482_Mechanics SolutionInstructors_Sol.Manual-Mechanics_Materials_7e.book_Gere_light.1

482_Mechanics SolutionInstructors_Sol.Manual-Mechanics_Materials_7e.book_Gere_light.1

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Unformatted text preview: 05Ch05.qxd 9/25/08 476 2:29 PM Page 476 CHAPTER 5 Stresses in Beams (Basic Topics) Solution 5.12-1 Brace and bit P M Pb MAXIMUM STRESSES 25 lb (compression) 121.9 lb-in. P M + A S d diameter 166 psi + 14,828 psi 14,660 psi d 7/16 in. 14,828 psi A pd2 4 P A (25 lb)(4 7/8 in.) st sc 0.1503 in.2 121.9 lb-in. 25 lb + 2 0.1503 in. M S 166 psi 0.008221 in.3 ; ; 14,990 psi 3 pd 32 S 0.008221 in.3 Problem 5.12-2 An aluminum pole for a street light weights 4600 N W2 = 660 N and supports an arm that weights 660 N (see figure). The center of gravity of the arm is 1.2 m from the axis of the pole. A wind force of 300 N also acts in the ( y) direction at 9 m above the base. The outside diameter of the pole (at its base) is 225 mm, and its thickness is 18 mm. Determine the maximum tensile and compressive stresses st and sc, respectively, in the pole (at its base) due to the weights and the wind force. 1.2 m P1 = 300 N W1 = 4600 N 18 mm 9m z y x y x Solution 5.12-2 W1 4600 N W2 660 N h P1 300 N d1 d2 d1 A p2 1d1 4 A 1.171 * 104 mm2 b 1.2 m Mx Mx 9m 225 mm t 18 mm 2t W2 b + P1h 3.492 * 103 N # m MAXIMUM STRESS st d222 p 1d1 4 64 I I d2 42 st sc W1 + W2 sc 3 Pz 5.26 * 10 N Vy P1 Vy (Axial force ) 300 N (Shear force) a Pz Mx d1 + b A I2 5.77 * 103 kPa ; 5770 kPa 6.317 * 107 mm4 AT BASE OF POLE Pz (Moment) a Pz A Mx d1 b I2 6.668 * 103 6668 kPa ; ; 225 mm ...
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