Art. 176. STRESSES DUE TO CURVED TRACK. 



351 



If D c he the degree of curve, r = 

 curves under 5, from which 

 CP = 



5730 



, approximately for 



PV 2 D C 





32.2X5730 



If the velocity of the train be taken at 50 mi. per hour 

 =73 ft. per sec., equation (190) becomes CP= 73x73 p/) c> 



or CP=0.02S8PD C . In other words, the centrifugal force equals 

 neirly 3% of the load for every degree of curvature. It is 

 frequently specified 3% for all curves up to 5 and the additional, 

 reduced to 1% for every degree over 5 on account of the slower 

 speed on sharp curves. 



To illustrate the method of calculating live load stresses in 

 bridges having curved track, lei us consider a 160 ft. span, single 

 track, through bridge, of 8 panel*- ^u 20 ft. Let us suppose the 

 track to be on a 5 curve, that the axis of the stringers corres- 

 ponds with the axis of the bridge, and that the latter bisects the 

 middle ordinate of the curve in the span length. Fig. 226 shows 

 the eccentricity of the center line of track at the floor beams. 



Fig. 226. 



In Fig. 227 C.G. is the center of gravity of the' train, sup- 

 posed to be at a uniform height k above the center of the track. 



i See Carhart's "Field Book for Civil Engineers," page 31, 32 & 33. 



