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Re: Texas Twisters

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> From: "Caldwell, Stan" <scaldwell(--nospam--at)halff.com>

> There are 6 to 8 industrial buildings just west of downtown, however, that
> have fully collapsed and are currently the object of an intensive search for
> survivors.  These buildings appear to have been one story reinforced masonry
> and/or concrete tiltwall construction with open web steel joist roof framing
> and steel deck diaphragm roofs.  Now they are piles of rubble.  My guess is
> that the overhead doors blew open and the roof decks then failed in uplift.
> At that point, the decks could no longer serve as diaphragms and the walls
> lost their lateral stability.  In the next few days, we'll see if I'm right.

> Also, as you might imagine, buildings with standing seam metal roofs also
> fared quite poorly, including a large state office building in Arlington.

I'm not completely surprised by your matter-of-fact assessment of
standing seam roofs. Unfortunately, it's one of those comments that
paints with a very broad brush.

>From testing that I have done, there are certain types of standing seam
roof that are more prone to wind damage than others. Of course, the
failure mode that you describe is completely true for many buildings
except that damage to a ssr should not lead to progressive structural
collapse as you described for masonry/tilt-up buildings which rely
completely on the diapragm - and we see the result.

There are good metal roofing systems with poor implementation (design,
detailing, erection). There are some roofing systems, which tend to be
targeted to the architectural market, that need serious help at the
project design/detailing stage to avoid failure during wind events.

Both the ssr and tilt-up designers will be able to point to the building
codes and prove compliance to the letter. So much for codes ....

I wonder if some of the perceptions are due to the fact that huge sheets
of metal can blow for miles whereas other materials may drop much closer
to the point from which they were plucked. It makes good press to show a
helicopter view of an open roof or cladding wrapped around a tree a mile
from its source but a failure in any roof is still a failure.

I expect that the area will be crawling with metal building
representatives (among others) looking for examples that came through
the event unscathed. The ads in the industry magazines will appear very
quickly.

-- 
Paul Ransom, P. Eng.
Civil/Structural/Project/International
Burlington, Ontario, Canada
<mailto:ad026(--nospam--at)hwcn.org> <http://www.hwcn.org/~ad026/civil.html>