Eccentric vs. Concentric Continuous Footings

There are two types of continuous footings that can be used to support exterior walls in residential construction.

The eccentric continuous footing,

 

and the concentric continuous footing.

 

However, after conducting many post-earthquake damage assessments, we believe the eccentric continuous footing is susceptible to cracking in the slab.

When the walls rack in an earthquake, a downward force is exerted on the footing by the wall. Because the eccentric continuous footing is not centered under the wall, a rotational force is introduced into the footing. If this force is great enough, the slab will crack to relieve the induced stresses. This can be seen in Figure 3. It is our opinion that the concentric continuous footing is structurally more sound than the eccentric continuous footing.

Therefore, a better product is delivered to the owner when exterior walls are supported by concentric continuous footings.

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