05-04ChapGere.0001 - fir with average diameter 300 mm A...

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Shear Stresses in Circular Beams Problem 5.9-1 A wood pole of solid circular cross section ( d 5 diameter) is subjected to a horizontal force P 5 450 lb (see figure). The length of the pole is L 5 6 ft, and the allowable stresses in the wood are 1900 psi in bending and 120 psi in shear. Determine the minimum required diameter of the pole based upon (a) the allowable bending stress, and (b) the allowable shear stress. Solution 5.9-1 Wood pole of circular cross section 338 CHAPTER 5 Stresses in Beams (Basic Topics) L P d d P 5 450 lb L 5 6 ft 5 72 in. s allow 5 1900 psi t allow 5 120 psi Find diameter d (a) B ASED UPON BENDING STRESS M max 5 PL 5 (450 lb)(72 in.) 5 32,400 lb-in. d min 5 5.58 in. (b) B ASED UPON SHEAR STRESS V max 5 450 lb d min 5 2.52 in. (Bending stress governs.) t 5 4 V 3 A 5 16 V 3 p d 2 Ê d 2 5 16 V max 3 p t allow 5 6.366 in. 2 s 5 M S 5 32 M p d 3 Ê d 3 5 32 M max p s allow 5 173.7 in. 3 L P d d Problem 5.9-2 A simple log bridge in a remote area consists of two parallel logs with planks across them (see figure). The logs are Douglas
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Unformatted text preview: fir with average diameter 300 mm. A truck moves slowly across the bridge, which spans 2.5 m. Assume that the weight of the truck is equally distributed between the two logs. Because the wheelbase of the truck is greater than 2.5 m, only one set of wheels is on the bridge at a time. Thus, the wheel load on one log is equivalent to a concentrated load W acting at any position along the span. In addition, the weight of one log and the planks it supports is equivalent to a uniform load of 850 N/m acting on the log. Determine the maximum permissible wheel load W based upon (a) an allowable bending stress of 7.0 MPa, and (b) an allowable shear stress of 0.75 MPa. W 2.5 m x 850 N/m 300 m A-PDF Split DEMO : Purchase from www.A-PDF.com to remove the watermark...
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