280 STRESSES IN A PETTIT TRUSS. Art. 138. 



The second term is greater; therefore the loading extends 

 to joint 13. 



Center of moments at A, Arm of Z>4 = 118.6 ft. 

 118.6>4=7iPxlOO-P(120 + 140 + 160)+D'4a=420P. D. L. 



01 7QSO 



= ^P X 100 -P X 160 +D' ,a =-P for live load. 

 16 16 



116,800 Ibs. (-) D.L. 

 = 168/200 Ibs. (-) L.L. 



118.6 



7980X40,000 

 16X118.6 



285,000 Ibs. (-) Total. 



34 



Sab-diagonal D' = X33,000 =24,900 Ibs. ( -) D. L. 

 45 



34 



= X 40,000 =30,200 Ibs. (-) L.L. 

 45 



55,100 Ibs. (-) Total. 



Counter Z>' 5 . Loading from left to joint 12. 



Center of moments at B, Arm of D' 5 =269.1 ft. 

 D 6 is not in action and D$ acts as a sub-diagonal. 

 269.1Z)' 5 =7JP X280 -P(300 +320 +340 +360) -> 5 X299. 



269. ID's =580P, for dead load. 



269. 1D' 5 =-PX 600 =375P, for live load. 

 16 



^,^580X33,000 =7MQQlbs (+) D L 



' ). ' . 1 



375X40,000 - r7nftll f \ T T 

 = 269 i =55,700 Ibs. (-) L.L. 



No reversal. 



Post F 3 , applying the criterion developed for the position 

 of the load for maximum compression : 



__]25 25 _125 



(h-d-i 10' 16 16* 



The first term is greater; therefore the loading follows 

 the regular rule. 



