GIRDERS AND TRUSSES 



W 



Then, in a single system truss, P =- 



129 



In a double-system truss, P 

 In a triple-system truss, P = 

 In a four-system truss, P 



W 



(2n) - 



W 



(3n) - 1 

 W 



(4n) - 1 



Having found the panel load, P, each system is figured as a 

 frame, and the combined strength of the systems determines the 



Fig. 83 Warren Truss. 



strength of the completed truss. The systems are connected 

 together at every joint where the members meet or cross. The 

 lower apices are the panel joints when the load is on the lower 

 chord and the upper apices are the panel joints when the load is 

 on the upper chord. 



In Fig. 83 (a) the load is on the lower chord and in (6) the load 

 is on the upper chord. The truss is here assumed to be uniformly 

 and symmetrically loaded. Coefficients may be written by start- 

 ing from the center line of the span. On the upper and lower 

 chords are placed the summation of the coefficients for the chords 

 in the respective panels. In Fig. 83 (a) the coefficient for L Li is 

 one-half that for Ui U t and in (6) the coefficient for Uo V\ is one- 

 half that for LiLj. The dotted parallelograms at L and LI, 

 and Uo and Ui, represent to scale the panel load set off vertically 



