Bridges and culverts for highway traffic, flat slab and girder type ... . oncrete will he taken as 2,ooo pounds per square inch. This com-pressive strength should be easily obtained with average aggregates Using a I :2 .4 mix. The critical amount of reinforcement corresponding,using steel with an elastic limit of 50,000 pounds would be .0085 bd. Girder Bridges—For single span bridges figure the insidegirders as T-beams; in this case the cross section of the reinforcementshould not exceed 2x/2% of the area of the rectangle inclosing the stemFor bridges with two or more spans the girders mould h
Bridges and culverts for highway traffic, flat slab and girder type ... . oncrete will he taken as 2,ooo pounds per square inch. This com-pressive strength should be easily obtained with average aggregates Using a I :2 .4 mix. The critical amount of reinforcement corresponding,using steel with an elastic limit of 50,000 pounds would be .0085 bd. Girder Bridges—For single span bridges figure the insidegirders as T-beams; in this case the cross section of the reinforcementshould not exceed 2x/2% of the area of the rectangle inclosing the stemFor bridges with two or more spans the girders mould he fig-ured as continuous rectangular beams and provision made for reversemoment over the supports. Percentage of Reinforcement—Use .85$ of reinforcement in slabs and rectangular beams for concrete of 2,000 pounds compressive strength. In T-beam designs limit the amount of reinforcement to of bd. These figures are based on the use of mechanical bond with an elastic limit of 50,000 pounds per square inch. a IBl a -a t ? ? ? ? . b . Figure 7. Rectangular Figure 8. T-Benm. 84 FORMULAE TO BE USED IN DESIGNING. Let Af=moment of resistance of section in inch lbs. .Vo—ultimate moment of resistance of section in inch ;/=area of reinforcement,/?^percentage of stee\=g^ limit of steel=so,ooo lbs. All dimensions as shown, in inches, and stresses in lbs. per sq. we have for rectangular beams: M0=$70 bd2 for ^=.0085 for T-beams: J/o=.86 Fp bd2=.S6Xso,oooXp bd2. =43,000 p bd2, using- high elastic limit corrugated bars. For complete discussion of these formulae, see May and June bulletins.) WORKING STRESSES. If it is desired to design for working stresses in the steel, use theformula: Af= d, where s=unit stress in the steel. Shearing Provisions—In flat slab bridges it will not be necessaryto make other provision for shearing stresses than by bending up partof the main reinforcing bars as required. In girder bridges, however, special prov
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectconcrete, bookyear190
