112 STEEL HIGHWAY BRIDGES. CHAP. III. 



WEIGHTS OF STEEL HIGHWAY BRIDGES. The following data may be used in calcu- 

 lating the dead loads in the design of highway bridges or as a basis for preliminary estimates. 



AMERICAN BRIDGE COMPANY. Standard Steel Highway Bridges with Timber Floor. 

 Timber floor, 3-in. plank on roadway and 2-in. plank on footwalks. Live loads for floor and its 

 supports, 100 Ib. per sq. ft. of floor surface, or 6 tons on two axles 10 ft. centers and 5 ft. gage, or a 

 15-ton road roller. For trusses 100 Ib. per sq. ft. of roadway up to a span of 75 ft., 75 Ib. per sq. ft. 

 of roadway for spans of 168 ft. and over, and proportional for intermediate spans. No allowance 

 is made for impact. Designed for allowable stresses given in specifications in the latter part of this 

 chapter. Let W = weight of the structural steel per lineal foot of span; L = length of span in feet, 

 b = width of roadway in feet (without sidewalks). 



1. Steel Through Plate Girders. Through plate girder spans 36 ft. to 70 ft., roadway 20 ft. 

 wide, without sidewalks, but including stringers. The weight of structural steel per lineal foot 

 of span is 



W = 300 + 3.8L. (i) 



For sidewalks with steel joists add about 12 Ib. per sq. ft. of sidewalks. 



2. Steel Low Riveted Truss Spans, with Timber Floor. For low truss spans 36 ft. to 102 ft., 

 with timber floors, the weight of structural steel per lineal foot of span, not including the weight 

 of the stringers and the railing, is given approximately by the formula for a i6-ft. roadway 



W = 100 + 2.oL. (2) 



and for a 2O-ft. roadway 



W = 150 + 1.7 L. (3) 



3. Steel Low Riveted Truss Spans, with Reinforced Concrete Floors. For low truss spans 

 36 ft. to 102 ft., with reinforced concrete floors, 5 in. thick with 6 in. of gravel at center and 3 in. 

 of gravel at curb, the weight of structural steel per lineal foot of span, not including the weight of 

 the stringers and the railing, is given approximately by the formula for a i6-ft. roadway 



W = 150 + 3-5L. (4) 



and for a 2O-ft. roadway 



W = 185 + 3.5!*. (5) 



4. Steel High Truss Spans, with Timber Floor. For high truss spans 104 to 204 ft., with 

 timber floors the weight of structural steel per lineal foot of span, not including the weight of the 

 stringers and the railing, is given approximately by the formula for a i6-ft. roadway 



W = 250 + i.sL. (6) 



and for a 2O-ft. roadway 



W = 285 + 1.2 L. (7) 



IOWA HIGHWAY COMMISSION. Steel Highway Bridges with Reinforced Concrete 

 Floor. Reinforced concrete floor slabs 6 in. thick for all spans in which stringers are used. Slabs 

 for stringerless floors 1\ in. thick for 8-ft. span, 8 in. thick for g-ft. span, and 85 in. .thick for xo-ft. 

 span. Live loads for the floor and its supports a uniform live load of 100 Ib. per sq. ft., and a 15-ton 

 traction engine with two-thirds of the load on the rear axle; axles spaced n ft. centers, and rear 

 wheels spaced 6 ft. centers. Rear wheels 22 in. wide. The trusses are to be designed for the 

 uniform loads given in Table I. No allowance is made for impact. 



Let W = weight of structural steel in Ib. per lineal foot of span; L = length of span in feet; 

 b = width of span in feet (without sidewalks). 



i. Steel Beam Spans. The weight of steel beam spans from 16 ft. to 32 ft. and with i6-ft., 

 i8-ft., and 2O-ft. roadway are given in Table IX. 



