JedClampett
Structural
Not an engineering disaster, but there's going to be engineering fallout.
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Hurricane Harvey 17
- Thread starter JedClampett
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- #81
JedClampett
Structural
You guys (or gals) are right about water pressure. But there is no way those buildings are sealed. One the water is about 6 inches high (and I'm probably being generous) it will leak in through doors and under the siding. This equalizes the water pressure. And unless the water is moving extremely fast (> 8 ft/sec) the velocity pressure is less than 30 psf. That speed would be unusual for urban flooding.
The pictures I see are not from engineers. But they look more like wind failures. I think dik is on the right path. The fasteners fail and the siding or roof ends up supported by a whole different mechanism than it's designed for. One girt or purlin might be taking three times the tributary area it was planned for. When it fails, it twists the main frames and that's all she wrote.
Note that the wood framed commercial buildings and residences are even worse. You've got some guy with a nail gun shooting nails blindly into a 1 1/2 inch wide truss or rafter. Even if they were designed correctly, what's the odds that they're dead center in the 2 by? Some of the roofing sits on my favorite, OSB. The advantage of this besides its price is, when it gets wet, you can spoon it off.
When Florida had hurricane and wind failures they beefed up their codes. Any chance Texas will follow? And by the way, Florida is thinking about relaxing their codes.
The pictures I see are not from engineers. But they look more like wind failures. I think dik is on the right path. The fasteners fail and the siding or roof ends up supported by a whole different mechanism than it's designed for. One girt or purlin might be taking three times the tributary area it was planned for. When it fails, it twists the main frames and that's all she wrote.
Note that the wood framed commercial buildings and residences are even worse. You've got some guy with a nail gun shooting nails blindly into a 1 1/2 inch wide truss or rafter. Even if they were designed correctly, what's the odds that they're dead center in the 2 by? Some of the roofing sits on my favorite, OSB. The advantage of this besides its price is, when it gets wet, you can spoon it off.
When Florida had hurricane and wind failures they beefed up their codes. Any chance Texas will follow? And by the way, Florida is thinking about relaxing their codes.
Jed,
Your windspeed comment is a concern I have have with the code changes. It is my understanding that Rockport got up to 130 mph sustained winds.
Based on ASCE7-10: ULT 3 sec gust varies between 136 and 156 mph in Rockport. (147 for Risk Cat II)
Based on ASCE7-05, ASD 3 sec gust is 130 mph
Based on ASCE7-93, fastest mile (ASD) is 93 mph
The calculated pressures are relatively close to each other.
This has been one of my pet-peeves with these code changes. Clients can't comprehend that 147 mph now is the same as 130 mph a few years ago, which is the same as 93 mph before that. What design wind speed is the media using when they say winds are higher than code requirements???
Your windspeed comment is a concern I have have with the code changes. It is my understanding that Rockport got up to 130 mph sustained winds.
Based on ASCE7-10: ULT 3 sec gust varies between 136 and 156 mph in Rockport. (147 for Risk Cat II)
Based on ASCE7-05, ASD 3 sec gust is 130 mph
Based on ASCE7-93, fastest mile (ASD) is 93 mph
The calculated pressures are relatively close to each other.
This has been one of my pet-peeves with these code changes. Clients can't comprehend that 147 mph now is the same as 130 mph a few years ago, which is the same as 93 mph before that. What design wind speed is the media using when they say winds are higher than code requirements???
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JedClampett
Structural
I looked at the weather service website. For Port Aransas, the fastest gust was 132 mph. I'm not sure who said that the winds exceeded code design, but reporters are very bad at anything regarding numbers.
As hawkaz said, the Port Aransas (I'm sure Rockport is about the same)ASCE 7-10 mapped values range from 138 mph to 158 mph, depending on the design category.
I think what we structural engineers are going to find is that there are details that are design critical, but are not designed. For Hurricane Andrew, is was the gable ends, These fail, and start stressing our critical members. Mother nature is very good at finding the weak link.
As hawkaz said, the Port Aransas (I'm sure Rockport is about the same)ASCE 7-10 mapped values range from 138 mph to 158 mph, depending on the design category.
I think what we structural engineers are going to find is that there are details that are design critical, but are not designed. For Hurricane Andrew, is was the gable ends, These fail, and start stressing our critical members. Mother nature is very good at finding the weak link.
HamburgerHelper
Electrical
JedCampett,
I purchased a stucco home in Houston and was very leary and still am some about it due to the humidity we have. The issue with stucco is that it doesn't breath well. Planked siding allow breathing. You never want to seal up a building. Newer stucco homes have venting put in the stucco to help facilitate breathing. Brick I believe has weep holes for breathing as well.
I purchased a stucco home in Houston and was very leary and still am some about it due to the humidity we have. The issue with stucco is that it doesn't breath well. Planked siding allow breathing. You never want to seal up a building. Newer stucco homes have venting put in the stucco to help facilitate breathing. Brick I believe has weep holes for breathing as well.
Properly designed and constructed homes that are nearly completely 'sealed' can be done and the Canadian codes are pushing for this condition from an energy point of view. Gone are the days of leaky walls, doors, windows, etc.
There have been huge social changes over the decades... more moisture generated in homes, more time spent in homes, etc. The problem is getting more complicated from the inside and the outside...
Dik
There have been huge social changes over the decades... more moisture generated in homes, more time spent in homes, etc. The problem is getting more complicated from the inside and the outside...
Dik
Houses that don't breathe are ripe grounds for molds and fungi; it's a pretty well known phenomenon that houses are like one-way moisture traps.
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! faq731-376 forum1529 Entire Forum list
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! faq731-376 forum1529 Entire Forum list
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- #87
KoachCSR:
The info contained in your link:
has more information. If I were the insurance companies, based on the new information, that was not acted on, I'd be refusing coverage to at least the City of Houston. It would be a hardship to refuse coverage to the residents... but, they could start up a class action...
Good post...
Dik
The info contained in your link:
has more information. If I were the insurance companies, based on the new information, that was not acted on, I'd be refusing coverage to at least the City of Houston. It would be a hardship to refuse coverage to the residents... but, they could start up a class action...
Good post...
Dik
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- #91
JedClampett
Structural
dik, if you think the insurance companies are worried about a "hardship to refuse coverage to the residents" you're sorely mistaken. They'll drop their clients in a millisecond if it's costing them money. And they really hate flooding or windstorms, because the damages are extensive in an area. Because of this, I'd say the insurance companies have the one and only hammer to get things to change. They can refuse coverage until meaningful change happens. As I said above, this is how the building code got improved in Florida. Unless you're a psychopath, you're not going to build or move to a place that is uninsurable. And that hurts the real estate market. Until now, the voters are apparently not interested, so politicians get re-elected based on unlimited sprawl platforms.
From this observer, it seems like until Houston starts condemning and tearing out houses in the flood plane, creating retention areas and encouraging vertical growth, rather than horizontal, this flooding will repeat.
From this observer, it seems like until Houston starts condemning and tearing out houses in the flood plane, creating retention areas and encouraging vertical growth, rather than horizontal, this flooding will repeat.
JohnRBaker
Mechanical
It appears that in addition to Irma, there are TWO additional tropical storms that are being watched as potential hurricanes; Jose, coming up behind Irma, and Katia, forming at the Southern edge of the Gulf of Mexico:
John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:
The secret of life is not finding someone to live with
It's finding someone you can't live without
John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:
The secret of life is not finding someone to live with
It's finding someone you can't live without
John those are all hurricanes currently. The deluxe "triple pack"!
Keith Cress
kcress -
Keith Cress
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![[flip]](/data/assets/smilies/flip.gif "[flip] [flip]")
HamburgerHelper
Electrical
The people of Houston didn't push on their officials to raise taxes to pay for a solution. Why is the city at fault for basically doing what the people wanted? Near no one was pushing for an expensive mitigation 3 months ago. The fact that a report shows that this could become a problem doesn't change anything, in my opinion. Anyone who has lived in Houston for the last 10 years knows that the flooding was getting worse. It isn't like people weren't aware that this was becoming a problem.
HamburgerHelper... This is getting a little far off track.
The city, being part of a government structure, has an obligation to look after the long term best interests of the people... Houston failed miserably. Like the Texas legislation where a chemical plant is not obligated/required to provide data on the chemicals on site; this IMHO, is not conscionable.
I'm certain, if I were an insurance company, I would be refusing coverage based on Houston's prior knowledge... it clearly falls under my 'definition' of negligence, "Negligence arises when one person owes to another a duty of care and breaches that duty, and reasonably foreseeable harm arises as a result of that breach."
Dik
The city, being part of a government structure, has an obligation to look after the long term best interests of the people... Houston failed miserably. Like the Texas legislation where a chemical plant is not obligated/required to provide data on the chemicals on site; this IMHO, is not conscionable.
I'm certain, if I were an insurance company, I would be refusing coverage based on Houston's prior knowledge... it clearly falls under my 'definition' of negligence, "Negligence arises when one person owes to another a duty of care and breaches that duty, and reasonably foreseeable harm arises as a result of that breach."
Dik
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- #99
The flooding of Houston is a problem of Houston's own making. They elected a pro development mayor in the 90's, Bob Lanier, whose friends & supporters are responsible for much of the flooded housing stock. He was mayor until 1997. Highway projects were his pet passion because they make land worth more. This all needs to be considered against Federal Highway Funds appropriations and the readiness of any State's highway project to utilize those funds. Perhaps the reason to move forward on the I-10 in spite of the Flood Assessment was because any reconsideration of the project would have knocked Houston out of the running for a lion's share of Transportation dollars. Reading Houston politics is engrossing but you'll want to take a shower when you are done.
I believe flood insurance is only sold by FEMA, and it only covers the structure, not the contents.
So why are we talking about insurance companies?
So if FEMA deems the land uninsurable no one can get a normal loan on those homes.
Now if your house were to burn down, that is a different story.
Flood-plain land is still usable, but not so much for housing. It would be a real good for selling boats, a race track, pasture land, etc.
A class action suit on the developers is an idea that can happen.
So why are we talking about insurance companies?
So if FEMA deems the land uninsurable no one can get a normal loan on those homes.
Now if your house were to burn down, that is a different story.
Flood-plain land is still usable, but not so much for housing. It would be a real good for selling boats, a race track, pasture land, etc.
A class action suit on the developers is an idea that can happen.
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