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A streel portal frame has dimensions, plastic moment capacities and applied lads as shown in the figure. The vertical load is always twice of the horizontal load. The collapse load P required for the development of abbeam mechanism is
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- 3Mp /L
- 4Mp /L
- 6Mp /L
- 8Mp /L
Correct Option: A
Internal work done,
wi = Mp θ + 2 Mp. θ + 2 Mp θ + Mp θ
= 6 Mp θ
External work done,
We = load × Δ
= 2 Pδ
= 2PLθ
Wi = We
6Mpθ = 2P Lθ
| ∴ P = | L |
