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Re: Seismic Design

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Mark,

If I am out at the project sight after the structure is up, then how do I
"see" the 2" pitched spiral steel?  ;-)  Just had to give ya a little
"guff" on that.

Beyond that, I would say that some of you items might be present in
non-seismic (or to be more accurate minimal seismic) areas.  Spiral
reinforced columns, while not wide spread, are used in low seismic areas
as well.  You will also see eccentric bracing in low seismic
areas...admittedly the eccentric area will likely look a lot different in
such areas when compared with high seismic areas (all the detailing
requiremetns to obtain the ductility).

While I agree that there will be a lot of differences in the connections
between something governed by seismic vs. something governed by wind, I am
not sure how much a "layperson" will notice.  There will be somethings
that they will notice (i.e. the ductile detailing requirements for
eccentric braced frames for seismic is pretty obvious as in reduced beam
sections), but many things that may not.  And to some degree, things like
dampers and base-isolation a likely to be relatively rare (I could be
wrong).

My point is that I doubt that in general a "layperson" is gonna notice the
difference between a moment connection for wind and a moment connection
for seismic.  They might, but it is also highly likely that they will not.

Regards,

Scott
Adrian, MI

On Sun, 28 Aug 2005, Mark Johnson wrote:

> For me, the difference is that buildings in seismic
> country have to be able to move.  Even if the building
> is "governed" by wind.  The word "mechanism" seems
> appropriate.
>
> Many differences aren't all that hard to see.  No
> mater how big the wind force in a non-seismic area,
> you won't see dampers, base isolation sliders, cables
> that attach overpass beams to piers so that the beams
> won't fall off the piers.  In steel frames, you won't
> see reduced beam section connections, gusset plate
> geometry that lets the plate bend without tearing.
> You won't see any EBF (eccentrically braced frames)
> that are meant to go plastic and move in fairly
> predictable ways.  You won't see ductile concrete with
> spirals with a 2" pitch, or heavy boundary elements on
> concrete shear walls, all designed to let them move
> and crack without coming down.  And this is just the
> stuff you can see without a calculator which would
> highlight things like connections and certain critical
> structural components.
>
> Inside buildings in seismic areas you see water
> heaters, shelves, etc. strapped to walls, cupboard
> doors with special latches.
>
> My two cents.
>
> MJ
>
>
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