Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: Katrina emergency response - Superdome

[Subject Prev][Subject Next][Thread Prev][Thread Next]
I'm not sure when the dome was built, to be quite honest (I only know the years that VT has attended the SugarBowl, and that's not necessarily a good indicter of historic dates more than a few years old ;-).

If the design was pre-95, remember that the old contours did not include hurricane effects, and there was a factor for hurricane prone regions (1.05?). This factor has been folded into the contours in the 3-sec gust charts. My understanding may be fuzzy - I'm just going from what I remember in the ASCE-7 commentary. Still, I think I'd be hoofin' it inland if I saw a storm of this magnitude coming for me. Also, I didn't realize the previous codes put the I factor on windspeed.  Just makes you realize how much of this we're making up as we go along.

I almost pointed out that NOAA has Saffir-Simpson Categories listed, and 135/145 puts it right in the middle of a Cat 4. And then I read the title paragraph and notices that the speeds listed are for one minute averages, not the peak gust (3 sec). 


Harold Sprague wrote:
Jordan,
It is interesting to note that a 135-145 mph peak gust wind load at the Superdome is the low end of a Saffir-Simpson Category 3 hurricane.  I would not want to have been in there in a Category 5.  The wind pressures for a Category 5 would have been about twice that of a Category 3.

I am glad I am not the one who said the Superdome could withstand a Category 5.  Obviously that was a bogus statement.

The Superdome was also not on the list of pre-approved shelters in the New Orleans emergency response plan.  I notified my FEMA contacts that this was a bad decision when I heard the announcement early on 4 September.

I had also contacted my wind guru buddies who said that it was highly unlikely that the Superdome was designed to resist a Category 5.  Given the codes in use at the time of design, the problems noted with analytical design from Andrew, and the lack of wind tunnel testing at the time of design.  At the time the Superdome was designed, the code used a fastest mile wind of about 105 mph.  This is about 128 mph 3 second gust.  Today's ASCE 7 would have had it designed for about 130 mph peak gust.  Not much difference.

The interesting thing is that the 1.15 importance factor would have been on the pressure today and not on the velocity as it was in the past.  This means that for the superstructure, the more conservative design would be for the ANSI A 58.1.

(v=130 mph peak gust, I = 1.15)
ANSI A58.1 -72 p = 57.2 psf
ASCE 7-02 p = 49.8 psf

The biggest difference in the codes would have been in the cladding coefficients with the ANSI A58.1-72 were much less conservative than the ASCE 7-02.

By the way ASCE 7-02
(Cat 5 v=190 mph, I = 1.15)
p = 106 psf.

I was just comparing stagnation pressures, but that is a pretty quick and easy way to get an overview of the design of the primary structural system.

Regards,
Harold Sprague





From: "Jordan Truesdell, PE" <seaint1(--nospam--at)truesdellengineering.com>
Reply-To: <seaint(--nospam--at)seaint.org>
To: seaint(--nospam--at)seaint.org
Subject: Re: Katrina emergency response
Date: Thu, 08 Sep 2005 10:50:01 -0400


I haven't had a chance to look at the NOAA site, but did d/l the wind
data from FEMA.  Just looking at the two .jpg files was quite
enlightening. If the windspeeds shown are accurate, there should be a
lot of accounting in MS and AL, as the winds were high, but not above
the published speeds in ASCE-7.   It does appear the NO took a direct
hit, and had windspeeds  5-10mi on either side of the storm track that
were 15-20mph above the published 50 year data, though most of that was
inland.  It looks like Katrina was above the design criteria for a
swath about 50 miles wide and 200-300 miles long, thogh most strucutres
should have held except where the winds were 10-15+mph above the
design.



I was interested to note that the windspeed at the superdome looks to
have been 135-145MPH. If you take the worst case speed around there at
150mph and take the square, you get about 1.15x force. Interesting that
for a strucutre of that size, the I factor would have been 1.15.



Thanks to both Jim and Harold for the links.



Jim Hannah wrote:


As an alternative you might also want to review the NOAA surface wind speed
maps from the following source:

http://www.aoml.noaa.gov/hrd/index.html

They have a whole library of surface wind maps for several years including
all of Florida's Hurricanes during last year.

Thanks,  Jim Hannah


----- Original Message -----
From: "Harold Sprague" <spraguehope(--nospam--at)hotmail.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Wednesday, September 07, 2005 3:18 PM
Subject: RE: Katrina emergency response

For those who are technically inclined, you may want to take a look at the
preliminary FEMA wind velocity maps at:
http://www.floodmaps.net/eftp/checkfile.asp?file=FA27_ARA27c.zip

Regards,
Harold Sprague

_________________________________________________________________
On the road to retirement? Check out MSN Life Events for advice on how to get there! http://lifeevents.msn.com/category.aspx?cid=Retirement


******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
* *   This email was sent to you via Structural Engineers *   Association of Southern California (SEAOSC) server. To *   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you *   send to the list is public domain and may be re-posted *   without your permission. Make sure you visit our web *   site at: http://www.seaint.org ******* ****** ****** ****** ******* ****** ****** ********


******* ****** ******* ******** ******* ******* ******* *** * Read list FAQ at: http://www.seaint.org/list_FAQ.asp * * This email was sent to you via Structural Engineers * Association of Southern California (SEAOSC) server. To * subscribe (no fee) or UnSubscribe, please go to: * * http://www.seaint.org/sealist1.asp * * Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you * send to the list is public domain and may be re-posted * without your permission. Make sure you visit our web * site at: http://www.seaint.org ******* ****** ****** ****** ******* ****** ****** ********