475_Mechanics SolutionInstructors_Sol.Manual-Mechanics_Materials_7e.book_Gere_light.1

475_Mechanics SolutionInstructors_Sol.Manual-Mechanics_Materials_7e.book_Gere_light.1

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Problem 5.11-5 A box beam is constructed of four wood boards as shown in the figure part (a). The webs are 8 in. ± 1 in. and the flanges are 6 in. ± 1 in. boards (actual dimensions), joined by screws for which the allowable load in shear is F ² 250 lb per screw. (a) Calculate the maximum permissible longitudinal spacing of the screws if the shear force is . (b) Repeat (a) if the flanges are attached to the webs using a arrangement of screws as shown in the figure part (b). horizontal 1200 lb V s max SECTION 5.11 Built-Up Beams 469 Solution 5.11-5 Wood box beam (a) Vertical screws ; s max ² 5.08 in. s max ² 2 FI VQ a f ² VQ I ² 2 F S Q a ² bt (4.5 in.) Q a ² 27 in. 3 I ² bh 3 12 ³ ( b ³ 2 t ) h 1 3 12 I ² 329.333 in. 4 t ² 1 in. b ² 6 in. h 1 ² 8 in. h ² 10 in. V ² 1200 lb F ² 250 lb (b) Horizontal screws ; s max ² 4.63 in. s max ² 2 FI VQ b f ² VQ I ² 2 F s Q b ² ( b ³ 2 t ) t (3.5 in.) Q b ² 21 in. 3 I ² 233.333 in. 4 I ² bh 3 12 ³ ( b ³ 2 t ) h 1 3 12 t ² 1 in. b ² 8 in. h 1 ² 6 in. h ² 8 in. (a) y 6 in. z O Web Flange
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Unformatted text preview: 1 in. 1 in. 8 in. 1 in. 1 in. (b) Web Flange 1 in. 1 in. 6 in. 8 in. 1 in. 1 in. Problem 5.11-6 Two wood box beams (beams and ) have the same outside dimensions ( ) and the same thickness ( ) throughout, as shown |in the figure on the next page. Both beams are formed by nailing, with each nail having an allowable shear load of 250 N. The beams are designed for a shear force . (a) What is the maximum longitudinal spacing for the nails in beam ? (b) What is the maximum longitudinal spacing for the nails in beam ? (c) Which beam is more efficient in resisting the shear force? B s B A S A V 3.2 kN t 20 mm 200 mm * 360 mm B A z y O z y O 200 mm 360 mm 360 mm t = 20 mm t = 20 mm A 200 mm B 05Ch05.qxd 9/25/08 2:29 PM Page 469...
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