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RE: omega level forces

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If you do not design your anchor bolts for forces comparable to those in
the frame your energy absorption will likely occur at the anchor bolts if
they do not fail.  Is this acceptable?

It often occurs that foundation rocking occurs at levels below the omega
level forces. Does it make sence to design foundation and anchor bolts for
forces in excess of that which will result in foundation rocking.

Mark Gilligan

>I am currently involved in some SCBF building projects and the question
has come up as to whether we need to design the foundation system for
omega level seismic forces.  Using the 1998 CBC we are required to check
the brace connections, the columns (@ braces), and the collector elements
for this increased force level.  (we could look for the "week link" to find
maximum force that can be transfer to the system, but have opted out of
We have debated whether the anchor bolts, baseplates, and foundation system
would also need to be checked (@ strength levels) for the omega level
We are using the allowable stress design provisions (Division V) (DSA
allow use of LRFD even though Division V seems to be LRFD in disguise)

Mark Pemberton, P.E..

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