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



14. Weight of Covering. Corrugated Steel. The weight of corrugated steel shall be taken 

 from Table I. 



When two corrugations side lap and six in. end lap are used, add 25 per cent to the above 

 weights; when one corrugation side lap and four in. end lap are used, add 15 per cent to the above 

 weights to obtain weight of corrugated steel laid. For paint add 2 Ib. per square. The weight 

 of covering shall be reduced to weight per sq. ft. of horizontal projection before combining with 

 the weight of trusses. 



15. Slate. Slate laid with 3 in. lap shall be taken at a weight of 1\ Ib. per sq. ft. of inclined 

 roof surface for ^ in. slate 6 in. X 12 in., and 6 Ib. per sq. ft. of inclined roof surface for ^ in. 

 slate 12 in. X 24 in., and proportionately for other sizes. 



16. Tile. Terra-cotta tile roofing weighs about 6 Ib. per sq. ft. for tile I in. thick; the actual 

 weight of tile and other roof coverings not named shall be used. 



17. Sheathing and Purlins. Sheathing of dry pine lumber shall be assumed to weigh 3 Ib. 

 per ft. and dry oak purlins 4 Ib. per ft. board measure. 



1 8. Miscellaneous Loads. The exact weight of sheathing, purlins, bracing, ventilators, 

 cranes, etc., shall be calculated. 



19. SNOW LOADS. Snow loads shall be taken from the diagram in Fig. i. 



20. WIND LOADS. The normal wind pressure on trusses shall be computed by Duch- 

 emin's formula, Fig. 3, with P = 30 Ib. per sq. ft., except for buildings in exposed locations, 

 where P = 40 Ib. per sq. ft. shall be used. 



21. The sides and ends of buildings shall be computed for a normal wind load of 20 Ib. per 

 sq. ft. of exposed surface for buildings 30 ft. and less to the eaves; 30 Ib. per sq. ft. of exposed 

 surface for buildings 60 ft. to the eaves, and in proportion for intermediate heights. 



22. Mine Buildings. Mine, smelter and other buildings exposed to the action of corrosive 

 gases shall have their dead loads increased 25 per cent. 



23. Concentrated Loads. Concentrated loads and crane girders shall be considered in 

 determining dead loads. 



24. Purlins. Purlins shall be designed to carry the actual weight of the covering, roofing 

 and purlins, but shall always be designed for a normal load of not less than 30 Ib. per sq. ft. 



25. Girts. Girts shall be designed for a normal load of not less than 25 Ib. per sq. ft. 



26. Roof Covering. Roof covering shall be designed for a normal load of not less than 30 

 Ib. per sq. ft. 



27. Minimum Loads. No roof shall, however, be designed for an equivalent load of less 

 than 30 Ib. per sq. ft. of horizontal projection. 



28. Loads on Foundations. The loads on foundations shall not exceed the following in 

 tons per sq. ft. : 



Ordinary clay and dry sand mixed with clay 2 



Dry sand and dry clay 3 



Hard clay and firm coarse sand 4 



Firm coarse sand and gravel 5 



Shale rock 8 



Hard rock 20 



For all soils inferior to the above, such as loam, etc., never more than one ton per sq. ft. 



29. Stresses in Masonry. The allowable stresses in masonry shall not exceed the following: 



Tons per Sq. Ft. Lb. per Sq. In. 



Common brick, Portland cement mortar 12 168 



Hard burned brick, Portland cement mortar 15 210 



Rubble masonry, Portland cement mortar 10 140 



First class masonry, crystalline sandstone or limestone 25 350 



First class masonry, granite 30 420 



Portland cement concrete, 1-3-5 2O 280 



Portland cement concrete, 1-2-4 3 4 2 



30. Pressures on Masonry. The pressure of column bases, beams, etc., on masonry shall 

 not exceed the following in pounds per sq. in. 



Brick work with cement mortar 250 



Rubble masonry with cement mortar 250 



Portland cement concrete, 1-2-4 500 



First class dimension sandstone or limestone 400 



First class granite 500 



