Art. 176. STRESSES DUE TO CURVED TRACK. 



353 



The sign of e in these equations depends upon which side of 

 the axis of the bridge the center of gravity falls. This is best 

 determined by making a free-hand sketch in each case and 

 putting the dimensions on it. 



Taking the third panel, for example, the average eccentricity 



of the center line of track = 



0.697 = 1.221 

 2 



=0.959 ft. This is 



decreased by the tilting of the train due to the elevation of 

 the outer rail, 0.5 ft., assuming 5 ft. between centers of rails. 

 Therefore, e =0.959-0.5 =0.459 ft. 



P(3.5-0.459) 



Maximum load on inner stringer 

 Maximum load on outer stringer = 



7.0 



=iPX0.87, 



P(3.5+0.4. C 9)+0.15PX6.833 

 7.0 



=iPXl.42. 



That is, the maximum load on the inner stringer of this panel 

 is 87%, and on the outer stringer 142% of what it would be if 

 the track were straight. 



The stresses are calculated as if the track were straight) 

 and then they are multiplied by the coefficients obtained as 

 above. 



The maximum load on any outer stringer will occur in the 

 panels nearest the middle of the span, and on any inner stringer 

 will occur in the end panels. In this case the maximum load on 

 any stringer will occur on the outer stringer of the panel next 

 to the middle of the span, and will be 153% of what it would 

 be for a straight track. 



The stringers are usually made alike throughout the span. 

 Sometimes they are off-set so as to have nearly the same eccen- 

 tricity in all the panels. This increases the shop work and the 

 cost per pound of the work, but may result in a saving in the 

 total weight of the structure. 



The top flanges of the stringers are subjected to transverse 

 shear and bending. If the shear be supposed equally divided 

 between the two stringers of a panel and if there is bracing 

 between the top flanges as shown in Fig. 228, there will be a 

 bending moment due to carrying the centrifugal force to the 

 panel points, a, b, c, d, and e. There will be tension in ac and 

 compression in bd. This action is a relief to the outer stringer 

 flange, which will be greater if the bracing is put as shown in 

 Fig. 229. 



