Art. 130. STRESSES IN PRATT TRUSS BY COEFFICIENTS. 251 



written on the members. The dead load panel concentrations 

 are indicated at the upper and lower panel points. The live 

 load is all applied at the upper panel points. The coefficients 

 for dead load on the web members are given near the upper ends 

 and those for live load near the lower ends. The diagonals are 

 shown in one direction only to avoid confusion. The main tie 

 stresses are figured on the left half and the counters on the 

 right. 



There are, two conditions affecting the stress in the middle 

 vertical V&. When the counter D 5 is acting as shown, 



but when the bridge is symmetrically loaded with a live load 

 at joint 4, the counter Z) 5 will not be in action and 



V 5 = (l-q) D. L.+l L. L. 



Both of these stresses must be calculated to see which is the 

 larger. 



131. Stresses in a Simple Warren Truss. Fig. 185 

 shows a simple Warren truss. The upper joints are vertically 



OU +2 



L 3 

 5 Panels at 15 ft.= 75 ft 



DL=2001bs. per ft. 



LL=700 Ibs. per ft. 



Fig. 185. 



opposite the middle of the lower panels ; which gives all of the 

 diagonals the. same angle of inclination. 



The coefficients for the web members are obtained in a 

 manner exactly similar to that shown in Fig. 182. The coeffi- 

 cients for dead load are shown near the top of the member and 

 for live load near the bottom. In this case all of the dead load 

 is considered as acting at the lower panel points, as the truss 

 is not deep enough for overhead bracing. The coefficients for 

 the chord members are obtained by resolving horizontally at 

 the joints as in the case of the Pratt truss. 



