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RE: Pier And Beam Foundation - Uplift

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Seems like it would depend on whether this is just a case of gradual
flooding, with only hydrostatic forces to be resisted, or if this structure
is on the beach somewhere and subject to potential ocean wave forces. If
it's the former, it just sounds like a routine buoyancy calculation.

If your superstructure is a dock and could be subject to wave forces, then I
don't think it is a simple problem. You can't just take the potential
submerged depth and convert things to an equivalent hydrostatic uplift,
because what is really going on are impulsive forces caused by the sudden
changes in wave momentum. The pressures generated by this sort of action can
be pretty high, and you need to have some estimates of wave amplitude,
frequency, etc. to examine the problem analytically--if you're up to the
math. ASCE had a task force that published a monograph in 1995 on wave
forces on inclined and vertical wall structures, but they didn't get into
wave forces on the underside of a structure.

If you know anybody in the business of designing offshore oil platforms,
I'll bet they could give you some good advice if this is a wave force
problem.

-----Original Message-----
From: Bill Polhemus [mailto:bill(--nospam--at)polhemus.cc]
Sent: Tuesday, July 16, 2002 11:30 AM
To: Residential(--nospam--at)structuralist.net; seaint(--nospam--at)seaint.org
Subject: Pier And Beam Foundation - Uplift


Are there any requirements in any of the building codes you can name, or in
a recommended practice anywhere, regarding the uplift forces on the
superstructure resting on a pier and beam foundation?

It seems like there'd be something, just to address the possibility however
remote of uplift due to flooding.

Anyone have any ideas?

William L. Polhemus, Jr. P.E.
Polhemus Engineering Company
Katy, TX, USA
Phone (281) 492-2251
FAX (281) 492-8203
email bill(--nospam--at)polhemus.cc



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