174 



STEEL RAILWAY BRIDGES. 



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ECONOMIC DESIGN OF RAILWAY BRIDGES. Pin-connected truss bridges have 

 been used for railroads on account of the ease of erection, ease in calculating the stresses, and the 

 simplicity of details which give small secondary stresses. The present practice in railway bridge 

 design is to use plate girders for spans up to about 115 ft., and riveted truss bridges for longer 

 spans; pin-connected bridges being used only for very long spans and for spans of 200 ft. and over 

 where there is some special reason such as ease of erection or low cost. The author would recom- 

 mend pin-connected truss bridges for all spans of 200 ft. and over for the following reasons: 

 (i) the weight of a pin-connected truss bridge with eye-bars is less than the weight of a riveted truss 

 bridge of the same span and capacity, and while the shop cost per pound of pin-connected truss 



