GATE 2025 CE (CE2) – Question 30
The design shear strength of a reinforced concrete rectangular beam with a width of 250 mm and an effective depth of 500 mm, is 0.3 MPa. The torsional moment capacity of the section (in kN.m) under pure torsion, as per IS 456:2000, is ______ (round off to one decimal place).
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Correct answer: 5.87 to 5.93
Explanation
Under torsion IS 456:2000 (clause 41.3) replaces the torsion by an equivalent shear $V_e = V_u + 1.6\frac{T_u}{b}$. For pure torsion $V_u = 0$, so $V_e = \frac{1.6T_u}{b}$ and the equivalent shear stress is $\tau_{ve} = \frac{V_e}{bd}$. No torsion reinforcement is needed while $\tau_{ve} \le \tau_c = 0.3$ MPa, so the capacity of the section is $T_u = \frac{\tau_cb^2d}{1.6} = \frac{0.3 \times 250^2 \times 500}{1.6} = 5.86 \times 10^6$ N mm $= 5.9$ kN m.