REINFORCED CONCRETE 79 



(6) The weight of the roof covering, flooring, paving, or ballast, 

 if any. (For weight of same see Pars. 3, 4, 5, 59, 109.) 



(c) The weight of railway tracks, if any. (For weights of 



same see Pars. 59, 109.) 



(d) The snow load, if any. (For weight of same see Par. 6.) 



337. Wind Pressure or Lateral Forces. (See Pars. 7, 62, 113, 

 114.) 



338. Centrifugal Forces. (See pars. 63, 116.) 



339. Traction Forces. (See Pars. 64, 1150 



340. Live Loads. (See Pars. 9, 10, 60, 110, 111.) 



341. Impact. An impact allowance shall be added to the 

 computed maximum live-load stresses, as follows: 



(a) For floors of schools, theaters, 100 



churches, armories, dancing or Impact = j Qnn 

 other public halls and factories . . . . J 



(6) For floors carrying moving machinery j , , 



for crane girders and posts; for ) Impact = ( r O r>nl- 



i i 1-1 \/-f-oUU/ 



highway bridges ................. J 



(OAQ \ 

 T , onn ). 

 L -f- oUU/ 



where S= computed maximum live-load stress, moment or shear, 

 L length of span in feet, or loaded length of span, which- 

 ever gives a maximum. 



No impact allowance shall be added to stresses produced by 

 traction, centrifugal, and lateral or wind forces. 



CALCULATION OF STRESSES 



342. General Dimensions. The following dimensions shall 

 first be calculated or assumed: 



Span of slabs, supported at ends, clear opening plus thick- 

 ness of slab., 



Span of slabs, continuous, c. to c. of beams. 



Span of beams and girders, c. to c. of support. 



Length of columns, the maximum unsupported length. 



343. Assumptions: 



(a) The ratio of the modulus of elasticity of steel (E 8 ) to 

 the modulus of elasticity of concrete (E c ) shall be taken 

 at 15, or E 8 + E C = 15. 



