true, take one fifth of ultimate strength. (b) If column has turned ends and is set with the usual care, as in ordinary buildings, take one sixth of ultimate strength. (f) If the ordinary mode of chipping off ends as with a chisel is employed, take one eighth of ultimate strength. EXAMPLE I. What safe load will a 12-inch-diameter column I inch thick, 1 5 feet long, support with a safety factor of 5, or one fifth the ultimate strength ? / 1 80 Opposite this number for round columns is 5 1,200 pounds, and dividing this by 5 we get 10,240 pounds, safe load per square inch of sectional area. A 12" dia. area = 113.10 sq. in. 10" " " = 78.54 " " 34.56 = area of a 12" dia. column i" thick. Then 34.56 inches X 10.240 = 353,894 pounds or 177 tons, total safe load the column will support. EXAMPLE 2. What safe load will a lo-inch square column I inch thick, 10 feet long, support with a safety factor of 6, or one sixth the ultimate strength ? 120 Opposite this number for square columns is 62,110, which 3 2 SKELETON CONSTRUCTION IN BUILDINGS. divided by 6 gives 10,352 pounds, safe load per square inch of sectional area. Area of column = 36 inches X 10,352 = 372,672 pounds or 1 86 tons, the total safe load the column will support. Strength of Wrought -iron and Steel Columns. Wrought-iron and steel columns fail either by deflecting bodily out of a straight line, or by the buckling of the metal between rivets or other points of support. Both actions may take place at the same time, but if the latter occurs alone it may be an indication that the rivet spacing or the thickness of the metal is insufficient. Until a few years ago we have had no experimental knowledge on this subject beyond the experiments of Hodg- kinson, which have furnished the constants for Hodgkinson's and also for Gordon's formula. Then we had Euler's formula, where it is assumed that for any given material there is a certain definite ratio of length to diameter below which a column will give away by direct crushing, while one whose ratio of length to diameter is greater will give way wholly by transverse strain. Hodgkinson's empirical formulae were based upon his ex- periments upon small columns of a variety of ratios of length to diameter. Then Gordon's formula, where it is assumed that all columns give way by a combination of crushing and bending. The formula which seems to most satisfactorily represent the result of experiments is that of Gordon, or, as it is some- times referred to, " Gordon's formula modified by Rankine ;" but the best usage gives to it the name of Rankine's formula. The disagreement of the formulas already referred to has led to the proposal of a number of similar formulae, each having its constants determined to suit certain definite set of tests, and all these thus proposed must be classed as empirical formulae, and applied within the cases experimented upon. COL UMNS, 33 In 1881, Mr. Clark, of the firm of Clark, Reeves & Co., presented to the American Society of Civil Engineers a report of a number of tests on full-sized Phcenix columns, made for them at the Watertown Arsenal, together with a comparison of the actual breaking weights with those which would have been obtained by using the common form of Gordon's formula for wrought iron : P_ A 36000 where P = breaking weight in pounds, A = area of section in square inches, / = length in inches, r = least radius of gyra- tion in inches. The table is as follows : No. of I Experiment. rf !i 3J u 28 28 25 25 22 22 19 I 19 i 16 i 16 \ 13 13! 10 10 7 7 4 4 i! ii 42 42 37*' 37f 33 33 ' 28* 24 j 19* 15 I0i 6 6 i j 1, 1 Sectional Area. Sq. In. Total Com- pression under Loads. Elastic Limit. Ultimate Strength. Total Ultimate Strength, in Ibs., by Gordon's Formula. Lbs. 200,000. Lbs. 300,000. Total Ibs. Lbs. per sq. in. Total Ibs. Lbs. per sq. in. I 2 3 4 I 7 8 9 10 ii 12 13 14 15 16 17 18 1,142 i,i53 1,034 1,023 920 773 777 650 |6 5 o 536 53i 415 418 291 284 164 164* 12.062 12.181 12.233 I2.IOO 12.371 12.311 12.023 12.087 12.000 12.000 I2.I85 12.009 12.248 12.339 12.265 11.962 12.081 12.119 0.190 0.186 o! 168 0.160 0.152 0.139 O.I2O 0.116 0.092 0.091 0.054 424,000 416,000 431,500 424.000 440,000 423,000 425,200 446,000 439,000 439,000 449,000 449,000 446,800 449- ioo 468,000 5i7.ooo 598,000 621,000 35,150 34,150 35,270 35,040 35,570 34,300 35,365 36,900 36,580 36,580 36,857 37,200 36,480 36,397 38,157 43,300 49,500 51,240 330,146 333,459 352,013 348,119 372.837 371,043 377,955 380,197 391,701 39^,701 410,660 406,886 423,886 427,047 433-021 469.324 432,132 433.507 0.255 0.264 0.243 0.236 0.198 0.213 342,000 27,960 354,000 2 9 ,29\> 0.142 342,000 28,890 O.IIO 0.109 330,000 350,000 360,000 354,000 26,940 28,360 29,350 29,590 0.031 0.025 0.042 340,000 28,050 Other tests made at the Watertown Arsenal will next be given. 34 SKELETON CONSTRUCTION IN BUILDINGS. WROUGHT-IRON COLUMNS. LATTICED COLUMN CHANNEL BARS SPACED 8" APART. Size of Bars. ! Sectional Area. 1 Lattice Spacing. Ultimate Strength. Manner of Failure. Actual. Per sq.in. in ft. in. sq. in. in. Ibs. Ibs. Flat ends 6 IO 4.760 18 174.800 36,720 Channels buckled. 6 IO O 4.670 18 165,000 35,330 " " Pin ends 6 12 4.600 18 159,800 34-740 Horizontal deflection. 6 15 4.480 18 151,500 33-820 6 17 6 4.660 18 152,600 32,750 ' 6 20 6 4.600 18 136,000 29,180 6 22 6 4-570 18 I39,8oo 30,590 1 6 25 o 4.7FO 18 110,000 23,350 i 6 27 6 4.690 18 102,500 21,850 6 30 o 4.700 18 69, 3 jo 14,740 ' 8 13 4 7-520 18 261,800 34,810 Defl. upward; ch. bars buckled. 8 16 8 7.480 18 254,100 33,970 " horizon. " 8 20 o 7-550 18 246,200 32,610 it 8 23 4 7.990 18 257,500 32,230 11 8 26 8 7.780 18 243,900 31,350 ' " 8 30 o 7.810 18 194,100 24,850 11 " 10 12 6 9.680 22 344,120 35,550 Channel bars buckled. IO 16 8 9-550 22 323,200 33,840 <> IO 20 IO 9.740 22 330,000 33,880 " " " IO 25 o 10.040 22 342,700 34.130 ii IO 12 29 2 2O 9-300 ii .980 22 22 299,300 411,600 32,180 34,360 Deflection horizontally. Channel bars buckled. 12 25 o 12.144 22 400,000 32,940 " " " 12 25 o 11.910 22 407,800 34,240 < ii 12 30 o 12.180 22 385,000 31,610 .1 n 12 30 o 12.540 22 393,000 31,340 Deflection horizontally. TESTS OF Z-BAR COLUMNS. Some tests were made on iron Z-bar column by C. L. Strobel, C.E., and reported in the Trans. Am. Soc., C.E. Paper, April, 1888. These tests were fifteen full-sized speci- mens, in which the central web-plates were replaced by lattice bars. The results for lengths ranging from 64 to 88 radii showed an average ultimate resistance per square inch of 35,650 Ibs. The tabulated values are based upon the formula, 46,000 125-, for lengths exceeding 90 radii and 35,000 for lengths equal to or less than 90 radii. COLUMNS. 35 Section of column : 4 Z-bars, 2j" X 3'' X 2$" (latticed). Radius of gyration (latticed bars not considered) = 2.05". Ultimate Ultimate Length of Column. Sectional Area. Square Inches. Strength by- Actual Tests. Lbs. per Square Inch. Ratio of Length to Least Radius of Gyration. Strength by Formula 46,000 125-. l5'-o" 9.480 34,600 88 35-000 i5'-o" 9.280 36,600 88 35,ooo I 9 '-Oi" 9.241 33,800 112 32,200 I 9 '-0|" 10.104 33,700 112 32,200 22'-o" 9.286 30.700 129 29,900 22'-o" 9.286 29,500 I2 9 29,900 22'-0" 9.286 30,700 129 29,000 25'-o" 9.156 28,IOO I 4 6 27,750 25'-o" 9-456 28,000 I 4 6 27,750 . 25-0" 9.516 28,400 I 4 6 27,750 28'-o" 9-375 27,700 I6 4 25,500 28-0" 9-643 28,000 164 25,500 28'-o' 9-375 27,600 I6 4 25,500 WROUGHT-IRON BOX COLUMNS WITH FLAT ENDS. Sec- Ultimate Strength Style of Column. Total Length. tional Area. Total Pounds Manner 01 Failure. Lbs. per Sq. Inch. Two 6" channels 5.5 inches apart, flanges turned out with two J- inch cover-plates 10 7.9 12.08 383,200 31,722 Plates buckeled be- do. do. 10 7.9 ii . ii 372,900 33'5 6 4 tween the rivets. Two 8" channels 7.6 inches apart, flanges turned out with two / s - inch cover-plates do. do. Four plates connected with four I 3 ". 13 "-8 17.01 17.80 594,5oo 633,600 34.950 35,595 do. Triple flexure. angles forming a box 7" x 7^" inside Plates and angles all ft" thick do. do. 13 11.9 1311.6 20 7.63 '5-74 15.84 15-68 517,000 SSS, 200 517,50 32-846 35-050 33-003 Ruckling plates. Buckling plaies. Deflecting upward. do. do. Single web columns with a}-inch 20 7.80 15-56 536,900 34,505 Buckling plates. pin-ends. One /" web 8" wide with four angles, and 8" channels used in place of cover-plates, flanges i"? 4 15.34 47,500 50.065 Deflecting upward in plane of pin. Strength of Steel Columns. Experiments thus far upon steel struts indicate that for lengths up to 90 radii of gyration their ultimate strength is about 20 per cent, higher than for wrought-iron. Beyond this point the excess of strength dimin- ishes until it becomes zero at about 200 radii. After passing this limit the compression resistance of steel and wrought-iron seems to become practically equal. SKELETON CONSTRUCTION IN BUILDINGS. ULTIMATE STRENGTH OF WROUGHT-IRON COLUMNS. 400OO , ,. , Square ends. By formula /= length in feet, r = least radius of gyration in inches. To be used for columns not cylindrical. For safe load take the ultimate. / Ultimate Strength in Ibs. / Ultimate btrength in Ibs. I Ultimate' Strength in Ibs. / Ultimate Strength in Ibs. I Ultimate Strength in Ibs. sq. in. sq. in. sq. in. sq. in. per sq. in. 3-o 38,610 6.0 34-970 9.0 3O,2IO 12. 25,380 15-5 20,290 3-2 38,430 6.2 34,670 9-2 29,880 12.2 25,070 15-8 20,020 3-4 38,230 6.4 34.370 9-4 29.550 12.4 24,770 16.0 19,760 3-6 38,030 6.6 34,060 9.6 29,230 12.6 24,470 16.2 19,510 3-8 37,820 6.8 33,750 9.8 28,900 12.8 24,170 16.5 19,150 4.0 37,590 7.0 33,440 10. 28,570 13-0 23,870 16.8 18,790 4-2 37,360 7-2 33,130 10.2 28,250 13.2 23,570 17.0 18,550 4.4 37,t20 7-4 32,8lO 10 4 27,920 13-5 23,140 17.2 18,320 4.6 36,870 7-6 32,490 10.6 27,600 13.8 22,7OO 17-5 17,980 4.8 36,620 7-8 32,170 10.8 27,270 14.0 22,42O 17.8 17,640 5-0 36,360 8.0 31,850 II. O 26,950 14.2 22,150 18.0 17,420 5-2 36,090 8.2 31,520 II. 2 26,640 14.5 21,740 18.2 17.200 5-4 35,820 8.4 31,190 11.4 26,320 14.8 31,320 18.5 16,880 5-6 35,540 8.6 30,870 ir.6 26,000 15-0 21,050 18.8 16,570 5-8 35,260 8.8 30,540 ii. 8 25,690 15.2 20,790 19.0 16,370 Radius of Gyration. In order to find the strength of long columns we need to know r 2 , or the square of the radius of gyration. We have, in general, r = -7 , or r = 4/ , where r is the radius of gyration, / is the moment of inertia of the cross-sec- tion to the required axis, and A is the area of the cross-section. The moment of inertia of such built- up sections, as in Fig. 30, with reference or FIG. 30. to the axis through its own centre of gravity parallel to its breadth, is N.B.li -' = f of an inch, b, = i inches. COLUMNS. ELEMENTS OF Z-BAR COLUMNS. X 37 / = Moment of inertia. A = Area. = Radius of gyration. THE THICKNESS OF WEB PLATE AND Z-BAR is THE SAME. 7" Web Plate. 7^" Face to Face. 7i" Web Plate. 7 J" Face to Face. Size of Z-Bar in Inches. Area of 4 Z- Axis XX. Axis YY. Area of 4 Z- Axis XX. Axis YY. Bars Bars and i and i Plate. f - . I. R*. Plate I. K*. I. *t. 3i 9 s x 6 T6 x 3i 9 B x /e 20 .99 24.62 264.18 36-4i 2-59 2-45 287.91 346.95 13-72 4 09 24-84 299-34 347-3 14.14 13-98 287.91 346.95 13.60 '3 97 28.26 347-81 2.31 409.27 4.48 28.51 392.86 13-78 409.28 14-36 3$- x 6 x 3! x ^ 9 g 30.66 365-24 426.30 3-9 3-94 4I5-23 13.42 426.31 13-78 34-22 403.02 489.32 4-3 34-53 38 16 458.45 13.28 489-33 14.17 448.24 1.26 628! 31 699.07 4-13 4-54 4-95 40.19 43-6i 47-20 S'i-45 549.08 587-80 '2-73 12-59 '2-45 562.42 628.33 699.10 '3-99 34 x6i x 3 4 x} 46.77 5'4-73 6}" Web Plate. 6J" Face to Face. 7" Web Plate. 7}" Face to Face. iS-47 169-65 10.97 147-39 9-53 '5-63 193.91 12.41 '47-39 9-43 21.84 202.04 233-93 10.84 10.71 183-47 223.00 9 84 10.21 .8.83 22.06 231.00 267.61 12.27 12.13 If3 47 223.00 9-74 10. It 335 x 5 x 33 ? 5 x * 24.17 249.97 234-39 9.70 24.42 287.67 11.78 2 34-39 9.60 3 9x 5^ 9x T 9 27.30 279-93 10.25 273-72 10.03 27-58 321.22 11.65 273-72 9-93 3^2 x 5& x 34i x 30.46 308.80 10.14 3'5-55 10.36 30.78 354-42 11-52 3'5-56 o-L x 5 x ? x Va 32.31 3'6-97 9.81 320.08 9.91 32-65 364 83 11.17 320.09 9.80 3iB x 5A x 3iB x J 35-44 9.69 36293 10.24 35-8' 395-52 11.04 362.95 10.14 6" Web Plate. 6i" Face to Face. 6J" Web Plate. 6J" Face to Face. , , , 10.78 as 18.47 101.90 126.20 49-9' 66.01 9-45 9-34 8-99 65.72 85.86 107.47 115.63 6.10 it 6.26 10.91 13-67 16.44 18.68 117.62 I45-72 173.18 192.14 10.78 10.06 10.29 65.72 85.86 107.47 115.64 6.02 6.28 6-54 6.19 |r; l l5!!i| 33% x 4lB x 331 x i 21.24 88.60 8.88 138.44 6.52 21.49 218.39 10.16 6.44 3& x 4t xsjxft 24.02 25.87 10.67 21.21 8.77 8-55 163.09 166.90 6-79 6-45 2:5 244.05 256.76 10.04 9-83 163.10 166.91 6.71 6-39 "34- x 4fa x ik x li 28.69 42.12 8.44 192.70 6.72 29.03 281.15 9-69 192.70 6.64 3&X4* x 3fB x t 3* -S 262.65 8.32 220.68 7.OI 3'- 88 305.12 9-57 220.70 6.92 5!" Web Plate. 5}" Face to Face. 6" Web Plate. 6J" Face to Face. 2 *B x 3 3 Ax2*4xt< s 9.14 7-59 90.17 7-94 7.85 31-74 42.14 3-47 3.67 9.26 11.64 84.82 105.31 9.16 9.05 3i 74J 3-43 42-15 362 2 J x 3i x 2 f x f 13.82 107.05 7-75 53-40 3.86 14 01 125.14 8-93 S3-4 1 3-OI 25 X 3 X 2i X y'g '5-53 115.58 7-44 55.61 3.58 '5-75 '35-63 8.61 55.61 3-53 iix 3 A*lixi '7-75 i3-45 7-35 67.20 3-79 18.00 '53-M 8.51 67.20 3-73 38 SKELETON CONSTRUCTION IN BUILDINGS. ELEMENTS OF Z-BAR COLUMNS. / = Moment of inertia. Y r = Radius of gyration. THE THICKNESS OF WEB PLATE AND Z-BAR is THE SAME. 8" Web Plate. 8}" Face to Face. 8J" Web Plate. 8}" Face to Face. Size of Z-Bar in Inches. Area of 4 Z- Axis XX. Axis YY. Area of 4 Z- Axis XX. Axis YY. Bars Bars and i and i Plate. I. X*. I. **' Plate I. R*. I. R 1 . 3 t x 6 x 3^ x | 21.36 25.06 337-17 391-37 15-78 15-62 287.92 346.96 3;g 21-55 25.28 377-65 438 55 17-52 17-35 287.92 346-96 3-36 3-73 3t x 6fr x ^f x ^ 28.76 444-57 15-46 409.28 4-23 29.01 498-35 17.18 409.29 4.11 3 J x6 x 3 J xj s 3 ,.22 469,6 426.32 3-65 3i so 527.03 16.73 16 65 426.33 3 53 3* *6fr x 3 f x 8 3* x6 x 3 * x 38.50 40.56 566.43 579-76 622.59 14-72 14.29 14.14 555-82 562.44 628.36 4-44 3-8? 4-27 38.84 40.94 44-43 636.74 653.06 701.62 16.39 15-95 iS-79 555-83 562.46 628.38 3-74 4.14 3* x6* x 3 f x 47 64 666.83 14.00 699.13 4-67 48.08 751. 66j 15.63 699-15 4-54 7i" Web Plate. 7}" Face to Face. 8" Web Plate. 8}" Face to Face. 3Axs xsAx'A 3* x 5 ^x 3 i xf 3l8 x 5t x 3T 8 e x A 3&x S x 3s ' s xi 15.78 19.01 22.28 24.67 220.13 262.32 303.96 13-95 13-80 13-64 '47-39 183-47 223.00 234 4 10.01 9-50 iS-94 19.20 22.50 24.92 248.29 296.02 343-21 370-53 15-58 15-42 15-25 14-87 147-39 183.48 234-40 III 9.91 9.41 3&X5& X 35* X A 27.96 365-87 13-13 273 73 9-83 28.14 414.08 14.72 273-74 9-73 3ii x 5k x 3 4i x 4 31.09 403-93 22.99 315-57 10 15 31.40 457-31 14.56 10.05 |AX!AX?AX? 33-oo 36-19 452.01 ,2.63 12.49 320.10 9.70 362 .'96 10.03 33-34 36.56 472-79 14^05 3 20. 12 3 62. 9 8 9.60 9-93 7" Web Plate. 7*" Face to Face. 7i" Web Plate. 7}" Face to Face. 2| X 4 X2j Xj 11.03 134.71 I?. 21 65.72 5-96 ii. ,6 I53-I7 13-72 65.72 5-89 2 IB X 4 A X 2 j-| X | 13-83 ,66.97 12.07 85.86 6.21 13-98 189-95 13-59 85.86 6.14 3 x 4 $ x 3 x 16.63 198.52 11.94 107.47 6.46 i8.ii 225-94 '3-44 07-47 6-39 18.90 220.75 11.68 115.64 6.12 19.12 251.40 6.05 3A x 4 A x 3 3 l z x i 21.74 250.90 "54 138-45 6.37 21-99 286.10 13.01 38.46 6.30 3-ft x 4t x 3^, x A 24-58 280.48 11.41 163.10 6.64 24.86 319.96 12.87 6^.11 6.56 3i*s x 4 x 3^ x 26.50 295-54 11.15 166.92 6.30 26.81 337-59 12.59 66.93 6.23 3* AX3* xH 29-37 32-25 323-83 35i-6o 11.03 10.90 192-73 220.72 29.72 32-63 370-17 402.09 14-45 12.32 92.74 20.73 6-49 6-77 6J" Web Plate. 6}" Face to Face. 7" Web Plate. ?i" Face to Face. 2* X 3 X2| X* 9-39 98.12 10.45 3 J .74 3.38 9-Si .'265! ...85 3'-74 3-34 Hx 3 AxttxA 11.79 121.99 10.35 42.15 3 58 11-95 140.07 11.71 42.15 3 53 2 X 3 i X2j Xf 14.20 M4.98 10.21 53-41 3-76 14-39 166.60 ii 58 53-41 3-71 15.96 I57-65 9.88 55-62 3-49 16.18 181.67 11.23 3-44 *Hx3Ax>iixt 18.25 178.09 9-76 67.2, 3-68 18.50 205.32] ii. 10 67.21 3-63 COL UMNS, SAFE LOADS IN TONS OF 2000 LBS. * STEEL Z-BAR COLUMNS, SQUARE ENDS. 39 Allowed strains per square inch for steel, safety factor 4: 12,000 Ibs. for lengths of 90 radii or under. 17,100-57- for lengths over 90 radii. 6" STEEL Z-BAR COLUMNS. Section : 4 Z-bars 3" deep and i web plate 5}" x thickness of Z-bars. Length of 8 "4* !n 4ft ii I, B 5; s in Feet. 2 o,^ S " B S"" e % ** C S e Jg'f 5J! 11! 11 f Sill 5J! 12 and under 14 55-9 55-7 70.3 70-3 8t!ti 95-8 958 105.7 '05.7 jlg'8 16 52-3 66.5 76.6 9' 3 99-9 114.8 18 48.8 62,3 71.7 85-6 93-6 IO7.8 20 45-4 S 8. i 66.7 79 9 87.2 100.8 22 S 53 9 49-7 5'.9 8:1 80.9 74.6 93-8 86.8 26 35- a 45-5 51-9 63.0 68.2 79-8 28 47.0 57-3 61.9 72.8 3 28.3 37-x 42.0 55-5 65.8 8" STEEL Z-BAR COLUMNS. Section : 4 Z-bars 4" deep and i web plate 6J" x thickness of Z-bars. Length of Column in Feet. *j? ^^-^ ill s 3ib iSand under 67.5 65.0 61.9 58.8 55 -i 52.6 49-4 46.3 43.2 40.1 37-0 33-9 82.5 74-8 71.0 67.1 63-3 59-5 S:S 48.0 44.1 100.5 82.3 77-7 73-2 68.7 64.1 59.6 55-o 114.2 89.6 84-4 79 2 74.0 68.7 6.3-5 58.3 M8.5 ,46.4 39-9 ^ 1 I0 7-3 100.8 15:1 81.3 '57-5 153-3 146.2 '39-i 132-0 124.8 117.7 M0.6 ?* 89.4 174-3 171.3 163.5 55-8 48.1 40.4 32.7 25.0 '7-3 109.6 101.9 94-2 81.3 39-9 31.6 23 3 From Carnegie, Phipps & Co.'s Hand Books. 40 SKELETON CONSTRUCTION IN BUILDINGS. SAFE LOADS IN TONS OF 2000 LBS. STEEL Z-BAR COLUMNS, SQUARE ENDS. Allowed strains per square inch for steel, safety factor 4: 12,000 Ibs. for lengths of 90 radii or under. 17,100-57- for lengths over 90 radii. 10" STEEL Z-BAR COLUMNS. Section : 4 Z-bars 5" deep and i web plate 7 " x thickness of Z-bars. S-3* $3* "* s nag $A ir! s S.S A Bed "id* Length of Column 111 7! oW [C ^ "?" cd O !?? ill M ""IT Hi tg ?*? in Feet. s "1 oJ M a 2"! ".S 2 g 2 "I S".f I" 1 ! I*! 1^1 li - - - ^~ *^ 3sS *^s 22 and 1 under ) 94-7 114.2 133-9 147.0 166.2 185.6 196.0 214.9 234.0 26 89-3 112. 6 1 08. 6 133-1 128.3 144-6 139.2 a; 185.3 178.7 193.6 186.5 213 9 206.2 234.0 226.6 28 85.8 104.4 123-5 3- 152.7 172.1 179-3 198-5 2,8.4 30 82.3 100.2 1.8.7 128. 146.7 165.5 172.2 190.8 210.2 32 78.8 96.1 1.3-8 123. 140.7 158.9 165.0 .83.1 Tfl _ i 75-3 71.8 83^6 104.3 99-5 112. 106.8 122.7 '45-7 139.1 150.7 143-6 ifcio 193-0 185.6 177-4 40 64.8 79-4 94-7 101.4 116.7 132-5 ^.5 152-3 169.1 42 61.3 75-3 89.9 96.0 no. 6 125-9 129.4 144.6 160.9 57-7 71.1 85. z 90.6 104.6 119.3 122.2 136-9 .152.7 4^6 54-2 67.0 80.3 8 5 .2 98.6 112.7 II5.I 129.2 '44-5 48 5-7 62 8 75-5 79-8 92.6 106.. 107.9 121.5 136-3 50 47-2 58.6 70.7 74-4 86.6 99-5 100.8 1.3-8 I28.I 12" STEEL Z-BAR COLUMNS. Section : 4 Z-bars 6" deep and i web plate 8" x thickness of Z-bars. ri-S^ SfS "s'S .! s R ^"" ^ "-s's lz* re 4 i^t ;^^ **n JJ ?" jjsf J nn 'Jsr 1 *' Column in Feet. 1| ij! m li 3*7 gi & I'll IT.I 26 and 1 under f 128.3 150.3 .72.6 187.3 209.1 231.0 243-0 264.5 286.1 28 27.0 49-7 172.5 186.0 208.9 230.3 240.8 26,. 4 282 I 30 23.0 45 i 167.6 180.2 202.5 223.3 233-2 253-2 273.2 3 2 19.0 40.5 .62.4 174.5 196.1 2.6.3 225.7 245.0 264.2 in. i 35-9 5:1 157.2 162! 9 a: 209.2 2.8.2 210.6 236-7 228.4 2t.3 40 22.Z 4^5 151-4 170.7 1^8.0 19^6 II. 3:1 4 99-1 ^7-5 136.3 M5-S 64.4 ISO.Q 188.0 203. 219.4 44 X2-9 131-1 139-8 58.0 173.9 I80.5 195. 210.4 ;i 103.6 126.2 120.7 134.0 128.2 51-6 45 3 159.8 172.9 165.4 .87. .79. COL UMNS. SAFE LOADS IN TONS OF 2000 LBS. STEEL Z-BAR COLUMNS, SQUARE ENDS. Allowed strains per square inch for steel, safety factor 4: 12,000 Ibs. for lengths of 90 radii or under. 17,100-57- for lengths over 90 radii. 14" STEEL Z-BAR COLUMNS. Section : 4 Z-bars 6%" x }J"- i web plate 8" x \\". 2 side plates 14" wide. NO o .0 * t > t "2 c< d E-.S H &4 "S.s 8. a ^ ^c ^. c ' 1 e ' ?c - "S7 II 6- m II ty* *n 11 S 11 " "* II 'd-* Column in Feet. S 2fl HBjf iff 13 ?jsf HI III * r 3 2 - ?"~ S^ ?" 28 and 1 under [ 294.0 304-5 315-0 325-5 336.0 346.5 357-0 367-5 378.0 30 286.6 297.2 307.7 318.3 328.9 339-5 350.0 360.4 370.9 32 34 277.8 269.0 288.1 278.9 298.3 308.6 298.9 318.9 308.9 329.2 318.9 339-4 328.8 34 f'i 338.6 359 ,-Z 348.6 36 260.1 269.8 279.5 289.2 298.9 308.6 318.2 327-7 337-4 38 40 251-3 242.5 260.7 251.6 2 7 o.i 260.7 279.5 269.7 289.0 278.9 298.3 288.0 307.6 297.0 316.8 306.0 326.2 315-0 42 44 233-7 224.9 242.5 233-3 241.9 260.1 250.4 269.0 258.9 277.8 267.4 286.4 275.8 295.1 284.2 303.8 292.6 $ 207.2 223.0 230.9 238.9 246.9 254-6 262.4 270.3 5 198.4 2 o6.o 213.6 221.3 229.0 236-5 244.0 251-5 259-1 Section : 4 Z-bars 6" STEEL Z-BAR COLUMNS. %". i web plate 8" x %". 2 side plates 14" wide. W "" t^ ijt &S* 2-.5 &u bj | s -. c j i,, Length of Column Jst 2 ^ ii &A i-ji II &A |Jn II o-rf, 1?? ill S?JL Jjf Iff in Feet. &ni E ""-S pa II '3 S ""- S !?- JS 3>c ft, i, = E^-=' K'S-a fcf- s ' & a ^-K^- 35^-E H \5 ^^ ^5- ?~ ar s* *~ ?" *~ ? 28 and | under f 306.0 316.5 327-0 337-5 348.0 358.5 369-0 379-5 390.0 296.7 307.2 317-8 328-3 338 9 349-4 359-9 370-5 381.1 32 287.4 278.1 268.8 297.6 278.4 i : ! Si 297.9 328.4 318.0 307 4 338.7 327-9 317-2 348.9 337-8 326.8 359-1 347-8 336.4 369-4 357-8 346.1 38 259-5 268.8 2781 287.7 297.0 306-4 3'5-7 325-I 334-5 40 250.2 259-3 268.4 277-5 286.5 295.6 304-7 3I3-7 322.8 42 240.9 249.7 258.5 267.3 276.1 284 8 293-6 302.4 3".2 44 231.6 240.1 248.6 257-1 265.6 274.1 282.5 2QI.O 299.6 46 222.4 230.5 238.7 246.9 255.1 263.4 271-5 279.7 287.9 48 213.0 228.8 236.8 244.7 252-6 260.4 268.3 276.2 50 203.7 211.3 219.0 226.6 234-2 241.8 249.4 257.0 264.6 SKELETON CONSTRUCTION IN BUILDINGS. SAFE LOADS IN TONS OF 2000 LBS. STEEL Z-BAR COLUMNS, SQUARE ENDS. Allowed strains per square inch for steel, safety factor 4: 12,000 Ibs. for lengths of 90 radii or under. 17,100-57- for lengths over 90 radii. 14" STEEL Z-BAR COLUMNS. Section : 4 Z-bars 6^" x \\". i web plate 8" x \\" '. 2 side plates 14" wide. o?e ^ 5-C 4 lag S'e'-o %c . 5. " e od g = o- IN o' II 6-m II crS II cfS 1! cr II cr^ Length of Column gfl 8 mil 8 "II ^i- jfj! 8 8*11 11 8 in Feet. *?1 5;| |;t ^ |*l ?i ill !;.! ;t 2"~ r~ Z~ ?* ' 26 and | under j 327-5 338.0 348-5 359-0 369.5 380.0 390.5 401.0 4"-5 28 326.7 337-5 348.5 359-0 369-5 380.0 390.5 401.0 4II-5 3 327.2 337-7 348.3 358.9 369-5 380.0 390.6 401.1 32 34 206.6 296.6 g3 S 337-4 326.5 347-7 358.0 346.5 368.2 356-4 3&S 388.8 376.4 286.7 296.4 306.0 3I5.7 325-3 335-0 344-7 354-3 364.0 38 276.7 286.0 295-4 304.8 SH- 2 323-6 332-9 342.3 351-7 40 266.6 275-7 284.8 293-9 303.0 312.1 330-3 339-3 42 3 256.6 246.6 236.6 265.5 255-2 244.9 274-3 263.6 253-0 272.2 261.3 291.8 280.6 269.5 300.6 289-2 277-7 309.4 297.6 285.8 318.2 306.1 294.0 327-0 3'4-6 302.3 48 226.7 234.6 242-5 250.4 258-3 266.2 274.1 282.0 290.0 50 210. 6 224.3 231.0 239-5 247.1 254.8 262.3 269.9 277-6 14" STEEL Z-BAR COLUMNS. Section : 4 Z-bars 6J" x ". i web plate 8" x J". 2 side plates 14" wide. 00 00 t;. ^. VO " > * JT.SM "j .-, ^ S.S 4 S.S.O 8.S^ ff.sV " " S 01 "S. Length of Column "?* Zttt lid- A S ^.ll Jj? si? oll ii|f } Ho-A in Feet. E 1 e " g ""o E jj E H> <9 If.? s" c ' E * c ' K.5 E ^^ s?'.5- >^".J. 3l" g".. xjs 35 5 ^''1 1 vjc'll ^ r^ ^" r^" xj v x|, r^" x|v r^ v 26 and I under f 349-1 359-6 370.1 380.6 391-1 401.6 412.1 422.6 433 -i 28 347-4 358.3 369-1 380.0 390.9 4 0!. 6 412.1 422.6 43?. I 30 336.7 347-2 357-9 368.4 378.9 389.5 400.1 410.7 f 421.2 32 i 326.0 315.3 34-5 293-8 336.3 325-2 3'4-2 303.2 346.6 335-2 324.0 312.6 356.8 345-2 333-6 322.0 367-1 355-1 343-3 331-4 377-3 365-2 353-0 340.8 387.6 375-2 362.7 350.2 KS 372.4 359-6 408.2 395-1 382.0 369.0 40 283.! 292.2 301.3 3'9-S 328.6 337-7 346.8 ; 355.9 42 272.3 281.2 290.0 298.8 307.6 3.6.4 325-2 334-0 342.8 44 261.6 270.2 278.7 287.2 295-7 304.2 312.7 321.2 329.8 46 250.9 259-1 267.4 275.6 283.8 300.3 308.5 316.7 48 240.2 248.1 256.! 264.0 272.0 279.8 287.8 295-7 303-6 50 229.5 237.1 244.8 252-4 260.0 267.6 275-3 283.0 290.6 COL UMNS. SAFE LOADS IN TONS OF 2000 LBS. STEEL Z-BAR COLUMNS, SQUARE ENDS. Allowed strains per square inch for steel, safety factor 4: 12,000 Ibs. for lengths of 90 radii or under. 17,100-57- for lengths over 90 radii. 43 16" STEEL Z-BAR COLUMNS. Section : 4 Z-bars 6J6" x %". i web plate 10" x i". z side plates 16" wide. Length of Column in Feet. -5 II a-4 "" i 5 ti *JU Usr: 32 and under 9 397-7 387.6 357-1 347-0 336.9 326.7 316.6 412.1 409.8 399-3 388.9 378.5 SS st; 326.3 424.1 421.9 411.1 400.4 389.6 378.9 368.2 357-4 346.7 336-0 436.1 400.9 389-8 378.8 367-7 356.7 345-7 448.1 446 434 4 2 3 412 460.1 458.1 446.5 434-8 423.2 376.8 365.1 472.1 470.2 458.2 446.3 434-4 422.5 410.5 398.6 386.7 374-8 484-1 482.2 470.0 457-9 445-6 433-4 421.1 409.0 396.7 384-5 496.1 U:S 69.3 56.7 44-2 31-7 4oT 7 394-2 18" STEEL Z-BAR COLUMNS. Section : 4 Z-bars 6}^" x %". i web plate 12" x i". 2 side plates 18" wide. T . q 5 q q *>. 3 . tr.s-- .S d * .5 00 .S VO ^c N._ "*"' il 8>.S Si" *-" ~ SV ^' r ;i r 34 and 1 under j 424.1 437-6 451.1 4 6 4 .6 478.1 491.6 505-1 518.6 532.1 36 419.7 436.8 451.1 464.6 478.1 491.6 505.1 518 6 532-1 38 409-4 426.4 443-2 456 2 476.8 491.6 505.1 sisie 532.1 40 399-2 416.0 432-7 449-5 466.0 482.6 499.1 514-2 42 388.9 405.6 422.3 438.8 455-3 471.7 488.1 503.0 516.0 48 368.4 358.1 384-9 374-5 401.2 390.7 4'7-S 406.9 433 8 423.0 449-9 439-0 466.0 454-9 480.5 469.3 54-5 493-0 481.4 50 347-9 364.1 380.2 396-2 412.2 428.1 443-9 458-1 469.9 44 SKELETON CONSTRUCTION IN BUILDINGS. SAFE LOADS IN TONS OF 2000 LBS. STEEL Z-BAR COLUMNS, SQUARE ENDS. Allowed strains per square inch for steel, safety factor 4 : 12,000 Ibs. for lengths of 90 radii or under. 17,100-57- for lengths over 90 radii. 20" STEEL Z-BAR COLUMNS. Section : 4 Z-bars 6J" x %". i web plate 14" x i". Side plates 20" wide. a Side Plates. 4 Side Plates. Length of Column in Feet. it t* H 8 * Se ex v5 1 I s 38 and under 538.1 532-9 553- S5- 539-2 527-3 503-6 491.8 568.1 557-2 545-3 533-3 521.2 509.2 583-1 583-1 574-5 562.3 SSO.i 538.0 525 7 598.1 S9'-9 579-4 554-6 542-2 583-8 571-2 558.6 626.4 613-7 600.9 643-1 643-1 643-1 630.7 617.8 604.8 591.8 658.1 658.1 658.1 648.0 634.8 621.6 608.4 ao" STEEL Z-BAR COLUMNS. Section : 4 Z-bars 6^" x %". i web plate 14" x i". 4 side plates 20" wide. ! J*: 3*J - * iTj? is.* l?i ai ii n;| 673.1 665.0 lll:l 625.0 668.8 655-3 641-7 672.2 658.4 718. i 717.0 703.1 689.2 675-3 733-1 720.2 748.1 748.1 735-6 763- 763. 7.SO. 735- 720. 778.1 778., 764.7 749.8 734-8 793-1 779-3 764.1 COLUMNS. SAFE LOADS IN TONS OF 2000 LBS. STEEL Z-BAR COLUMNS, SQUARE ENDS. 45 Allowed strains per square inch for steel, safety factor 4: 12,000 Ibs. for lengths of 90 radii or under. 17,100-57- for lengths over 90 radii. 20" STEEL Z-BAR COLUMNS. Section : 4 Z-bars 6^" x %". i web plate 14" x i. 6 side plates 20" wide. Lengt Colu th of Column in Feet. *l Ifc 44 and under 793-7 778.2 762.6 823. 792-5 776.7 790.8 853-1 837-5 821.2 804.7 852.1 835.5 818.7 883.1 866.7 849.7 832.8 846.7 878.3 860.7 928.1 910.4 892.6 874.7 20" STEEL Z-BAR COLUMNS. Section : 4 Z-bars 6}^" x %". i web plate 14" x i". 6 side plates 20" wide. in o 9 *> q ^>G JC . ing *8 c Sc B " S.G *t !l sr$ *i srl 11 ?A W fH Length of Column in Feet. " 2." n~ JJi ||I E"? HA m ii| e"s fjx MI! r 8 8" 8" a" r 8" 42 and 1 under ) 943 - 1 958.1 973-1 988.1 1003.1 I018 , 1033.1 1048.1 44 943-1 958.1 973-0 987.8 1002.5 1017.5 1032.3 1047.3 46 925.0 939-6 954-2 968.8 983-3 997-7 1012.3 1026.8 48 966.9 921.1 935 4 949-6 963.9 978.1 992-3 1006.5 5 888.7 902.6 916.6 930-5 944-5 958.4 972.4 986.1 SKELETON CONSTRUCTION IN BUILDINGS. Phoenix Columns. To determine the value of Phcenix columns under loads, from tests, the following formula has been adopted : P S 42,000 5o,ooor* The expression -^- represents the total load in pounds - sectional area in square inches ' or, in other words, the crushing strain per square inch of sec- tion ; / is the length in feet between bearings, and r is the least radius of gyration. Applying the above formula to the several patterns of seg- mental columns, the table of allowable working strains per square inch of section has been prepared ; the allowable work- ing strains being in each case about one fourth of the ultimate strength of the column. SAFE LOADS FOR PHCENIX COLUMNS, IN POUNDS PER SQUARE INCH OF SECTIONAL AREA. SQUARE-END BEARINGS. Length in Feet. Col. A. Col. B*. Col. B*. Col. C. Col. . Col. G. 10 9.323 9,833 10,024 10,195 10,351 10,411 12 8,885 9,564 9,830 10,067 10,288 10,371 14 8,420 9,267 9,607 9,924 10,215 10,326 16 7,943 8.944 9,364 9,783 10,131 10,275 IS 7,463 8,610 9-105 9,575 10,037 10,216 20 6,997 8,260 8,830 9,386 9>935 10,152 22 6,526 7,906 8,541 9,185 9,824 10,082 2 4 6,090 7,550 8,250 8,973 9.705 10,005 26 7,201 7,955 8,755 9,58o 9,926 28 6,860 7,660 8,527 9-450 9,841 1O 6 527 7 366 8 207 32 7,O75 8 070 34 7 837 36 7 604 8 870 og 8 561 COLUMNS. 47 TABLE OF DIMENSIONS OF PHCENIX COLUMNS. The dimensions given in the following table are subject to slight variations, which are unavoidable in rolling iron shapes. The weights of columns given are those of the 4, 6, or 8 segments of which they are composed. The shanks of the rivets used in joining the segments together only make up the quantity of metal removed in making the holes, but the rivet- heads add from 2 to 5 per cent to the weights given. The rivets are spaced 3, 4, or 6 inches apart from centre to centre, and somewhat more closely at the ends than toward the centre of the column. Any desired thickness between the minimum and maximum for any given size can be furnished. columns have 8 seg- ments, E columns 6 segments, C, B*, B\ and A have 4 segments. I,east radius of gyration equals D X .3^6. One Segment. Diameters in Incl'^s. One Column. Thick- ness in Inches. Weight in Lbs. per Yard. d Inside. D Outside. 01 Over Flanges. A rea of Cross- section. Sq. In. Weight per Foot in Pounds. Least Size of Radius of, Rivet*. Gyration | in Ins. A 9i f 4 # 3-8 12.6 45 tx i ft t 12 14* '7 \\ 4i 4i 4f 6ft 6ft 6y 7 8 4-8 l:l 16.0 >9-3 22.6 5 55 59 i 16 r ST'B 8ft 6.* 21-3 .92 *x A 19^ 5T 7 8 S| -7.fi 26.0 .96 i 23 25 5ft 8 9-" 30-6 .02 ft 26* 1 5U 8| io.4 35-3 .07 i 3 CO 9tt 8ft 12.0 40.0 .11 ft 33i sH N 13-4 44-6 .16 t 37 I *A H 14.8 4^-3 .20 i rti 6& 9i 7-4 24. 34 4X & 22i 6ft 9i 9.0 30. 39 t 26* 3! 6*J 9ft 10.6 35- 43 * 30* J ' 6ti 9l 12.3 4- 48 i * 34* n 6H 9* 13-8 46. 5i ^ ft 38* 7,V 9* IS-4 5'- . i 42} 7ft yii I 7 .0 56.6 61 * 48 SKELETON CONSTRUCTION IN- BUILDINGS. Least radius of gyration equals D X .3636 (continued). One Segment. Diameters in Inches. One Column. Thick- ness in Inches. Weight in Lbs. per Yard. d Inside. D Outside. Over Flanges Area of Cross- section. Sq. In. Weight per Foot in Pounds. Least Radius o Gyration in Ins. Size of Rivets. i 25 7*4 A 10. 33-3 .80 *Xi} A 3 7H "I 12.0 40.0 .85 2 * 35 7ii tt 14.0 46.6 .90 4 ft 40 8A nt l6.0 53-3 94 2* | 45 A i'le 18.0 60.0 98 2f A 48 e BA nf 19.2 64.0 3-3 2* f 53 * BA 12 21.2 70.6 3-o8 2* H 58 Q BA i 2 A 2 3 .2 77-3 3-12 1 63 8H *A 2 5 2 84.0 3.16 2f U 68 m I2A 27.2 90.6 3-21 4 1 73 S il 1218 29.2 97-3 3.26 3 i 83 A I2A 33-2 no. 6 3-34 2f 4 93 9/8 13} 37-2 124.0 3-43 4 x * 103 9H "if 41.2 137-3 3.52 3 J 28 i ISA 16.8 56 4.18 4X2 A S 2 ii* J sA 19.2 64 4 23 36 i if J 5il 21.6 72 4.28 2* A 40 J isli 24.0 80 -32 4 * 44 12 I5f 26.4 88 36 2f A 48 - 12* 16 28.8 96 .40 2t f H 53 58 I 3 i6A 31.8 34-8 106 116 45 5 2* t 63 12* l6 A 37-8 126 55 2f H 68 I2f i6A 40.8 136 .60 73 I2j i6f 43-8 146 .64 2t i 83 13 i6f 49-8 1 66 4 73 2} 4 93 I3t '7 55-8 186 4.82 3 * 103 13* i7A 61.8 206 4-9i 3* A 3 15 19* 24 80.0 5-45 *X2 t 35 '5* 19} 28 93-3 5-5 2 A 40 IS* igf 3 2 io6.5 5-55 2} i 45 I5t i9A 36 120.0 5-59 4 A 50 ist igf 4 133-3 5 63 4 f 55 +, J 5t 19* 44 146.6 5.68 4 H 60 ( M '5t J 9i 48 160.0 5-72 fX2f 1 65 o IS* 19} 52 173-3 5-77 4 H 70 16 20 56 1 8 6. 6 5-82 2} i 75 tfft 20} 60 200.0 5-87 4 i 85 i6| Mf 68 226.6 5-95 3 4 95 16* 20* 76 253-3 6.04 3* ij 105 i6f 2of 84 280.0 6.14 3} if "S *7i 21 92 306.6 6.23 3t CHAPTER III. COLUMN CONNECTIONS. Column Connections. It was previously mentioned that the advantages of different shape columns for connections FIG. 31. with the floor girders, wall girders, and with each other per- form an important part in their selection; in fact, it is so SKELETON CONSTRUCTION IN BUILDINGS. important that the entire strength and rigidity of the struct- ure depends upon these connections. Cast-iron columns with wooden girders, as in Fig. 31, were used extensively at first for the interior columns of buildings ; in fact, are used to a considerable extent at the present time. By glancing at the details it will be seen that bolts or rivets are not used in any manner whatever, and the equi- librium depends solely upon the wooden girders and imposed weight holding the entire connection in place, and, as one writer has stated, " much the same as a child would pile blocks up and steady the pile with its hands." Then again the col- umns are also connected to each other in the same style of construction by flanges as shown in Fig. 32. In the first detail the pintle A is cast as a part of the upper columns, and the shape as shown. In the second, the lower column remains the same diameter, and the wooden girders are cut to fit the shape of the column. The columns are SECTION. FIG 32. secured to each other by bolts through their flanges, and the wooden girders are secured by straps placed each side, as shown in the detail. The change from wooden floor beams and girders to iron COLUMN CONNECTIONS. and steel brought about some alterations in the general details of the columns, which is shown in Fig. 33. Iron beams were FIG. 33. placed side by side, as shown at B, in place of the wooden girders ; then secured to the column by bolts to cast-iron lugs, forming at the same time 'a separator in the girder. These separators were made in two ways one cast solid, as at By the other as shown at A, Fig. 3, and the girders rest upon brackets cast with the column. The floor beams are se- cured to the columns by bolts in the same manner as the girders, 52 SKELETON CONSTRUCTION IN BUILDINGS. and also rest upon brackets. The lugs and brackets are cast about the same thickness as the column, and project 5 or 6 inches from the body. This later detail, Fig. 33, is generally adopted as the connections for all interior cast-iron columns, and the joints, if covered by a cast-iron base, can be at any distance above the floor beams. Cast-iron Column Connections in the Skeleton Frame. In changing from the ordinary method of building to the skeleton frame, the joints of the columns were altered some- what, and the beams and girders when cast-iron columns are used should be secured by wrought-iron knees and bolts, as shown at Fig. 34. The columns were also changed from FIG. 34. circular to square to allow the masonry to fit square with the column. This form provides a simpler connection for the COLUMN CONNECTIONS. 53 cm tain wall and floor girders than the circular shape. The flanges of the joint are reinforced by small brackets, as shown. The curtain-wall girders are secured to the side of the col- umn by knees and bolts, and further secured by straps placed at the back and extending to the girders on the opposite side. This system of bolting the floor girders to the cast-iron columns is to be preferred to that of depending upon lugs cast with the column, as in Fig. 33, for the reason that any number of bolts can be placed in the head to make a rigid connection when the joint especially is above the girders. The same system could be used for the curtain-wall girders ; and instead of using those made up of beam sections, plate or lattice girders could be adopted. The weakest point of the connection is at the joint of the column, and depends solely upon the strength of the bolts in the flanges. Z-bar Column Connections. A material change has been effected from cast-iron columns to those made up of rolled shapes. In these rolled material columns numerous sections are formed by riveting together angles, plates, channels, I-beams, Z-shapes, etc., or of some patented shape which form segments of a circular section such as herein de- scribed ; and, as previously mentioned, the requirement is that the column used shall be well adapted for connection. It is well known that metal near the neutral axis of a column is not of much value, and that a proper disposition of metal farthest from the neutral axis is best effected in the cylindrical section. Therefore, the unit strength of this sec- tion is somewhat greater in long columns than that of others. For proportion of length to diameter, which occurs in the ma- jority of buildings, there is little or no difference in strength among the various sections as mentioned above. To overcome the bending tendency of the column caused 54 SKELETON CONSTRUCTION IN BUILDINGS. by eccentric loading, the floor and wall girders should be ap- plied as close as possible to the neutral axis. The advocates of the Z-bar column, a section made up of four Z-bars and a plate, as shown in Fig. 35, claim that it is FIG. 35. probably the best section which meets the general require- ments for the construction of buildings. This section, they claim, combines a minimum of shop- work with good adaptation for connection and accessibility of all its surfaces. The sketch shows a single beam entering between the Z-bars almost to the very centre of the column, and secured by rivets through the top and bottom flanges ; it also rests upon a heavy bracket made up of angles and riveted to the outer legs of the Z-bars. A beam can also be placed between the legs of the Z-bars at right angles to the one that is shown, and supported upon brackets riveted to the middle web of the Z-bars. The connection of one column to another is not shown in COLUMN CONNECTIONS. 55 this figure, but is shown better in Fig. 36. The columns are separated by a plate made of various thicknesses, depending in a great measure upon the load transmitted to the column from the floor girders. The curtain-wall girders are placed higher than the bottom of the latter and rest upon cast-iron blocks as at A, which are secured to the plate by bolts passing FIG. 36. through the flange of the beams, then through the cast blocks and through the plate. Stiffness and strength is given to the plate under this girder by angle brackets riveted to the body of the column, as at B. The plate is also reinforced under the floor girder by angle-knees, which also serve to join the col- umns together, with rivets passing through this lower and upper knee, as at D. The columns are again stiffened at the back by a splice plate, riveted by any number of rivets, and shown at E. $6 SKELETON CONSTRUCTION IN BUILDINGS. The dotted line C represents the party wall of the building. If this connection is to be used on the inner columns of a build- ing, the plates between the columns will extend to receive a beam or girder on the opposite side ; then the splice plate is not required. When the Z-bar column stands clear of any wall, and is placed to carry beams and girders at right angles to each other, being open on four sides, so that every beam or girder may enter between the flanges, a stiffer connection could not be desired. In fact, the entire load is concentrated near the centre, and every gain in this direction adds greatly to the efficiency of the column ; and one in which a one-sided load can be applied close to the axis is good for a much greater unit strain than where the application must be made farther from the centre. The joint of these Z-bar columns is frequently made at the top of the girders, a plate also being used to make the separation ; then heavy brackets are riveted to the body of the column, as shown at B, to support all beams and girders. Phoenix Column Connections. The makers of the Phoenix column claim, among the many advantages of that section, that the means for applying the loads closely to the axis of the column is an advantage which places it among the many desirable sections to use. For instance, if the load is applied to the shell of the column at one side, this load travels around the column and downward, at an angle of about 45, so that, at a distance below the load equal to the diameter of the column, the whole column will receive an equal load on all parts. There are several methods of making connection to the flanges. In some cases, where filler bars are used between the flanges, the load can be transmitted directly to the opposite flange by means of a gusset plate, or the filler bars can be forged out to form a connection. In a four-segment column COLUMN CONNECTIONS. 57 four loads can be applied at the four connecting flanges, in a six-segment column six, an eight-segment column eight. In order to make a desirable connection to any column, the bracket holes must fit the holes in the column exactly, and the rivets must completely fill the holes. To carry any great load, the brackets must necessarily extend a great distance below the seat in order to get enough rivets in to take the shear. This is not the case with the filler-bar, it extends the full height of column. In Fig. 37 it will be noticed that the cross-pintle extends to B, or is simply a continuation of the web of the floor girder carried clear through the column, distributing the load to all parts of the column, and overcoming in a great measure the tendency of eccentric loading. The wall girders are carried in the same manner and riveted to the pintles shown in plan view. Those which carry the wall girders are riveted to the floor-girder pintle by angles the full height of the pintles. The joint of the columns is at C, plates between being dispensed with. By means of these cross-pintles it is possible to make a continuous column from cellar to roof in which the joints are actually stronger than the body of the column. By referring to the detail (Fig. 37) it will be noticed that the wall girder is composed of angles and plates similar in construction to the floor girder ; an angle is riveted to the side level with the bottom of the floor beam. This is to receive the floor arch. A plate D is also riveted to the bottom of the FIG. 37. SKELEl^ON CONSTRUCTION' IN BUILDINGS. girder, so that the curtain wall may be supported at each story. The entire distance from the party line E to the inside angle of girder being equal to 12 inches, is supported upon a plate II inches wide, if the wall is 16 inches the plate is increased in width and the girders in section- al area. These plates are gener- ally f of an inch thick and riveted to the angles with rivets about 6 inches centres. This section of wall girder may be applied to any column or number of columns ; in fact, the plate girder and lattice girder seem to be the best sec- tion that could be used. The lattice section is so arranged that the wall is built enclosing it completely. Angles are also riveted to the latticing to receive the floor arches. Connections of Column Sections Made up of Angles and Plates. Girders of built sections of plate and angles make more efficient connection than those made up of rolled beams. Columns built of the same sections are more readily joined together at the floor levels, and with each other than any other form, they give a great amount of rigidity, and are recommended to be used, especially when the arrangement of the doors and other openings which occur in the partitions and outer walls are such that it would be impossible to devise a system of lateral bracing. The stiffness of the individual COLUMN CONNECTIONS. 59 column in a skeleton-framed structure or in any building construction is an element of resistance of considerable value if the connections are rigid. If it is impossible to apply lateral bracing to the frame work, the columns should be joined to- gether by complete splice plates on all sides that have no beam or girders connected ; these splice-plates could be used to ad- vantage between the columns and the girders. An ideal column, therefore, is one in which each column is a unit throughout the entire height of the building, which condi- tion is possible when they are made up as shown in Figs. 36 to 40. A considerable degree of security against injury from any cause to which buildings are subjected can be obtained when the columns are constructed in this manner; in fact, the joints at the floor level are stronger than the body of the column. Columns constructed as shown in Figs. 36 to 40 can be made to any practical length, some of which are further illus- trated, where the same section is carried through three stories making the columns nearly 40 feet in length. Where so much depends upon the columns as in the skel- eton frame, every precaution against accidents should be taken. The rolled iron and steel, before the members are riveted together, should have these members inspected singly, for the quality of the material and for surface, and then the finished column inspected for workman- FIG. 39. ship; this offers a guaranty against any serious failure. 6o SKELETON CONSTRUCTION IN BUILDINGS. The connection shown at Fig. 38, of the box column made up of two webs, two cover plates, and joined together by angles, may be applied to single web, Z-bar, or any rectangular sec- tions. In joining the upper and lower columns, they are first separated by the plate B t angle-knees being riveted top and bottom, through which holes for bolts or rivets are punched. An angle-knee is also placed on the inside face over the floor girder. At the back a splice plate C, the full width of the covers, is placed, extending at least 2 feet from the joint. When the work is riveted a stiff and rigid joint is secured. This same connection may be improved upon in the manner shown by Fig. 39. When the column sections are decreased at certain floor levels a filler plate will be required, as shown at C. The joint of the column is more rigid in this connection, but to prevent any lateral dis- placement of the floor girdeis and columns the knee-braces are preferred. When high and narrow buildings are designed the ideal joint is that shown at Fig. 40, the plate sepa- FIG. 40. rating the upper and lower column being placed at the centre COLUMN CONNECTIONS. 6 1 of floor girder ; the knee-brace A placed at the ceiling and the brace B at the floor level. The curtain-wall girder, if made of I-beams, will be level with the bottom of floor beam D\ if made of a plate or latticing it can be secured to the lower and upper column much the same as shown in Fig. 39, a portion of the girder being cut out to pass the connection plate. The position of the columns in the building using such joints will be determined in a great measure by the partitions, then the knee-braces will not be seen. If such is impossible, the floor brace B may be dispensed with, and the inside splice plate, as shown in Fig. 39, be adopted. All connections as described are to be riveted at the works and building with hot wrought iron or wrought steel rivets, thus insuring more rigidity against wind pressure than can be obtained with bolt connections. Rivet Spacing in Column Joints. The rivet spacing in all the above details is determined by certain fixed laws. The rivets connecting the girders with the columns depend upon the load to be supported. For example, if there is 27 tons (54,000 Ibs.) to be supported at one end of a floor girder and \" diameter rivets are used, the shearing strain being measured on the area of the cross-section and allowing 7500 pounds for wrought iron and steel rivets, the area of a rivet $ of an inch in diameter is 0.6013 square inches. This multiplied by 7500 pounds, the safe shearing, = 4510 pounds, the safe amount of strain each rivet can sustain without shearing ; dividing 5400 by this we get 12 rivets to support the girder. If knee-braces are used, a portion of these 12 rivets can be counted in as those supporting the girder. The rivets in the column are generally spaced closer at the joints, say 3 inches for f ", and 4 inches for " diameter rivets ; for the body of the column they should be spaced at a maximum of 6 inches. If there is more than one cover plate over f-" thick each, 62 SKELETON CONSTRUCTION IN BUILDINGS. $" in diameter rivets should be used ; less than that, use f " rivets. If the thickness of plates and angles equals 3 inches, use i" diameter rivets. The rivets in the splice plates are determined by those in the column ; in the knee-braces by the girder and column rivets. The rivets connecting the angle-knees of the top and bottom column through the joint plate are of the same diam- eter as the rest of the lower column. CHAPTER IV. FLOOR LOADS AND FLOOR FRAMING. EQUALLY important in the construction of the skeleton frame as the columns and column connections is the arrange- ment of the floor beams and floor girders. Very many mistakes are undoubtedly due to errors in the calculation of the floor loads. The arrangements must be such that the material is used in the most economical manner ; every member must be calcu- lated. There must be sufficient material, no more nor less ; for it is essential not only from economy, but also to reduce the weights of the dead loads on the foundations, and the construc- tion should be as light as consistent with perfect stability. Dead Loads. All materials used as a part of the construc- tion of the building are rated as dead loads ; that is, the floor- beams, girders, arches, columns, walls, flooring, water in tanks, machinery, partitions, plastering, and anything actually a part of the building. Live Loads. The weight of persons, office furniture, or stores of any kind that can be moved or changed are usually classed as live loads. For such weights as is usual to apply to the floors, the New York Building Law of 1892 is a good guide to follow: "SEC. 483. In every building used as a dwelling-house, tenement- house, apartment-house, or hotel, each floor shall be of sufficient strength in all its parts to bear safely, upon every superficial foot of its surface, 70 pounds ; and if to be used for office purposes 63 64 SKELETON CONSTRUCTION IN BUILDINGS. not less than 100 pounds upon every superficial foot ; if to be used as a place of public assembly, 120 pounds; and if used as a store, factory, warehouse, or for any other manufacturing or commercial purpose, 150 pounds and upward upon every super- ficial foot ; and every floor shall be of sufficient strength to bear the weight to be imposed thereon in addition to the weight of the materials of which the floor is composed. The roofs of all buildings shall be proportioned to bear safely 50 pounds upon every superficial foot of their surface, in addition to the weight of materials composing the same." In several buildings used as offices the author has calculated the dead loads, and found the average weight to be 100 pounds per square foot. This included the terra-cotta arches eight inches in depth, sleepers, wooden floors, beams, girders, parti- tions, and plastering on partitions and ceiling ; the last two items being actually calculated, and then rated so much per square foot of floor surface. The usual practice in New York is to make the upper floors of office buildings carry the minimum weight, 70 or 75 pounds, as required by the New York Building Law, and then increase the weight upon the lower floors, say from 75 pounds ; for all stories above the third, to 150 pounds upon the first story and basement. One 12-story skeleton-constructed building in particular in New York the live load upon every floor excepting the roof has a calculated area of 350 pounds per square foot. The building is used as a printing establishment ; it is therefore likely that every floor, or portion, will at some time or other be loaded to that extent. The greatest weight, according to the dead and live load supported by the lower columns, is 800 tons. Chicago's Practice Relating to the Calculations of the Dead and Live Load upon the Floors. It seems to be the practice in Chicago's high buildings, in regard to the floor loads, to calculate all the beams for the total dead and live FLOOR LOADS AND FLOOR FRAMING. 65 loads, while the girders are required to carry the dead load and about 80 per cent, of the live load, and the columns the dead load and half, or even less, of the live load. This practice is based on the theory that it is quite possible the beams will some time have to carry all the live load, while the chances are increasingly less that the girders and columns will ever be required to do so. Take, for example, the Venetian Building, Chicago. The dead weight on the office floors is 100 pounds per square foot ; the live loads on the floors above the fourth is taken at 35 pounds per square foot. On the second, third, and fourth floors it is taken at 60 pounds, and on the first floor at 80 pounds. The whole of the dead load and about one half the live load is carried to the columns. The building is 12 stories, the greatest load on the lower columns being about 327 tons. The Fair Building, Chicago, is 16 stories in height, and the beams above the fifth story are calculated to carry 75 pounds per square foot of live load, the fifth story 130 pounds, the fourth 200 pounds, and all below the fourth, including the first story, 130 pounds. The floor beams are calculated to carry all the dead load plus the full amount of the live load designated as the maxi- mum for said story. The girders are calculated to carry all the dead load plus 90 per cent, of the live load designated for said story. The columns are calculated to carry all the dead loads plus 45 per cent, of the live load on first story, and increases on each story, from that to the sixteenth story, where it is 90 per cent. an average of about 64 per cent, throughout the building. It would be good practice and within the limit of safety to have for each story : The beams sustain dead load -|- live load. girders " " " -j- 85 per cent, of live load, columns " " " +75 " " " " 66 SKELETON CONSTRUCTION IN BUILDINGS. Floor Framing. In designing the floor framing of a build- ing the beams and floor girders should be arranged to be strained up to the allowable fibre strain, and if the positions of the columns were fixed according to this arrangement, much economy of material would be gained. The proper way is to fix upon the loads which the floor- beams must carry per square foot of floor area; that is, the dead and live loads. Then the spans determined by the loads which will strain the beams to the allowed fibre strain. Suppose, for example, the columns in the side walls of the skeleton frame are spaced 20 feet from centre to centre, and the beams 5-feet centres, this being a practicable distance for the floor arches, and an equal spacing between side walls. The dead and live load to be carried by the beams is 225 pounds per square foot of floor area. The load upon the beam would be 5 X 20 X 225 22,500 pounds, whose coefficient is 20 X 22,500 = 450,000 pounds. By referring to the table of properties of steel beams, page 69, the coefficient corresponding to this would be a 12" X 40 pound per foot I, whose coefficient is 500,100. This is an excess of strength, and if 12" X 32 pounds per foot I were used, whose coefficient is 395,000 pounds, there would be too little strength. To accommodate this gain and loss, one of two things must be done, viz., the column centres or the depth of beams be changed. If we increase the column centre to 21 feet, the total load would be 5 X 21 X 225 23,625, and the coefficient correspond- ing to this would be 21 X 23,625 =496,125 pounds. If a deeper beam is used, say a 15 X 41 pounds per foot I, the coefficient by the table is 603,200 pounds a still greater excess of strength, and the former should be adopted. It is therefore more economical to space the columns to accommodate the full strength of the beams. It will be found in working out these floor beams that the FLOOR LOADS AND FLOOR FRAMING. 67 deeper beam is more economical not only for strength, but for stiffness. If thin floors are not required deep beams should be used ; then the arches become heavier, the filling above the arches becomes considerable, and if this is of concrete the dead load will have to be increased. It is therefore desirable that a few trials be given to this important question before its final settlement. Rolled solid sections should be used in preference to the built-up girders, for these section beams are rolled as deep as 24 inches, with 7^-inch flanges. In the skeleton frame, or in narrow buildings, the girders generally extend parallel with the narrow front and the beams at right angles. Having determined the load per square foot to be sup- ported, the following tables will aid the designer in the con- truction of the floors: To Determine Coefficient for Beams. The following formula for uniform weights gives coefficient for 12,000 pounds strain : $WL= 12, where W= weight in pounds uniformly distributed L = length in inches; / moment of inertia; e = distance of extreme lamina from neutral axis (half the depth of I-beam) ; C ' = coefficient. WL = 96,000^ ; or if L be given in feet as is usual, then WL = 8000- = C. e EXAMPLE. The moment of inertia of a 1 5-inch beam 50 pounds per foot = 522.6. Distance of extreme lamina, 7". 5. ^22.6 Coefficient = 8000 X - = 557,5oo. 68 SKELETON CONSTRUCTION IN BUILDINGS. PROPERTIES OF WROUGHT-IRON I BEAMS. "3* Beam. Weight per ft. Area of Section. Thickness of Web. Width of Flange. Moment of Inertia, axis perpendicular to web at centre. Coefficient, 12,000 IbS. strain. inches. IDs. inches. inches. inches. 20 90.7 27.2 .69 6-75 1650.3 1,320,000 2O 66.7 2O. O 50 6.00 1238.0 990,000 15 8O.O 24-0 .76 6.08 813-7 868,000 15 66.7 2O.O2 50 6.00 707.0 748,000 IS 6O.O 18.0 57 5-45 625-5 667,200 15 50.0 15-0 49 5-05 522.6 557-500 * I2j H. 56.7 16.77 .60 5-50 391.2 511,000 12 56.5. 17.0 78 5.16 348.5 464, 800 12 42.0 12.6 51 4-63 274.8 366,400 12* L. 41-7 12.33 47 4-79 288.0 377,000 lo^H. 45-0 13-36 47 5.00 233-7 356,000 E0| 40.0 12. 55 4-80 201.7 307,200 ioiL. 35-0 10.44 38 4-50 185.6 283,000 10* 31-5 9-5 .41 4-53 165.0 251,200 10} Ex. L. 30.0 8.90 3i 4-50 164.0 250,000 10 42.0 12.6 50 4-75 198.8 318,100 IO 36.0 10.8 44 4-50 170.6 273,000 10 30.0 9.0 37 4-31 145.8 233,300 9 38.5 ii. 6 .46 4.71 I50.I 266,900 9 28.5 9.6 .40 4.16 110.3 196,000 9 23-5 7-1 34 3-96 92-3 164,000 8 34-o IO.2 50 4-50 IO2.O 203,900 8 27.0 8.1 .41 4.09 82:5 165,100 8 21.5 6-5 33 3-71 66.2 132,300 7 22. 6.6 38 3-82 Si-9 118,500 7 18.0 5-4 .26 3-52 44-2 101,100 6 16.0 4.8 25 3-44 29.0 77,400 6 13-5 4.1 .24 3-24 24.4 65,100 5 12. 3-6 .28 2.96 14.4 46,000 5 10. 3-o 23 2.85 12.5 40,000 4 7.0 2.1 .18 2.50 5-7 22,800 4 6.0 1.8 .18 2.18 4.6 18,300 3 9.0 2.7 .40 2.58 3-5 18,900 3 5-5 i-7 .16 2.22 2-5 13,400 To find the safe load in pounds equally distributed, divide the coefficient by the span in feet. To find the safe load in pounds, weight in centre of span, divide the coefficient by the span in feet, and take one half the quotient. Deflection. To find the deflection of beams for the above distributed loads, divide the square of the span in feet by 70 times the depth of beam in inches. * Letters designate Heavy and Light sections. FLOOR LOADS AND FLOOR FRAMING. 69 Coefficients for Steel Beams. If L be given in feet, as before for iron beams, but using 16,000 pounds strain, then WL = 10,666 ~=C. EXAMPLE. The moment of inertia of a 9-inch beam 27 pounds per yard is 1 10.6. Distance of extreme lamina, 4.5. Coefficient = 10,666 X r~ = 262,200. 4-5 PROPERTIES OF STEEL I BEAMS. Moment of Depth of Beam. Weight per ft. Area of Section. Thickness of Web. Width of Flange. Inertia, axis perpendicular to web at Coefficient, !6,ooo Ibs. strain. centre. inches. Ibs. inches. inches. inches. 24 IOO 3O.O 75 7.20 2322.3 2,064,000 24 80 23.2 50 6-95 2059-3 1,830,500 20 80 23-5 .60 7.00 1449.2 1,545,600 20 64 18.8 50 6.25 1146.0 1,222,400 15 75 22.1 .67 6.31 757-7 1,077,300 15 60 I 7 .6 54 6.04 644.0 916,300 15 50 14.7 45 5-75 529.7 753,300 15 4i 12.0 .40 5-50 424.1 603,200 12 40 II.7 39 5-50 281.3 50O,IOO 12 32 9.4 35 5-25 222.3 395,200 IO 32 9-7 37 5.00 161.3 344,000 10 25-5 7-5 32 4-75 123-7 263,800 9 27 7-9 31 4-75 no. 6 262,200 9 21 6.2 .27 4-5 84-3 199,900 8 22 6-5 27 4-5 71.9 191,600 8 18 5-3 25 4-25 57-8 154,000 7 2O 5-9 27 4-25 49-7 151,400 7 15-5 4.6 23 4.00 38.6 117,600 6 16 4-7 .26 3-63 28.6 101,800 6 13 3-8 23 3-50 23.5 83,500 5 13 3-8 .26 3-13 15-7 67,000 5 IO 3-0 .22 3.00 12.4 52,900 4 IO 2-9 .24 2-75 7-7 41,200 4 7-5 2.0 .20 2.63 5-9 31,400 To find the safe load in pounds equally distributed, divide the coefficient by the span in feet. To find the safe load in pounds, with weight in centre of span, divide the coefficient by the span in feet, and take one half the quotient. 7 in!u ( u 1 L-L-l-i-i. EAST FIFTH AVENUE FIG. 75. TYPICAL FLOOR PLAN. The elevator enclosure of the west side is constructed of HOTEL WALDORF. 169 wire-work and angle-iron, surrounded by a staircase built of cast-iron strings, cast risers, and slate treads. Beam Plan. On account of the construction being simi- lar throughout, only that portion of the building is shown fn ' ^""Slfi' rTI ~ - ri~l I -*-h*4 -*- * .9i. '~~ftj_^ FIG. 76. BEAM PLAN AT FIFTH AVENUE END. bounded by Fifth Avenue and the east light-court ; the plan represents the arrangement of the columns, girders, and beams above the first story. I/O SKELETON CONSTRUCTION IN BUILDINGS. The columns are so arranged upon the plan, Fig. 76, to not interfere with the planning of the rooms ; the beams and gir- ders being spaced to support 175 Ibs. per square foot of floor surface, which includes the total live and dead load. The cross-girders are two 15" X 125 Ibs., and two 15" X 150 Ibs. per yard I-beams, depending upon the span ; the beams of the 24.0 span are 15" X 125 Ibs. per yard, of the 19.2 span ioy X 90 Ibs. per yard, with smaller beams in the shorter spans, all spaced from 3 ft. 6 in. to 4 ft. 4 in. centres. The columns range from 16" x 16" X i" in the basement to 7" x 7" X f " in the roof. The connections with the floor beams and girders are made similar to the detail of cast-iron columns with iron girders under chapter on Column Connec- tions. The outer or wall columns of this portion of the plan, as well as those throughout the building, extend through the entire height of the masonry, resting upon cast-iron foot-blocks and rock bottom. The inside columns, or those marked 81 to 84, 87 to 90, 93 and 94, are all supported upon heavy double box girders in the ceiling over the large dining-room of the first story ; these girders are four in number, 4 ft. in depth at the centre, 32 in. in width, and 36 to 38 ft. in length, and sup- ported upon large cast-iron columns 16 in. in diameter. The slope of the entire roof is constructed of 6-in. light I-beam rafters, placed about 4 ft. centres and covered with 3"X 3"X Ts 25 in. centres supporting porous roofing-blocks; then finished off with English roofing-tile. The entire con- struction of the gables and towers is similar to the main roof. THE POSTAL TELEGRAPH BUILDING. The Postal Telegraph Building, as designed by George Edward Harding and Gooch, architects, at the corner of Murray Street and Broadway, New York, is a fireproof struct- ure fourteen stories in height, with a sub-basement and cellar below the sidewalk. The constructive material is of cast-iron THE POSTAL TELEGRAPH BUILDING. 171 columns and steel floor beams and girders throughout. Above the sixth story the walls are carried on steel girders, thus economizing the floor space on the lower stories. The entrance is 30 feet wide, semicircular in shape, and from it the doors leading to the main hall, store, messenger, FIG. 77. THE POSTAL TELEGRAPH BUILDING, NEW YORK. and despatch rooms. This circular entrance is trimmed largely with choice marbles, with which material the main hall, as well as all the halls, are wainscoted. Mosaic tiling is employed in the hallways and in other 1/2 SKELETON CONSTRUCTION IN BUILDINGS. prominent places throughout the building, which aid in making it one of the attractive and complete structures in Broadway. The entrance is flanked by massive piers projecting from the main walls, and capped by bas-reliefs representing light and electricity. Indiana limestone effectively carved and wrought is carried up four stories ; above the fourth story the building is finished in light gray brick, with terra-cotta ornamentation. All partitions are constructed of terra-cotta or fireproof blocks ; the fireproof floor arches are covered with a smooth surface of Portland cement. Iron stairways with marble steps extend from the main floor to roof, and from large passenger elevators give access to all the floors, while two express elevators are used exclu- sively for the four upper stories. The building -covers a plot of ground 70 feet 2f in. on Broadway by 155 feet 6 in. on Murray Street, with an exten- sion at the west end north from Murray Street. The beams and girders are arranged to support 175 Ibs. per square foot of floor surface, the beams being 15 in. by 41 and 12 in. by 32 Ibs. per foot spaced from 4 to 4 feet 6 inches centre. The construction of the column joints and beam connec- tions are similar to those of the Waldorf. CHAPTER IX. WIND-BRACING. THE subject of wind-bracing is receiving considerable atten- tion at the present time among those directly interested in the designing and constructing of high and narrow buildings. Very many criticisms by en- gineers have appeared from time to time in the weekly and monthly periodicals ; but we have failed to see any system, with one or two exceptions, proposed that would meet the full requirements of architects. It is no doubt a difficult prob- lem at the least, and whether lateral bracing is adopted will de- pend in a great measure upon examples of buildings which have been previously built, and which seem to be perfectly secure from all lateral displacement. In using columns and girders made up of plates and angles with knee-braces, as those shown under .chapter on Column Connections, a great amount of rigidity is secured, and these connections will serve in the majority of cases where the regular transverse bracing would interfere with the necessary openings in the partition and otherwise with the planning of the structure. 173 FIG. 78. VENETIAN BUILDING, CHICAGO, ILL. 174 SKELETON CONSTRUCTION IN BUILDINGS. The action of the wind against the side of a building pro- duces the effects of overturning and shear, both greatest at the highest point of external resistance, which is the roof of adjoining building, if there be any, or otherwise the surface of the ground. The overturning or the lift on the windward side is likely always to be less than the resistance of dead weight ; but the shear is liable to be overlooked, and is probably the cause of the collapse of most of the buildings destroyed by wind, especially during construction, while the walls are newly set. Wind-pressure. Experimenters upon the subject of wind- pressure assume that the horizontal pressure of wind against an inclined surface, as a roof, is about I Ib. per square foot per degree of inclination to the horizontal. For example, if the roof has an inclination of 30 degrees with the horizontal, the pressure of the wind will be about 30 Ibs. per square foot of sur- face. Roofs are generally designed for pressures averaging about 40 Ibs. per square foot, but the sides upon which the roof rests for little or none. The experiments of the Forth bridge engineers, and also other experiments, show conclusively that the pressure per unit of surface is less over a large area than over a small one, and what intensity of wind-pressure it is proper to assume upon a high building is an important question to settle. We are well aware that wind develops considerable energy at times, and we cannot expect to resist its utmost power in the design- ing of the structure; but we can at least estimate for high velocities of wind, say from 30 to 50 Ibs. per square foot, and low intensities of strain in the material. Wind-bracing in the Venetian Building, Chicago, 111. An article by C. T. Purdy, C.E., in the Engineering News, of December, 1891, describes in detail the wind-bracing used in the Venetian Building, Chicago. The Venetian Building is probably as well braced and WIND-BRACING. its bracing as well disposed as any building using a system of lateral braces. Fig. 79 is a diagram of the floors of this building, show- ing the arrangement of the columns and position of the bracing. Fig. 80 shows the position of the struts and diagonals and the position they occupy in relation to the floors. The struts of the first and second stories are I foot 9 in. below the next story above, and those above slightly less. Fig. 8 1 is a strain sheet for the wind-bracing, excepting only the column strains, which were included in the schedule given for the vertical loads on the columns. The dead weight of the floors is taken at 100 Ibs. per square foot. The live load on the first floor 80 Ibs., and floors above 60 Ibs. The whole of the FIG. 79. TYPICAL FLOOR PLAN OF dead load and about one half VENETIAN BUILDING, CHICAGO, ILL. the live load is carried into the columns. The calculations of the strains given on the diagram were made as follows : Each set of bracing was figured to resist the wind-force for an area equal to half the height of a story and half the height of the next one above by 21 ft. 7 in. multiplied by 40 Ibs., the calculated wind-pressure per square foot of surface. The total shear at any of these points that is, at any floor SKELETON CONSTRUCTION IN BUILDINGS. level is equal to the sums of the shears acting directly on the points above it. It has not been deemed necessary, however, to carry the whole amount of this shear into the bracing, as in any build- ing the dead weight of the structure itself acts to some extent to counteract the distorting effect due to lat- eral force. These shears are reduced to some extent on this ac- count. The bracing is then made to resist 70 per cent of the wind-pressure. All the columns affected by this bracing have been made continuous from the basement to the second floor. In the cases where the rods come down to the first floor level the bottom strut is connected to the columns so as to take both tension and compression horizon- tally, as well as to resist the vertical component of the rod strain. This insures the resistance of both columns to the horizontal thrust of the strut, whichever pair of rods is strained, and the columns are calculated to resist the bending moment incurred, as well as to carry their regular column load. FiG.Si. FIG. 80. PART TRANSVERSE SECTION AND WIND- STRAIN DIAGRAM OF THE VENETIAN BUILDING. WIND-BRA CING. I // The horizontal struts from the first to the eighth floor are made of two nine-inch channels, arranged somewhat similar to those shown on the Havemeyer Building ; flat latticing 2^ X ^ in., being used top and bottom in place of a plate. Above the eighth floor lighter channels were used. The struts are reinforced at the pier points to resist the bending moment of the strut caused by moving the pier centre so far from the centre of the column. The diagonal steel rods are all dimensioned for 20,000 Ibs.. unit strain, and no rod is less than inch square. All these rods are provided with turn-buckles. The channel struts are so arranged between the columns that the rods pass each side of the column girders, as shown on Fig. 80. By this arrangement they do not interfere with the door-openings in the partitions. There is but slight connection made to these columns by the horizontal struts. The struts are planed at both ends and no clearance is allowed for connection, so that they have butting joints to the columns. Open holes are provided for four rivets connecting the columns, but these are hardly necessary. Underneath the end of the strut is a solid cast-iron block,, and underneath the block are two bracket-angles, secured to the column with sufficient rivet area to resist the vertical com- ponent of the rods in this direction. Above the end of the strut is another cast-iron block, planed on top and bottom to fit in tightly between the strut and the cap plate of the column. This block is made to fit the recess made by the flanges of the Z-bars so closely that the f-inch cap plate is. brought into direct shear entirely around three sides of the block. The shear resistance of the plate together with the weight of the beam directly upon it are more than enough to resist the upward vertical component of the rods. The use of cast-iron blocks in this connection has been found very con- venient, for it often occurs that the bracket angles cannot be 1/8 SKELETON CONSTRUCTION IN BUILDINGS. brought directly under the channels of the strut, and the medium between the strut and the bracket angles must act as a beam as well as a filler. From the above system of bracing we find that every weight caused by the horizontal wind-pressure against a building is transmitted through its own system of triangles to the base or foundation. The load on any brace is equal to the sum of all the weights upon its system between it and the upper portion or unsupported end of the building. In the majority of cases the wind-pressure need not be considered below the fifth or sixth story, this being the aver- age height of adjoining buildings. CURTAIN WALLS. Section 485 of the New York Building Law, given in Chapter I of this volume, describes the thicknesses and manner of supporting the curtain walls of the skeleton frame, and will not be repeated. In making a comparison between that required by the skeleton frame and the old method we find that considerable space is gained on the inside measure- ments of the building. In the ordinary method, by the same law, in an example of a warehouse, store, factory of, say, twelve stories (150 feet in height): "If over 85 feet in height and not over 100 feet in height, the walls shall not be less than 28 inches thick to the height of 25 feet or to the nearest tier of beams to that height ; thence not less than 24 inches thick to the height of 50 feet or to the nearest tier of beams to that height ; thence not less than 20 inches thick to the height of 75 feet or to the nearest tier of beams to that height ; and thence not less than 16 inches thick to the top. " If over 100 feet in height each additional 25 feet in height or part thereof, next above the curb, shall be increased 4 WIND -BRA CING, 179 inches in thickness, the upper 100 feet of wall remaining the same as specified for a wall of that height. Or, by the ordinary method : 1st story. 36 inches 2d " " " 3d 32 " 4th " " 5th " 28 " 6th " . . " " 7th story ....24 inches 8th " " " 9th " 20 " loth " o. " " iith " 16 " I2th " .." " By the skeleton construction : 7th 2d " 8th id " nth 4th " loth t;th " 16 " i ith 6th < 1 2th 7th story. .......... 16 inches 12 The height from floor to floor is generally 12 feet 6 inches. Curtain-wall Supports. The simplest supports for cur- tain walls are these girders made up of beams and channels, as shown in Figs. 82 and 84. These girders extend between the wall columns at about the floor levels and are made to re- ceive the floor arch next the wall, as shown in the detail, which also shows the section of the sleepers, floor arches, and concrete filling. The outer beam of the girder is placed 4 inches from the party FlG - 82 ' line, so that a width of brick can be built in to properly fire- proof the girder. Then, to support the overhanging portion of i8o SKELETON CONSTRUCTION IN BUILDINGS. the brick wall, a plate rests upon and is secured to the top of the girder. Probably a better manner of building this outer 4 or 8 inch wall would be by that shown at the section of the channels, Fig. 84. The channel flanges are turned inside, so as to give a perfectly square and smooth surface for building this over- hanging portion of the wall. Then again if the curtain wall occurs along the wall of a higher build- ing the space back of the channel is clear, the plate being secured after the section is filled in. This same thing may be accomplished in heav- FIG. 84. FIG. 85 ier walls when two beams are not sufficient and plate or lattice girders are used, as shown in the sections, Fig. 83. In Fig. 85 the plate girder is raised sufficiently to receive the floor arch upon the bottom flange ; then the joint of columns is about the centre of the girder. In Fig. 85 an angle is riveted to the web of the plate girder to receive the floor arch. The manner of connecting these wall girders is shown in the chapter on Column Connections. The entire fronts of these skeleton buildings may be sup- ported in such a manner that an entire story or number of stories may be removed without injury to the other portion of the structure or, in other words, an exterior finish entirely in- dependent of the rest of the construction, an example of which is shown by Fig. 86 (a section of the spandrel under the front windows of the Venetian Building, Chicago, 111.) ; the outside view or perspective is shown by Fig. 78, Chapter VIII. These spandrel beams are placed over the windows in such a way that all the load is taken off from the window-caps, how- ever it may appear in the finish. The outside is covered with WIND-BRA CING. 181 brick, terra-cotta,tile, marble, or granite, or combination of these materials, as the architect may design, supported by the above spandrel beams. The section, Fig. 87, represents a portion of the front wall of the Ashland Block, Chicago, 111. ; the wall is only 8 in. thick, and the spandrel channel is 15 in. by 32 Ibs. per foot, with an angle riveted to the upper edge to make a FIG. 86. FIG. 87. broad support for the wall. In Fig. 86 the wall is 16 in. thick, and to support the overhanging thickness cast brackets are secured to a 20 in. X 64 Ibs. per foot I-beam, upon which is secured a 5-in. Z-bar. In each case the terra-cotta window head is secured to the construction. Figs. 88 and 89 represent other modes of supporting the spandrel walls. Fig. 88 is another section of the Ashland Block, and Fig. 89 is a section of the spandrel walls of the Fair Building, Chicago. In all of these cases it will be noticed that the spandrel beams or girders connect to the columns near their centres; the building line represents the faces of piers or face of the building. An excellent arrangement for radiators under the window- 1 82 SKELETON CONSTRUCTION IN BUILDINGS. sills is shown in Fig. 89 ; the spandrel wall is only 8 in. in thickness at this point. In almost all of the above sections the spandrel beams are so arranged, as to size and position, that the floor beams are FIG. 88. CSH/H6 UMf FIG. 89. not required to be framed ; this, if carried out extensively throughout the construction, will save considerable in the cost of the building. CHAPTER X. THE OLD COLONY BUILDING, CHICAGO, ILLINOIS. THE Old Colony Building is situated on Van Buren and Dearborn streets, Chicago, 111. It extends from Dearborn Street to Plymouth Place, thus having a frontage on broad streets of 368 feet. It is in the heart of the new business centre which has grown up on Dearborn Street, and is accessi- ble to all suburban and street transportation, hotels, Post- office, Board of Trade, Custom House, and the United States Courts. It was designed by Messrs. Holabird and Roche, archi- tects, assisted in the construction by Corydon T. Purdy, C.E., to whom the author is indebted for the information. The exterior is of blue Bedford stone to the fifth story, and above of Philadelphia white brick with white terra-cotta trimmings. The entrances from the three streets are finished in elegance and richness of design with marble and elaborate Italian mosaic. The interior finish is of the best, with the corridors all wainscoted in marble and the floors of mosaic. The building consists of sixteen floors, basement and attic, of which the plan Fig. 91 is a typical floor. This plan de- scribes clearly the arrangement of the offices, divided in a sys- tematic and advantageous manner, and on account of the favorable site all the offices open to the outer air and are all connected to the wide and commodious corridor in the centre of the building. Six large elevators with the newest appliances, constructed 183 1 8 4 SKELETON CONSTRUCTION IN BUILDINGS. of iron, extend from basement to attic and are arranged as shown on each side of the stairway. Directly to the right of FIG. 90. THE OLD COLONY BUILDING. the stairs is the boiler-flue, which is constructed of iron and encased in brick. THE OLD COLONY BUILDING, CHICAGO, ILLINOIS. 185 In construction it is probably as perfect a type of the steel skeleton building as any that has been erected. There are no self-supporting walls, and all loads brick, terra cotta, tile, and stone in walls and floors are carried at each floor-level on the steel frame. The special features of its construction pertain to the can- tilever supports at the south end, the lateral strength of the structure, the column construction, and the protection against fire. These have all attracted considerable attention from archi- tects and engineers during the World's Fair months, and are deserving of special notice in this volume. To protect the steel skeleton frame against fire, special precaution was taken, and all the columns were entirely sur-. rounded with a 3-inch hollow tile wall, which in turn was covered, in the case of the outside wall columns, with a solid brick wall on three sides 13 inches thick. Then, again, these outside columns were placed 2 feet back from the street line, in contrast with columns which are usually placed 12 inches from the street line, which is so common in that city, and protected from any outside heat by only 4 or 5 inches of limestone or granite, or even of brick. The Building Law of Chicago especially calls for the above mentioned protection : "SEC. 101. Fireproofing of the steel and iron structural parts of buildings shall, for the purposes of this ordinance, be defined as follows: 'All iron and steel used for a supporting member of the external construction of any building exceeding 90 feet in height shall be protected, as against the effects of external changes of temperature and of fire, by a covering of brick, terra cotta, or fire-clay tile, completely enveloping said structural members of iron and steel. If of brick, it shall be not less than 8 inches thick. If of hollow tile, it shall be not less than 6 inches thick, and there shall be at least two sets of 186 SKELETON CONSTRUCTION IN BUILDINGS. THE OLD COLONY BUILDING, CHICAGO, ILLINOIS. 187 air-spaces between the iron and steel members and the outside of the hollow-tile covering. In all cases the brick or hollow tile shall be bedded in mortar close up to the iron or steel members, and all joints shall be made full and solid. Where skeleton construction is used for the whole or part of a building, these enveloping materials shall be independently supported on the skeleton frame for each individual story.' " SEC. 102. If iron or steel plates are used in each story for the support of this covering within the said story, such plate must be of sufficient strength to carry, within the limits of fibre strain for iron and steel elsewhere specified in this ordi- nance, the enveloping material for the said story, and such plates may extend to within 2 inches of the exterior of said covering. " SEC. 103. If terra cotta is used as a part of such fire-proof enclosure, it shall be backed up with brick or hollow tile ; whichever is used being, however, of such dimensions and laid up in such manner that the backing will be built into the cavities of the terra cotta in such manner as to secure perfect bond between the terra-cotta facing and its backing. " SEC. 104. If hollow tile alone is used for such enclosure, the thickness of the same shall be made in at least two courses, breaking joints with and bonded into each other. " SEC. 105. The horizontal filling between the iron and steel vertical members of skeleton construction shall be of brick, terra cotta, or hollow tile, and, in case of less thickness than 12 inches, subject to the same conditions as to bond and courses as specified for the enveloping materials of structural members, and these horizontal fillings shall be bonded into the enclosures of the vertical members. " SEC. 106. The upper surfaces of all breaks or offsets in external coverings and fillings and walls, as well as the tops of walls, shall be covered with stone, terra-cotta, or fire-clay 1 88 SKELETON CONSTRUCTION IN BUILDINGS. copings set in cement mortar and having lapped joints pointed with cement. " SEC. 107. The internal structural parts of buildings of the skeleton construction shall be fireproofed by coverings of brick, hollow tile, porous terra cotta, or plastering on metal lath and metal furring. " SEC. 108. In the case of buildings of Class I the coverings for columns shall be, if of brick, not lesn than 8 inches thick ; if of hollow tile, these coverings shall be in two consecutive layers, each not less than 2^ inches thick. If the fire-proof covering is made of porous terra cotta, it shall consist of at least two layers not less than 2 inches thick each. " Whether hollow tile or porous terra cotta is used, the two consecutive layers shall be so applied that neither the vertical nor the horizontal joints in the same shall be opposite each other, and each course shall be so anchored and bonded within itself as to form an independent and stable structure. " In all cases there shall be on the outside of the tiles a covering of plastering with any cement which is established as a standard cement by the society of civil engineers of the northwest or of other mortar of equal hardness and efficiency when set. " SEC. 109. In places where there is trucking or wheeling or other handling of packages of any kind, the lower five feet of the fireproofing of such pillars shall be encased in a protective covering either of sheet iron or oak plank, which covering shall be kept continually in good repair. " SEC. no. If plastering on metallic lath be used as fire- proofing for columns, it shall be in two layers. The metallic lath shall in each case be fastened to metallic furrings and the plastering upon the same shall be made with cement. " Protection for the lower five feet shall be required in this case the same as where porous terra cotta or hollow-tile cover- ing is used." THE OLD COLONY BUILDING, CHICAGO, ILLINOIS. 189 190 SKELETON CONSTRUCTION IN BUILDINGS. THE LOADS USED IN CALCULATIONS FOR THE BUILDING, IN POUNDS PER SQUARE FOOT OF FLOOR. On Beams. On Girders. On Columns. On Foundation Footings. Live , 70 50 40 Dead 90 90 Total 1 60 140 130 The above 90 Ibs. of dead load is made up as follows : Floor-arches 35 Ibs. Concrete.., 18 " Plastering 5 " Flooring 4 " Iron 10 " Marble and Partitions 18 " Total 90 Ibs. By referring to the plan Fig. 92 the arrangement of beams and girders is seen. The outer lines of girders on the long sides of the building are formed of a 20- inch beam and angles. The two lines of inside girders running parallel to the above are 2O-inch beams for the longer spans, 1 5-inch and 1 2-inch beams for the shorter spans. The columns supporting the girders are spaced about 22 feet apart. The floor-beams throughout the building are generally 12 inch by 32 Ibs. per foot spaced about 5 ft. 6 in. apart ; those adjoining the elevators for the short spans are 9 in. by 21 Ib. and 6 in. by 13 Ibs. per foot. The entire work being accurately and securely fitted with heavy knees. When the planning of the building began, the support of the south end was the first really difficult problem encoun- tered. The other three sides are bounded by streets, but this south end adjoins another property, which is occupied by an - THE OLD COLONY BUILDING, CHICAGO, ILLINOIS, igi old brick building six stories high w^th exterior walls and foundation built centrally upon party lines. A new party-wall foundation extending somewhat over both lots, and large enough to carry its share of a new build- ing on this neighboring property would, of course, have been the best and easiest solution of the problems. It could have been made without disturbing the old wall above the first floor, except to cut vertical openings in the outside wall for FIG. 93. FOUNDATION-PLAN, SHOWING NUMBER AND POSITION OF COLUMNS. the steel columns which an old party-wall contract permitted in any case. However no arrangement could be made to that end, and it became necessary to keep the foundations of the new building away from the old wall entirely or shorten the building. The cantilever construction was therefore adopted. The plan Fig. 93 shows the columns, their position and the clay areas of the foundations. There are thirty-two columns in all. All the foundations of the building are made of steel beams and Portland-cement concrete, several of them carrying three or more columns each. The areas are proportioned to 192 SKELETON CONSTRUCTION IN BUILDINGS. 3200 Ibs. per square fopt of dead load, including the weight of the foundation. This limit of loading made it necessary to include three columns in each cantilever foundation, and owing to the larger loads on the columns next the street, Nos. 8 and 25, it was necessary to combine the interior ones (9 and 24), making six columns in all on one area. Fig. 94 is a vertical section through the foundation for columns 25, 26, and 27. Column 25 is 3 ft. 6f in. from the south party line and placed upon a triple-web box girder 2 ft. 6 in. wide by 2 ft. 6 in. deep, which in turn rests upon the ends of twenty-four beams 42 ft. io in. long bedded in concrete. Under columns 26 and 27 there are eight 2O-inch beams 22 ft. 4 in. and 20 ft. 3^ in. long respectively, upon which the cast-iron base of each respective column is bedded. This figure also clearly shows box-girder cantilever connecting with column 26, and the off- setting of the 25th column to its proper place for the support- ing of the wall and floors above. This same construction applies to all the party-line columns. All the other foundations throughout the building are arranged in the same manner as that shown in Fig. 1 14, page 236, of this volume, with the exception that very heavy beams were used and the height of the steppings limited to two layers of beams and the lower bed of concrete about 12 inches in thickness. Chicago Building Law relating to setting of steel or iron beams in foundations: " SEC. 79. If steel or iron rails or beams are used as parts of foundations, they must be thoroughly imbedded in concrete, the ingredients of which must be such that, after proper ramming, the interior of the mass will be free from cavities. The beams or rails must be entirely enveloped in concrete, and around the external surfaces of such concrete foundations there must be a coating of any cement mortar not less than one inch thick. THE OLD COLGNY BUILDING, CHICAGO, ILLINOIS. 193 194 SKELETON CONSTRUCTION IN BUILDINGS. " SEC. 80. If concrete foundations are used by themselves and without the insertion of beams, the offsets on top of same shall not be more than one half the height of the respective courses, and such concrete foundations must not be loaded more than 8000 pounds per square foot. If reinforced by iron or steel beams, the loads and offsets in the same must be so adjusted that the fibre strain upon the metal if of iron shall not exceed 12,000 pounds per square inch, or if steel, that the fibre strain shall not exceed 16,000 Ibs. per square inch." The calculations of the foundations for the three columns relating to each cantilever are much alike, and a description of the interior one may easily answer for all. The clay load was determined by the following. The dead load includes floors, columns, and coverings, walls, etc. Live Load, Dead Load, Total on Basement Ibs. Ibs. Cols... Ibs. Col. No. 9 190,400 7 1 2,900 903,300 " 10 323,700 666,940 990,640 " ii 359>!40 896,010 1,255,450 " 22 375,000 917,010 1,292,010 " 23 323,700 666,940 990,640 " 24 190,400 712,900 903,300 The additional load of the foundation itself is treated as though concentrated at column centres and in the same pro- portion as the loads carried by the column. This is not theoretically correct, though practically so, for the weight of the foundation, made as it is, is very evenly distributed, and therefore its centre of gravity should correspond with the cen- tre of gravity of the loads. The actual weight of the founda- tions proved to be about 36,000 Ibs. more than the estimated load, or about 20 Ibs. per square foot more than the 3200 Ibs. figured for. THE OLD COLONY BUILDING, CHICAGO, ILLINOIS. 1 95 Quite sufficient time was allowed for the preliminary study of this cantilever problem, but all the final calculations had to be made as rapidly as possible. The column loads were obtained and various efforts were made to fix upon a footing that would bring the centre of gravity of loads and resistances together, but none could be made on a basis of 3200 Ibs. per square foot on the clay. The plan shown fails of this by about 5^ inches, the centre loading being that distance nearer the party wall than the centre of gravity of the clay area. For various practical reasons, it seemed better to construct the work with this variation of centres than to recast all the foundations of the building to a basis which would not require such a variation, or do any of the several other things that might have been done. After nine months, the average settlement of the founda- tions in the building is 4 T 3 ^ inches, while the average settlement of the centre cantilever foundation is 5^ inches, and columns 9 and 24 on the small side of the footing have settled an inch more than the average of the other four. The latter fact may be due in some measure to the 5^ inches variation in load and resistance centres, although columns 9 and 24 had received 90$ to 95% of their full load, while the other four columns had not received more than 75$, when these observations were taken. The explanation for the greater average settlement of the whole pile probably lies in the fact that this area is so completely and closely surrounded with the other foundations of the building and of the party wall of the adjoining building that most of the lines of resistance through the clay structure must necessarily be vertical, and all the advantage of its large perimeter is lost. Wind-bracing Portal Arches. The lateral strength of this building has been provided for by four sets of portal arches 196 SKELETON CONSTRUCTION IN BUILDINGS. reaching from foundation to roof, as shown in the transverse section Fig. 95, being a sec- tion through columns 6, u, 22, and 27. Two other sets similarly designed are placed between columns the same distance from the other end of the building. The position which it was to occupy was fixed early in the work, but the portal construction was not decided upon until after the contract was let and it was determined to use Phoenix columns. The arrangement under which the contract was made was a combina- tion of arches and tension- bars, and the change was made partially to save the eccentric load it brought on the columns, but largely for the advantage this system would have in the arrange- ment of the rooms, being un- obtrusive and not injurious to renting interests. The chief advantage of FIG. 95. TRANSVERSE SECTION SHOWING this construction is its adapt. PORTAL ARCHES. ^.^ ^ may be put Jn almost any building somewhere without serious injury to the structure. THE OLD COLONY BUILDING, CHICAGO, ILLINOIS. IQJ Even the stores and banking rooms of the building are ar- ranged with the arches, so there will be no serious reduction of income nor an unpleasant appearance in the finish. The portal may be fireproofed so that the space on each side can be joined in one room, or if they are covered in a partition, doorways may be cut through to suit the arrangement of the rooms, except at the extreme sides. It is also believed that it will stiffen the building more than any system of tension rods against the minor vibrations to which Chicago buildings in par- ticular are subjected. These vibrations are caused by street traffic or anything else that gives the neighboring ground a jar, and they are felt in Chicago more than elsewhere on account of the very mobile nature of the clay soil that under- lies the entire business portion of the city. In point of cost they will compare favorably with any sys- tem of rod-bracing, especially if the rods are designed so that doorways may be constructed through the partitions that cover them. In this respect the rods are at a disadvantage in having to be doubled to resist wind from both ways, while all the metal in the portals is strained from whichever way the wind may blow. When these tension-rods are connected to the struts, as they generally are, the column strains are eccentric, while the portal construction, detailed as it is in this case, practically eliminates eccentricity of column strains from the top to the bottom of the system. The same result as the above in appearance could be obtained by using knee-bracing at the ceiling line as shown in Fig. 40, and constructing a light fire-proof arch par- tition, or suspending from the girder between the column light furring lath and covering with the plaster finish. Sec. 123 of the Chicago Building Law calls for wind-braces in all buildings the height of which is more than one and one half times their least horizontal dimensions, and they should 198 SKELETON CONSTRUCTION IN BUILDINGS. be figured at not less than 30 Ibs. for each square foot of ex- posed surface. The precautions against the effects of wind- pressure may take the form of any one, or more, or all of the following factors of resistance to wind-pressure : first, dead weight of structure, especially in the lower parts; second, diagonal braces ; third, rigidity of connections between verti- cal and horizontal members. The accumulated shears and the resultant column strains due to wind-bracing in the Old Colony Building are as follows : Shear. Column Strain. Roof and ceiling 7,860 Ibs. 4,220 Ibs. Attic floor 19,580 " 15,660 " i6th " 31,620 " 33.390 " I5th " 43.570 " 57.820 " I4th " 55,76o " 89,400 " I3th " 67,900 " 127,170 " 2d " 185,120 " 1,006,990 " The strains in the second row of figures apply to the col- umns carrying the floors given in the same line in the first row of figures. They increase the regular load on the column away from the wind and reduce the regular load on the column next the wind. It matters little how the initial loads were obtained so long as they were properly proportioned, for their full application would practically reduce the working column load, that is, the full dead load and a small live load, to zero. More than this would, of course, lift the columns. They are equivalent to a pressure of about 27 Ibs. per square foot over the entire surface of one side of the building at one time. The inertia of the building, the strength of the exterior walls, THE OLD COLONY BUILDING, CHICAGO, ILLINOIS. 1 99 and the stiffness of the connections, especially of beams to columns, and the strength of partitions are all supplementary to this bracing, and probably make laterally one of the strongest steel-constructed buildings in the country. Each FIG. 96. GENERAL ELEVATION OF PORTAL ARCHES. portal was calculated independently of those above and below, for the sections of both top and bottom flanges, thickness of webs, cross-shear on rivets connecting curved flanges, and for splices and connections both to the columns and to adjoining 2OO SKELETON CONSTRUCTION IN tnJILDINGS. portals. The calculations were made as though the two halves of each portal were connected in the top or straight flange with an ordinary pin connection. In the actual construction, how- ever, they were riveted together to secure simplicity in detail ## FIG. 97. DETAIL OF ONE HALF ELEVATION OF PORTAL ARCH. (see general elevation, Fig. 96), ease of erection, increased re- sistance to vibration, a stiffer member which counts for a good deal during erection because it carries a floor and to that extent must be treated as a beam. In Fig. 96 the sizes of arch and other measurements are given. The stories are about 12 feet from floor to floor, the outer columns are 2 feet from the building line, and the arches 15 feet 8 inches be- THE OLD COLONY BUILDING, CHICAGO, ILLINOIS. 2OI tween columns and 9 feet 5 inches high from top of horizontal member to crown. Each portal was designed in two pieces as shown in Fig. 97, which is a shop drawing of one piece as it was delivered for erection. The long splice outside the column was made in two pieces to admit of its erection after the other iron around it was in place. This proved a fortunate precaution, for the delivery of the portals was extremely slow. The splices in the web on each side are in the interests of economy. The straight 3 X 2|- X iV m - angles are flush with the bottom of the regular 12-in. floor-beams, and are so ar- ranged that they can carry the tile floor-arch. Each leg is attached to the portal below with three lug-angles and a rivet- section equal to one half the initial shear. The top and bottom plates in the centre have only a few rivets, but enough to make the member good as a beam, supporting a small floor- area, and to ease the erection somewhat. The lightest metal used in the arches near the top of the building where the shears are so small is T 5 ^- in. thick, the flange-angles being 3" X 3" X -fa" The design calls for a great quantity of field-rivets, but from what we understand it was such easy work that this riveting was not so costly as might be expected. The design is entirely new with this building and the " Monadnock," it being put into both build- ings at the same time. Referring to Fig. 98, the rest of the beam connections and column connections are shown. The specification relating to the detailing of the columns under which the contract was let is as follows : " Beams connecting to columns shall have four rivets in the bottom flange wherever the details of the columns will permit of that number, and in all cases the beams must extend as 2O2 SKELETON CONSTRUCTION IN BUILDINGS. closely as possible to the axis of the column. The top con- nection angles connecting the beams to the columns shall be omitted on all floors, and bent strips of heavy sheet-iron or especially designed wedges must be driven in at the end of FIG. 98. DETAIL OF COLUMN CONNECTIONS. each beam in place of the top connection angle until the clearance between the end of beams and the metal of the columns is tightly closed. In case the flange of the columns will not serve to hold these wedges in place, some other means must be employed to serve the same purpose. " All columns shall be provided with cap-plate inch thick, and, in general, the columns shall be cut so the floor-beams of girders shall rest directly upon them ; dependence, however, must not be placed entirely on the shear of the plate to carry the beams. . . . Columns shall be connected to columns, when possible, by at least four rivets passing through the cap-plate, and two lug-angles, one on each column. All rivets used in THE OLD COLONY BUILDING, CHICAGO, ILLINOIS. 2O3 connecting beams to columns must pass through the lug-angles connected directly to the columns, and riveting such connec- tions to the cap-plate without a lug-angle will not be allowed." The ordinary Phoenix columns did not conform to the specifications, and the only system of connection in use to any extent which it was hoped could be made to apply was the Phoenix improved column, of gusset-plates and fillers, as de- scribed page 57, Fig. 37. There were, however, immediately three objections : first, the Phoenix Company objected on the score of cost, it being too great for the price they were to re- ceive per pound; second, it would have added materially to the tonnage ; and third, the great irregularity of beams, not only in the spandrels but in the floors both as to height and as to position relative to the axes of the columns, made even that system seem impracticable. Finally a general scheme was devised for these connections as mentioned before (detail Fig. 98). In a few cases where heavy spandrel loads had to be carried 16 or 1 8 inches from the centre of the column, gusset-plates and fillers were introduced. The gusset-plate without the fillers was also used in all wind-bracing columns to connect to the portals. The gusset-plates in all cases extended the entire length of the column. The architects have broken up each long facade of the building by inserting at each end a circular bay (see plans and perspective). The metal construction of one of these bays is shown in plan view Fig. 99, and a small section also shown on the same figure. Twelve-inch heavy beams connect with each column ; to these beams, cantilevers composed of plates and angles are secured as shown, and constructed in such a manner as to keep the floor and ceilings level. The column in bay has a bracket with a gusset-plate ex- tending through the column. To the outer ends of the 204 SKELETON CONSTRUCTION IN BUILDINGS. THE OLD COLONY BUILDING, CHICAGO, ILLINOIS. 2O$ bracket bent channels and Z bars are secured which support the sprandrel wall between each story. FIG. loo. SECTION OF BAY. Fig. 100 shows a section through the centre of the bay at the base. A seat of solid granite extends around on top of bent 15 inch channels. CHAPTER XL THE MANHATTAN LIFE INSURANCE BUILDING, N. V. THE new building erected by the Manhattan Life Insur- ance Company at 64, 66, and 68 Broadway, New York, is undoubtedly one of the most conspicuous and the highest office-building in the world. On a comparatively small plot of ground 67 feet front on Broadway, 119 feet deep on the north line to New Street, and 125 feet on the south line, Kimball & Thompson, architects, and C. O. Brown, civil engineer, of New York, have designed and constructed a building of the skeleton type 16 stories high on the Broadway front and 17 stories on New Street. It has a height of 242 feet from the Broadway sidewalks to the top of the main roof and a height of 254 feet 4 inches on New Street. From the main roof on the Broadway front rises a tower termi- nating in a dome, which increases the height of the building from the Broadway curbstone to the foot of the flagstaff to 348 feet. The style of the Broadway and New Street fronts is Italian Renaissance richly ornamented. The Broadway front is of limestone, and the New Street front of light-colored brick and terra cotta ; the side walls are of brick and supported as is usual in the skeleton frame. The special feature of the Broadway front is the arched doorway extending through two stories, with a recessed vesti- bule of stone extending back in the building 13 feet, the sides and ceiling being richly ornamented. The spandrels of the arch have cartouches, on which are inscribed the 206 THE MANHATTAN L2FE INSURANCE BUILDING^ N. Y. 2O/ FIG. 101. THE MANHATTAN LIFE INSURANCE BUILDING, NEW YORK. 2O8 SKELETON CONSTRUCTION IN BUILDINGS. date of the foundation of the company, erection of the build- ing, together with the seal of the company. The other special features are the sixth and seventh stories, which are designed to emphasize the location of the offices of the company, and which are especially marked by the recessed arcade and the projecting balcony. In the design the architects have aimed to preserve as much as possible a solid and dignified character and to avoid excessively large openings. From the sixth story upward the front is more irregular and is marked by side pavilions, the central portion being slightly raised. These pavilions terminate in small domes above the main roof. At the level of the fourteenth story the front recedes from the front line of the building for the width of the central portion and is carried back to the face of the tower, which stands feet / in the rear of the front. The inside of offices are lighted from a large open court on the south side of the building, thus giving every office abundant light and air. On the sixth floor there is a spacious rotunda two stories in height, with a domed ceiling richly decorated in relief. This rotunda is designed for the public entrance to the company's offices. There are five hydraulic elevators for the use of the public and two electric elevators for the use of the company. Careful attention has been paid throughout to the fire- proof qualities of the building. There is no metal work exposed to the action of fire, all being covered with fire-proof materials. All the staircases above the first story to the eighth floor are of marble and iron ; above that of slate and iron. The elevator fronts are of cast iron and wrought grille-work heavily electroplated. All the floors, halls, and corridors are laid with mosaic. Marble, concrete, hollow brick, and THE MANHATTAN LIFE INSURANCE BUILDING, N. Y. 209 tile are largely used throughout the other portions of the building. A ventilating chamber is formed overhead in each corridor (but not in elevator halls), by suspending from the floor-beams, above two angles, one on each side, running the entire length of corridors and to the ventilating shaft, with which the chamber connects. On these angles are placed 3" X 3" tees, set 20 inches on centres, for holding porous terra-cotta blocks. Each office is connected with the above chamber by registers under the control of the tenant. At the head of each ventilating shaft there are electric exhaust fans, supplying the motive power for the extraction and discharge of the vitiated air. The heating and power system is supplied by three marine boilers placed under the sidewalk on Broadway. The care taken in the manufacturing and designing of the steel skeleton frame bore fruit in the erection of the work. The first- material was set September i, 1893, and the setting of the roof-tier was completed December I, 1893. In spite of the rapidity with which the work was prosecuted, the only accident recorded against it was the dropping of a small girder from the roof, which caused but little damage. The total weight of the iron and steel work in the building amounts to 5800 tons. Some of the sections are of an enormous size and weight. The cantilever girders in the basement are 65 feet 10$ inches long, 3 feet 4 inches wide, and 8 feet deep. They weigh eighty tons each. They came to the building in four sections 10 inches wide and the same length as above. The cantilever girder over the second story on New Street is 66 feet long, 2 feet 6 inches wide, and 4 feet 6 inches deep. It weighs forty tons. The front of the building is self-sustaining, that is, it is calculated to support its own weight, but not that of the 2IO SKELETON CONSTRUCTION IN BUILDINGS. floors. The pressure at its base is such that it was necessary to carry the base up to the Broadway level of solid granite. All the other walls of the building, including the New Street front, are carried at the floor levels upon steel girders inserted between the columns. Office Arrangement The subdivision of the rentable space of a building into offices determines at once its financial success. Therefore a good office building should contain, as belonging to the above requirement, good light, ease of access, good service, etc. New York real-estate men state that offices containing 1 50 to 250 square feet are always to be rented in a desirable building, and the large majority of office buildings are so divided as to permit of the renting of such small units. That being the case, those offices containing over the above amount must inevitably be more difficult to rent. In referring to the plan Fig. 102, it will be seen at once that such requirements as the above have been well applied in this building. The rooms are convenient, well lighted, and open into agreeable halls which are also well lighted and acces- sible. Every possible necessity has been provided. The main elevators, five in number, as well as the stairway, are placed in a most desirable position. The division of the offices has been based on the experience of the latest and best examples of commercial buildings, and the interior court, which is believed to be the largest for the size of the building of any in existence. Arrangement of Beams and Girders. The building is calculated to sustain upon every superficial foot of floor and roof surface 175 pounds the standard fixed by the present Building Law of New York. This includes the weight of beams, floor-arches, hollow-block partitions, furniture, ordinary safes, and the weight of people occupying the building, sufficient THE MAN HA TTAN LIFE INSURANCE. BUILDING, JV. 211 allowance being made to have it crowded with people as closely as they can be packed. In addition to the above, special provisions have been made to sustain the concentrated weights of the large vaults which are located in the basement, and also the vault for the company's use at the fifth floor. In both practical and theoretical solutions the best of the 212 SKELETON CONSTRUCTION IN BUILDINGS. Chicago buildings seem at once by comparison more successful than those of New York, in that the former deal with actual loads and actual conditions, and the steel and masonry work is exactly proportioned to the duties to be performed ; whereas in the latter, on account of the provisions of the building law, THE MANHATTAN LIFE INSURANCE BUILDING, N. Y. 21$ the buildings are more massive structures. The difference in principle between Chicago and New York practice is not only confined to floor and column loads, but also to the thickness of walls, which involves heavier foundations and heavier columns, beams, girders, and consequently larger bills to pay. The beams in this building are proportioned to carry nearly the same load as that required by the Chicago Law. The longer spans have 1 2-inch and the smaller spans Q-inch beams placed about 4 to 6 inches apart. The different classes of girders used throughout the building are known as single-plate, double-plate, box and lattice-truss girders. The single-plate girders 20 inches deep are generally used for the support of the floor-beams. Those for the sup- port of 12- and i6-inch walls and the beams resting thereon are generally 24 inches deep. These wall-girders, as shown in the detail section Fig. 104, are supplied with stiffeners at the ends and at intervals in the length of girder of not over three feet between centres. The double-plate and box girders are used for the support of 2O-inch walls and over. Those for the 2O-inch walls are spread to make 1 5^ inches in width over flanges ; those for 24-inch walls to 1 8 inches over flanges ; those for 28-inch walls to be 20 inches over flanges; and for greater thickness of walls are made in like proportion. The stiffeners of the 2O-inch and 24-inch wall- girders are shown in the detail, and spaced the same as in single-plate girders. All double-plate girders are supplied with stay-plates on top and bottom sides, 9 // Xf // , of lengths sufficient to cover over flanges, and are riveted to each flange- angle with three rivets. These plates are staggered in spacing, so that the upper plate comes over the centre of space be- tween the lower ones, which allows the brick walls to be built through the girders and retain a proper bond. The row of girders in New Street wall (see cross-line section) at level of sixth floor, the flanges of which are too close to 214 SKELETON CONSTRUCTION IN BUILDINGS. admit of the width of a brick, have been run in solid with con- crete. The box girders are of two kinds those made of two webs, angles and cover-plates, and those of a series of single-web FIG. 104. SECTION OF NEW STREET AND SIDE WALLS. girders, bolted together with separators between, and placed at intervals of not over three feet on centres. Cast-iron Columns. Throughout the lower stories and largely through the interior of the building cast-iron columns have been used. The requirements of construction were that THE MANHATTAN LIFE INSURANCE BUILDING, N. Y. 21$ they should be castings of uniform quality and subject to the following test: sample pieces one inch square and five feet long cast from the same heat in sand moulds, placed on sup- ports 4 feet 6 inches apart and capable of sustaining a centre load of 500 Ibs. when tested in the rough bar. The flanges of columns were turned true in the lathe to FIG. 105 CAST-IRON COLUMN-JOINT DETAIL. exact lengths as required, to make a perfect contact, and the thickness of flanges was the specified thickness after planing. The detail Fig. 105 shows the system of connections adopted for the cast-iron columns generally throughout the building, The seats for beams and girders are cast with the column, pro- ject 5 inches, and are 2 inches thick. All girders and beams when resting on the above seats are connected together by one-inch bolts running through the column, the holes for which were bored through steel tern- plates, the templates then used for reaming out corresponding holes in end-stiffeners of girders and in angle-iron lugs of beams. When the sectional area of cast-iron columns called for in- terior webs, said webs were cast the same thickness of metal 2l6 SKELETON CONSTRUCTION IN BUILDINGS. as the outer shell, and the area of section maintained through- out the full length of column. Where a smaller column rests upon a column of larger size the core of the larger column at the place of contact is the same size as the core of the smaller, and the metal tapered down for a distance of at least six inches. The bolt-holes in flanges were accurately cored \\ inches in diameter for one-inch bolts. The cores for the columns were rounded off at the corners to a one-inch radius ; the outer corners were rounded off to a radius of \ inch. Ample fillets are provided at all corners of flanges, lugs, and brackets, excepting where interfering with connections of beams and girders. Steel Columns. The steel columns throughout the build- ing, as shown on the beam plan, are composed of Z bars, angles, channels, and such combinations of shapes as indicated. The different members are all riveted together by machine and made in lengths about 40 feet long, or equal in most cases to three stories in the height of building. All abutting ends are planed, the joints fully spliced with steel plates and cover-angles, and when the columns were placed in position were securely riveted together. All seats for beams and girders consist of 6" X 6" X \" angles, as shown in the detail Fig. 106, and riveted to the column ; a similar angle of corresponding size is provided on top side of girder as shown ; it is also riveted to the column, beam, and girders. Where a steel column starts upon one of cast-iron, the foot of the steel column is reinforced by plates and angles and riveted to a wrought-steel plate, which latter is bolted to the flange of the cast-iron column with one-inch bolts. The splices are arranged so that they come above and as near the floor- level as practicable; the full section of the lower heavy column THE MANHATTAN LIFE INSURANCE BUILDING, N. Y. 2\J extends up to the joint. The splicing of one of the lighter side-wall columns is shown in detail, Fig. 106. FIG. 106. STEEL COLUMN-JOINT DETAIL. In proportioning the splices of the other columns, the area of the splices, plates, and angle-splices is equal to the area of the next column above, and the number and size of rivets are such that they transmit the full strain of the upper column. Where the section of the lighter columns is thinner the dif- ference is made up by filling-plates of proper size and thick- ness. Where the steel columns are made up of plates and chan- nels, they are put together in box form, as nearly square as practicable, and the channels placed with flanges facing each other and connected together with lattice-bars 2^" X f" of flat rolled steel. The bars are set at an angle of 60 to the axis 21 8 SKELETON CONSTRUCTION IN BUILDINGS. of the column and riveted to the flanges of channels. The latticing on one side is run in a direction opposite to that on the other. Where the columns are made of more than one web with no cover-plates, the web-plates are spread as indicated on wall- section, Fig. 104, with stay-plates 9'' wide by the width of the column, and of a thickness equal to the angle-iron used in the column, placed not over three feet from centres on each side, and riveted to each flange with three rivets. In addition to stay-plates there are angle-stiffeners placed every three feet apart each side of the web, inch less than the general size of angles used in the column, and in thickness \ less, but none less than T 6 F inch. Filler-plates are placed back of each angle-stiffener which completely fill the intervening space to web. The detail shows in plan view angle knee-braces of 3" X 3" X i" L's and position of wall line, which is 4^ inches inside the building line. It also shows the 2O-inch floor-girder and beam connection to the same. The girders are riveted to the columns as shown in the detail, and the number of rivets forming this connection is such that the shearing strain on the rivets does not exceed 9000 pounds per square inch. The rivets in the girder-stiffener are calculated to carry the entire load. Riveting. The rivets throughout the building are gen- erally f ", $", and i" in diameter. The size used, however, is not less than the thickness of the heaviest member through which the rivet passes. The rivet-pitch is not less than three times its diameter, nor more than 6 inches, and proportioned to sustain the loads on columns, girders, and beams without being strained to exceed 9000 Ibs. per square inch in shear or 15,000 Ibs. per square inch on the bearing surface. No rivets are closer to the edge of any member than i inches for one- THE MANHATTAN LIFE INSURANCE BUILDING, N. Y. 2ig inch rivets, if for seven-eighths rivets, and I J for three-quarter rivets. Cast-iron Lintels. Cast-iron lintels were provided over each and every opening in outside walls and where walls were of masonry. The width of lintels over the windows of side walls is 4" less than the thickness of wall. In the court they cover the entire wall and sustain the brick head. The outside face is neatly moulded. Those for New Street are nearly the full thickness of wall and support the terra-cotta head. Those for Broadway are governed by the reveal of the granite, and support the full brick wall back of granite. The thickness of metal up to a four-foot span is inch, up to five-foot spans, $ inch, and above five feet I inch. Framing in Fire-proof Block Partitions. All openings of doors and windows in block partitions are framed of 4-inch channel uprights extending through the height of story, and secured top and bottom by 3-inch angles to beams or girders as the case may be. A similar channel is placed horizontally at the heads of all doors, at the heads and sills of all windows, with the flanges turned outward in all cases, to hold the blocks of partition in position. Anchoring of Walls. Spear-anchors were provided throughout the building above the level of adjoining buildings, of l" X li" flat iron with f-inch spear ends, to tie all walls pass- ing in front of the wall columns on the outside, and were placed every 5 feet in height on each side of the columns. Similar anchors were provided at the top and bottom flanges of wall- girders at intervals of 5 feet, and so placed in the walls that the spears were vertical. Heavy anchors were provided in the Broadway front, formed of 4" X 4" X \" steel angle double lugs riveted to the columns every 5 feet vertically, with 3" X \" flat steel bars bolted between each pair of lugs and extending out as far as the granite facing permitted, with a spear I inch in diameter 22O SKELETON CONSTRUCTION IN BUILDINGS. and 24 inches long. The New Street wall and court walls were provided with the same anchors as used in the side walls. Arcade at Fifteenth and Sixteenth Stories. At the fifteenth and sixteenth floor-levels there is constructed an ar- cade, as shown upon the perspective Fig. ioi,a skeleton struc- ture supported upon two latticed arches of heavy 6" X 6" angles and latticing connected at the ends by bolts running through columns 12 and 16. These arches are connected together on top with 5-inch steel beams, and at bottom by 3" X 3" angles spaced 3 feet apart. The entire framework is covered with copper, and not only improves the appearance of the south side, but acts in a great measure as a suitable brace for the upper portion of the building. Tower and Dome. The recessed portion of the fifteenth and sixteenth stories of the front is built upon four plate girders running parallel with the front and supported upon two trusses, shown at Fig. 107. The structural work of the FIG. 107. TRUSSES SUPPORTING RECESSED FRONT AT FIFTEENTH FLOOK. tower and dome rests upon a foundation prepared upon the level of the main roof and upon the columns which are sup- ported by the above trusses. From this foundation twelve columns start, made of plates THE MANHATTAN LIFE INSURANCE BUILDING, N. Y. 221 and angles and latticed with steel angles. These latticed angles, and diagonal angles to resist the wind-strains, are placed be- tween the columns and also on ?he outside, and connected to the columns and to each other by connecting plates at the in- tersections. These columns form the tower, 29 feet 9^ inches square by 34 feet high, up to the beginning of the circular portion. At this height they are connected to a box girder extending around the four sides of tower. The floor at the beginning of the circular portion is framed with plate girders and beams, upon which the eight latticed ribs rest. This circular frame is 24 feet in diameter by 27 feet high ; the ribs are constructed of four angles 4" X 4" X f" with single latticing on four sides of 2^" X 2%" X i" L's. Eight arched ribs start from the eight ribs before described, 26 feet 9^ inches high, terminate and butt against a circular girder made of a steel plate 18" X %", and two angles 6" X 6" X i" fully spliced and bent to a circle. The eight arched ribs are made of four flange-angles 4" X 3" X |", double-latticed with angle-bars, 3" X 2" X i", all securely riveted together. The head and foot of arched ribs are reinforced by plates and angles. From the foot of the arched ribs an eight-inch steel pipe starts, and extends through the lantern. The lantern is 5 ft gin. in diameter, 14 ft. high, and formed of eight 6" X 3i" X f " angles riveted together in pairs, bent to a circle at the top and connected to the compression-ring by steel plates. The dome portion of the tower is covered with 3" X 3" X f " tees, bent and twisted to the shape of the dome, placed 20 inches between centres to hold terra-cotta blocks. The entire exterior facing of the tower and dome is covered with cold-rolled copper upon fire-proof block. All cornices, mouldings, and ribs are secured to wrought-iron brackets. 222 SKELETON CONSTRUCTION IN BUILDINGS. The entire height of tower, dome, and lantern, from the roof-level, is 101 feet 9^ inches, and is constructed with ample rigidity to resist a wind-pressure of 50 pounds per square foot upon its surface blowing in any direction. The rest of the building is calculated to withstand a pressure of 30 pounds per square foot. Foundations by the Pneumatic Process. The great height, the massive metal and masonry construction, impose enormous loads on the foundations, amounting to as much as 2000 tons for some single columns, and giving about 7300 pounds per square foot on the whole area of the lot. For this reason the so-called pneumatic process of sinking a pier was adopted ; and the cantilever principle, so well known in bridge construction, has been employed in distributing the load of the column proper over the piers formed by caissons. This is probably the first time this construction has ever been em- ployed for carrying down the foundations of a large building, although common enough in the construction of bridge piers and foundations in or near the water. The enormous weight referred to above could not be safely carried on the natural soil, upon which this site, which is es- sentially of mud and quicksand to the bed-rock. The latter has 'a fairly level surface about 54 feet below the Broadway street- level. Above this rock the water percolates very freely, standing at a level of about 22 feet below the Broadway level. If piles had been driven as close together as the city regu- lations permit i.e., 30 inches centre to centre over the whole area, about 1323 might have been placed, and would have carried an average load of 45,300 pounds each, which was inad- missible, the statute law of New York allowing only 40,000 pounds each on piles 2 ft. 6 in. apart and with a smallest diam- eter of 5 inches. Special foundations were therefore neces- sary, and it was imperative that their construction and duty THE MANHATTAN LIFE INSURANCE BUILDING, N. Y. 22$ should not jeopardize nor disturb the existing adjacent build- ings. On the south side the six-story Consolidated Exchange Building is founded on piles, which are supposed to extend to the rock. On the north the foundations of a four-story brick building rest on earth about 28 feet above the rock, and were especially liable to injury from disturbances of the adjoining soil, which was so wet and soft as to be likely to flow if the FIG. 108. SECTION SHOWING MANNER OF EXCAVATING IN CAISSONS. pressure was much increased by heavy loading or diminished by the excavation of pits and trenches. It was determined, therefore, to carry the foundations on solid masonry-piers down to bed-rock. The construction of the piers by the pneu- matic-caisson process adopted was after careful consideration by the architects, backed by opinions from prominent bridge engineers as to its feasibility. In executing the work an excavation about 28 feet below 224 SKELETON CONSTRUCTION IN BUILDINGS. grade (to water-line) was made over the whole area of the lot. Then the steel caissons were received, the smaller ones com- plete and the larger ones in sections, bolted together when necessary, and located in their exact horizontal positions, calked and roofed with heavy beams to form a platform, on which the brick masonry was started and built up for a few feet before the workmen enfered the excavating-chamber and began digging out the soil. See the following vignette, which shows a vertical section through caisson, pier, air-lock, and shaft, reprneseting the excavators at work and shovelling mud into the foot of the blowpipe, from which it is ejected above. One man is stationed in the chamber at the valve to close it as soon as the air begins to escape. (See Engineering Record, Jan. 20.) The removal of the soil allowed the caissons to gradually sink to the rock below, without disturbing the adjacent earth, which was kept from flowing in by maintaining an interior pneumatic pressure slightly in excess of the outside hydro- static pressure due to the distance of the bottom of the caisson below the water-line. The adjacent buildings were shored up at the outset and scrupulously watched, observations being made to determine any possible displacement or injury of their walls, which were not seriously damaged, though the pressure they exerted on the yielding soil tended to deflect the caissons which were sunk within a foot of the walls. The caissons encountered boulders and other obstructions, and were sunk through the fine soil and mud at an average rate of four feet per day. No blasting was required until the bed-rock was reached and levelled off under the edges, and stepped into horizontal surfaces throughout the extent of the excavating-chamber. Usually one caisson was being sunk while another was being prepared, there being only one time when air-pressure was simultaneously maintained in two cais- THE MANHATTAN LIFE INSURANCE BUILDING, N. Y. 22$ sons. Generally about eight days were required to sink each caisson. Before beginning the caisson-work the adjacent wall of the building north of the lot was temporarily supported by the insertion of needle-beams to permit the removal of the old footing, which was replaced by a new concrete footing, about 10 feet wide by 4 feet high, which formed a continuous foun- dation for that wall, and also for the lower part of the light side-wall of the new building. The caisson, considered as an aid in sinking foundation through wet material, consists of an inverted box having a sectional shape according to the work it is intended to do sometimes circular as shown under column 5, which is 13 feet 4 inches in diameter sunk 30 feet under column 10, 15 feet in diameter sunk 32 feet 8 inches, under column 24, 14 feet in diameter sunk 33 feet 6 inches, under column 25, 10 feet in diameter sunk 33 feet 9 inches and also made sometimes square, rectangular, or irregular. The principle is that, as long as the air-pressure in the box is maintained equal to or slightly above the water-pressure upon the outside down to the shoe or lower edge of the cais- son, it will be impossible for any water to enter. Work is car- ried on in the chamber formed by the caisson, in the vast ma- jority of cases, at the same time as the masonry is placed on top. As the work of excavation advances the caisson sinks, the air-pressure in the inside being reduced slightly until the dead weight of the caisson itself and the masonry upon the top of it are sufficient to overcome the frictional grip or resistance due to the bearing upon the outside surface of the material that it is passing through. In some cases it is necessary to increase the dead load by piling pig-iron on top. Entrance to the cais- son is effected through the so-called air-lock ; sometimes only one of which is employed and sometimes two, one being for 226 SKELETON CONSTRUCTION IN BUILDINGS. men and the other for material. This air-lock is a small cham- ber provided at each end with a door, these doors opening in- wardly toward the inside of the caisson. We will suppose that the inner door of the caisson is closed and the outer door open. The inner door is firmly held in closed position by reason of THE MANHATTAN LIFE INSURANCE BUILDING, N. Y. 22J the interior air-pressure, which, it is not expected, will at any time exceed 12 or 15 pounds to the square inch, equal to about from 27 to 34 feet head of water. Entering the air-lock the outer door is closed, and the air under pressure admitted through a suitable valve into the air-lock. When the air in the air-lock has become of the same pressure as that in the caisson it is evident that the pressure on the inner door will be equal on both sides and it can be opened, the outer door then preventing the escape of the air under pressure. The re- versal of this operation, of course, permits of the air under pressure in the air-lock to escape into the atmosphere. After the caissons have been sunk to bed-rock, they are cleaned out and filled with concrete, thus forming a continuous pier from the rock up to the surface of the ground. The fifteen caissons are arranged as shown upon the plan view Fig. 109, and the location of the main columns above them, all but one of which are supported by the caissons. The exception, column No. 6, is carried by 25 piles driven to refusal and capped with a concrete block 10 ft. X 10 ft. X 3 ft. Cylindrical caissons are the most economical and convenient, and would have been used throughout if the conditions had permitted, but the positions of the columns and the necessity of distributing the load along the building lines, and other con- siderations, determined the use of rectangular ones, except in four cases, B, E, /, and G, under columns 5, 24, 10, and 25. Caisson Detail. The illustration Fig. no represents in detail the construction of caisson M, which supports columns 15, 16, 22, and 23. This caisson is 25 ft. 6 in. by 21 ft. 6 in. and II ft. 6 in. high. It is built of steel plates, angles, beams, and plate girders. The sides are of -inch steel plates, stiffened with angle-brackets made of 6" X 6" angles and further strengthened by /-inch steel bulbs placed horizontally between the brackets. The roof is of f-inch plates, and upon these are placed steel I beams and steel plate girders (see the 228 SKELETON CONSTRUCTION IN BUILDINGS. sections Fig. in), to support the loads of masonry while sink- ing progressed. The sides are carried down a few inches z-J ! FIG. no. SECTIONAL PLAN AND TOP VIEW OF CAISSON M. below the bulbs and the foot of the brackets, and reinforced by heavy steel plates 16 in. wide and $ in. thick and riveted to FIG. in. CAISSON SECTIONS. the outer shell with f-inch countersunk rivets. In the center of roof a shaft 4 ft. in diameter is constructed with air-lock for THE MANHATTAN LIFE INSURANCE BUILDING, N. 22 9 the use of men in entering and leaving the working chamber, and also for filling the chamber after the cassion had reached rock. There are also from four to six 4-inch pipes in the roof of each caisson for use as " blowouts " and for the admisions of air. This caisson contains 467 cubic yards of brickwork and 173 cubic yards of concrete in the chamber. The construction of the circular caissons is essentially the same as the above. The substructure contains about 1260 cubic yards of con- crete and 3400 cubic yards of brickwork, Cantilever Construction. The columns supporting the outer side-walls of the building are locate'd so near the building lines as to be near or beyond the outer edge of the foundation- FIG. ii2. TRANSVERSE SECTION OF FOUNDATION AND CANTILEVER GIRDER. piers, so that if they had been directly supported therefrom they would have loaded it eccentrically and produced un- desirable irregularities of pressure. This condition is avoided and the weights transmitted to the centre of the piers by the intervention of heavy plate girders as cantilevers, which sup- port the columns in the required positions and transfer their 230 SKELETON CONSTRUCTION IN BUILDINGS. loads to the proper bearings above the piers. See the trans- verse section Fig. 112. From these bearings the load is distributed over the whole area of masonry by special steel bolsters that diminish the unit strains and equalize them throughout. The bolsters as shown under the ends of the cantilever girders consist of a row of plate girders 2 ft. high, and upon these another row at right angles, 3 ft. 6| in. high, rest. This section also shows the continuous cantilever girders, and the relative location of the three caissons carrying this particular structure. These cantilever girders consist of a system of plate girders FIG. 113. CANTILEVER-GIRDER DETAIL. arranged in a box form as shown in the detail Fig. 113. The height of the girders under centre of column or the bracket part is 6 ft. ;| in. It should be particularly noted that the columns at the ends of the cantilevers are on the building line with the exception of space sufficient for the insertion of fire- proof bricks. The inner ends of this cantilever are united by THE MANHATTAN LIFE INSURANCE BUILDING, N. Y. 2$l a connecting bridge of plate girders 4 feet deep at columns 21 and 22, columns 23 and 33 being supported at the outer ends. The load supported by the outer columns is trans- ferred to the bolster-shoes at the centre, so that although both of the end columns are outside of the outside edges of their respective caissons, the load they bear is transferred by means of the cantilever and bolster-shoes so as to be evenly distrib- uted over the base of the piers formed by these caissons. That portion of the specification under details of con- struction describes in general the conditions upon which this work is constructed. " All stiffeners shown upon the cantilevers are to be 5" X 3" X f" steel angles on the inside and 5" X 4" X f" angles on the outside. The cantilevers within the building are to rest on steel shoes. The bottom and top bearing surfaces of said shoes shall be planed off perfectly true and lev$l, and that portion resting upon said shoes; and where the columns rest on the cantilevers per- fectly level seats shall be prepared as follows: "A rolled steel plate, one inch thick, of the width of the cantilever in one direction and the width of the steel shoe or the flange of column in the other direction, planed perfectly true, to be riveted to the cantilever with counter- sunk rivets. " A solid bearing of the four girders forming a cantilever to be obtained, if necessary, with thin steel plates of such thickness as will bring the bearing surface to a perfectly solid and true contact. " The tops of the cantilevers to be set level throughout, and the difference in height to be made up in the granite capstone. " The steel shoe on which cantilevers rest shall be set on the stone caps on a bed formed of heavy sheet lead bedded in Portland cement. " The girders composing the cantilevers shall be bolted 232 SKELETON CONSTRUCTION IN BUILDINGS. together with one-inch bolts through and through the stiffener angles ; under each line of columns resting on said cantilevers and over the shoe bearing, spaced vertically one foot apart ; there will also be two vertical lines of bolts under each column and four lines over the shoe bearing. " Before setting the cantilever girders in position, the inner sides of the outer girders and both sides of inner girders shall be run full with concrete, and be allowed to set hard." The first tier of floor-beams are supported by the cantilever girders and so framed as to make the top of beams flush with the top of highest rivet-heads in said girders. The shoes under cantilevers and the shoes of columns setting directly on granite capstones are made of the best quality cast steel, and free from blow-holes. The cantilevers designed to be placed under the pj^ers and columns of Broadway front are composed as follows: Two layers of beams, the lower composed of ten 1 5-inch steel beams, 200 pounds per yard, running parallel with the front ; the upper composed of four beams of the same height and set at right angles to the lower. Each layer is thoroughly and securely bolted together with separators and bolts, and the spaces between beams are filled with cement. The failures of the other portions of the work throughout a building due to faulty workmanship are rare in comparison with those due to defective foundations ; therefore, a few re- marks are inserted on account of the importance the subject bears to the construction of these high buildings, but for fuller information the reader should refer to works which treat solely upon " Masonry Construction." In designing the foundations of walls and piers when they rest upon a yielding stratum, proper provision must be made for the uniform distribution of the weight, and to form such a THE MANHATTAN LIFE-INSURANCE BUILDING, N. Y. 233 solid base for this superstructure that no movement shall take place after its erection. But all structures built of coarse masonry, whether of stone or brick, will settle to a certain extent ; and, with few exceptions, all soils will become com- pressed under the weight of almost any building. The main object, therefore, is to proportion the different loads so that the bearing unit of ground area will be equal, and a uniform settlement of the completed structure is ensured. To Determine the Nature of the Soil. If the nature of the soil upon which the building is to be constructed cannot be determined by excavations made for surrounding buildings, wells, etc., proper arrangements must be made for testing the subsoil by boring holes at intervals considerably deeper than the walls are intended. It will usually be sufficient to examine the soil with an iron bar, driving it from 4 to 5 feet deeper than the foundation trenche.3. In soft soil, a small gas-pipe is driven with a maul from a temporary scaffold, the height of which will depend upon the length of the section of the pipe. Soundings 30 to 40 feet deep can be made in this manner. Foundations on Rock. To prepare a rock bed for a foun- dation, cut away the lower and decayed portions of the rock, and dress it to a plane surface as nearly perpendicular to the direction of the pressure as practicable. If there are any fissures they should be filled with concrete. The ultimate crushing strength of stone, as determined by crushing small cubes, ranges from 180 tons per square foot for the softest stone to 1800 tons per square foot for the hardest. The safe bearing power of rock should be about one-tenth of the ultimate strength of cubes ; that is to say, the safe-bear- ing power of solid rock is not less than 18 tons per square foot for the softest, and 180 tons for the hardest. Almost any rock when well-bedded will bear the heaviest load than can be brought upon it by any masonry construction. 234 SKELETON CONSTRUCTION IN BUILDINGS. Foundations upon Clay. Foundations on clay should be laid at such depths as to be unaffected by the weather ; since clay, at even considerable depths, will gain and lose consider- able water as the seasons change. The bearing power of clayey soils can be very much improved by drainage or by preventing the penetration of water. When coarse sand or gravel is mixed with the clay, its supporting power is greatly increased, being greater in proportion as the quantity of these materials is greater. When they are present to such an extent that the clay is just sufficient to bind them together, the combination will bear as heavy loads as the softer rocks. From the experiments made in connection with the con- struction of the capitol at Albany, N. Y., upon blue clay con- taining from 60 to 90 per cent of alumina, and the remainder being fine siliceous sand, less than 6 tons per square foot was the extreme supporting power, and 2 tons per square foot the load which might be safely imposed. The safe load allowed upon ordinary clay if in danger of being saturated by water, is from i to 2 tons per square foot ; if kept dry, 3 to 4 tons. Foundations upon Sand. Sandy soils vary from coarse gravel to fine sand, and when mixed make one of the best and firmest of foundations. Sand well cemented with clay and compacted, if protected from water, will safely carry 4 to 6 tons per square foot. Foundations upon Piles. A pile is generally understood to be a round timber driven into the soil ; or, what is called a bearing-p\\e, one used to sustain a vertical load. Spruce and hemlock answer for foundation-piles in soft or medium soil, or for piles always under water ; the hard pines, elm, and beech for firmer soils ; the hard oaks for still more compact soils. The following paragraph from the New York Building Law of 1892 makes provision for the construction of pile and other foundations : THE MANHATTAN LIFE-INSURANCE BUILDING, A r . Y. 235 " Every building, except buildings erected upon wharves or piers on the water-front, shall have foundations laid not less than four feet below the surface of the earth, on the solid ground, or level surface of rock, or upon piles or ranging timbers. " Piles intended for a wall, pier, or post to rest upon shall not be less thanyw inches in diameter at the smallest end, and shall not be spaced more than 30 inches on centres, or nearer, if required by the superintendent of buildings, and they shall be driven to a solid bearing. " No pile shall be weighted with a load exceeding 40,000 pounds. The tops of all piles shall be cut off below the lowest water-line. When required, concrete shall be rammed down in the interspaces between the heads of the piles to a depth and thickness of not less than 12 inches and for I foot in width outside of the piles. " When ranging and capping timbers are laid on piles for foundations they shall be of hardwood, not less than 6 inches thick, and properly joined together, and their tops laid below the water-line. " When crib-footings of iron or steel are used below the water-level, the same shall be entirely coated with coal-tar, paraffine varnish, or other suitable preparation before being placed in position. " When footings of iron or steel for columns are placed below the water-level, they shall be similarly coated for preser- vation against rust." * " All base-stones shall be well bedded and crosswise, edge to edge. If stepped-up footings of brick are used in place of stone above the concrete, the steps or offsets, if laid in single courses, shall not exceed i in. ; or, if laid in double courses, then each shall not exceed 3 in., starting with the brick-work covering the entire width of the concrete, so as to properly distribute the load to be imposed thereon." * For foundation-walls and footings, refer to article under New York Build- ing Law relating to skeleton construction, Chapter I. 230 SKELETON CONSTRUCTION IN BUILDINGS. " If in place of a continuous foundation-wall isolated piers are to be built to support the superstructure, where the nature of the ground and the character of the building make it neces- sary, inverted arches shall be turned between the piers, at least 12 in. thick and of the full width of the piers, and resting upon a continuous bed of concrete of sufficient area and at least 18 in. thick. Or two footing-courses of large stone may be used, the bottom course to be laid crosswise, edge to edge, and the top course laid lengthwise, end to end ; or one course of con- crete and one course of stone. The stones shall not be less than 10 in. thick in each course, and the concrete shall not be less than 18 in. thick, and the area of the lower course shall be equal to area of the base-course that would be required under a continuous wall ; and the outside pier shall be secured to the second pier with suitable iron rods and plates." Foundation upon Steel Rails and I-beams. Steel, usu- ally in the form of railroad rails or I-beams, is used instead of timber in foundations. The rails or I-beams are placed side by side as shown (Fig. 1 14), and concrete is rammed in between them. The important advantage steel has over wood is that the offset can be much greater, and hence the foundations may be shallow and still not occupy the cellar-space. The foundation should be pre- pared by first laying a bed of con- crete to a depth of from 4 to 12 in., and then placing upon this a row of I-beams or rails. They should be placed far enough apart to permit the introduction of the concrete fill- ing and its proper tamping between the beams. FIG. 114. STEEL-RAIL FOUNDATION. THE MANHATTAN LIFE-INSURANCE BUILDING, N. Y. 2tf Unless the concrete is of unusual thickness, it will not be advisable to exceed 2O-in. spacing, since otherwise the concrete may not be of sufficient strength to properly transmit the up- ward pressure of the beams. The area of the foundation having been determined and its centre having been located with reference to the axis of the load, the next step is to determine how much narrower each footing-course may be than the one next below it. The projecting part of the footing resists as a beam, fixed at one end and uniformly loaded. The load is the pressure on the earth or on the next course below. The offset of such a course depends upon the amount of pressure and the transverse strength of the material. Evidently the size of beams required will depend upon their strength as cantilevers sustaining the upward reaction, which may be regarded as a uniformly distributed load. Then, for a beam fixed at one end and uniformly loaded, Coefficient Safe load in Ibs. = j . 4** The coefficients for all the different sizes of steel and iron beams are given in Chapter IV, " Floor Loads and Floor Framing." SHORT-TITLE CATALOGUE OF THE PUBLICATIONS OP JOHN WILEY & SONS, NEW YORK, LONDON: CHAPMAN & HALL, LIMITED. ARRANGED UNDER SUBJECTS. Descriptive circulars sent on application. Books marked with an asterisk (*) are sold at net prices only, a double asterisk (**) books sold under the rules of the American Publishers' Association at net prices subject to an extra charge for postage. All books are bound in cloth unless otherwise stated. AGRICULTURE. Principles of Animal Nutrition 8vo, 4 /o OO Budd and Hansen's American Horticultural Manual: Part I. Propagation, Culture, and Improvement . . . I2mo, i 50 Downing's Fruits and Fruit-trees of America 8vo, 5 5o 00 Elliott's Engineering for Land Drainage tamo 5 Practical Farm Drainage . . .I2mo, I oo Green's Principles of American Forestry . . . I2mo, i 50 Grotenfelt's Principles of Modern Dairy Practice. (Woll.) . . . I2mo, 2 oo Kemp's Landscape Gardening . . . i2mo, 2 50 Maynard's Landscape Gardening as Applied to Home Decoration. . . ...12010, I 50 * McKay and Larsen's Principles and Practice of Butter-making . . ....8vo, i 50 Sanderson's nsects Injurious to Staple Crops . . . 1 2 mo, i So Insects njurious to Garden Crops. (In preparation.) Stockbridge' Rocks and Soils ..8vo, 2 50 Winton's Mi roscopy of Vegetable Foods 8vo, 7 50 Woll's Handbook for Farmers and Dairymen. . . . . . i6mo, i 50 ARCHITECTURE. Baldwin's Steam Heating for Buildings Bashore's Sanitation of a Country House Berg's Buildings and Structures of American Railroads Birkmire's Planning and Construction of American Theatres Architectural Iron and Steel Compound Riveted Girders as Applied in Buildings Planning and Construction of High Office Buildings Skeleton Construction in Buildings Brigg's Modern American School Buildings Carpenter's Heating and Ventilating of Buildings Freitag's Architectural Engineering Fireproofing of Steel Buildings French and Ives's Stereotomy 1 i amo, 2 50 I2mo, i oo 4to, 5 oo 8vo, 3 oo 8vo, 3 50 8vo, 2 oo 3 50 3 oo 4 oo 4 oo 3 50 2 50 2 50 8vo, 8vo, Gerhard's Guide to Sanitary House-inspection. lOmo, i oo Theatre Fires and Panics izmo, i 50 *Greene's Structural Mechanics 8vo, 2 50 Holly's Carpenters' and Joiners' Handbook i8mo, 75 Johnson's Statics by Algebraic and Graphic Methods 8vo, 2 oo Kidder's Architects' and Builders' Pocket-book. Rewritten Edition. i6mo,mor., 5 oo Merrill's Stones for Building and Decoration 8vo, 5 oo Non-metallic Minerals : Their Occurrence and Uses 8vo, 4 oo Monckton's Stair-building 4to, 4 oo Patton's Practical Treatise on Foundations 8vo, 5 oo Peabody's Naval Architecture 8vo, 7 50 Richey's Handbook for Superintendents of Construction i6mo, mor., 4 oo Sabin's Industrial and Artistic Technology of Paints and Varnish 8vo, 3 oo Siebert and Biggin's Modern Stone-cutting and Masonry 8vo, I 50 Snow's Principal Species of Wood 8vo, 3 50 Sondericker's Graphic Statics with Applications to Trusses, Beams, and Arches. 8vo, 2 oo Towne's Locks and Builders' Hardware i8mo, morocco, 3 oo Wait's Engineering and Architectural Jurisprudence 8vo, 6 oo Sheep, 6 50 Law of Operations Preliminary to Construction in Engineering and Archi- tecture 8vo, 5 oo Sheep, 5 50 Law of Contracts 8vo, 3 oo Wood's Rustless Coatings: Corrosion and Electrolysis of Iron and Steel. .8vo, 4 oo Worcester and Atkinson's Small Hospitals, Establishment and Maintenance, Suggestions for Hospital Architecture, with Plans for a Small Hospital. I2mo, i 25 The World's Columbian Exposition of 1893 Large 4to, i oo ARMY AND NAVY. Bernadou's Smokeless Powder, Nitro-cellulose, and the Theory of the Cellulose Molecule I2mo, 2 50 * Bruff 's Text-book Ordnance and Gunnery 8vo, 6 oo Chase's Screw Propellers and Marine Propulsion 8vo, 3 oo Cloke's Gunner's Examiner 8vo, i 50 Craig's Azimuth 4to, 3 50 Crehore and Squier's Polarizing Photo-chronograph. 8vo, 3 oo * Davis's Elements of Law 8vo, 2 50 * Treatise on the Military Law of United States 8vo, 7 oo Sheep, 7 50 De Brack's Cavalry Outposts Duties. (Carr.) 241110, morocco, 2 oo Dietz's Soldier's First Aid Handbook i6mo, morocco, i 25 * Dredge's Modern French Artillery 4to, half morocco, 15 oo Durand's Resistance and Propulsion of Ships 8vo, 5 oo * Dyer's Handbook of Light Artillery I2mo, 3 oo Eissler's Modern High Explosives 8vo, 4 oo * Fiebeger's Text-book on Field Fortification Small 8vo, 2 oo Hamilton's The Gunner's Catechism i8mo, i oo * Hoff 's Elementary Naval Tactics. 8vo, i 50 Ingalls's Handbook of Problems in Direct Fire 8vo, 4 oo * Ballistic Tables 8vo, i 50 * Lyons's Treatise on Electromagnetic Phenomena. Vols. I. and II. . 8vo, each, 6 oo * Mahan's Permanent Fortifications. (Mercur.) 8vo, half morocco, 7 50 Manual for Courts-martial. i6mo, morocco, i 50 * Mercur's Attack of Fortified Places I2mo, 2 oo * Elements of the Art of War 8vo, 4 oo 2 Metcalf's Cost of Manufactures And the Administration of Workshops. .8vo, 5 oo * Ordnance and Gunnery. 2 vols 121110, 5 oo Murray's Infantry Drill Regulations i8mo, paper, 10 Nixon's Adjutants' Manual 24010, oo Peabody's Naval Architecture 8vo, 50 * Phelps's Practical Marine Surveying 8vo, 50 Powell's Army Officer's Examiner I2mo, oo Sharpe's Art of Subsisting Armies in War i8mo, morocco, 50 * Walke's Lectures on Explosives 8vo, oo * '.^heeler's Siege Operations and Military Mining 8v, oo Winthrop's Abridgment of Military Law i2mo, 50 Wcodhull's Notes on Military Hygiene i6mo, 50 Young's Simple Elements of Navigation x6mo, morocco. oo ASSAYING. Fletcher's Practical Instructions in Quantitative Assaying with the Blowpipe. 1 2mo, morocco, i 50 Furman's Manual of Practical Assaying 8vo, 3 oo Lodge's Notes on Assaying and Metallurgical Laboratory Experiments. . . .8vo, 3 oo Low's Technical Methods of Ore Analysis 8vo, 3 oo Miller's Manual of Assaying 121110, i oo Minet's Production of Aluminum and its Industrial Use. (Waldo.) I2mo, 2 50 O'Driscoli's Notes on the Treatment of Gold Ores 8vo, 2 oo Ricketts and Miller's Notes on Assaying 8vo, 3 oo Robine and Lenglen's Cyanide Industry. (Le Clerc.) 8vo, Ulke's Modern Electrolytic Copper Refining 8vo, 3 oo Wilson's Cyanide Processes I2mo, i 50 Chlorination Process I2mo, i 50 ASTRONOMY. Comstock's Field Astronomy for Engineers 8vo, 2 50 Craig's Azimuth 4to, 3 90 Doolittle's Treatise on Practical Astronomy 8vo, 4 oo Gore's Elements of Geodesy 8vo, 2 50 Hayford's Text-book of Geodetic Astronomy 8vo, 3 oo Merriman's Elements of Precise Surveying and Geodesy 8vo, 2 50 * Michie and Harlow's Practical Astronomy 8vo, 3 oo * White's Elements of Theoretical and Descriptive Astronomy I2mo, a oo BOTANY. Davenport's Statistical Methods, with Special Reference to Biological Variation. i6mo, morocco, i 25 Thome and Bennett's Structural and Physiological Botany i6mo, 2 25 Westermaier's Compendium of General Botany. (Schneider.) 8vo, 2 oo CHEMISTRY. Adriance's Laboratory Calculations and Specific Gravity Tables I2mo, i 25 Allen's Tables for Iron Analysis 8vo, 3 oo Arnold's Compendium of Chemistry. (Mandel.) Small 8vo, 3 50 Austen's Notes for Chemical Students I2mo, i 50 Bernadou's Smokeless Powder. 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(Wells.) 8vo, 5 oo Manual of Qualitative Chemical Analysis. Part I. Descriptive. (Wells.) 8vo, 3 oo System of Instruction in Quantitative Chemical Analysis. (Cohn.) 2 vols 8vo, 12 50 Fuertes's Water and Public Health I2mo, i 50 Furman's Manual of Practical Assaying 8vo, 3 oo * German's Exercises in Physical Chemistry I2mo, 2 oo Gill's Gas and Fuel Analysis for Engineers : i2mo, i 25 Grotenfelt's Principles of Modern Dairy Practice. (Well.) I2mo, 2 oo Hammarsten's Text-book of Physiological Chemistry. (Mandel.) 8vo, 4 oo Helm's Principles of Mathematical Chemistry. (Morgan.) I2mo, i 50 Bering's Ready Reference Tables (Conversion Factors) i6mo, morocco, 2 50 Hind's Inorganic Chemistry 8vo, 3 oo * Laboratory Manual for Students I2mo, i oo Holleman's Text-book of Inorganic Chemistry. (Cooper.) '. . . .8vo, 2 50 Text-book of (Jrganic Chemistry. (Walker and Mott.) 8vo, 2 50 * Laboratory Manual of Organic Chemistry. (Walker.) I2mo, i oo Hopkins's Oil-chemists' Handbook 8vo, 3 oo Jackson's Directions for Laboratory Work in Physiological Chemistry. .8vo, i 25 Keep's Cast Iron 8vo, 2 50 Ladd's Manual of Quantitative Chemical Analysis I2mo, i oo Landauer's Spectrum Analysis. (Tingle.) 8vo, 3 oo * Langworthy and Austen. The Occurrence of Aluminium in Vegetable Products, Animal Products, and Natural Waters 8vo, 2 oo Lassar-Cohn's Practical Urinary Analysis. (Lorenz.) i2mo, i oo Application of Some General Reactions to Investigations in Organic Chemistry. (Tingle.) I2mo, i oo Leach's The Inspection and Analysis of Food with Special Reference to State Control 8vo, 7 50 Lob's Electrochemistry of Organic Compounds. (Lorenz.). . . ,- 8vo, 3 oo Lodge's Notes on Assaying and Metallurgical Laboratory Experiments. .. .8vo, 3 oo Low's Technical Method of Ore Analysis 8vo, 3 oo Lunge's Techno-chemical Analysis. (Cohn.) I2mo, i oo Mandel's Handbook for Bio-chemical Laboratory I2mo, i 50 * Martin's Laboratory Guide to Qualitative Analysis with the Blowpipe . . I2mo, 60 Mason's Water-supply. (Considered Principally from a Sanitary Standpoint.) 3d Edition, Rewritten 8vo, 4 oo Examination of Water. (Chemical and Bacteriological.) I2mo, i 25 Matthew's The Textile Fibres 8vo, 3 50 Meyer's Determination of Radicles in Carbon Compounds. (Tingle.). .I2mo, i oo Miller's Manual of Assaying , i2n:o, i oo Minet's Production of Aluminum and its Industrial Use. (Waldo.) .... zamo, 2 50 Mixter's Elementary Text-book of Chemislry. . . ; I2mo, i 50 Morgan's Elements of Physical Chemistry I2mo, 3 oo * Physical Chemistry for Electrical Engineers I2mo, i 50. 4 Morse's Calculations used in Cane-sugar Factories i6mo, morocco, i 50 Mulliken's General Method for the Identification of Pure Organic Compounds. Vol. I Large 8vo, 5 oo O'Brine's Laboratory Guide in Chemical Analysis 8vo, 2 oo O'DriscolFs Notes on the Treatment of Gold Ores 8vo, 2 oo Ostwald's Conversations on Chemistry. Part One. (Ramsey.) I2mo, i 50 " Part Two. (Tiirnbull.) i2mo, 2 oo * Penfield's Notes on Determinative Mineralogy and Record of Mineral Tests. 8vo, paper, 50 Pictet's The Alkaloids and their Chemical Constitution. (Biddle.) 8vo, 5 oo Pinner's Introduction to Organic Chemistry. (Austen.) i2mo, i 50 Poole's Calorific Power of Fuels 8vo, 3 oo Prescott and Winslow's Elements of Water Bacteriology, with Special Refer- ence to Sanitary Water Analysis I2mo, i 25 * Reisig's Guide to Piece-dyeing 8vo, 25 oo Richards and Woodman's Air, Water, and Food from a Sanitary Stand- point 8vo, 2 oo Richards's Cost of Living as Modified by Sanitary Science I2mo, i oo Cost of Food, a Study in Dietaries i2mo, i oo * Richards and Williams's The Dietary Computer 8vo, i 50 Ricketts and Russell's Skeleton Notes upon Inorganic Chemistry. (Part I. Non-metallic Elements.) 8vo, morocco, 75 Ricketts and Miller's Notes on Assaying 8vo, 3 oo Rideal's Sewage and the Bacterial Purification of Sewage 8vo, 3 50 Disinfection and the Preservation of Food 8vo, Rigg's Elementary Manual for the Chemical Laboratory 8vo, Robine and Lenglen's Cyanide Industry. (Le Clerc.) 8vo, Rostoski's Serum Diagnosis. (Bolduan.) I2mo, Ruddiman's Incompatibilities in Prescriptions 8vo, Whys in Pharmacy Sabin's Industrial and Artistic Technology of Paints and Varnish 8vo, Salkowski's Physiological and Pathological Chemistry. (Orndorff.) 8vo, 50 Schimpf's Text-book of Volumetric Analysis izmo, 50 Essentials of Volumetric Analysis I2mo, 25 * Qualitative Chemical Analysis 8vo, 25 Spencer's Handbook for Chemists of Beet-sugar Houses i6mo, morocco, Handbook for Cane Sugar Manufacturers i6mo, morocco, Stockbridge's Rocks and Soils 8vo, 50 * Tillman's Elementary Lessons in Heat 8vo, 50 * Descriptive General Chemistry 8vo, oo TreadwelPs Qualitative Analysis. (Hall.) 8vo, oo Quantitative Analysis. (Hall.) 8vo, oo Turneaure and Russell's Public Water-supplies 8vo, oo Van Deventer's Physical Chemistry for Beginners. (Boltwood.) I2mo, 50 * Walke's Lectures on Explosives 8vo, Ware's Beet-sugar Manufacture and Refining Small 8vo, cloth, Washington's Manual of the Chemical Analysis of Rocks 8vo, Wassermann's Immune Sera : Haemolysins, Cytotoxins, and Precipitins. (Bol- duan.) I2mo, oo Well's Laboratory Guide in Qualitative Chemical Analysis 8vo, 50 Short Course in Inorganic Qualitative Chemical Analysis for Engineering Students I2mo, 50 Text-book of Chemical Arithmetic 12 mo, 25 Whipple's Microscopy of Drinking-water 8vo, 50 Wilson's Cyanide Processes I2mo, 50 Chlorination Process I2mo, 50 Winton's Microscopy of Vegetable Foods 8vo, 7 SO Wulling's Elementary Course in Inorganic, Pharmaceutical, and Medical Chemistry I2mo, 2 oo 5 CIVIL ENGINEERING. BRIDGES AND ROOFS. HYDRAULICS. MATERIALS OF ENGINEERING RAILWAY ENGINEERING. Baker's Engineers' Surveying Instruments I2mo, 3 oo Bixby's Graphical Computing Table Paper 19* X 24* inches. 25 ** Burr's Ancient and Modern Engineering and the Isthmian CanaL (Postage, 27 cents additional.) 8vo, 3 50 Comstock's Field Astronomy for Engineers 8vo, 2 50 Davis's Elevation and Stadia Tables 8vo, i oo Elliott's Engineering for Land Drainage I2mo, i 50 Practical Farm Drainage '. I2mo, i oo *Fiebeger's Treatise on Civil Engineering 8vo, 5 oo FolwelTs Sewerage. (Designing and Maintenance.) 8vo, 3 oo Freitag's Architectural Engineering. 2d Edition, Rewritten 8vo, 3 50 French and I/es's Stereotomy 8vo, 2 50 Goodhue's Municipal Improvements I2mo, i 75 Goodrich's Economic Disposal of Towns' Refuse 8vo, 3 50 Gore's Elements of Geodesy 8vo, 2 50 Hayford's Text-book of Geodetic Astronomy 8vo, 3 oo Bering's Ready Reference Tables (Conversion Factors) i6mo, morocco, 2 50 Howe's Retaining Walls for Earth I2mo, i 25 Johnson's ( J. B.) Theory and Practice of Surveying Small 8vo, 4 oo Johnson's (L. J.) Statics by Algebraic and Graphic Methods 8vo, 2 oo Laplace's Philosophical Essay on Probabilities. (Trusccit acd Emory. ).i2mo, 2 oo Mahan's Treatise on Civil Engineering. (1873.) (Wood.) 8vo, 5 oo * Descriptive Geometry 8vo, i 50 Merriman's Elements of Precise Surveying and Geodesy * Whelpley's Practical Instruction in the Art of Letter Engraving izmo, 2 oo Wilson's (H. M.) Topographic Surveying 8vo, 3 50 Wilson's (V. T.) Free-hand Perspective 8vo, 2 50 Wilson's (V. T.) Free-hand Lettering , 8vo, i oo Woolf's Elementary Course in Descriptive Geometry Large 8vo, 3 oo ELECTRICITY AND PHYSICS. Anthony and Brackett's Text-book of Physics. (Magie.) Small 8vo, 3 oo Anthony's Lecture-notes on the Theory of Electrical Measurements. . . . 12010, i oo Benjamin's History of Electricity 8vo, 3 oo Voltaic Cell 8vo, 3 oo Classen's Quantitative Chemical Analysis by Electrolysis. (Boltwood.).8vo, 3 oo Crehore and Squier's Polarizing Photo-chronograph 8vo, 3 oo Dawson's "Engineering" and Electric Traction Pocket-book. i6mo, morocco, 5 oo Dolezalek's Theory of the Lead Accumulator (Storage Battery). (Von Ende.) I2mo, 2 50 Duhem's Thermodynamics and Chemistry. (Burgess.) 8vo, 4 oo Flather's Dynamometers, and the Measurement of Power izmo, 3 oo Gilbert's De Magnete. (Mottelay.) 8vo, 2 50 Hanchett's Alternating Currents Explained I2mo, i oo Bering's Ready Reference Tables (Conversion Factors) i6mo, morocco, 2 50 Holman's Precision of Measurements 8vo, 2 oo Telescopic Mirror-scale Method, Adjustments, and Tests. . . .Large 8vo, 75 Xinzbrunner's Testing of Continuous-current Machines 8vo, 2 oo Landauer's Spectrum Analysis. (Tingle.) 8vo, 3 oo Le Chateliers High-temperature Measurements. (Boudouard Burgess.) I2mo, 3 oo Lob's Electrochemistry of Organic Compounds. (Lorenz.) 8vo, 3 oo * Lyons's Treatise on Electromagnetic Phenomena. Vols. I. and II. 8vo, each, 6 oo * Michie's Elements of Wave Motion Relating to Sound and Light 8vo, 4 oo Niaudet'g Elementary Treatise on Electric Batteries. (Fishback.) I2mo, 2 50 * Rosenberg's Electrical Engineering. (Haldane Gee Kinzbrunner.). . .8vo, i 50 Ryan, Norris, and Hoxie's Electrical Machinery. Vol. 1 8vo, 2 50 Thurston's Stationary Steam-engines 8vo, 2 50 * Tillman's Elementary Lessons in Heat 8vo, i 50 Tory and Pitcher's Manual of Laboratory Physics Small 8vo, 2 oo Ulke's Modern Electrolytic Copper Refining 8vo, 3 oo LAW. * Davis's Elements of Law 8vo, 2 50 * Treatise on the Military Law of United States 8vo, 7 oo * Sheep, 7 5<> Manual for Courts-martial i6mo, morocco, i 50 Wait's Engineering and Architectural Jurisprudence 8vo, 6 oo Sheep, 6 50 Law of Operations Preliminary to Construction in Engineering and Archi- tecture 8vo 5 oo Sheep, 5 50 Law of Contracts 8vo, 3 oo Winthrop's Abridgment of Military Law lamo 2 50 10 MANUFACTURES. Bernadou's Smokeless Powder Nitro-cellulose and Theory of the Cellulose Molecule I2mo, 2 50- Holland's Iron Founder I2mo, 2 50 "The Iron Founder," Supplement lamo, 2 50 Encyclopedia of Founding and Dictionary of Foundry Terms Used in the Practice of Moulding I2mo, 3 oo Eissler's Modern High Explosives 8vo, 4 oo Effront's Enzymes and their Applications. (Prescott.) 8vo, 3 oo Fitzgerald's Boston Machinist I2mo, I oo Ford's Boiler Making for Boiler Makers i8mo, I oo Hopkin's Oil-chemists' Handbook 8vo, 3 oo Keep's Cast Iron 8vo, 2 50 Leach's The Inspection and Analysis of Food with Special Reference to State Control Large 8vo, 7 50 Matthews's The Textile Fibres 8vo, 3 50 Metcalf's Steel. A Manual for Steel-users 121110, 2 oo Metcalf e's Cost of Manufactures And the Administration of Workshops . 8vo, 5 oo Meyer's Modern Locomotive Construction 4to, 10 oo Morse's Calculations used in Cane-sugar Factories i6mo, morocco, i 50 * Reisig's Guide to Piece-dyeing 8vo, 25 oo Sabin's Industrial and Artistic Technology of Paints and Varnish 8vo, 3 oo Smith's Press-working of Metals 8vo, 3 oo Spalding's Hydraulic Cement I2mo, 2 oo Spencer's Handbook for Chemists of Beet-sugar Houses i6mo, morocco, 3 oo Handbook for Cane Sugar Manufacturers i6mo, morocco, 3 oo Taylor and Thompson's Treatise on Concrete, Plain and Reinforced 8vo, 5 oo Thurston's Manual of Steam-boilers, their Designs, Construction and Opera- tion 8vo, 5 oo * Walke's Lectures on Explosives 8vo, 4 oo Ware's Beet-sugar Manufacture and Refining Small 8vo, 4 oo West's American Foundry Practice tamo, 2 50 Moulder's Text-book I2mo, 2 50 Wolff's Windmill as a Prime Mover 8vo, 3 oo Wood's Rustless Coatings: Corrosion and Electrolysis of Iron and Steel. .8vo, 4 oo MATHEMATICS. Baker's Elliptic Functions 8vo, i 50 * Bass's Elements of Differential Calculus I2mo, 4 oo Briggs's Elements of Plane Analytic Geometry i2mo, i oo Compton's Manual of Logarithmic Computations 12 mo, i 50 Davis's Introduction to the Logic of Algebra 8vo, i 50 .* Dickson's College Algebra Large 12 mo, i 50 * Introduction to the Theory of Algebraic Equations Large 12 mo, i 25 Emch's Introduction to Projective Geometry and its Applications 8vo, 2 50 Halsted's Elements of Geometry 8vo, i 75 Elementary Synthetic Geometry 8vo, I 50 Rational Geometry I2mo, i 75 * Johnson's (J. B.) Three-place Logarithmic Tables: Vest-pocket size. paper, 15 100 copies for 5 oo * Mounted on heavy cardboard, 8 X 10 inches, 25 10 copies for 2 oo Johnson's (W. W.) Elementary Treatise on Differential Calculus . . Small 8vo, 3 oo Johnson's (W. W.) Elementary Treatise on the Integral Calculus . Small 8vo, i 50 11 Johnson's (W. W.) Curve Tracing in Cartesian Co-ordinates i2mo, i oo Johnson's (W. W.) Treatise on Ordinary and Partial Differential Equations. Small Svo, 3 50 Johnson's (W. W.) Theory of Errors and the Method of Least Squares. i2mo, i 50 * Johnson's (W. W.) Theoretical Mechanics I2mo, 3 oo Laplace's Philosophical Essay on Probabilities. (Truscott and Emory.). I2mo, 2 oo * Ludlow and Bass. Elements of Trigonometry and Logarithmic and Other Tables Svo, 3 oo Trigonometry and Tables published separately Each, 2 oo * Ludlow's Logarithmic and Trigonometric Tables Svo, i oo Mathematical Monographs. Edited by Mansfield Merriman and Robert S. Woodward Octavo, each i oo No. i. History of Modern Mathematics, by David Eugene Smith. No. 2. Synthetic Projective Geometry, by George Bruce Halsted. No. 3. Determinants, by Laenas Gifford Weld. No. 4. Hyper- bolic Functions, by James McMahon. No. 5. Harmonic Func- tions, by William E. Byerly. No. 6. Grassmann's Space Analysis, by Edward W. Hyde. No. 7. Probability and Theory of Errors, by Robert S. Woodward. No. 8. Vector Analysis and Quaternions, . by Alexander Macfarlane. No. g. Differential Equations, by William Woolsey Johnson. No. 10. The Solution of Equations, by] Mansfield Merriman. No. 1 1. Functions of a Complex Variable, by Thomas S. Fiske. Maurer's Technical Mechanics Svo, 4 oo Merriman and Woodward's Higher Mathematics Svo, 5 oo Merriman's Method of Least Squares Svo, 2 oo Rice and Johnson's Elementary Treatise on the Differential Calculus. . Sm. Svo, 3 oo Differential and Integral Calculus. 2 vols. in one Small Svo, 2 50 Wood's Elements of Co-ordinate Geometry Svo, 2 oo Trigonometry: Analytical, Plane, and Spherical I2mo, i oo MECHANICAL ENGINEERING. MATERIALS OF ENGINEERING, STEAM-ENGINES AND BOILERS. 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