Civil Engineering MCQAE Level Civil Engineering
For a singly reinforced beam with b=230mm, d=450mm, M25 concrete, Fe415 steel with A_st=1000mm², the neutral axis depth x_u is computed from:
RCCNeutral Axis Depth LSMMEDIUM
Choose the correct answer
A
x_u = A_st × f_y / (0.36 × f_ck × b)
B
Xu = 0.87f_y × A_st / (0.36 × f_ck × b)
C
x_u = A_st × f_ck / (f_y × b)
D
x_u = 0.48d
Correct Answer
B. Xu = 0.87f_y × A_st / (0.36 × f_ck × b)
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From force equilibrium in LSM: 0.87f_y × A_st = 0.36 × f_ck × b × x_u. So x_u = 0.87f_y × A_st / (0.36 × f_ck × b). Check x_u < x_u,lim for under-reinforced design.
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