62 STANDARD SPECIFICATIONS 



where S= allowable working stress per square inch; 

 ci = " compression with grain " given above; 

 / = unsupported length of column in inches ; 

 d= least width of column in inches; 



and maximum -7 35. 



a 



277. Piles. The maximum load per pile due to the combined 

 effect of dead and live loads, lateral and longitudinal forces, 

 including impact, if any, shall not exceed the following- 



2.5WH 

 = ( + !).' 

 where P= allowable pressure in pounds per pile, limited as per 



belowj 



W= weight of drop hammer in pounds; 

 H= height of drop in feet; 



s= average sinking in inches due to the last five blows 

 when squarely struck. 



When the piles are driven through wet and loose soil to a good 

 bearing the pressure shall not exceed 300 Ibs. per sq.in. of their 

 average cross-section. When driven through a firm soil this 

 pressure may be increased to 600 Ibs. (Par. 270.) 



DETAILS OF DESIGN 



278. Flooring and Joists (Buildings). Floor planks and 

 floor joists in buildings, carrying plastering, shall be proportioned 

 with regard to their stiffness, limiting their deflection to one-three- 

 hundred-and-sixtieth Cg^) of the span. 



All other timber in buildings may be proportioned with 

 regard to its strength. 



279. Flooring (Highway Bridges). Floor planks for the 

 roadway, when a single thickness is used shall have a minimum 

 thickness of 3 in., shall be laid with J-in. open spaces and shall 

 be securely spiked to the joists. 



Footwalk planks shall have a minimum thickness of 2 in., 

 shall be at least 6 in. wide and shall be spaced with i-in. openings. 



Where an additional wearing surface is being used, the min- 

 imum thickness of which shall be 1 in., the thickness of the 



