GENERAL SPECIFICATIONS FOR STEEL RAILWAY BRIDGES.* 



American Railway Engineering Association. 

 Fourth Edition. 



STANDARD SPECIFICATIONS. 



PART FIRST DESIGN. 



I. GENERAL. 



1. Materials. The material in the superstructure shall be structural steel, except rivets, 

 and as may be otherwise specified. 



2. Clearances. When alinement is on tangent, clearances shall not be less than shown on 

 the diagram; the height of rail shall, in all cases, be assumed as 6 in. The width shall be increased 

 so as to provide the same minimum clearances on curves for a car 80 ft. long, 14 ft. high, and 60 ft. 

 center to center of trucks, allowance being made for curvature and superelevation of rails. 



3. Spacing Trusses. The width center to center of girders and trusses 

 shall in no case be less than one-twentieth of the effective span, nor less than 

 is necessary to prevent overturning under the assumed lateral loading. 



4. Skew Bridges. Ends of deck plate girders and track stringers of 

 skew bridges at abutments shall be square to the track, unless a ballasted 

 floor is used. 



5. Floors. Wooden tie floors shall be secured to the stringers and shall 

 be proportioned to carry the maximum wheel load, with 100 percent impact, 

 distributed over three ties, with fiber stress not to exceed 2,000 Ib. per sq. in. 

 Ties shall not be less than 10 ft. in length. They shall be spaced with not 

 more than 6-in. openings; and shall be secured against bunching. 



II. LOADS. 



6. Dead Load. The dead load shall consist of the estimated weight of 



the entire suspended structure. Timber shall be assumed to weigh 4^ Ib. per -r O c\o :t 



ft. B. M.; ballast 100 Ib. per cu. ft., reinforced concrete 150 Ib. per cu. ft., ' I 



and rails and fastenings, 150 Ib. per linear ft. of track. 



t/. Live Load. The live load, for each track, shall consist of two typical engines followed 

 by a uniform load, according to Cooper's series, or a system of loading giving practically equivalent 

 strains. The minimum loading to be Cooper's -40, and the special loading, the diagram as 

 shown in the following diagrams, that which gives the larger strains to be used. 



f8. Heavier Loading. Heavier loadings shall be proportional to the above diagrams on the 

 same spacing. 



9. Impact. The dynamic increment of the live load shall be added to the maximum computed 



-7QQ 



live load strains and shall be determined by the formula I = S , , 



L, -J- 3OO 



where I = impact or dynamic increment to be added to live-load strains. 

 5 = computed maximum live-load strain. 



L = loaded length of track in feet producing the maximum strain in the member. For 

 bridges carrying more than one track, the aggregate length of all tracks producing 

 the strain shall be used. 



Impact shall not be added to strains produced by longitudinal, centrifugal and lateral or 

 wind forces. 



10. Lateral Forces. All spans shall be designed for a lateral force on the loaded chord of 

 200 Ib. per linear foot plus 10 per cent of the specified train load on one track, and 200 Ib. per 

 linear foot on the unloaded chord; these forces being considered as moving. 



* Adopted by the American Railway Engineering Association, 

 t See Addendum, clause (a). 



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