Question

Unfactored maximum bending moments at a section of a reinforced concrete beam resulting from a frame analysis are 50, 80, 120 and 180 kN-m under dead, live, wind and earthquake loads respectively. The design moment (kN-m) as per IS : 456-2000 for the limit state of collapse (flexure) is

• A. 195
• B. 250
• C. 345
• D. 372

Answer 1

The correct option is D 372

Design moment will be maximum of

1. 1.5 (D.L + L.L)
2. 1.5 D.L+ 1.5 max(EL, W.L)
3. 1.2 DL + 1.2 LL + 1.2 max (EL, W.L)

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Note: Earthquake load and wind load will not act simultaneously.
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Unfactored maximum bending moment due to
Dead load (DL),
$M_d=50$ kN-m
Live load (LL),
$M_L=80$ kN-m
Wind load (WL),
$M_w=120$ kN-m
Earthquake load (EL),
$M_E=180$ kN-m
Design moment due to DL and LL
$M_{desgin}=1.5\times 50+1.5\times 80$
= 195 kNm
Due to DL and EL
$M_{design}=1.5\times 50+1.5\times 180$
$=345$ kNm
Due to DL, LL, EL
$M_{design}=1.2\times 50+1.2\times 80+1.2\times 180$
$=372$ kN-m
Taking maximum value of design moment,
$M_{design}=372$ kN-m