Art. 145. MAXIMUM MOMENT IN DECK PLATE GIRDER. 291 



That is, the total load per foot on the span must equal the 

 load per foot to the left of the point at which the maximum mo- 

 ment is desired. In other words, if P be the load at the point, 



C 1 -\- C* -\- P C* /"* -I- C* 



must be greater than -=- and must be less than 

 a L a 



G_ 



L 



Equation (84) applies at any point of a truss having a single 

 system of web bracing with alternate members vertical, whether 

 the chords are inclined or parallel. It also applies to any point 

 of a girder or beam, G^+G^ being the load to the left of the section. 



145. Maximum Moment in a Deck Plate Girder. Fora 

 truss, moments are always wanted at the panel points, but in a 

 deck plate girder carrying concentrated loads, the maximum wo- 

 ment is wanted and the center of moments must be found. While 

 this occurs near the center of the span, the maximum moment at 

 the center is materially different from the maximum moment in 

 the girder. (101). 



The problem is to find under which load and for what posi- 

 tion of the loads the maximum moment occurs. In Fig. 201 let 



O Ol O 



o n 



mom. 



Fig. 201. 



the load at which the maximum moment occurs be at a distance x 

 from the center of the girder, e is the distance of this load from 

 the center of gravity of all the loads on the span. 



For a maximum 



-,e) (y 2 Lx)G 1 a 

 AJ 



^ =0= T (e-2x) 



Therefore for a maximum e=2x (85) 



That is, the load at which the maximum moment in the girder 

 occurs, must be as far on one side of the center of the girder as 



