202 



STEEL RAILWAY BRIDGES. 



CHAP. IV. 



Cooper's Specifications. The additional clearance for curves is to be as follows: 0.85.0 

 = inches on each side; 1.70!) = inches between track; where D = degree of curve. 



N. Y., N.H. & H. R. R. The additional clearances on curves will be as follows: i.oo X D 

 = inches on each side; 1.75.0 = inches between tracks, where D = degree of curve. 



Types of Bridges. The present practice is to use plate girders for spans up to no or 120 ft., 

 riveted trusses for spans of from 100 to 200 or 250 ft., and pin-connected trusses for spans of 

 about 200 ft. and upwards. Riveted truss bridges of 300 and 400 ft. span are not uncommon. 

 The types of bridges and minimum lengths of span as given in twelve specifications are given in 

 Table XII. 



TABLE XII. 



TYPES OF BRIMES AHD LENGTHS OF SPAH- 



3. Spacing of Trusses. The present practice is not to put requirements for spacing of 

 trusses, lengths of span, types of bridge, etc., in the specifications but to prepare office standards 

 for the use of engineers and draftsmen. Data on spacing stringers, girders and trusses are given 

 in Table XIII. The spacings for Illinois Central R. R. deck girders are given in Figs, n, 12 and 

 13, and of Common Standard Bridges in Table I. 



The Chicago, Milwaukee and St. Paul Ry. spaces girders 7 ft. 6 in. west of the Missouri 

 River, and 8 ft. east of the Missouri River. The Northern Pacific R. R. spaces stringers 8 ft. 

 for spans of 150 to 200 ft. ; and deck girders 8 ft. for 80 ft. spans. 



5. Ties. The present practice is to calculate the size of stringers for the specified fiber 

 stress. Fifteen specifications require that the wheel load be considered as carried by three ties, 

 and one specification by four ties. Data on ties are given in Table XIV. 



The Illinois Central R. R. uses ties on deck girders as follows: 



Dead Loads. Data on dead loads are given in Table XV. 



