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Walls Overturning

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You might try checking out ATC 40. Chapter 10 addresses foundation response
and emphasizes that foundation stiffness and strength can affect not only
walls but other elements attached to the walls.

Large wall displacements due to rocking at the base can cause frame and
nonstructural damage where displacement incompatibilities occur.

It is common for structural engineers to underestimate the amount of
displacement associated with wall systems and overlook these displacement
incompatibilities. Most walls are not entirely "fixed" at their bases.

Observed earthquake damage due to overturning or toppling is rare, but
displacement incompabilities due to rocking walls are quite common.

ATC 40 also raises the caveat that stiff/strong foundations are not always
favorable, nor are flexible/weak foundations always conservative. One way to
evaluate the concern at present is to envelope the conditions and explore
the effect that various foundation/stiffness assumptions have on overall
building response. This is not an easy task.

On a related note, soil pressures on retaining walls can be self-relieving
once they induce small movements in the walls. Mononabe/Okabi force levels
seem to be greatly conservative and don't account for normally-expected
nonlinear effects.

Fred Turner, Staff Structural Engineer, California Seismic Safety
Commission, 1900 K St. #100, Sacramento, CA 95814 916-327-1606 Work Phone,
916-322-9476 Fax fturner(--nospam--at)