418_Mechanics SolutionInstructors_Sol.Manual-Mechanics_Materials_7e.book_Gere_light.1

418_Mechanics SolutionInstructors_Sol.Manual-Mechanics_Materials_7e.book_Gere_light.1

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Unformatted text preview: 05Ch05.qxd 9/24/08 412 4:59 AM Page 412 CHAPTER 5 Stresses in Beams (Basic Topics) Solution 5.5-25 (a) RESULTANT LOAD F ON SIGN s 12.5 in. p 20 psf b 360 p a b n 180 A b ns2 cot a b 4 2 b n L 0.785 rad pA F 72 in. c1 8 0.769 in. A 754.442 in.2 sc c2 FL Mmax 12 sc 0.731 in. 628.701 ft-lb ; 36.0 ksi (max. bending stress at base of post) ; 104.8 lb 0.16101 in.4 IZ Mmax c1 Iz Mmax 5.239 ft2 or A F (b) MAX. BENDING STRESS IN POST st Mmax c2 Iz st 34.2 ksi Design of Beams P Problem 5.6-1 The cross section of a narrow-gage railway bridge is shown in part (a) of the figure. The bridge is constructed with longitudinal steel girders that support the wood cross ties. The girders are restrained against lateral buckling by diagonal bracing, as indicated by the dashed lines. The spacing of the girders is s1 50 in. and the spacing of the rails is s2 30 in. The load transmitted by each rail to a single tie is P 1500 lb. The cross section of a tie, shown in part (b) of the figure, has width b 5.0 in. and depth d. Determine the minimum value of d based upon an allowable bending stress of 1125 psi in the wood tie. (Disregard the weight of the tie itself.) P s2 Steel rail Wood tie d b Steel girder (b) s1 (a) Solution 5.6-1 Railway cross tie Mmax S bd 2 6 Mmax s1 d 50 in. b depth of tie 5.0 in. P s2 1500 lb Solving, 30 in. sallow 1125 psi s2) P(s1 2 15,000 lb-in. 1 (50 in.)(d 2) 6 s allow S d2 15,000 16.0 in. 5d 2 6 d (1125) a dmin NOTE: Symbolic solution: d 2 inches 5d 2 b 6 4.0 in. s2) 3P(s1 bsallow ; ...
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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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