COMPARISON OF RAILWAY BRIDGE SPECIFICATIONS. 



201 



Association are reprinted in the last part of this chapter. To show the present practice in the 

 if railway bridges as given in the sixteen different specifications the most important vari- 

 ations from the American Railway Engineering Association Specifications will be briefly discussed. 

 Tin- sections in the specifications of the American Railway Engineering Association will be referred 

 to by mi'iilier. 



2. Clearances. The clearances for through single track bridges on tangent are given in 

 Table XI. The clearances on curves differ considerably. Standard formulas for calculating 

 bridge clearances on curves are as follows: 



AI ' D 



Formulas: 



A * t t^ 



a= - (nearly) 



= .00002181 jA* -D 

 b = .00002 1817 5 s -D 

 c = .00002 1 81 7 L*'D 



s = - X h = o.2e-h (c. to c. rails 







= 5 ft. nearly) 



Nomenclature, Fig. 47: 

 D = degree of curve 

 R = radius of curve, in feet 

 w = clearance width on tangent 

 a = mid-ordinate to chord of length A 

 b = mid-ordinate to chord of length B 

 c = mid-ordinate to chord of length L 

 e amount of superelevation in feet which is 



taken up in floor of span 

 h height of car or distance from top of upper 



flange or chord, whichever is least G = \- a b -\ 



s = additional clearance required on account 2 



of superelevation jf = H!_i_j_L-.-i- 5 



G = outside clearance from center line of bridge 2 2 



H = inside clearance from center line of bridge For Standard Car 



A = 8o'-o" B = 6o'-o" 



a = o.i 3961* 

 b = .07854!) 



Mp 



G = h (.06109 + -ooooi 0909 U}D 



H = 1- (.07854 + .OOOOIOQOQL*)D 



2 



+ 0.26 -h 



The following specifications indicate the present practice of several railroads. 

 New York Central Lines. Single-track through bridges on curves shall have the location of 

 trusses or girders and the width between clearance lines as shown in Figs. 48 and 49. 



CLEARANCE 



ClfAMHCE Line- 



CENTER LM/_ QF_T#ACK 



1CT 



">" 



CLEAKAHCE xf LIHE - 



FIG. 48. 



L_EH6TH_ OF 5PAH_ 

 FIG. 49. 



lateral clearance from center line of track required by. clearance diagram for tangent aline- 



ment. 



middle ordinate of curve for a chord equal to span length. 

 X = addition for overhang of a car 85 ft. long, with trucks 60 ft. c. to c. ; to be taken as one inch 



for each degree of curve. 

 Y = addition in inches (on the inside of the curve only) on account of the superelevation of the 



outer rail, to be taken as follows: 



For heights from 15 ft. to 22 ft. above the top of rail; Y = 3 inches per inch of superelevation. 

 For heights from 3 ft. 9 in. to 15 ft. above top of rail; Y = s-h/5 (to use with W = 7 ft. 



6 in.). 



For heights from top of rail to 3 ft. 9 in. above; Y = s(h + l-5)/4. 

 s = superelevation in inches. 

 h = height above top of rail in feet. 



