Art. 153. STRESSES IN A PRATT TRUSS FROM WHEEL LOADS. 299 



Wheel 3 at joint 6, 36 ft. of uniform load on: 

 G 356 



N 



=30. 



_ 

 =oO. 



This does not satisfy the criterion. 



Wheel 4 at joint 6, 41 ft. of uniform load on: 



N 



= 50. 



=70. 



This satisfies the criterion, as 52 is greater than 50 and 

 less than 70. 



Wheel 5 at joint 6, 46 ft. of uniform load on and wheel 1 off: 



= 60. 



= 80. 



This does not satisfy the criterion. 



It will perhaps be found that some of the wheels of the 

 second engine will satisfy the criterion for this joint, but the 

 stresses given by them will be less than that for wheel 4, because 

 there will be so much less load on the bridge. 



By the same process it is found that wheels 6, 7, 11, and 12 

 will satisfy the criterion for joint 5, and wheels 10 and 11 for 

 joint 4. 



The maximum moment at joint 6 occurs with wheel 4 at 

 that point. Taking moments about the right-hand reaction, 

 we get, in 1000-pound units: 



29689 



^ I= ^T- 



M G =Ri X22 - (10 X 18+20 X 10 +20 X5) =4241.3 -480 =3761.3 



= 134.3 (-)L.L. 



= 68.7 (-) D. L. 

 203.0 (-) Total 



28 



00 



=3X29.15X- 



Similarly for joint 5, 

 Wheel 6 at joint 5, M 5 =6024.3. 

 Wheel 7 at joint 5, M 5 =6016.4. 

 Wheel 11 at joint 5, M & =5751.7. 

 Wheel 12 at joint 5, M 5 =5768.9. 



