14 STANDARD SPECIFICATIONS 



tional clearance shall be computed by assuming the extreme 

 length of car as 45 ft. ; width 8 ft., and distance between centers 

 of trucks 20 ft. 



Through bridges, not carrying electric cars, shall have a 

 minimum head-room of 14 ft. above roadway, for classes A and 

 B, and of 12 ft. 6 in. for class C, unless otherwise required by 

 local ordinances. 



53. Paved Floors. Pavements consisting of stone blocks, 

 paving bricks, asphalt, etc., resting upon a bed of concrete, not 

 reinforced, shall be supported upon buckled or corrugated plates. 

 The minimum thickness of this concrete bed shall be 3 in. for 

 the roadway and 2 in. for the sidewalks. Such floors shall be 

 pitched transversely and proper provisions for their thorough 

 drainage shall be made. 



Pavements consisting of wooden blocks may rest on a timber 

 floor, consisting of planks laid transversely and at least 4 in. 

 thick. 



54. Wooden Floors. (See Pars. 271, 279 to 281.) 



55. Cross-Ties. (See Par. 283.) 



56. Guard-Rails. (See Par. 284.) 



57. Handrailing. A handrailing 3 ft. 6 in. high shall be 

 placed on each side of the bridge, except where plate girders 

 serve the same purpose. Where the handrailing is of rolled 

 steel or cast iron it shall be of pleasing design and shall be rigidly 

 attached to the superstructure. For wooden handrailing see 

 Par. 282. 



58. Approaches. All floor-timbers,^ rails, guards and hand- 

 railiiiirs shall extend over all piers and abutments and shall make 

 suitable connection with the embankments at either end of the 

 structure. 



LOADS 



59. Dead Load. The dead load consists of: 



(a) The weight of the steelwork; 



(6) The weight of the paving, if any; 



(c) The weight of the wooden flooring, if any, and 



(d) The weight of the electric railway tracks, if an}', 



The approximate weight of the steelwork shall be obtained 

 either by trial design or otherwise. 



The weight of the paving shall be taken at 160 Ibs. per cu. 



