\'2 UN B-LOAD -i i 



9. Find position- of loading for maximum counter-ten- 

 sions in posts and compute values by use of formulas (25) 

 and (26). 



PROBLEM 1 



Calculation of Live-load Stresses in a Pratt 7Y//.s,s ////// 

 I m -lined Chord. 



The complete data for this problem are given in Fig. 

 13. Items 1 to 5 of the above method of procedure need 

 no explanation. The values of the coefficients (i and //. 

 the position of the loading for maximum stress, and the 

 value of the maximum strese \\ill be determined for several 

 typical members; for example, vertical post, inclined \vel. 

 member-, hori/ontal chords, end po-t , and inclined chord-. 



Verticdl 7W KF. 

 Formula S< = (^) M, - (^) M, ...... (23) 



Refer to Fig. 11 for definition of dimensions. 

 G = - = \\ (.00480) = .00373 



Olj OO 



H = - = .0385 



Try Wi at panel point 3. Use Table 2. L, == 143'. 



(n ' 37.5 



I* -* 



'i herefore t^, at 3 gives a maximum. 



= GM< - HM, = .i"'.;:: 1 . :::; ( .'70) - .n385(287.:> 

 121 11. (i nr,.7 fc 



300 

 Impact factor , + ^ = |j; =.677 



Impact stress = .677 X 115.7 = 78.3*. 



