ARC322 Homework 19 SOLUTION 2008

ARC322 Homework 19 SOLUTION 2008 - ARC322 Homework 19 29...

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ARC322 Homework 19 29 points Key 1. A simple DFL 4x8 No.1 beam spans 18 ft and carries a load of 325lb/ft. Show that the Beam specified is OK in bending. If it is not OK, select an appropriate size beam. Is it OK with respect to horizontal shear? It rests on a 2x4 wall at each end. Is it OK with respect to compression perpendicular to grain? 13 points 2 points dwgs A 4x8 is Dimension Lumber Moment = w L 2 /8 = 325 lb/ft x (18 ft) 2 / 8 = 13,162.5 ft-lb 1 point Section Modulus = M/ f = (13,162.5 ft-lb x 12 in/ft)/1000 lb/in 2 = 157.95 in 3 1 point 4x8 S = 30.66 in 3 < 157.95 in 3 … NOT OK 1 point 4x16 S = 135.7 in 3 < 157.95 in 2 … NOT OK Since the 4x’s didn’t work, there is no Dimension Lumber that will work … so, move on … Try it as a Beam … Moment = w L 2 /8 = 325 lb/ft x (18 ft) 2 / 8 = 13,162.5 ft-lb no points … they already did this Section Modulus = M/ f = (13,162.5 ft-lb x 12 in/ft)/ 1350 lb/in 2 = 117 in 3 1 point 6x12 S = 121.2 in 3 > 117 in 3 … OK 1 point
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ARC322 Homework 19 SOLUTION 2008 - ARC322 Homework 19 29...

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