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RE: Max. Allowable Story Drift per IBC 2000?

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Harold,

Interesting comments on the Pre-engineered Metal Building Industry.  I was a
facilities engineer for Lockheed and we installed a lot of these buildings,
all based on liberal wind drift allowances from MBMA.  As a result of the
these structures "working" in the wind, the screw holes in the steel sheet
siding quickly became elongated and the things leaked terribly.

Bob G.

-----Original Message-----
From: Harold Sprague [mailto:spraguehope(--nospam--at)hotmail.com]
Sent: Wednesday, October 13, 2004 12:24 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Max. Allowable Story Drift per IBC 2000?


David,

The assumption " From what I can gather, the limits from Seismic story drift

are applicable to Wind loading." is not correct.

Seismic design assumes nonlinear performance for the design ground motion.  
We (code writers) craft linear solutions to provide a SWAG about nonlinear 
seismic performance in our building codes.  Wind design assumes a linear 
response for the service loads.  The seismic design section needs to control

the lateral drift to achieve the nonlinear performance required.

The building codes are focused on life safety.  Serviceability is generally 
not a consideration for global structural performance for either seismic or 
wind.  There are Serviceability recommendations available depending on the 
occupancy and structural materials, but they are not building code.

Prefabricated metal building manufacturers are all over the map on this one.

  At the low end they will use h/30 for a 10 year wind.  This will result in

a lateral drift of 12" on a 30' eave height building.  Some will use h/100.

The only thing that the MBMA requires is that lateral drift is to be 
calculated.  There is no required limit.  The MBMA even cautions that some 
clients will get upset when the lights sway during a wind storm.

There is no commonly used drift limit for low rise buildings.  I would 
advise that you read AISC Design Guide 3 for some "recommendations".

Regards,
Harold Sprague




>From: David Topete <davetopete(--nospam--at)yahoo.com>
>Reply-To: <seaint(--nospam--at)seaint.org>
>To: seaint(--nospam--at)seaint.org
>Subject: Re: Max. Allowable Story Drift per IBC 2000?
>Date: Wed, 13 Oct 2004 10:24:34 -0700 (PDT)
>
>From what I can gather, the limits from Seismic story
>drift are applicable to Wind loading.  I guess it
>would fall under the "Wind and Seismic Detailing"
>section, IBC 1609.1.5.
>HTH.
>David Topete, PE
>SF, CA
>--- Daniel Boltz <dboltz(--nospam--at)1st.net> wrote:
>
> > I cannot find an allowable story drift for wind
> > loads in IBC 2000.  I have a Steel Design Handbook
> > that states one-story buildings can have H/300 for
> > drift and multi-story buildins should have less than
> > H/400 for drift.
> >
> > IBC 2000 sets maximum story drifts per Table 1617.3
> > for Seismic Loads, but nothing for Wind Loads.  The
> > discrepency is that the maximum drift per IBC is
> > H/480 for all buildings unless the connections are
> > designed to account for more drift.
> >
> > What is commonly used for allowable story drift of
> > one-story and multi-story buildings?
> >
> > Thanks.
> > Dan

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