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# Re: Define walls as thick plate

• To: <seaint(--nospam--at)seaint.org>
• Subject: Re: Define walls as thick plate
• From: Christopher Wright <chrisw(--nospam--at)skypoint.com>
• Date: Wed, 18 Jan 2006 11:58:21 -0600

On Jan 18, 2006, at 1:20 AM, Amir Gomma wrote:

My question is what is the limit for wall thickness to can consider the wall as thin or thick plate.and what is the effect of this definition on the wall behavior.
First off, you haven't said squat about what you're trying to do or what aspects of plate theory you're wanting to use, so you're making us all guess.

My guess is that you're looking at some sort of FEA involving the wall. You should first be aware that your FEA results aren't a complete alternative to building code provisions that may apply. You can probably use FEA to develop loads and predict displacements or structural frequencies, but you shouldn't simply lift out stresses to validate your design.

The big assumptions behind ordinary plate theory are very much like beam theory except in two dimensions. Strain is assumed to vary linearly across the thickness; shear deformations are considered small and stresses in the thickness direction are negligible. Deformations much greater than half the thickness violate the original assumptions. Thick plates are those where shear deformations aren't negligible, but those situations don't happen very often. Plates also have somewhat more complex boundary conditions to consider. For example the corners of 'simply supported' rectangular plates want to lift, so the simple support may not be what you think it is to give zero edge moments.

You should read up on plate theory in Timoshenko's books or some other good strength of materials text to see if what you might have in mind squares with the theoretical basis of plate theory. For example, you can probably consider composite construction, like plywood stiffened by studs as a sort of plate using an equivalent stiffness parameter D = Et^3/12(1-mu^2) based on calculated moment of inertia of the wall and stiffeners or even do reinforced concrete panels using composite plate theory, but it's no job for a newbie or someone who doesn't understand both plate theory and structural design practice very, very well. Judging from my experience with pressure vessels you're also going to need persuasive powers like Richard Feynman to explain what you've done to building officials.
Christopher Wright P.E. |"They couldn't hit an elephant at
chrisw(--nospam--at)skypoint.com   | this distance" (last words of Gen.
.......................................| John Sedgwick, Spotsylvania 1864)
http://www.skypoint.com/~chrisw/

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