Chegg Guided Solutions for Mechanics of Materials 5th Edition Chapter 5 Problem 96P

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A bridge of length L = 48 ft is to be built on a secondary road whose access to trucks is limited to two-axle vehicles of medium weight. It will consist of a concrete slab and of simply supported steel beams with an ultimate strength σU = 60 ksi. The combined weight of the slab and beams can be approximated by a uniformly distributed load w – 0.75 kips/ft on each beam. For the purpose of the design, it is assumed that a truck with axles located at a distance a = 14 ft from each other will be driven across the bridge and that the resulting concentrated loads P1 and P2 exerted on each beam could be as large as 24 kips and 6 kips, respectively. Determine the most economical wide-flange shape for the beams, using LRFD with the load factors γD = 1.25, γD = 1.75 and the resistance factor ϕ = 0.9. [Hint: It can be shown that the maximum value of |ML| occurs under the larger load when that load is located to the left of the center of the beam at a distance equal to aP2/2(P1 +P2).]

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