Art. 176. STRESSES DUE TO CURVED TRACK. 355 



V, the reaction at the inner truss, is a maximum when the 

 train is standing still and V is a maximum when the train is 

 running at maximum speed. The maximum V and V do not 

 occur at the same time. From these, the maximum moment 

 and shear in the floor beam are obtained. As in the case of 

 the stringers, the floor beams are usually all made alike. 



In our example, taking the floor beam between the second 

 and third panels, Fig. 226, we have 



1.221+2X0.697-0.176 

 Eccentricity of track = =0.61 ft. 



g=0.61 0.5 (decrease due to elevation of outer rail) =0.11 ft. 

 Max. V (inner truss) = g (8 - 5 -- n) =L P x . 9S7> 



. P(S.5+0.11)+0.15PX10.3 

 Max. V (outer truss) = =i/ J Xl.l9o. 



That is, the maximum reaction at the inner end of the beam 

 is 98.77 , and at the outer end 119i% of what it would be if 

 the track were straight. 



The moment in the beam at the inner stringer is VQb-^bJ, 

 and at the outer stringer is V'Qb-bbJ. Use the larger. 



Use V or V for the live load, to find the number of rivets 

 required in bearing on the beam web at the stringer connections, 

 remembering that these rivets also take a horizontal shear of 

 \CP and a moment of CPd s (d s being the depth of the stringer) 

 when the train is moving. 



The compression in the bottom flange of the floor beam, 

 as a member of the lateral system, tends to reduce the tension 

 from direct load and, therefore, need not be considered. 



Trusses. The panel loads for the trusses are equal id 

 the respective floor beam reactions. These must be obtained 

 for each panel point using P to represent the load on the track 

 in each panel. These panel loads then may be used to get 

 coefficients on the truss members, which may be divided by the 

 ordinary coefficients for uniform load (130). This gives a per- 

 centage of the straight track stress for each member. The stresses 

 may be calculated as if the track were straight, by the method 

 of wheel loads or from equivalent uniform loads, and the stresses 

 multiplied by their respective percentages. 



