STEEL ROOF TRUSSES AND MILL BUILDINGS. 



CHAP. I. 



W = weight of steel roof truss in pounds; 



P = capacity of truss in pounds per square foot of horizontal projection of roof (30 to 80 lb.); 



A = distance center to center of trusses in feet (8 to 30 ft.) ; 

 L = span of truss in feet; 



was deduced by the author from the computed and shipping weights of mill building trusses of 

 the Fink type. 



Weight of Purlins, Girts, Bracing, and Columns. Steel purlins will weigh from i to 4 lb. 

 per sq. ft. of area covered, depending upon the spacing and the capacity of the trusses and the 

 snow load. Girts and window framing will weigh from i| to 3 lb. per sq. ft. of net surface. Brac- 

 ing is quite a variable quantity. The bracing in the planes of the upper and lower chords will 

 vary from | to I lb. per sq. ft. of area. The side and end bracing, eave struts and columns will 

 weigh about the same per sq. ft. of surface as the trusses. 



Weight of Roof Covering. The weight of corrugated iron or steel covering varies from 

 1 5 to 3 lb. per sq. ft. of area. The weight of corrugated steel is given in Table I. The approxi- 

 mate weight per square foot of various roof coverings is given in the following table: 



Corrugated steel, without sheathing I to 3 lb. 



Felt and asphalt, without sheathing 2 



Tar and Gravel Roofing, without sheathing 8 to 10 " 



Slate, ?V in. to j in., without sheathing 7 to 9 



Tin, without sheathing I to i " 



Skylight glass, & in. to 5 in., including frames 4 to 10 " 



White pine sheathing I in. thick 3 



Yellow pine sheathing I in. thick 4 



Tiles, flat 15 to 20 " 



Tiles, corrugated 8 to 10 " 



Tiles, on concrete slabs 30 to 35 " 



Plastered ceiling 10 " 



The actual weight of roof coverings should be calculated if possible. 



Snow Loads. The annual snowfall in different localities is a function of the humidity and 

 the latitude and is quite a variable quantity. The amount of snow on the ground at one time 

 is still more variable. The snow loads given in Fig. I were proposed by the author in "The Design 

 of Steel Mill Buildings" in 1903 and have been generally adopted. 



35 40 45 



Latitude in Degrees 

 FIG. i. SNOW LOAD ON ROOFS FOR DIFFERENT LATITUDES, IN POUNDS PER SQUARE FOOT. 



One of the heaviest falls of snow on record occurred at Boulder and Denver, Colorado on 

 Dec. 5 and 6, 1913, when 36 inches of snow weighing 9 lb. per cu. ft. fell during two days. Many 



