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

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On 25 May 2004, at 8:13, Nels Roselund, SE wrote:

> 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


While I've not seen any research on this topic, I would think that its likely
been done.  I've used Butler Mfg's roof system for concrete tilt-up buildings.
They are using a truss system that is rather rigid, but seems could be
adapted, through a reduction in member sizes, to give a more flexible diaphragm
system.  I don't know if they would be willing to share their calculations or
methodologies, but there must be some work out there on the subject.
Butler's website is:  http://www.butlermfg.com

Sorry that I couldn't be more help.
Lloyd


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