Well - I guess I just can't see the dome getting blown away. Most major structures are designed for standard wind in the wind zone and NO is very close to the coast so at least a 120 (the article says 130) mph wind would have been used. In addition - the shear size of the dome and the way its built would suggest that the overall stability of the dome isn't in question - as the primary wind would average smaller than the peak hot spots (component wind)that usually cause so much damage in homes and smaller structures.
In addition - being within an urban setting, the wind speeds are knocked down from the weather service speeds which are taken at specific "clear" zones at a set height above the ground - so the real wind hitting the dome wouldn't be the 165 mph speeds that you hear bandied about on the news.
Good point but remember we design for 3-second gust not sustained wind speed. So lets say the winds reduce to 150mph sustained when it hits New Orleans. This translates to a 3-second gust of around 190mph.
The speed can't be at any altitude, especially that high. I think this chart is a ground level speed as they compare this to a giant force three tornado that last for hours instead of seconds.
I know that in IVAN I was measuring sustained wind speeds in excess of 120 MPH for several minutes at 16 ft. The wind never dropped under 100 MPH for over 1 hour, that’s all I could measure because my anemometer went away. I was told, never checked, that this the standard height for a wind gauge.
The Superdome was designed and built when it wasn't surrounded by tall buildings. It was the highest thing around. There was some discussion during the construction of the Dome as to the actual design speed. I know we had to upgrade the plant site form 100 MPH to 135 MPH. Apparently 100 MPH was the accepted standard for many years.
Would they have done wind tunnel testing to develop the winds loads on this building due to its unusual shape? If so, it would be interesting to know what wind speed they used.
In Australia, we get some pretty severe Category 5 tropical cyclones on our mid- and north-west coast. Structures that have a special post-disaster function are designed for an ultimate limit state wind speed of up to 99m/s (221mph), based on an annual probability of exceedance of 1/2000.
Yes, but how you accurately perform a wind tunnel test on a structure back in the 1970's with new structures now adjacent to the Superdome? The necking of wind between buildings can really increase pressures on adjacent structures. I just heard on the news that the occupants inside the structure can see some daylight thought the Superdome’s roof.
Great discussion. Funny how we engineers ponder these things. This morning I found myself wondering just how many older structures could sustain a category 4 or even a 5 hurricane.
I've never designed a dome, but having visited a few I would still think that the dome would be a safer place to go than most structures. If it's like any of the ones I've seen it has huge concrete beams and columns inside, which I would think would be great things to take shelter under/beside in the event of a hurricane. But I wouldn't want to be out in the middle of the dome with just the roof over my head. I would think that would be the weakest link.
I'm curious to see how much damage it does sustain.
Lets think about this a second. Obviously someone has given the city the ok to put people in the superdome. I would find it very odd that they would pile thousands of people into an unsafe structure.
Lets also not forget about all of the redundancy of a building of this caliber. Obviously this structure has a specified lateral supporting system. But factor in all the other structural elements that aren't accounted for. Plus all the factors of safety and so forth. I've seen alot of unsafe structures (unsafe according to the building code) sustain substantial lateral loads.
I don't know how the dome exactly works, but it sounds like a couple of roof panels may have blown off. I can't imagine the wind "ripped out a chunk of concrete". Yeah, they'll get wet, but it doesn't seem like a real structural problem.
"Lets think about this a second. Obviously someone has given the city the ok to put people in the superdome. I would find it very odd that they would pile thousands of people into an unsafe structure."
If you read the articles relating to the discussion, the problem they have is there isn't anywhere else that's any safer. Any place low will flood, and other buildings aren't designed for any higher wind speeds than the Superdome. Whether it's safe is immaterial, it's still safer than the alternative.
I heard that they were putting people under the upper seating overhangs, so any roof debris or rain would fall on the football field, not on the inhabitants. So essentially, they are covered with hard material all around and the small holes in the roof panels wouldn't pose any significant risk.
If you look at the pictures of them, in yahoo, for example, they were actually sitting on the field, but after some of the roofing came off they moved them to safer areas. Who wouldn't prefer sitting on soft grass to hard seats and floors? But still, if it were me I would have felt uneasy on the grass under the main roof.
I read an account that stated that they had to move the people under the damaged areas, but I don't necessarily believe anything I read in the news media without some other type of verification.
The superdome was built after Betsy and Camille, both worse storms than this one as measured by low pressure measurements, so I would imagine that it has a pretty stiff wind loading rating in its design.
