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Re: Seismic Design

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I was waiting for someone to bring up wind.  Depending on the
"particulars" of this fictional 20 story building (or not so fictional
maybe), the differences between the building being in high seismic (i.e.
LA) and Chicago may not be that much...at least on a "global" sense.  A 20
story building in Chicago is still gonna have to be design for wind, which
more than likely means that it still have a rather extension lateral
systems such as a moment frame.

Now, the member sizes of the moment frames could be rather similar or
somewhat different depending on the specifics of the building.  There will
certainly be differences in the detail requirements of a moment from in
the high seismic area compared to Chicago (i.e. connection requirements
and other things potentially including member sizes) due to the need to
design for a ductile frame in the seismic situation.

My point is that Gail's problem is not easily solved by just talking about
the lateral system.  A 20 story building in Chicago will still need to
have an extensive lateral system to resist wind loading.  So, to use
Christopher's paper and flat pen analogy, remember the third thing that
you would have to show...blow on the pen and watch it fall...that will
show how wind will cause it to fall laterally.  This can still explain the
difference between wind lateral loads (blowing on the pen to make it fall)
and seismic loading (pulling on the paper to have the inertia of the pen
make it fall).

This is why I did not respond right away...I was dwelling on how best to
respond.  It is not an easy thing to answer.

Regards,

Scott
Adrian, MI


On Sat, 27 Aug 2005, Stanley E Scholl wrote:

> I often find that wind governs on wood frame buildings in CA and I wonder
> why more buildings don't become damaged from wind in the mid-west
>
>
> Stan Scholl, P.E.
> Laguna Beach, CA  (BS/MS U. of Illinois)
> (former SE in Illinois)
>
>
> On Sat, 27 Aug 2005 15:05:58 -0400 gskwy(--nospam--at)aol.com writes:
> Actually, what I want to tell him is how the building would be different.
>
> I.e., how someone could look at the plans for an office building in
> Chicago and know it had not been designed for high seismic forces.   What
> zone is Chicago in now?
>
> Gail Kelley
>
> -----Original Message-----
> From: Christopher Wright <chrisw(--nospam--at)skypoint.com>
> To: seaint(--nospam--at)seaint.org
> Sent: Sat, 27 Aug 2005 13:22:00 -0500
> Subject: Re: Seismic Design
>
>
> On Aug 27, 2005, at 12:26 PM, GSKWY(--nospam--at)aol.com wrote:
>
> > How would you explain to a non-engineer  how a building that has been >
> designed for a place where earthquakes are likely would be different >
> from a building designed for say, Chicago.
> The difference is response to lateral loads. If I wanted to go to no
> trouble at all I'd find a marker pen with a flat end and set it upright
> on a sheet of paper. Show him that it can support a lot of load in
> compression provided there's no side loads. When you jerk the paper
> sideways even a little the pen falls down. That really demonstrates
> kinematic instability and not structural instability, but there's no
> point beating the subject to death. You want to demonstrate the
> difference between gravity and lateral base load response.
> Christopher Wright P.E. |"They couldn't hit an elephant at
> chrisw(--nospam--at)skypoint.com | this distance" (last words of Gen.
> .......................................| John Sedgwick, Spotsylvania
> 1864)
> http://www.skypoint.com/~chrisw/
>
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