TGPSC HMWSSB Manager 2015 Paper 2 · Question 139
Question 139 of the TSPSC Manager (Engineering), HMWSSB, 2015: Paper 2 (Civil Engineering) (1 November 2015). Try it first, then open the answer and explanation.
The expression working out the thickness of slab base is given by ______. If t = thickness of slab base, w = pressure under slab base, σ_bs = permissible bending stress in slab base, a, b = longer and shorter projections of the slab base edge to the column member, Poisson's ratio = 0.25.
- t = ((3w/σ_bs)(a-b/4))^(1/2)
- t = ((3w/σ_bs)(a²-b²/4))^(1/2)
- t = ((3w/σ_bs)(a²-b²))^(1/2)
- t = ((3w/σ_bs)(a-b²/4))^(1/2)
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Answer: (2) t = ((3w/σ_bs)(a²-b²/4))^(1/2)
For a slab base under uniform pressure w, the working-stress formula (IS 800:1984) is t = √[(3w/σ_bs)(a² − b²/4)], where a and b are the greater and lesser projections beyond the column. The b²/4 term allows for two-way bending of the plate with Poisson's ratio 0.25; options (1) and (4) are dimensionally inconsistent and option (3) uses b² instead of b²/4.