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[cckeshav]

Dear SEFIans:

I am having difficulty in designing foundations for shear walls, particularly in soils with adequate bearing capacity. In these soils most columns can be founded on isolated footings (or combined footings). We do not need a raft. Since shear wall is provided, it draws most of the lateral shear (upto 90%), but the axial load on the wall would be about 10% resulting in a large eccentricity. The resultant force (under seismic load combinations) many times passes beyond the base of the footing. Somehow, I feel that most designers are overlooking this and designing the shear wall foundations for dead load and live load combinations. They may also consider soil to take up the tension as most software are not efficient in considering no-tension supports.

As I see, there are only three possibilities for the foundation of shear walls. 1. Provision of a raft for the whole building with due consideration for compression only springs and resulting local loss of support under the raft. 2. Anchoring the shear wall foundations to heavily loaded farther off column foundations so that the net resultant is still within the base. 3. Provision of rock anchors or tension piles.

I request our esteemed community to come of with proper guidelines in this regard.

C.Channakeshava

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