Civil Engineering MCQJE Level Civil Engineering
A beam with rectangular cross-section b × d has a bending stress of 10 MPa at the extreme fibre. The moment of resistance is: (b = 150 mm, d = 300 mm)
Strength of MaterialsStrength of MaterialsMEDIUM
Choose the correct answer
A
10 kN·m
B
22.5 kN·m
C
45 kN·m
D
5.6 kN·m
Correct Answer
B. 22.5 kN·m
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Z = bd²/6 = 150 × 300²/6 = 2.25 × 10⁶ mm³. M = σ × Z = 10 × 2.25×10⁶ = 22.5×10⁶ N·mm = 22.5 kN·m. Moment of resistance = allowable stress × section modulus. This is the basic flexure formula rearranged: M = σmax × I/ymax = σmax × Z.
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