SPECIFICATIONS. 139 



26. Drainage. Provision shall be made for drainage clear of all parts of the metal work. 



27. Floor of Classes EI, E z , and E t . The floors of classes EI, E if and EI shall consist of 

 cross-tics not loss than 6 in. by 6 in. for stringers spaced 6J ft.; and larger for greater spacings, 

 they shall be spaced with openings not exceeding 6 in., shall be notched down \ in., and secured 

 to the supporting stringers by J in. bolts spaced not over 6 ft. apart. The ties shall extend the 

 full width of the bridge on deck bridges, and every other tie shall extend the full width in through 

 tni(l<vs to carry the footwalk. Ties shall be designed for the same allowable unit stresses as 

 wooden joists. 



There shall be guard timbers not less than 6 in. by 6 in., or 5 in. by 7 in., on each side of 

 each track, with their inner faces not less than 9 in. from the center of the rail. They shall be 

 notched I in. over every tie, and shall be spliced over a tie with a half-and-half joint with 6 in. 

 lap. Each guard timber shall be fastened to every third tie and at each splice with a f in. bolt. 

 All heads or nuts on the upper faces of ties or guards shall be countersunk below the surface of 

 the wood. 



PART II. LOADS. 



28. Dead Load. The dead load will consist of (r) the weight of the metal, and (2) the weight 

 of the timber in the floor, or of the material other than steel. In determining the dead load the 

 weight of oak or other hard wood shall be taken at 4^ Ib. per foot board measure, and the weight 

 of pine or other soft woods at 3^ lb. per foot; the weight of asphalt at 130 Ib., of concrete and 

 paving brick at 150 Ib., and of granite at 160 lb per cu. ft. 



The rails, fastenings, splices and guard timbers of street railway tracks shall be assumed to 

 weigh not less than 100 lb. per lineal foot of track. 



29. Live Load. The bridges of different classes shall be designed to carry, in addition to 

 icir own weight and that of the floor, a moving load, either uniform or concentrated, or both, as 



:ified below, placed so as to give the greatest stress in each member. 



Class A. For City Traffic. For the floor and its supports, on any part of the roadway or 

 each of the street car tracks, a concentrated load of 24 tons on two axles 10 ft. centers and 5 ft. 

 ige (assumed to occupy 12 ft. in width for a single line or 22 ft. for a double line), and upon 

 ic remaining portion of the floor, a load of 125 lb. per sq. ft. and a concentrated load as for class 

 Sidewalks a load of 100 lb. per sq. ft. 

 Loads for the trusses as per Table I. 



Class B. For Suburban or Interurban Traffic. For the floor and its supports, on any part 

 the roadway, a concentrated load of 12 tons on two axles lo-ft. centers and 5-ft. gage (assumed 

 occupy a width of 12 ft.), or on each street car track a concentrated load of 24 tons on two 

 Jes lo-ft. centers; and on the remaining portion of the floor, a load of 125 lb. per sq. ft. and a 

 jncentrated load as for class DI. Sidewalks a load of 100 lb. per sq. ft. 

 Loads for the trusses as per Table I. 



Class C. For Highway and Light Interurban Traffic. For the floor and its supports, on 

 ly part of the roadway, a concentrated load of 12 tons on two axles lo-ft. centers and 5-ft. gage 

 ssumed to occupy a width of 12 ft.), or on each street car track r concentrated load of 18 tons 

 two axles xo-ft. centers; and upon the remaining portion of the floor, a load of 125 lb. per sq. ft. 

 id a concentrated load as for class DI. Sidewalks a load of 100 lb. per sq. ft. 

 Loads for the trusses as per Table I. 



Class DI. Heavy Country Bridges. For the floor and its supports, a load of 125 lb. per sq .ft. 

 total floor surface or a 2o-ton motor truck with axles spaced 12 ft. and wheels with a 6-ft. gage, 

 nth 14 tons on rear axle and 6 tons on front axle. The truck to occupy a space 10 ft. wide and 

 ft. long. The rear wheels to have a width of 20 in. 



Loads for the trusses as per Table I. No bridge, however, to be designed for a load of less 

 an 1,000 lb. per lineal foot of bridge. 



Class D t . Oridnary Country Bridges. For the floor and its supports, a load of 100 lb. per 

 1. ft. of total floor surface or a 1 5-ton motor truck with axles spaced 10 ft. and wheels with a 6-ft. 

 ige, and occupying a space 10 ft. wide and 30 ft. long, with 10 tons on rear axle and 5 tons on 

 jnt axle, and with rear wheels 15 in. wide. 



Loads for the trusses as per Table I. No bridge, however, to be designed for a load oi less 

 in 800 lb. per lineal foot of bridge. 



Class EI. For Heavy Electric Railways Only. On each track a series of concentrations 

 insisting of two pairs of trucks, the axles of the pairs being spaced 5 ft. centers, while the distance 

 etween centers of interior axles is 10 ft., the pairs of trucks being spaced 15 ft. centeVs. The 

 des are loaded with a load of 40,000 lb., making a total of 160,000 lb. Or a uniform load of 6,000 

 >. per lineal foot for all spans up to 50 ft., reduced to 4,500 lb. per lineal foot for spans of 200 ft. 

 id over, and proportionately for intermediate spans. 



