HIGHWAY BRIDGES 15 



it. for stone blocks, at 150 Ibs. per cu. ft. for paving bricks, and 

 -at 130 Ibs. per cu. ft. for concrete and asphalt. 



The weight of the wooden flooring shall be taken at 4| Ibs. 

 per foot-board measure for oak, yellow pine and other hard 

 woods, at 3J- Ibs. per foot-board measure for white pine and 

 other soft woods. 



The minimum weight of cross-ties and guard rails shall be 

 taken at 200 Ibs. per lin.ft. of each track, and the weight of rails, 

 fastenings and splices at 100 Ibs. per lin.ft. of each track. 



60. Live Loads. All bridges shall be designed to carry cer- 

 tain concentrated and certain uniformly distributed loads, as 

 .specified below, placed so as to give the greatest stress in each 

 part of the structure. 



(a) Class A. For the floor system and local truss mem- 

 bers a concentrated load of 40,000 Ibs., distributed on two 

 axles 8 ft. centers and 5 ft. gauge (occupying a length 

 of 20 ft. and a width of 10 ft.) , and upon the remaining 

 area of the floor, including sidewalks, a load of 100 

 Ibs. per sq.ft. 



For the trusses or girders, 100 Ibs. per sq.ft. of entire 

 roadway and sidewalks for spans of 100 ft. or less, 80 

 Ibs. for spans of 200 ft. or over, and proportionally for 

 intermediate spans. 



{b) Class B. For the floor system and local truss members 

 a concentrated load of 30,000 Ibs., distributed on two 

 axles 8 ft. centers and 5 ft. gauge (occupying a length 

 of 20 ft. and a width of 10 ft.), and upon the remaining 

 area of the floor, including sidewalks, a load of 90 

 Ibs. per sq.ft. 



For the trusses or girders, 90 Ibs. per sq.ft. of entire 

 roadway and sidewalks for spans of 100 ft. or less, 70 

 Ibs. for spans of 200 ft. or over and proportionally for 

 intermediate spans. 



ic) Class C. For the floor system and local truss members 

 a concentrated load of 20,000 lbs. ; distributed on two 

 axles 8 ft. centers and 5 ft. gauge (occupying a length 

 of 20 ft. and a width of 10 ft.), and upon the remaining 

 area of the floor, including sidewalks, a load of 80 Ibs. 

 per sq.ft. 



For the trusses or girders, 80 Ibs per sq.ft. of entire 



