12 



INFLUENCE DIAGRAMS 



or 



(W 2 + W 2 + TF 3 ) tan 8 5 = (W 2 + W 2 ) tan 4 , . (30) 



which becomes 



_^+JY 



d , .... (61) 



I 



The points m and m' and the value of d' are found in the 

 manner explained for Figs, 1, 2 and 3. 



Bottom Chord of Curved-chord Simple Truss. The influence 

 diagram for this case is constructed according to the general 

 directions as shown in Fig. 5. The points E and A coincide. 



-, . W Wi Wi 



Criterion. -7- = : =-r~- 

 I s b 



Tan ft =1. Tan 62 = S -^. Tan Ot =~. 

 d I 



FIG. 5. 



The positive sign indicates that the resultant moment is 

 positive and that the moment of the stress in LL f is negative. 

 This shows that LL' is in tension. 



The criterion for the maximum moment when wheel 

 loads are on the bridge is found as follows: (see equation 

 13). 



-tan fli+tan 9 3 ) +W2 tan fl 3 + Wa tan0 3 =0 (32) 

 tan 6 3 -Wi tan 0i=0; . . (33) 



