50 



STEEL ROOF TRUSSES AND MILL BUILDINGS. 



CHAP. I. 



ELEVATION' 



FIG. 42. PLANS OF A TRANSFORMER BUILDING. 



are 4 in. channels @ 5J Ib. The purlins are spaced less than 4 ft. 9 in., which is a maximum spac- 

 ing where corrugated steel roofing is used without sheathing. The steel framework is braced in 

 the plane of the top chord and the sides and ends of the building by means of diagonal rods f in. 

 in diameter. The crane girder beams in the plane of the lower chord brace the building longi- 

 tudinally, the diagonal bracing being composed of angles. 



