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RE: Wind drift

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Seismic performance is intended to be a yielded non-linear response.  Proper seismic performance (collapse prevention) requires a limit of the lateral drift.   
Wind performance is in the linear range.  Lateral drift requirements (other than P delta) are serviceability issues only. 

Harold Sprague

From: charles(--nospam--at)
To: seaint(--nospam--at)
Subject: RE: Wind drift
Date: Wed, 7 Nov 2007 08:07:30 -0800

How can deflection from wind forces be different from deflection from seismic forces?  Deflection is deflection.


I would think that any excessive deflection, no matter what the source, would eventually cross the threshold from serviceability to life safety.


And I think that once the IBC starts telling me how to design for wind forces, then the establishment of some upper limits is the logical next step.


But there I go using that “logic” word again… ß Sorry my caffeine hasn’t kicked it yet.



From: Scott Maxwell [mailto:smaxwell(--nospam--at)]
Sent: Thursday, November 01, 2007 5:51 PM
To: seaint(--nospam--at)
Subject: RE: Wind drift


It makes a lot of sense that the IBC does not address it.  It is a serviceability issue, not a code/life safety issue.  That does not mean that there should not be limits.  There should be a limit that you check against, but the IBC is a life safety code...not a catch all code.  Thus, it is up to other sources to establish wind drift limits.





Adrian, MI

-----Original Message-----
From: Casey K. Hemmatyar [mailto:khemmatyar(--nospam--at)]
Sent: Thursday, November 01, 2007 7:49 PM
To: seaint(--nospam--at)
Subject: RE: Wind drift

Although IBC 2006 does not address the wind drift issue but it  does not make sense to me if there is no limit on Wind Drift.
There must be a Drift limit to consider Deformation Compatibility/P-Delta effect and glazing/partition/non-structural components' tolerance.
Additionally In tall building the perception of motion due to wind becomes a design issue.

As far as my serves Canada and UK use L/500 and L/600 respectively for a 10 year return period for serviceability.
Casey (Khashayar) Hemmatyar, SE
Private <k(--nospam--at)>

From: Mark Deardorff [mailto: mark(--nospam--at)]
Sent: Thursday, November 01, 2007 3:51 PM
To: seaint(--nospam--at)
Subject: Wind drift


I hate to ask a stupid question. I have only been designing structures since 1976 so senility may have crept in to cleanse my brain from most information and memories. Nevertheless, I have never known of a limitation on wind drift. Once, I think in the Blue Book commentary, there was a mention of it but nothing official. Please fill me in.




Mark E. Deardorff, SE
R & S Tavares Associates, Inc
9815 Carroll Canyon Road
Suite 206
San Diego, CA 92131
Phone: 858-444-3344
Phone: 209-863-8928


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