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RE: Relative Stiffness of Wood Shearwalls

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I spoke with Hardy the other day and this is not correct. Their values are based on testing and their current ICC reports indicate that the drift calculations can be interpolated in a straight line interpolation which is considered conservative to their test data. Hardy (Mitek) has been listening to this thread and I would recommend that they respond to your comments. They asked if it was appropriate for them to participate and I felt it was as long as they were not attempting to sell product. I think they are in a better position to respond to you than I am, but I do know that they recommended an interpolation of in plane drift based on height changes in each frame or panel. Also, as I mentioned, when different panels/frames are used in the same line of shear, the drift/stiffness should be calculated based on relative rigidity.

Shearmax also uses an interpolation for non-standard frame heights. I have not spoken to Simpson or TJ, so others may respond to this.


I will admit that much of this is new information to me as my general notes and frame/panel database was old until my last two projects where I was forced to update my binders and review the revised cyclic testing information subsequent to the 1997 UBC that was released in the last three years. Personally, I would not have mixed frames and in the past and prior to the change of ownership to Mitek Industries and the additional investment they made in panel testing and increasing the product line, it was recommended not to mix aspect ratio’s or frame capacities in the same line of shear. This has changed and the information is indicated in their ICC report. Furthermore, there are some greater restrictions in the Los Angeles City COLA Research Report so some of this is contingent upon what the local municipality will allow. In my area the less restrictive ICC is allowed.


Dennis S. Wish, PE

California Professional Engineer

Structural Engineering Consultant



-----Original Message-----
From: Keith De Lapp [mailto:keith(--nospam--at)]
Sent: Tuesday, May 25, 2004 2:03 PM
To: seaint(--nospam--at)
Subject: Relative Stiffness of Wood Shearwalls


Hey Dennis:  In regards to Hardy Frame panels and frames, the published values for allowable in-plane shear and drift are based on calculations not tests.  Hardy reports that static cyclical tests are used to confirm published calculations which yield a minimum FS of 3.


Keith De Lapp, P.E.



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