35 



RELATIVE COST OF BRIDGES 



Built Under These Specifications 

 FOR THE 



DIFFERENT CLASSES OF LOADINGS. 



The increased cost and weight of metal bridges of all kinds, 

 built under the requirements of these specifications, will be 

 approximately as follows : 



For bridges of Class E 35 over those of Class E 30 will be ] 



:: : ir $ : : 1 3 4 > 



F 50 - K 45 - 



Recommendation. 



Table III gives a selection of heavy passenger and freight 

 engines typical of those in use on the principal railroads of 

 the United States at the beginning of the Twentieth Cen- 

 tury. 



As far as the effects upon the bridges are concerned, these 

 (ii^ines are represented by the typical train loadings of these 

 specifications, E 38 to E 50. 



The heavier of these engines are close to the possible maxi- 

 mum, considering the limitations of the permissible cross 

 section of existing railroads, fixed wheel base and the 

 mechanical details of design and proportions. 



There are now in general use cars of a nominal capacity of 

 100,000 pounds which have on four axles a total load of 

 146,000 pounds (10 per cent, increase over nominal capu< 

 on a wheel base, for two adjacent cars, of 17 ft. 2 ins. These 



