356 



STRESSES DUE TO CURVED TRACK. 



Art. 176. 



Figure 230 shows the straight track coefficients, curved 

 track coefficients, and the percentages of the straight track 

 stresses to use for the curved track stresses. 



Straight Track + + 7^ +8 



Curved Track 6.819 7.1'Ju 7.649 



Percentage 97.0 95.9 95.6 



Straight Tr. . tl j* x 8 

 Curred Tr. 3.4S4/ 1.090 2 } 

 Percent. 98.77 109.0 95.2> 

 Straight Tr/ -3^ 



0.730\ 

 97.3" 



0.383\ 

 102.1\ 



0.13G 



Curved Track 3.454 | 

 Percentage 98.7 j 



3.454 

 98.7 



5.819 

 97.0 



7.196 

 95.9 



Inner Truss 



Straight Track + 6 +7^ + 

 Curved Track 7.271 9.166 9.804 



Percentage 121.2 122.2 122.6 



Percent. 119.^ 109.2 12 



Straight Tr/ - ?< - $X 



Curved Track 4.182 4.182 

 Percentage 119.5 2 119.5 3 



6_\ 

 8 \ 

 0.906\ 



120.8 N 



i.N 



8 \ 

 0.435\ 

 116.0 N 



8 N v 



nissN 



109.2 



9-166 Outer Trues 



122.2 ! 



Fig. 230. 



It is evident that the outer truss will have larger stresses 

 than the inner, nevertheless, the trusses are usually made alike. 

 The inner truss is made stronger than necessary. When the curve 

 is sharp, it might be desirable, on account of economy, to move 

 the track nearer the inner truss, thus equalizing the stresses in 

 the trusses. This cannot be done in the bottom chord (of a 

 through bridge) because this also belongs to the lateral system. 

 The- stresses in the top chords may be made equal. This will 

 necessitate spreading the trusses in order to preserve the required 

 clearance. On account of the slope of the end post in a through 

 bridge, the clearance is calculated at some distance inside the 

 ends of the bridge. 



Moving the track nearer to the inner truss does not save 

 material in the trusses, but it saves drafting and shop work by 

 making the trusses alike (except the bottom chords). This is 

 done in through bridges at the expense of extra material in 

 the floor beams and lateral systems, and if the substructure is to 

 be new, at considerable extra expense in it, because of the in- 

 creased width. 



