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RE: Drift

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Actually, some building codes DO specify drift limits for seismic loading.
I know that BOCA (93 and 96), IBC (2000), UBC (97), and SBC (91 is all I
have access to) have drift limitation for seismic loading.

I am NOT aware of any specified drift limitations in any codes for wind
loading.  I AM aware of some guidelines.  One of AISC's Design Guides (I
believe No. 3: Serviceability Design Consideration for Low-Rise Buildings)
does provide some suggestions/guidelines.


Ypsilanti, MI

On Wed, 27 Jun 2001, Bill  Marczewski wrote:

> John:
> As you probably know, few codes or standards address drift limitations.  I
> work in seismic zone 1 (Denver, Colorado), and we therefore limit our
> building drift to account for a desired building performance due to wind
> loading.  For wind drift on buildings we typically limit those values from
> 0.0015 to 0.0035 times the building/story height, and simultaneously limit
> seismic drift to a value of about 10 times greater (0.015 to 0.035).
> As in the case of your auto dealership, I concur with the previous response
> from another, that the window manufacturer or architect can provide
> information on how much movement the window can tolerate within the frame.
> We often ask this question when designing office buildings to determine how
> much beam deflection to allow.  The typical response is that the window can
> move about 1/2" within the window frame.
> If you have a higher risk of an seismic event than we do here in Denver,
> than I would suggest you consider designing your structure to account for
> drift due to seismic forces with (0.0035)*(H) being your maximum allowable
> displacement.  In doing so, you should have covered drift requirements for
> daily loadings such as wind/gusts, and still have a sound structure after a
> seismic event.
> Bill S. Marczewski 
> Denver, CO 80210 
> bmarczewski(--nospam--at) <mailto:bmarczewski(--nospam--at)> 

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