460_Mechanics SolutionInstructors_Sol.Manual-Mechanics_Materials_7e.book_Gere_light.1

460_Mechanics SolutionInstructors_Sol.Manual-Mechanics_Materials_7e.book_Gere_light.1

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Unformatted text preview: 05Ch05.qxd 9/25/08 454 2:29 PM Page 454 CHAPTER 5 Stresses in Beams (Basic Topics) Solution 5.9-2 Log bridge (b) BASED UPON SHEAR STRESS Diameter d 300 mm sallow 7.0 MPa tallow 0.75 MPa Find allowable load W Maximum shear force occurs when wheel is adjacent to support (x 0). (a) BASED UPON BENDING STRESS Vmax Maximum moment occurs when wheel is at midspan (x L/2). qL WL + 4 8 Mmax W+ qL 2 A pd 4 newtons) 2 0.070686 m2 tmax 4Vmax 3A 0.625W + 664.1 (N # m) (W Vmax 3Atallow 4 pd3 32 Mmax 2.651 * 10 Ssallow 3 newtons) m3 (2.651 * 10 ‹ 0.625W + 664.1 28,600 N 3 (0.070686 m2)(0.75 MPa) 4 39,760 N 3 m3)(7.0 MPa) ‹ W + 1062.5 N W 18,560 N # m W 1 (850 N/m)(2.5 m) 2 W + 1062.5 N (W 2 W 1 (2.5 m) + (850 N/m)(2.5 m)2 4 8 S W+ 39,760 N 38,700 N 38.7 kN ; 18,560 28.6 kN ; b Problem 5.9-3 A sign for an automobile service station is supported by two aluminum poles of hollow circular cross section, as shown in the figure. The poles are being designed to resist a wind pressure of 75 lb/ft2 against the full area of the sign. The dimensions of the poles and sign are h1 20 ft, h2 5 ft, and b 10 ft. To prevent buckling of the walls of the poles, the thickness t is specified as one-tenth the outside diameter d. (a) Determine the minimum required diameter of the poles based upon an allowable bending stress of 7500 psi in the aluminum. (b) Determine the minimum required diameter based upon an allowable shear stress of 2000 psi. h2 d t=— 10 Wind load d h1 Probs. 5.9.3 and 5.9.4 ...
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This note was uploaded on 12/22/2011 for the course MEEG 310 taught by Professor Staff during the Fall '11 term at University of Delaware.

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