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RE: Drift Requirements

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The reason that this is not a code requirement is that it is a service issue.

There are many sources of drift limits. Drift limits rarely are a problem for a 3 story residence. If you want a good source of information, I would suggest, AISC, Designing Steel for Serviceability, Lecture 4, Contol of Lateral Drift. It includes a 1993 First Quarter, AISC Journal artical by Griffis, Serviceability Limit States Under Wind Load. AISC's Charlie Carter may be able to tell you if this is available. Basically most respondants to an ASCE survey used L/400.

According to some notes I had from Joe Colaco and Mark Fintel, use a limit of 19 mili G's for residential for a 10 year wind. There is also the Weiskopf & Pickworth Deflection Index of 0.0025 for a residential building.

Regards,
Harold Sprague


From: "G M" <newabhaju(--nospam--at)hotmail.com>
Reply-To: <seaint(--nospam--at)seaint.org>
To: seaint(--nospam--at)seaint.org
Subject: RE: Drift Requirements
Date: Mon, 26 Jul 2004 16:52:37 +0000

List Members:

I am working on a renovation project. The building is a 3 story residential structure. The project consists of converting the structure to a commercial/residential structure. Project involves both raising the first story (clear story height of 16 feet) as well new addition to the side. The building is long and narrow (25? wide x 100 feet) so that wind load controls design (load perpendicular to the long side). Because the client?s requirement, there are no interior shear walls. The lateral load resisting system consists of a series of moment frame. The question I have for the list is regarding the moment frame drift requirements.

The drift requirement is spelled out in section 1630.9 of the UBC/CBC. However, this equation does not really apply as it includes inelastic deformation, which I do not want to see for wind driven design. The code is silent with regards to drift requirement for wind driven design. How have members of the list tackled this problem?

Gautam Manandhar

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