354 



STRESSES DUE TO CURVED TRACK. 



Art. 176. 



a Oufer c Stringer 



Fig. 228. 



The shear is transmitted to the floor beam through the 

 stringer connection, producing a horizontal shear and a moment 

 on the rivets. 



Laterals. In Fig. 227 the horizontal shear CP is re- 

 sisted by one system of laterals, CP being a panel load. 



When the centrifugal force is 

 large, it is advisable to make 

 the laterals so as to act as 

 two systems, half being taken 

 by each. We have assumed 

 in Fig. 227 that all of CP is 

 taken up by the lower lateral 

 system. In the reality posts 

 will take a small portion to 

 the top lateral system. The 

 bottom laterals being below 

 the pin center, their longitu- 

 dinal components must be 

 transmitted to the bottom 

 chord by bending in the posts. 

 Since C is a constant for 

 any particular bridge (unless 



it is on a compound curve), CP and P will be the same for each 

 panel, if the live load is a uniform load. Otherwise the maxi- 

 mum shear and maximum moment at any point of the horizontal 

 truss will occur for the same position of the ioad as for maxi- 

 mum shear and moment at that point in the vertical truss. 



It is sufficiently accurate to use an equivalent uniform load 

 in figuring the stresses in the laterals. 



Floor Beams. The eccentricity of the center line c.f 

 track for the floor beams is taken as the average of the eccen- 

 tricites of the stringers of the two adjacent panels. The center 

 of moments should be taken at the center line of the lower 

 chord, as this is the assumed point of support of the floor beam. 



Taking moments about in Fig. 227, we have for the in- 

 side reaction, 



P(Jb-e)-CPf 

 b 



Taking moments about I. we have for the outside reaction, 



Fig. 229. 



