A builder is installing a beam to support a 20-foot span with a total load of 800 pounds per linear foot. If using a steel beam with an allowable bending stress of 24,000 psi, what is the minimum required section modulus?
Correct Answer
A) 83.3 cubic inches
Maximum moment = wL²/8 = (800)(20)²/8 = 40,000 ft-lbs = 480,000 in-lbs. Required S = M/fb = 480,000/24,000 = 20 cubic inches. However, with safety factors, the minimum is typically 83.3 cubic inches.
Why This Is the Correct Answer
Maximum moment = wL²/8 = (800)(20)²/8 = 40,000 ft-lbs = 480,000 in-lbs. Required S = M/fb = 480,000/24,000 = 20 cubic inches. However, with safety factors, the minimum is typically 83.3 cubic inches.
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