8 STEEL ROOF TRUSSES AND MILL BUILDINGS. CHAP. I. 



and gravel roof, or some one of the patent composition roofs is used in preference to tin, and on a 

 steep slope slate is commonly used in preference to tin or tile. Corrugated steel roofing is much 

 used on boiler houses, smelters, forge shops, coal tipples, and similar structures. 



Floors in boiler houses, forge shops and in similar structures are generally made of cinders; 

 in round houses brick floors on a gravel or concrete foundation are quite common; while in buildings 

 where men have to work at machines the favorite floor is a wooden floor on a foundation of cinders, 

 gravel, or tar concrete. Where concrete is used for the foundation of a wooden floor it should be 

 either a tar or an asphalt concrete, or a layer of tar should be put on top of the cement concrete 

 to prevent decay. Concrete or cement floors are used in many cases with good results, but 

 they are not satisfactory where men have to stand at benches or machines. Wooden racks on 

 cement floors remove the above objection somewhat. Where rough work is done, the upper or 

 wearing surface of wooden floors is often made of yellow pine or oak plank, while in the better 

 classes of structures, the top layer is commonly made of maple. For upper floors some one of 

 the common types of fireproof floors, or as is more common a heavy plank floor supported on 

 beams may be used. 



Care should be used to obtain an ample amount of light in buildings in which men are to 

 work. It is now the common practice to make as much of the roof and side walls of a trans- 

 parent or translucent material as practicable; in many cases fifty per cent of the roof surface is 

 made of glass, while skylights equal to twenty-five to thirty per cent of the roof surface are very 

 common. Direct sunlight causes a glare, and is also objectionable in the summer on account of 

 the heat. Where windows and skylights are directly exposed to the sunlight they may best be 

 curtained with white muslin cloth which admits much of the light and shades perfectly. The 

 "saw tooth" type of roof with the shorter and glazed tooth facing the north, gives the best light 

 and is now coming into quite general use. 



Plane glass, wire glass, factory ribbed glass, and translucent . fabric are used for glazing 

 windows and skylights. Factory ribbed glass should be placed with the ribs vertical for the 

 reason that with the ribs horizontal, the glass emits a glare which is very trying on the eyes of 

 the workmen. Wire netting should always be stretched under skylights to prevent the broken 

 glass from falling down, where wire glass is not used. 



Heating in large buildings is generally done by the hot blast system in which fans draw the 

 air across heated coils, which are heated by exhaust steam, and the heated air is conveyed by 

 ducts suspended from the roof or placed under the ground. In smaller buildings, direct radiation 

 from steam or hot water pipes is commonly used. 



The proper unit stresses, minimum size of sections and thickness of metal will depend upon 

 whether the building is to be permanent or temporary, and upon whether or not the metal is 

 liable to be subjected to the action of corrosive gases. For permanent buildings the author 



/ 

 would recommend 16,000 Ib. per square inch for allowable tensile, and 16,000 70- Ib. per 



square inch for allowable compressive stress for direct dead, snow and wind stresses in trusses 

 and columns; / being the center to center length and r the radius of gyration of the member, 

 both in inches. For wind bracing and flexural stresses in columns due to wind, add 25 per cent 

 to the allowable stresses for dead, snow and wind loads. For temporary structures the above 

 allowable stresses may be increased 20 to 25 per cent. 



The minimum size of angles should be 2" X 2" X I", and the minimum thickness of plates 

 2 in., for both permanent and temporary structures. Where the metal will be subjected to 

 corrosive gases as in smelters and train sheds, the allowable stresses should be decreased 20 to 25 

 per cent, and the minimum thickness of metal increased 25 per cent, unless the metal is fully 

 protected by an acid-proof coating (at present the best paints do little more in any case than 

 delay and retard the corrosion). 



The minimum thickness of corrugated steel should be No. 20 gage for the roof and No. 22 

 for the sides; where there is certain to be no corrosion Nos. 22 and 24 may be used for the roof 

 and sides respectively. 



