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RE: Texas Twisters

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Title: RE: Texas Twisters

Dan:

First of all, these were not large tornadoes (probably F1 and F2).  The damage and devastation are due to where they touched down.  These areas, including downtown Fort Worth, have been shut down and sealed with a police perimeter.  They apparently will remain off limits until at least next Monday.

It will take some time to evaluate the structural integrity of the dozens of affected buildings.  My guess is that the mid-rise and high-rise steel and concrete frame office buildings in downtown Fort Worth will ultimately be found to be structurally sound, albeit with some localized damage.  The glass curtainwalls that are common on these buildings failed quickly, like "structural fuses", allowing the wind to blow right through the open building frames.  Once the sail is gone, the forces become manageable.  By the way, Fort Worth uses UBC, with a 70 mph basic wind speed. 

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.

If you are interested, I will provide more information as the facts come out.

Best Regards,

Stan R. Caldwell, P.E.
Dallas, Texas  

-----Original Message-----
From: Dan Vines [mailto:dan(--nospam--at)willettengineering.com]
Sent: Wednesday, March 29, 2000 1:43 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Texas Twisters


Okay all you Texans out there.  News reports show a lot of buildings w/o any
glass left in them, but I haven't seen anything (except residential
buildings) that fell down (or up).  How are the STRUCTURES holding up?

Dan