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RE: steel formdeck as shearwall?

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And don't forget the plan aspect ratio of the building.  Seismic can
"control" in one direction is relatively low seismic areas even with long
skinny buildings.  I have had numberous situations in my neck of the woods
(basically seismic zone 0 or 1 per UBC nomenclature) where a building that
was long and skinny was "controlled" by seismic loading in the long
direction (i.e. perpendicular to the short side of the building), even for
one story buildings.

This is mostly similar to what Roger was talking about as "being
controlled" by seismic in my mind generally means that the base shear
value is greater under seismic...when then means that the main lateral
elements would have to be designed by seismic.  One has to be in a
relatively low wind and moderate to high seismic area for seismic to
generally "govern" the out of plan design of walls (or have REALLY massive
walls).

And that does not even get into the fact that even IF the wind loads are
greater, the building still must be detailed per seismic provisions.  Even
if the seismic loads don't "control" the design of the size/strength of
the main lateral elements (or other elements), you must still meet the
detailing requirements for the particular zone (UBC), SPC (BOCA and SBC
and pre-97 NEHRP), or SDC (IBC and NFPA and newer ASCE 7 and newer NEHRP).

And I would second Harold's caution with seismic...even with using the SBC
and not the IBC.  Even though the version of the SBC being used may not be
based upon the 97 NEHRP and thus you don't have to deal with the soil
conditions bumping up the SDC, it is still based upon the 91 or 94 NEHRP
(don't know which).  From my experience, buildngs with relatively high
mass (i.e. precast planks) can result in some rather decent size seismic
loads.  And, more that likely you will still be in a SPC B unless the
seismic "zone" per the 99 SBC is very low in Birmingham.  Thus, even if
the seismic loading does not govern, your building still must meet the
seismic detailing requirements of SPC B.

Granted the IBC could cause a bump in the SDC (equivalent to the SPC for
those not familiar), which would result in more detailing requirements.
And the seismic loads can get greater due to the rho and omega factors, as
Harold pointed out.  Not to mention that the maps from the 97 NEHRP (and
thus 2000 IBC) are supposed to be more "up to date" on pontential seismic
hazards outside of the West coast area.

HTH,

Scott
Ypsilanti, MI


On Thu, 30 Oct 2003, Roger Turk wrote:

> John Jones wrote:
>
> . > I'm not ignoring seismic, I've just yet to see it control in this area
> . > unless it's a hospital, fire station, etc.
>
> Hmmm.  A 6-story building not controlled by seismic somewhere in the
> structure???
>
> I have had colleagues say that in this area (Arizona, Seismic Zone 2) that
> seismic does not control on single story buildings, however, on a small (30'
> X 40' IIRC) single story cmu bearing wall building, I got:
>
> 1. Wind controlled wall design.
>
> 2. Wind controlled roof diaphragm design.
>
> 3. Seismic controlled base shear.
>
> Similarly on a single story cmu bearing wall post and beam showroom type
> retail store, seismic controlled on base shear (and possibly roof diaphragm
> -- the building was quite wide).  I have seen calcs on similar buildings that
> just have the notation, "Single Story --- Wind Controls," and no calcs on
> seismic, but I have not been able to show that with my calcs.
>
> A. Roger Turk, P.E.(Structural)
> Tucson, Arizona
>
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