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Shear Key in Basement walls

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To all:

I recently designed a basement wall as a cantilever retaining wall with a shear key. The slab within the two ends of the retaining walls is a 5 inch slab on grade. Due to field condition, the contractor does not want to intstall the shear keys.

One way to reduce the shear demand at the base of the retaining wall is to account for the fact that the first floor provides some lateral support. However, because the first floor consists of wood construction, I am hesitant to do this and prefer to be conservative. ( I do reinforce the wall stem for this condition,though).

The second alternative is to assume that the active force on the retaining wallls at the opposite ends of the basement cancells each other out - therefore, a shear key is not necessary. This condition should hold true no matter how far the two retaining walls are located - in finite terms, thoguh - provided they are of the same height and have simillar backfill. The slab-on-grade will be subjected to compressive forces from the retaining wall and should act as a plate with compressive forces on all four sides ( four sides of the basement).

My question to you all is - how do you design the slab? I am thinking of taking a unit width of slab and finding the allowable compressive load based on Euler's formula with a factor of safety. Since water will be drainded, moment due to water pressure should not be an issue.

If the wall design were to include seismic forces - (Mononobe-Okabe equation)- how would one dissipate the shear for the worst case scenario for seismic forces acting in the same direction for the two opposite walls.

Your comments would be highly appreciated.


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