304 STRESSES IN A PRATT TRUSS FROM WHEEL LOADS. Art. 153. 

 Wheel 13 at joint 6, 



Panel 6-7 R& = 



Panel 5-6 R Q = 



10X4+20X12+20X17 

 22 



13X3+13X8+20X17+20X22 



22 



=28.14 



=41.95 



Fi =70.09 (-) L.L.Max. 

 0.69X29.15=20.11 (-) D. L. 

 90.20 (-) Total. 



For the purpose of comparing the results obtained by the 

 use of an equivalent uniform load (142) with the wheel load 

 stresses, the stresses have been calculated for a uniform load 

 which will give the same shear in the end panel as the wheel 

 loads, and tabulated below. 1 



COMPARISON OF LIVE LOAD STRESSES. 



Member. 



, 



-L. 

 -L 



Wheel Load Stress. 



217.4 

 156.4 

 103.5 



58.8 



29.0 



70.1 



81.4 



46.2 . 

 134.3 

 215.2 

 256.8 



Equiv. Uniform Load Stress. 



217.4 

 155.2 

 103.5 



62.1 



31.0 



57.0 



81.4 



48.8 

 134.3 

 223.8 

 268.6 



With the exception of the hip-vertical, for which the wheel 

 load stress should always be calculated, the equivalent uniform 

 load gives results which are within about 4^% of the wheel 

 load stress in the worst case, and which are all on the side of 

 safety. 



1 Curves showing the equivalent loads for Cooper's loadings are given in 

 Johnson's " Modern 'Framed Structures," Ninth Edition, Part I, page 251, 

 and in Morris's " Designing and Detailing of Simple Steel Structures," page 

 118. 



