tornadoes

[Jarhead]

martinjc once bubbled...
FYI - Actually there are many industries (Insurance & Construction being the biggest) investigating the best ways to build 'Fortified' homes. Although efforts have mostly been targeted at hurricane plagued staes (Florida/the Carolinas) as opposed to 'Tornado Alley' areas.

"Fortified" guidelines in North Carolina are designed to better protect homes primarily against high winds and flooding. Construction features include:

* Non-combustible roof materials that also better withstand high winds;
* Stronger connections tying the roof and walls to the foundation;
* Windows protected by shutters;
* Reinforced entry doors;
* Building site and landscaping techniques that reduce wildfire and flooding vulnerability.

I would venture a guess that as insurance costs increase for homeowners in more disaster prone areas - construction features like these will be required to receive premium discounts.

None of these mentioned have much effect on tornado-proofing. The problem with tornados is the air pressure drop as the tornado passes over (or very close by). Since the house can't "vent" (or off-gas ) the air inside fast enough, the house quite literally explodes. Sorta like filling a milk jug with at 100fsw and letting it ascend until the jug can no longer hold the expanding air pressure. (Except today cheap plastice milk jugs just blow the cap off).
You can plan for wind. The Geodisic (spelling) Dome houses along the coast were the only ones that stood up to Opel.
You can plan for flooding. Buildup the ground level, put the house on stilts, build the house somewhere else, etc.
But some only the Seminole summer houses seem to work well for rapid air pressure changes. (Thatch roof, wood floor and NO walls).

Jarhead

 

[ScubaTexan]

I'm not at all sure any building will ever be totally tornado-proof, for the very reasons that Jarhead mentioned. I live in the southern edge of Tornado Alley, and I've seen a funnel cloud form before. It really will make the hairs on the back of your neck stand on edge. Thankfully, this one only came down about a quarter of the way and then went back up, but it was enough to scare the waste outta me (especially watching it from a distance in the press box at Texas Memorial Stadium). I never really saw the one that hit downtown Fort Worth a few years ago, but I was driving in the middle of a bad rain and wind storm along DFW Airport at the same time, so I knew it was in the area. The one in Austin is the only one I've ever seen -- I do not wish to see a repeat performance.

 

[wrecNcaver]

I think many of the posts have addressed the issue of why it is so hard to build structures that can withstand tornados. If you have never seen or been near one you just cannot understand the forces of nature at work. It can go from dead calm to 80 mph winds a heart beat! Having been through two, I do not care to ever experience that again. One of the tornados that hit Van Wert Ohio was an F4. Nothing stands up to a direct hit from that. My heart goes out to all who were effected by this storm and sincere condolences to all who lost loved ones. I have family in the area of Ohio that was hit but we were very lucky in that everyone is ok and only some damage to their home. Thank you to all who have been so sensitive to those effected. That is what makes this board so special!

 

[clive francis]

shellbird once bubbled...
A bit insensive aren't you?

I was in Hopkinsville a few years back and not even brick buildings could survive.

Many people lost their lives, true, they are in tornado alley but how many buildings are actually tornado proof?

I wasn't being insesative, I was asking a question, what are you suposed to do not talk about bad things that happen and hope they never happen again?

if that was the case, then your houses and offices and freeways would get damaged more than they already do due to earthquakes!

you don't have to be in the path to get killed!

and i understand that brick buildings get damaged as well, i saw a bank that got ripped up, the only thing left was the safe and the people that locked themselves inside it, but the people that are on the edges that die need not if houses were built of stronger materials rather than match wood

 

[wrecNcaver]

clive francis once bubbled...


I wasn't being insesative, I was asking a question, what are you suposed to do not talk about bad things that happen and hope they never happen again?.........

I don't think people have a problem with questions being asked, I think it was the way it was phrased. It came off as being rather harsh.

I think most of us on the board find the interaction with people from all around this liquid planet part of what makes it a great board. We don't want to stiffle interaction, just to be more aware of how the structure of the wording can set a tone that may or may not be what was intended.

 

[FredT]

Other things are beyond the pale within reasonable $s. I know I could design a "typical" house suitable for the400MPH winds and >4psi pressure differential typical of a large tornado. I'm also reasonably sure Bill gates and maybe 20 others in the world could afford to buy one. Everyone else would simply be SOL. 4psi x 2800 sq ft = about 1.6 milliion pounds lift. That's one heavy slab needed to hold it down even if slab, walls, and roof are unitized. Assuming a square floor plan and 8' high walls the outer walls will have to withstand a bursting force of over 975,000 pounds, plus a bending moment or torque of several times that. Designing structures for 250 MPH hurricane winds and rising water is a snap compared to tornado proofing a house. The only close to reasonable option for a tornado proof house is to build the entire house completely underground.

I grew up in the middle of tornado alley in NW Oklahoma. The basic rule was that in a tornado warning you got below ground. If you couldn't get below ground you simply rolled over and went back to sleep. If you were above ground and the tornado wanted your ass, it owned it. No further discussion possible. I had a small tornado roll over me while a hunting buddy and I were in a culvert (the only place to hide for about a mile, and we had to run like hell to get to IT!). There wasn't room for the rifles to fit in in there with us. After searching the area for about 6 months while hunting jack rabbits we eventually found 1/2 the stock of Richard's rifle. We never did find anything of mine. Let's just say I know how a champagne cork feels after that little adrenalin rush.

Of course you _can_ afford to build a small strong room in the center of the house as a tornado shelter. This works well untill the clueless east coast native ATF and FBI agents find out about it and determine it is a "bunker". Then you'll need a bulldozer proof and fire proof house!

FT

 

[clive francis]

I'm not saying build a house of solid concrete, but a brick house is likely to fare better to a near miss or even a direct hit of a small one than a wooden house would, and that doesn't take a lot of thinking about or equations to work out.

we get them here in the uk as well, I even saw a report on the news one night that we get more than you guys, it is just that ours are normaly very small and not very destructive.

but when they do hit, and they are big enough to do some damage, the house is still there after, yeah maybe part of the roof is gone, and the windows blown out, but it doesn't look like the after effects of a a bomb

 

[Rick Murchison]

shellbird once bubbled...
A bit insensive aren't you?

Often it is useful to remember that we Americans and the Empire are two peoples separated by a common language.
Clive ain't tryin' to be mean, he's just never been up close and personal with a no-joke tornado alley tornado.
Rick

 

[jselz1]

Jarhead once bubbled...

None of these mentioned have much effect on tornado-proofing. The problem with tornados is the air pressure drop as the tornado passes over (or very close by). Since the house can't "vent" (or off-gas ) the air inside fast enough, the house quite literally explodes. Sorta like filling a milk jug with at 100fsw and letting it ascend until the jug can no longer hold the expanding air pressure.
Jarhead

Damage from pressure differential is now thought to be non-existant. Most damage to structures comes from the debris circulating around the tornado and from the high wind speeds itself. In fact, it is now recommended by the National Weather Service not to open windows but to stay well away from windows.

Even though the central pressure of a tornado has never been measured, current computer models and theoretical research estimates an approximately 100 mb pressure differential or ~880 mb sfc pressure within the tornado which equates to about .9 lbs/square inch, not 4 as elsewhere mentioned in this forum. It is also becoming pretty conclusive that the pressure differential force encompasses a small amount of the total windfield.

Today's houses are built far from airtight and can and will "vent". Even if a structure is "airtight", small and large fast moving debris will ensure that the structure is no longer "airtight" before the low central pressure of a tornado are overhead.

And while I am on the subject of Tornado safety, if caught on a highway please think twice about hiding under overpasses for safety. We probably have all seen the infamous video of the media taking shelter under an overpass claiming the tornado went right over them. In fact, the center of the tornado pass 100-200 meters from their position and was a relatively weak tornado. Current researchers estimate, if in fact the tornado passed directly overhead, windspeeds underneath the overpass structure would increase significantly due to the venturi affect and the people within would not have been able to hold on. In effect, 0% of survival either to being blown away or hit by debris. In the open country it is still recommended to find a low-ditch or even stay in your car and drive away from the tornado at right angles of its path of movement if possible. Please see the Norman, Ok. National Weather Service guidelines at www.srh.noaa.gov/oun/papers/overpass.html for more information on this topic.

 

[Big-t-2538]

plsander once bubbled...
Sirens are good, but they are really designed to alert people who are outdoors. Though I can imagine how loud one must be one block away.

Or you can go all out and get trained as a weather spotter...

-- Peter Sanders, kb0fqd

As a resident of OH, not far from infamous Xenia, when the sirens go, you hear them. You would be surprised how many sirens there are in the area of Dayton, Cincinnati, and their suburbs.

The F4 that hit cincy about 4 years ago hit less than 3 miles from my house. The destruction was eerie and unbelievable. It was random and wierd...one house was levelled, but it's neighbor (50 feet away) was just fine. It doesn't matter if you have a 2 million dollar home, or a 50 dollar shack, the twister doesn't care.

That day changed my life as far as opening my eyes, and I send my deepest sympathies to all those families and friends of victims.