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RE: wind gust response -Reply

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Thank you for your comments. My situation is a hypothetical one at this
point -- I am still in the process of continual modeling refinements. My
initial question stemmed from a curiosity as to how far people have pushed
things in the past. Of course, a 30-story building with a 5.5 second period
is probably undesirable. But, I wanted to see what the community had to
offer as well -- in terms of experience and professional judgement. The
comments seem to suggest more or less the same types of considerations. Once
again, thanks for the great responses.

> -----Original Message-----
> From:	Scott Gamble [SMTP:SLG(--nospam--at)rwdi.com]
> Sent:	Tuesday, September 28, 1999 9:06 AM
> To:	seaint(--nospam--at)seaint.org; mtv(--nospam--at)skilling.com
> Subject:	Re: wind gust response -Reply
> 
> 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.
> 
> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> 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
> 
>