STEEL WINDOWS AND DOORS. 54m 



operated by the crane operator or from the floor. Additional doors should be provided for the 

 lo.nl, .iiul for the crane cage where necessary. Folding and sliding doors are also made by the 

 Kinm'ur Manufacturing Company, Columbus, Ohio. 



Rolling Steel Doors. Rolling steel doors are made by several firms. The J. G. Wilson 

 Corporation, New York, manufactures rolling steel doors that may be operated by hand with 

 widths of 3 ft. to 6 ft. and heights of 6 ft. to 14 ft.; widths of 6 ft. to 10 ft. and heights of 13 ft. 

 to 17 ft.; widths of 10 ft. to 15 ft., and heights of 13 ft. to 15 ft. Doors operated by gear have 

 heights up to 21 ft. and widths up to 20 ft. The Kinnear Manufacturing Co., Columbus, Ohio, 

 manufactures rolling steel doors with widths of 3 ft. to 20 ft., and heights of 6 ft. to 18 ft. For 

 additional details and the names and addresses of other manufacturers of steel doors, see Sweet's 

 Architectural Catalog, published by Sweet's Catalog Service, New York, N. Y. 



CEMENT ROOFING TILE. Cement tile are made of Portland cement and clean, sharp 

 sand and are reinforced with steel rods. 



Data for "Bonanza" cement tile, manufactured by the American Cement Tile Mfg. Co., 

 Pittsburgh, Pa., are given in Fig. 59. The exposed surface of the tile is Indian red in color, while 

 the underside has a cement finish. The least desirable slope of roof is a pitch of one-fifth. Data 

 for Federal Cement tile, manufactured by the Federal Cement Tile Co., Chicago, 111., are given in 

 Fig. 60, and in the upper part of Fig. 61. Cement roofing tile have been very extensively used for 

 industrial plants. The cement tile have the following advantages: (a) are fire resisting; (b) 

 require very simple roof construction; (c) require no sheathing; (d) are non-conductors, (e) may 

 be erected rapidly; (f) the first cost is low for a permanent type of roof; (g) maintenance is low. 



Gypsum Roofing Tile. Gypsum roofing tile made by the United States Gypsum 

 Company, Chicago, are sold under the trade name of Pyrobar Gypsum Roof Tile. The tile 

 are 12 in. wide and 30 in. long, and weigh 13 Ib. per sq. ft. Data taken from the catalog for rafters 

 and purlins for Pyrobar Gypsum Roof Tile are given in the lower part of Fig. 61. Gypsum roof 

 tile have recently been used on buildings for the Navy Department at Norfolk, Va. The follow- 

 ing advantages of gypsum roof slabs were given by L. M. Cox, U. S. N., Engineering News, Jan. 

 2 5i 1 9 1 7- (a) Light weight; (b) rapid construction; (c) roof slab is non-conductor and non-con- 

 densing; (d) is fire resisting; (e) shows few cracks; (f) low cost of maintenance. Gypsum roofing 

 tile are made by several firms, and are also made at the building site. 



STRESSES IN MILL BUILDING COLUMNS CARRYING CRANE LOADS. The stresses 

 produced in columns of mill buildings by crane loads eccentrically applied depend upon the method 

 used in bracing the structure against lateral forces. If the kneebraces are omitted or only very 

 small kneebraces are used, the columns are practically hinged at the top and the lateral thrust due 

 to the eccentric crane loads must be carried to the ends of the building by the lateral bracing in the 

 planes of the chords of the trusses. Proper bracing must then be provided in the end bents. 



If rigid kneebraces are provided the columns may be considered as fixed at the top and a 

 transverse bent may be considered as carrying its load directly to the foundations. The lateral 

 load will in reality be distributed between the direct path down the columns and the indirect path 

 along the lateral bracing in the planes of the chords to the end bents. The portion carried by each 

 route will depend upon the relative rigidity of the routes. Since the transverse bent is much more 

 rigid than the lateral bracing, all of the load may be considered as carried by the transverse bent. 



In Fig. 62 three cases are considered. 



Case I. Columns Hinged at Base and Top. This case is statically determinate. The 

 lateral thrust is taken by the bracing in the plane of the chords and by the bracing in the end bents. 



Case n. Columns Hinged at Base and Fixed at Top. Columns with constant cross-section. 

 The formulas for rigid frames were used, making the ratio of the moment of inertia of the truss to 

 the moment of inertia of the column equal to infinity. The formula is sufficiently accurate when 

 this ratio becomes as small as four, and is on the safe side. The distance h is measured to a point 

 one-half way between the foot of the knee-brace and the top of the column. 



Case m. Columns Hinged at the Base and Fixed at Top. Columns with variable cross- 

 sections. In this case the column has a different cross-section above and below the attachment 

 of the crane girder. The formulas for rigid frames were used, making the ratio of the moment of 



