

HIGHWAY BRIDGE FLOORS. 112o 



Placing Wearing Surface. After mixing, the material shall be spread upon the roadway in 

 sufficient cjuantity to provide a thickness of J in., after rolling or tamping. 



Finish. After the material has been rolled or tamped smooth and to a uniform thickness of 

 I in., the surface shall be given a paint coat of the emulsion applied at the rate of J gal. per sq. yd., 

 and then shall be covered with coarse sand sufficient to take up any free asphalt and to fill all voids 

 in the surface. After the surface has stood for one day, it may be opened to traffic. 



Bituminous Pavement on Concrete. A bituminous wearing surface may be laid as on the 

 creosoted plank sub-floor, or the wearing surface may be laid according to the following standard 

 method. The concrete shall be dry and thoroughly clean. A bituminous wearing surface two 

 indies thick is applied as follows: The aggregate consists of broken stone or gravel passing a 

 oiK'-inch screen with the dust screened out to which is added sand equal to about one-quarter to 

 one-half the volume of the stone. The aggregates shall be heated and mixed with the bituminous 

 matt rial in a mechanical mixer or by hand with hot shovels. The asphalt shall be mixed not less 

 than 20 gallons to the cubic yard of aggregate at a temperature of 350 to 400 F. The mixture 

 shall be applied hot to the concrete surface and shall be raked with hot hoes or rakes and is rolled 

 with a roller weighing not less than 5 tons. After the surface has been rolled a layer of hot asphalt 

 shall be applied and a layer of coarse sand rolled into hot asphalt. 



Examples of Highway Bridge Floors. The following examples of highway bridge floors 

 specified by different highway commissions are of interest. 



The Illinois Highway Commission uses the following standard floors: (l) A reinforced con- 

 crete sub-floor 4 in. thick, and a concrete wearing surface 4 in. thick, weight 100 Ib. per sq. ft.; 

 (2) a reinforced concrete sub-floor 4 in. thick and a creosoted timber block wearing surface 3 in. 

 thick, weight 65 Ib. per sq. ft.; (3) a creosoted plank sub-floor 3 in. thick and a wearing surface of 

 creosoted timber blocks 3 in. thick, weight 32 Ib. per sq. ft.; and (4) a creosoted timber ship lap 

 floor 3 in. thick and a wearing surface of creosoted timber blocks 3 in. thick, weight 26 Ib. per sq. ft. 



The Michigan Highway Commission uses the following surface treatment on concrete floor 

 slabs. The surface of the concrete is thoroughly cleaned and $ of a gallon per sq. yd. of coal tar 

 heated to a temperature of 250 to 350 F. is spread over the slab. While the tar is hot the surface 

 is evenly covered with a layer in. thick of clean, sharp, coarse sand. 



I The Wisconsin Highway Commission does not specify a wearing coat on top of concrete floor 

 slabs. 



The Iowa Highway Commission uses either a 3 in. fill of gravel or a creosoted block floor 3 in. 

 thick. Concrete slabs are covered with a bituminous coating made by applying 5 of a gallon per 

 sq. yd. of hot tar to the clean dry slab. A layer of coarse dry sand is heated and sifted on top of 

 the tar. 



Cost of Floors. The costs of highway bridge floors were estimated by Mr. Clifford Older, 

 bridge engineer, Illinois Highway Commission in 1915 as follows: Concrete in sub-floors including 

 reinforcing steel, $12.00 per cu. yd.; concrete wearing surface, 4 in. thick, $0.90 per sq. yd.; 



eosoted sub-plank (i2-lb. treatment) in place, $70 per thousand feet B. M.; creosoted blocks 3 

 in. thick, in place, $1.80 per sq. yd.; bituminous gravel wearing surface, f in. thick, $0.60 per sq. 



d. The weights and costs of the Illinois Highway Commission standard floors were as follows: 

 oncrete sub-floor 4 in. thick and concrete wearing surface 4 in. thick, weighs 100 Ib. per sq. ft., 

 and costs $2.95 per sq. yd.; concrete sub-floor 4 in. thick, and creosoted blocks 3 in. thick, weighs 

 65 Ib. per sq. ft., and costs $3.25 per sq. yd.; creosoted plank sub-floor 3 in. thick, and creosoted 

 blocks 3 in. thick, weighs 32 Ib. per sq. ft., and costs $4.10 per sq. yd.; creosoted plank fub-floor 

 3 in. thick, and bituminous wearing surface j in. thick, weighs 26 Ib. per sq. ft., and costs $3.00 

 per sq. yd. 



DESIGN OF STRINGERS. Stringers or joists support the floor and in turn are supported 

 the floorbeams. The joists may be supported on the tops of the floorbeams or may be framed 

 into the floorbeam by the use of connection angles. Where concrete floors are used the steel joists 

 should either be supported on the tops of the floorbeams or if framed into the floorbeams should 

 have the upper flanges of the beams coped so that the tops of the joists will be on the same level 

 as the floorbeams. The loads carried by the joists are (i) the dead load which is made up of the 

 weight of the joists, the floor slab and the wearing surface; (2) a uniform live load, or a concen- 

 trated moving load. The uniform live load and the concentrated moving loads are the same as the 

 loads used in designing the floor slabs, but the distribution of the concentrated load is not the same. 



