COMPARISON OF RAILWAY BRIDGE SPECIFICATIONS. 



2C5 



TABLE XVI. 

 LIVE LOADS FOR RAILWAY BRIDGES. 



1. C. M. & St. P. Ry. uses E 55 east of the Missouri River and E 60 west. 



2. A uniform train load of 7,000 Ib. per lin. ft. on ore roads. 



3. A uniform train load of 5,000 Ib. per lin. ft. 



4. A uniform train load of 6,000 Ib. per lin. ft. 



5. Train load of 5,500 Ib. per lin. ft. and excess load of 66,000 Ib. 



9. Impact. Ten of the sixteen specifications use the impact coefficient as given in section 9, 

 3OO/(L + 300). Three specifications follow Cooper's method of using dead load unit stresses 

 jual to twice the live load unit stresses, with different stresses for different members. Two 



:ifications use Launhardt's formula, P = S [ I H ' 1 where P = allowable unit 



\ max. stress / 



ss, and 5 = allowable unit stress for live load alone. One specification uses the impact 

 . , _ Live Load Stress 



Live Load Stress + Dead Load Stress 



In the paper referred to in section 7, Mr. Greiner found that 26 roads used the A. R. E. A. 

 jrmula for impact. 



10 & ii. Wind Loads. The wind loads given in the different specifications are variable 

 and space will not permit going into detail. Most of the specifications require that the moving 

 wind load on the loaded chord be considered as applied at 6 or 7 ft. above the top of the rail. 



13. Centrifugal Force. Five of the sixteen specifications have the same requirement as in 

 section 13. The centrifugal force of a body moving in a circular path is C = W- J^/32 '2R, 

 where W = weight of live load per lineal foot; V = velocity of tram in feet per second, and 

 R = radius of curve in feet. For a speed of 60 2\D, C = 0.039^ for a I degree curve; C = 

 0.071 W for a 2 degree curve; C = 0.117^ for a 4 degree curve, and C = 0.143 W" for a 10 degree 

 curve. Five specifications require that the centrifugal force be applied at 5 to ^\ feet above the 

 rail. Two specifications take the centrifugal force as C = o.o^W-D, where W = equivalent 

 weight of live load per lineal foot, and D = degree of curve; one takes C = O.O2W-D, and two 

 take C = 0.045 W-D. The K. C. M. & O. R. R. takes C - W- V/32-2/?, where W = equiva- 

 lent weight of live load per lineal foot, V = velocity of train in feet per second (calculated for 50 

 miles per hour), and R = radius of curve in feet. This gives C = o.O2gW-D. 



