Art. 130. STRESSES IN PRATT TRUSS BY COEFFICIENTS. 247 



All vertical stresses = coefficient X P. 

 All diagonal stresses = coefficient XP sec 0. 

 All chord stresses = coefficient X P sec 6 sin Q. 

 = coefficientX-P tan 0. 



It is necessary to keep the coefficients for dead load and 

 live load in the web members separate, as the panel loads are 

 different. It is also necessary to keep clearly in mind what 

 loading will produce a maximum live load stress in any par- 

 ticular member as determined by the rules of Arts. 128 and 129. 

 This is shown in Fig. 182, in which the member having maxi- 

 mum stresses for a particular loading are shown in heavy lines. 

 The counter-tie live load stresses are determined on the right of 

 the center line and the main tie stresses on the left. Since the 



7 panels at \ 16ft. = /36ft. 



D. L. SOOIbs.per ft\ L.L 8OO J&s.per ft. 



Fig. 183. 



verticals are always in compression they are determined on the 

 left they have no counter stresses. The stress in a suspender 

 is a maximum whenever there is a full panel load at its lower 

 end. According to the rule, it requires a full load to produce 

 a maximum stress in the end diagonals. 



Fig. 183 gives the dimensions of a truss similar to that 

 shown in Fig. 182. Its stresses will now be calculated by the 

 method of coefficients. 



In Fig. 183, the diagonal length is V212+18 2 = 27.66 ft. 



Sec. 0=^- Tan.eJ^- 



LI zi 



D. L. P.=300X 18=5,400 Ibs. L. L. P.=800X 18=14,400 Ibs. 

 27.66 



/). L. P. sec 0= 5,400 



21 



=7120 Ibs. 



