ECN Forum Forums General Topics of the Trade General Discussion Area OT: Tornadoes.

32VAC, almost no homes are "timber" construction. Rather, they are "stick" or "balloon" frame .... light wood members, with gypsum board facing.

This method was developed so that lots of homes could be built fast, cheap, with minimally skilled workers. It has far surpassed expectations, and continues to be the method of choice.

Even where you see a brick home, the brick is usually just a thin veneer.

Storm shelters are not required, nor are they often designed into the home.

"Tornado Alley" sounds like a limited route, but the description actually applies to an area at least half as large as Australia.

As flimsy as this construction may sound ... and as dramatic as the pictures appear ... the USA actually has far fewer casualties from natural disasters than similar events elsewhere. Where a similar storm just a few miles off our borders will claim hundreds of lives, we lose only a few .... and suffer much less secondary loss (fires, disease, etc) as well.

Short of an areodynamicly designed dome building made of poured steel reinforced concrete, steel blast doors, and with earthen burms all the way around it - anything else is a sitting target for a tornado.

What gets me is that it seems every 4th one misses the trailer parks? So it would make sense not to live in anything that showed up on wheels.

Timber construction as in wooden frames & wooden sidings is what I was referring, forgot about the different terms across the Pacific Ocean

I find it funny that the brick construction is a "dying art" in the U.S. , most homes here are brick construction for insulation & termite (white ant) resistance.

lumber is cheaper than concrete, which seems to be the only material capable of withstanding the force of the powerful F5s...that or blocks that are filled with mortar or other aggregate..like concrete !.

there is nothing where I live that requires reinforced rooms or bunkers..not enough of a threat from twisters

one structure our little storm destroyed was made of block, and three walls and the roof and the boat inside are gone.

Tony

Thank You,

.....Tuscon ? Hangar ? good grief, what a wonderful shelter huh ?

I want to hear the lightning story

..oh man look at the time ! I gotta run, catch up with ya later

BOHICA..

Florida leads the pack with wind resistant construction but we only design for 130-150MPH winds. These F-5s get up over 200.
Basically the wind code plan is based on tying the roof to the foundation making a continuous matrix in the walls. In stick built every upright framing member has a steel strap that connects it above and below from the straps coming out of the footers to the straps going over the trusses. These are not those little "twisties" either. They are straps with about 15" of connection to the wood and about 30 nails.
In CBS construction (Concrete Block & Stucco), more common, you have a #5 rebar tied to the footer steel (2 #5s) coming 4' out of the footer every 4 feet on a running wall and in every door or window opening. This gets tied to another #5 that comes down from the top. There are 4 #5s that ring the top 2 courses of block which get poured solid along with all the "dowel" cells you have rebar in. This creates a matrix that makes a very tough building.
You can see the footer and dowel cell steel in my "ufer" pictures.

http://members.aol.com/gfretwell/ufer.jpg

They paint the cell with the Ufer in green it so some bozo doesn't pour it solid. That still happens about 5-10% of the time. The AHJ makes them chip it out, down to the steel for the ufer.

Once you get above 120mph, it becomes very difficult to build 2x4 homes because of the sheer magnitude of the forces involved- on a typical home in 120mph winds, you're looking at about 500lbs of uplift force on every joist-wall connection point to keep the roof from being torn off, which has to be transferred through the wall into the foundation to keep the entire house from taking off like an airplane. And laterally, there's 15-20 pounds per ever square foot of force exerted on exterior walls, doors and windows. It's counterintuitive, but the worst pressure is not on the windward side of the structure, but the leeward side where there is a negative pressure created- the differential pressure is enough to tear sheathing right off a wall.

One problem in particular is garages- that little stub wall framers love to build flanking garage doors to keep the garage as small as possible offers next to no strength when that wall is in shear. A storm with 120mph winds will exert leverage forces on that wall section can exceed 2 tons of force trying to pull out on the anchor bolts and rack it out of true and just push it right over, collapsing the 2nd floor right on top of the 1st.

Wood 2x4 construction is cheap in the US which is why it's so prevalant- cheaper than masonry or steel frame- except for Florida. In florida, you can still build multistory wood homes, but the building codes are so restrictive and techniques so expensive that single-family masonry homes might just as well be required. (Helps with termites, too!) If you get out to places like Guam where they build to exceed 150mph supertyphoons, the buildings are often solid concrete with concrete roofs and start to actually look like bunkers! The lesson here isn't that masonry is necessarily any better, but that US is smarter than the rest of the world and farms trees!

As a resident of "tornado alley" (Kansas) I might offer a couple more comments. As Steve Fehr mentioned, one reason 2x4 construction is so popular is that its cheap compared to other construction methods. But I want to dispell the idea that USA homes are cheap.....at least to build new. The cost of construction and real estate has risen so much over the past few years that the cost of home construction is beginning to make home ownership unattainable to a great many people. If this country built with a more expensive building method, I would imagine homeownership would be out of reach for the majority of the population.

As far as basements or storm shelters go, most homes in tornado alley have basements where ground conditions permit them to be built. In some areas, either shallow groundwater or rock formations make it unfeasible to build basements. Some new homes around here have concrete "safe rooms" in the basements, with steel doors on them. In an F-5 tornado, even a basement may not save your life. In the Greensburg, Kansas tornado, which wiped out the entire town, the only structure left standing was the grain elevator.

You're welcome Tom. Haven't chatted with you for a while..

Yeah, it was only well after the fact that we all realized how dumb it was to keep going in that hangar..not a good shelter against a twister. It had formed with virtually no warning though. I have since learned to trust my feelings and take shelter if I have any doubts.

Though here in So. Cali. it's earthquakes that are an issue.

The lightning incident was very scary...I was team leader on the End-of Runway (EOR) recovery crew..I was connected to the returning aircraft with a wired comm set as my crew safed up the A-10's gun and any unexpended ordinance. The usual afternoon monsoon storm had moved in, but a lot quicker than we had expected. We only had 8 aircraft to recover (four on the ground already parked and we were working them, and four in the air) and the tower instructed us to recover them ASAP, as they had detected no lightning within 3 miles. (3 miles was the limit, any flashes in that range and ALL ground work stopped.)

It was raining pretty hard at EOR, and we were on the next-to last of the birds on the ground. A tremendous boom, blinding flash and all three of us crew were knocked to the ground..and we all felt something, not like a regular electric shock but we all knew what had happened. The pilot of the plane I was connected to kept asking if we were o.k. I told him yes and had him key the radio so I could have a chat with the tower.

We sent the last plane of that group and the four that had just landed back to the ramp "hot".

The tower supervisor got called on the carpet and issued a letter of reprimand.

The base weather office determined that the lightning struck one of the landing system lights about a thousand or so yards from the ramp we were on.

So I think my crew and I had discovered what "step potential" can do. And we were darn lucky too.

jeezus. darn lucky is right. that is one cool story though

the pilots had to sit in their planes during the storm ?