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Re: wind gust response -Reply

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Mr. Valley's comments regarding flexible structures are right.  A 30 storey
building with a 5.5 second period can be described as "soft" in terms of
its aerodynamic response to wind.  This will result in many cases in
unacceptable comfort levels in the upper foors due to accelerations,
particularly for a residential building where the occupants cannot
conveniently leave the building during a storm event.  The inertial
component of the wind loads due to the motion of the building as it sways
and twists can also be significant on a "soft" building.  The response to
the local wind environment is quite complex especially for buildings
where there is a high degree of coupling between torsion and sway
modes.  In these situations wind tunnel testing is recommended.

My company provides this service for buildings all over the world and if
you would like to discuss specifics further, you can call or email me
directly.

Scott Gamble
RWDI Inc., Guelph, Ontario, Canada
slg(--nospam--at)rwdi.com
(519) 823-1311

>>> "Michael Valley" <mtv(--nospam--at)skilling.com> 09/27/99 05:49pm >>>
ASCE 7 defines a structure with a lowest natural frequency less than 
1 Hz (period > 1 second) as flexible.  For this class of structure, 
the dynamic response to wind can be significant for both safety 
(dynamic amplification of response) and serviceability (perception 
of motion).  Some guidance for such structures is provided in ASCE 7 
and the National Building Code of Canada.  However, the most common 
(and generally best) approach is to have wind tunnel testing 
performed.

> From:          "Aya-Welland, Ruben A." <RAyaWelland(--nospam--at)tt-cbm.com>
> To:            "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
> Subject:       wind gust response
> Date:          Mon, 27 Sep 1999 16:14:24 -0500
> Reply-to:      seaint(--nospam--at)seaint.org
> Organization:  http://www.seaint.org

> > I have a question:
> > 
> > I have a building whose preliminary fundamental frequency is rather
high
> > (about 5.5 seconds for a 30 story building). I am concerned that under
> > wind loading (no seismic zone) this arrangement will see some
undesirable
> > dynamic response --- in terms of wind gust response...not life-safety
> > issues, but rather, issues of comfort. It is a residential tower. The
> > drifts are not outrageous --- it is more of an issue where the lateral
> > system CR is quite eccentric to the building CM.

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Michael Valley                                   E-mail: mtv(--nospam--at)skilling.com
Skilling Ward Magnusson Barkshire Inc.                  Tel:(206)292-1200
1301 Fifth Ave, #3200,  Seattle  WA 98101-2699          Fax:        -1201