PART III 



RAILROAD BRIDGES* 



GENERAL REQUIREMENTS 



105. Material. The material in the superstructure shall be 

 structural steel, except rivets, and as may be otherwise specified. 



1 06. Clearances. On a straight line the clear height of 

 through bridges shall not be less than 22 ft. above the top of 

 rails. The minimum width shall be as follows: 10 ft. 6 in. at 

 the top of rail, 14 ft. Vetween points, 4 ft. and 18 ft. ahove 

 the rails, and 6 ft. at the top. 



The width shall be increased to provide the same minimum 

 clearance on curves, for a car 80 ft. long, 14 ft. high, and 60 ft. 

 center to center of trucks, allowance being made both for curva- 

 ture and superelevation of rail. 



107. Cross Ties. (See Par. 2S3.) 



1 08. Guard Rails. (See Par. 284.) 



LOADS 



109. Dead Load. The dead load shall consist of the estimated 

 weight of the entire suspended structure. 



The approximate weight of the steelwork shall be obtained 

 either by trial design or otherwise. 



The weight of the ballast shall be taken at 100 Ibs. per cu.ft. ; 

 the weight of the timber shall be taken at 4 Ibs. per foot-board 

 measure, with a minimum of 250 Ibs. per lin.ft. of track, and of 

 rails, fastenings, and splices at 150 Ibs. per lin.ft. of track. 



no. Live Loads. The live loads, for each track, shall consist 

 of two typical engines followed by a uniform load, according 



* Adapted from General Specifications for Steel Railroad Bridges, 1910 

 American Railway Engineering and Maintenance of Way Association. 



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