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Re: How to limit the Shear Capacity of a High-Load Diaphragm

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Nels:
I've used and seen other engineers specialized in designing reinforced Adobe wall system, using horizontal steel brace system in conjunction with the roof diaphragm to support the O-O-P forces in Reinforced Adobe wall
structures.
Khashayar (Casey) Hemmatyar, P.E.
California

----- Original Message -----
From: "Nels Roselund, SE" <njineer(--nospam--at)att.net>
To: <seaint(--nospam--at)seaint.org>
Sent: Tuesday, May 25, 2004 8:13 AM
Subject: How to limit the Shear Capacity of a High-Load Diaphragm


I need to develop a diaphragm system for a very large building with tall,
massive adobe walls.  I plan to use the Demand-Capacity concept of the
2003
IEBC or the 1997 UCBC procedure for analysis of diaphragm of URM buildings
with flexible diaphragms.  Nailed-wood diaphragms are anticipated by these
Codes because they have a limiting maximum shear capacity that tends to
limit the response of the system to strong shaking as the diaphragm yields
without failure.  The class of building for which these Codes were written
typically can be handled by nailed-wood diaphragms -- the diaphragms have
enough strength to brace the tributary mass without excessive deflection,
but yield at shear-load levels that limit the load that the shear walls
must
deliver to the diaphragm edges.

The seismic shear to be transferred to diaphragm edges by the end shear
walls of this project due to the massive out-of-plane walls that are
anchored to it is greater than can be accommodated by a conventional wood
diaphragm.  I'd like to be able to extend the demand-capacity concept into
a
system constructed of another material.  I can't visualize a yielding
concrete diaphragm, but I can visualize a steel-truss diaphragm that
incorporates horizontal moment frames or eccentrically braced frames that
would limit diaphragm capacity by yielding of the frames.  I can also
picture a horizontal steel truss system that includes viscous dampers that
would limit the load in the diaphragm.

Has anyone seen any research into diaphragm systems of this kind?

Nels Roselund
Structural Engineer
South San Gabriel, CA
njineer(--nospam--at)att.net



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