Civil Engineering MCQAE Level Civil Engineering
The ultimate moment of resistance M_u for a singly reinforced rectangular section in LSM (IS 456) when x_u ≤ x_u,lim is:
RCCDesign Flexural StrengthMEDIUM
Choose the correct answer
A
0.87f_y A_st (d - x_u/2)
B
0.87f_y A_st (d - 0.42x_u)
C
f_ck × b × d²
D
0.36 f_ck b x_u (d - 0.42x_u)
Correct Answer
B. 0.87f_y A_st (d - 0.42x_u)
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M_u = T × lever arm = 0.87f_y × A_st × (d - 0.42x_u), where 0.42x_u is the distance from compression face to centroid of stress block (NA to centroid of stress block = 0.42x_u). Equivalently: M_u = 0.36f_ck×b×x_u×(d-0.42x_u).
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