352 



STRESSES DUE TO CURVED TRACK. 



Art. 176. 



CP is the centrifugal force of the weight P, and e is the eccen- 

 tricity of the center of gravity with respect to the axis of the 

 bridge, e equals the eccentricity of the center line of track, 

 plus or minus k tana. 



Let us assume in our example, A; =6.0 ft., superelevation 

 of the outer rail =5 in. =0.417 ft., f, =6.833 ft., /=10.3 ft., 

 6 t =7.0 ft., 6 = 17.0 ft., and the centrifugal force as 3% per degree 

 of curvature. 



Stringers. For the stringers the eccentricity of the center 

 line of track is assumed to be the mean of the eccentricities at 



r 



U - 1 



the ends of the panel and the load is applied at the top of the 

 stringers. Taking moments about the outer stringer in Fig. 

 227, we get the load on the inner stringer, 



Taking moments about the inner stringer we get the load 

 on the outer stringer, 



, _p(lb l +e)+CPf l 



We see that the load on the inner stringer is a maximum when 

 CP = 0, that is, when the train is standing still, and that the load 

 on the outer stringer is a maximum when CP is a maximum, 

 or when the train is moving at maximum speed. 



