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Re: UBC 1997 - Non building structure - Section 1632.2 for A.bolt design

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It depends on the stiffness of your "pedestal".  If this is a grade mounted equipment sitting on top of a solid concrete mat (with period T less than 0.06 second) then you should probably be looking at UBC Section 1634.3, "Rigid Structures" and equation 34-1.  As your equipment gets elevated and the support gets more flexible (and more building like), such as a concrete moment frame, then you need to take into consideration the amplifications of the support structure and the application of Section 1632.2 and equation 32-2.

Thomas Hunt, S.E.
ABS Consulting

"Vasu, Ravi" <Ravi.Vasu(--nospam--at)>

12/24/2002 07:53 AM
Please respond to seaint

        To:        seaint(--nospam--at)
        Subject:        UBC 1997 - Non building structure - Section 1632.2 for A.bolt design

Please refer to Lateral force per section 1632 & 1632.2 (UBC 1997).

For equipments supported on concrete pedestals (T.O.C. at grade)

The critical force for the design of Anchor bolt will be per
section 1630.2 / eqn. 32-2 / eqn. 34-1 (depends on flexible or rigid)

In this, for pedestals at grade, hx = 0 in the equation 32-2.

My question is,

What is the minimum height for pedestal T.O.C.(top of concrete) above grade,
so that hx can be taken (or about) 0.  For example, if the pedestal TOC is about 2 or 3 or 4' above grade,

(for small heights above grade)

Fp increases almost 4 times than it is at grade(per eqn. 32-2).  
The critical force for the A.bolt can be very high.(than it is at grade).

I could not find any reference or example in 'Seismic design manual' .  Any guidance in this is

Happy Holidays.

Ravi Vasu, P.E.,

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