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Rigid VS Flexible Wood Diaphragms[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: "seaint(--nospam--at)seaint.org" <seaint(--nospam--at)seaint.org>
- Subject: Rigid VS Flexible Wood Diaphragms
- From: merrick group <merrickgroup(--nospam--at)compuserve.com>
- Date: Mon, 29 Mar 1999 12:35:27 -0500
Rigid VS Flexible Wood Diaphragms The following may not be statements of facts. The This document is an inquiry and is open to discussion. The nature of the tributary area method leaves the shear walls mostly balanced with the center of gravity. The exception may occur with a cantilevered diaphragm. Assumption: The shear wall flexibility is directly related to its capacity. An eight-foot wall will deflect a little less than half an inch when loaded to its capacity. Torsion is a global affect, not local. A test for a rigid diaphragm may not be realistic if the deflection is considered in a short span between two interior walls. Torsion may increase loads at the most distant shear walls. However, the rigid diaphragm in most cases of residential homes will reduce shears in overloaded walls and share the excess with over designed walls. Proprietary shear wall systems are recommended not to be mixed with standard shear walls in the same wall line. Then, for a rigid diaphragm, all or no walls shall be of a stiffer proprietary shear wall. If one models with the rigid diaphragm, the proprietary shear walls should not be needed. Deflections of longer cantilevered diaphragms can be justified. Over loaded walls will be unloaded by adjacent stronger and stiffer walls. If the rigid diaphragm is only proven with an interior short span, the rigid model should not be used to conclude loads less than that of the tributary area method. It is probably physically correct to reduce loads if the test for a rigid diaphragm is for the most flexible span possible by ignoring the interior shear walls. I propose creating a simplified design method that In theory would never violate a code procedure. Make a proof using the code to its most detail demands and reducing the base shear with the high period response that the flexible shear walls allow. The zone four base shear, on firm ground, is about a 30% reduction. The proof is then attached to your quick seismic analysis for lateral distribution. Attached to the last response to this subject was of a story of a site visit. Missing, is the proper response. What is the proper response when a shear wall is dangerously compromised by the contractor? Who do you communicate with and how. What is next if the dangerous condition is not abated? What to do if you never get the opportunity to determine the consequence of your report.
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