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Re: IBC 2006/2009 Assumption of flexible diaphragm.

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Again, I would consult the technical documentation of each product considered.  For example, the Simpson Steel Strongwall has drift limits.  I think it will come down to calculating the deflections of both the horizontal and vertical diaphragms and determining whether it's "flexible' or "rigid."

The reality is that most floors or roofs in residential construction would technically be considered "rigid" because of the diaphragm's aspect ratio, meaning the max deflection at midspan usually will not be greater than 2.5 times the deflection of the shearwalls or moment frames supporting them.


On Wed, Dec 1, 2010 at 4:19 PM, Freeman Tang <ftang(--nospam--at)> wrote:


Thanks for the quick reply.  The R factor for Hardy Panels is 6.5.  The R factor takes care of the ductility issue, but not the SW’s stiffness relative to the diaphragm’s stiffness.  If a horizontal wood diaphragm is supported by moment frames, it will behave more rigid than if it is supported by long concrete SWs.  So the flexibility of a diaphragm is relative to the stiffness of the vertical resisting elements supporting it.  If the diaphragm is supported by slender prefabricated SWs, it will behave more rigid than if its is supported by long wood SWs.

In the commentary of IBC 2006 item 3 limits this allowance of flexible diaphragm assumption to light-framed wood structures to those seismic-force-resisting system that traditionally have been designed assuming flexible diaphragm.  Does the “traditionally” include prefabricated SWs?  This is my doubt.



From: David Topete [mailto:d.topete73(--nospam--at)]
Sent: Wednesday, December 01, 2010 2:50 PM
To: seaint(--nospam--at)
Subject: Re: IBC 2006/2009 Assumption of flexible diaphragm.


I would say they would be considered the same, unless their respective documentation or testing report or ICC ESR indicates the use of an alternate response modification factor, R.  I recall Hardy Frames were designed as steel braced frames and indicated an R factor of 4 (or 4.5).  Off hand, I don't remember what their Hardy Panels were to be designed for...

On Wed, Dec 1, 2010 at 2:09 PM, Freeman Tang <ftang(--nospam--at)> wrote:

Hi list,


Per IBC 2006/2009 of section 1613.6.1 Assumption of flexible diaphragm, item 3 stipulates that “Vertical elements of the ………..with wood  structural panels for shear resistance or steel sheets”.  My question is that will proprietary prefabricated wood panels and steel panels be considered as the wood structural panels and steel sheets under item 3 of this section? 

I believe that the wood structural panels and steel sheets under this section refer to the conventional wood shear walls and sheet steel shear panels, but not including the proprietary SWs.  Do you have different opinions on this?  Any comments and suggestions will be appreciated.


Freeman Tang 

David Topete, SE

David Topete, SE