Tornado Alley

[Electron Tornado]

Just wondering - with the recent tornados in and around Oklahoma City, does anyone know how the folks at Keeley fared?

Hope all's well.

[R.G.]

Keeley is (or was) near Edmond, which is on the north side of OKC. Moore is on the south side. I have kin about 10 miles west of Edmond, and they were OK except for the usual thunderstorm damage.  I say "usual" accurately. My brother-in-law has had his roof replaced by insurance for storm damage three times in 5 years.

Moore appears to be a bad place even for tornado alley. This suburb of OKC has had three major tornados through the town since 1993.  It's possible that Mother Nature is trying to tell us something about putting houses there.

[Mark Hammer]

My son is a civil engineer, and while chatting yesterday, I mentioned that they probably spend little attention during their training to the sort of winds that occur in tornados.  He went on about wind shear, and wind tunnels, and how they test roofs, but at the end he had to admit that they had never discussed how to design a building in anticipation of air forces that pull roofs upwards, rather than blow at them sideways.  Kind of an important gap in their training, I think.

Sometimes it's worth it to put in the extra protection diode, isn't it?

Incidentally, PAiA is also in Edmond, so I gather they're alright too.

[PRR]

> how to design a building in anticipation of air forces that pull roofs upwards

A quick skim of the residential IBC (I recall BOCA was similar) requires computation of up-lift on all sides.

In quiet areas, like here, 70MPH (rarely), we can generally presume a few large nails rafter-plate, and the nail-schedule on the sheathing, will hold.

Down to FLA they are supposed to compute to 80MPH-110MPH (depending on exposure) and there are very detailed factors in Code and often suggested detailing from material makers/promoters(*). Good FLA homes are full of steel straps, have limited fenestration to keep ample sheer-wall effect, before they get to garage doors that don't pop-off and fly.

"Wind-Load" ASCE-7-02 is widely referenced by Codes. You are supposed to pay for it, but I have a partial PDF so it's around the webs.

(*) The Wood Frame council has documents like
http://www.awc.org/pdf/WFCM_120-B-Guide.pdf (4MB PDF)
with lots of strapping details.

Nothing about 300MPH wind. Recall the pressure is square of speed, so a tornado sucks 10 times harder than a near-hurricane wind which would terrify me and my roof. AFAIK there is only one building design which often survives a direct tornado: the storm-cellar. Perhaps a full-out Egyptian Pyramid. Or Grant's Tomb. I suppose the Codes must admit that a tornado-hit can not be built-against readily, and that so *few* buildings get direct-hit, that it is "accepted loss".

[armdnrdy]

I have nothing technical to add but...after seeing those huge tornados looming on the horizon and the "toothpick" piles left in their wake....I would never live in an area where that's the "norm"!

Oh well..I guess we have to rebuild now. 

I live in Southern California...you know....Earth Quake country. I've lived here all of my life and have witnessed many quakes including the Sylmar quake magnitude 6.6 in 1971 and the Northridge quake magnitude 6.7 (I was 7 miles from the epicenter) in 1994.

I have never seen anything even close to the devastation in Oklahoma.

[Jdansti]

+1. We dont have cellars or basements down here on the Gulf coast because the water table is so close to the surface that it would be a monumental effort to keep water out if it. If you have a pool down here you never want to completely drain it when cleaning it because it could pop out of the ground due to the hydrostatic pressure imparted by the ground water.  If you decide to fill in a pool with dirt or sand, you have to punch holes in the bottom and sides first. So building underground shelters is expensive.

I worked for a couple of years on a job site in trailer offices sitting on top of a 15' high mound that was constructed of compacted clay in the middle of a swamp. We had sections of concrete culverts, tall enough to walk into, strategically located to serve as tornado shelters. The interesting part was that we had to inspect them regularly because water moccasins liked to hide out in them. It wouldn't be too cool trying to shelter with a few venomous snakes!

A friend of mine was in a motel in North Texas when they had tornados come through a few days ago. He wrote on Facebook that he wasn't thrilled to see the tornado chaser trucks in the parking lot. His wife asked wrote back asking him if he could fit in the bath tub and if he could move the mattress.

[Electron Tornado]

Edmond took a hit the day before Moore did. My folks live in one of the OKC burbs, and fortunately missed the worst stuff. I have several other relatives around there. 

In quiet areas, like here, 70MPH (rarely), we can generally presume a few large nails rafter-plate, and the nail-schedule on the sheathing, will hold.

I'm guessing they're more concerned with insulating against winter temps. Do they have problems with frost heaves on the roads there?

[R.G.]

The interesting part was that we had to inspect them regularly because water moccasins liked to hide out in them. It wouldn't be too cool trying to shelter with a few venomous snakes!

Who needs venom?  I just read about a fellow who killed a 19 foot (5.8 meter) python in Florida. Some snakes just swallow you whole.

[PRR]

> Do they have problems with frost heaves on the roads there?

They put up signs. "BUMP". "Heavy loads restricted". (When the under-frost is half-melted, on a typical rural road, heavy trucks will RUIN the road by punching through to supersaturated mud.)

New construction gets lots of insulation, but the Inspector's main concern here has been working fire detectors. Which goes with the cold and our creative ways to stay un-frozen.

me> a tornado sucks 10 times harder

I musta had a finger-cramp. 300MPH is more like 4 times the max wind in most of the US, so a tornado sucks like 16-20 times harder than a bad wind.

IAC, I had to do a little creative design to get my garage loft space _and_ nominal 70MPH wind loading. If I had to do it again with _16_ times the lift forces, I'd hide in a hole.... wait, I can't, the bedrock is only a few feet down. (That also means no good electrical ground.)

[Jdansti]

I haven't seen any lift force requirements in the area where I live (probably because we often get hurricanes, but rarely get tornados), but the wind load requirement is 110mph for 3sec gusts. Further down the road in Galveston it is 130mph for 3sec gusts. There are extra requirements for all openings. Once an opening forms in hurricane winds, the wind destroys the building from the inside. The home on the left in this video was not built to withstand high wind loads as well as the one on the right, but notice that the building is destroyed shortly after the front door gives in.   

As for tornados, a simulator shows the weak points of buildings:

[R.G.]

IAC, I had to do a little creative design to get my garage loft space _and_ nominal 70MPH wind loading. If I had to do it again with _16_ times the lift forces, I'd hide in a hole.... wait, I can't, the bedrock is only a few feet down. (That also means no good electrical ground.)

I have similar issues. I required the builders to install tie-down straps to all the roof framing from the concrete walls of the house. They thought I was crazy, but took the money and did it.

I have bedrock, but it's porous limestone, so it's generally damp enough to conduct if you get into it. I had holes drilled  10 feet into it at each end of the house and ground rods buried into the holes, then bonded to the house wiring at each end. Seems to work so far, including a couple of nearby lighting strikes.

There is NO way to be sure you're safe against a direct lighting strike. Our in-laws in tornado alley had a direct strike on a 4 ft by 6 ft cross section stone chimney in one storm. It broke the chimney and toppled an 8 foot section of it into the back yard. Zeus throwing lightning bolts was no joke.

[Jdansti]

>I have bedrock, but it's porous limestone, so it's generally damp enough to conduct if you get into it. I had holes drilled  10 feet into it at each end of the house and ground rods buried into the holes, then bonded to the house wiring at each end. Seems to work so far, including a couple of nearby lighting strikes.

One of my job sites has 80 acres covered with a thick HDPE liner and then 18-in of compacted clay on top of the liner. We have a couple of buildings built on this that house pumps and air compressors.  We weren't able to use ground rods because the only penetrations that we could have through the liner were wells (long story dealing with how you seal the liner to the object making the penetration), so the engineers designed grounding grids in the 18-in of clay that surround the buildings. I guess the shallow soil connects with ground-ground at the perimeter of the liner.

>There is NO way to be sure you're safe against a direct lighting strike.

True, but there are ways to help direct lighting "safely" to ground if designed and installed correctly. Unfortunately, many people simply put lightning rods on buildings and run a wire to ground without knowing the "cone of protection" that they need or how to install the system. It's not a DIY project!  The lightning rod(s) have to be tall enough and properly sited on the building for their cone of protection to extend out beyond the building's perimeter.  There are requirements for how the rods are installed and specifications for cables, connectors, fasteners and grounding. And then you have to consider all of the electrical and plumbing pathways into the building that originate outside of the cone of protection.

[R.G.]

I used a metal roof grounded with braided aluminum down-cables to ground rods.

[artifus]

http://arstechnica.com/science/2013/05/i-was-struck-by-lightning-yesterday-and-boy-am-i-sore/

[Jdansti]

I used a metal roof grounded with braided aluminum down-cables to ground rods.

That pretty much covers the entire structure!

[Mark Hammer]

I required the builders to install tie-down straps to all the roof framing from the concrete walls of the house. They thought I was crazy, but took the money and did it.

I have bedrock, but it's porous limestone, so it's generally damp enough to conduct if you get into it. I had holes drilled  10 feet into it at each end of the house and ground rods buried into the holes, then bonded to the house wiring at each end. Seems to work so far, including a couple of nearby lighting strikes.

There is NO way to be sure you're safe against a direct lighting strike. Our in-laws in tornado alley had a direct strike on a 4 ft by 6 ft cross section stone chimney in one storm. It broke the chimney and toppled an 8 foot section of it into the back yard. Zeus throwing lightning bolts was no joke.

Years back you sent me some pics of the "Lego" house in its early construction stages.  Now you've made me curious again about its final state.  From yur description, I feel like my house has a volume and tone knob, and yours is like a 4-channel Marshall! 

John, That second video is absolutely kickass.

[Electron Tornado]

True, but there are ways to help direct lighting "safely" to ground if designed and installed correctly. Unfortunately, many people simply put lightning rods on buildings and run a wire to ground without knowing the "cone of protection" that they need or how to install the system. It's not a DIY project!  The lightning rod(s) have to be tall enough and properly sited on the building for their cone of protection to extend out beyond the building's perimeter.  There are requirements for how the rods are installed and specifications for cables, connectors, fasteners and grounding. And then you have to consider all of the electrical and plumbing pathways into the building that originate outside of the cone of protection.

The ham radio crowd has info on lightning strike protection. I haven't looked at it in a long time, but I'm guessing it's mostly about how to keep a strike on the antenna from blowing up your rig and burning down the house.

[mac]

I have similar issues. I required the builders to install tie-down straps to all the roof framing from the concrete walls of the house. They thought I was crazy, but took the money and did it.

RG,
That's the standard in my country. The main +2x10 inches woods and others are always hold in concrete. The flat ones are nailed to the main woods, and we use spanish or french tiles, french are way better, or galvanized steel sheets, and an isolation carpet below the tiles or steel.
We construct in a very different way than you do, bricks, concrete and iron everywhere. Tough as a MXR Dist+.
We build this way because our spanish ancestors did so, not because we fear tornados. Also, when they came here, they found a flat land with no trees at all (pampa argentina).

We also have tornados, mostly F3, and they cause minor damages to the roof, some tiles gone with the wind.
In rare case we have F2, and very few F1. Despite what you can read in the web, (goolge "are brick houses immune to a F1"), we never had the devastation seen in OKC.
Mmhh... well... we had that level of devastation or worst, but caused by our politicians...

It's difficult to compare the tests performed by US authorities with our standard constructions techniques. Our houses are oversized, like using a TIP31 to handle 1 micro ampere. A well built concrete and brick house can stand F1, roof blown and interior damage, but not completely destroyed beyond repair

I've just finished a couple of twin houses, one sold recently,
Can survive almost everything, except a bear market...
I deleted the pictures I had of the construction stages. It has concrete and iron foundations, concrete beams and columns with 4x 12cm irons inside, concrete floor with iron mesh for the first floor, 18cm exterior and 12cm interior walls + plaster, galvanized steel roof with woods hold to the walls, etc, etc.


Too expensive techniques for the american market I guess.


Some examples,






mac

[Thecomedian]

My son is a civil engineer, and while chatting yesterday, I mentioned that they probably spend little attention during their training to the sort of winds that occur in tornados.  He went on about wind shear, and wind tunnels, and how they test roofs, but at the end he had to admit that they had never discussed how to design a building in anticipation of air forces that pull roofs upwards, rather than blow at them sideways.  Kind of an important gap in their training, I think.

Sometimes it's worth it to put in the extra protection diode, isn't it?

Incidentally, PAiA is also in Edmond, so I gather they're alright too.

google CalEarth.

their dirt homes broke all the building codes and testing equipment.

We have the information and the capabilities of producing homes that can resist natural disasters far better than homes made of post and lintel style, which is a home that immediately starts trying to pull apart once it's completely built. It's not a good structural design.

The reason it is "glossed over" and ignored is not because design possibilities dont' exist, its because people dont make money from rebuilding houses that don't fall apart.

http://www.youtube.com/watch?v=o-jrvzrJ3Q0


a 2,000$ home isnt pie in the sky or a pipedream, it's a direct economic threat to the construction industry.

http://www.youtube.com/watch?v=1sYSf0b4N6A&feature=fvwp&NR=1

of course, such a good insulation source also lessens the burden of heating and cooling. economic threat to power industry.

Who here has heard of such techniques in their life? The answer is the point.

[PRR]

> I haven't seen any lift force requirements in the area where I live

Dig in the building code. There is probably a reference to ASCE. Here's a snippet of the 54 pages for wind load:



Take 85MPH for example.

My main roofs are 12:12 pitch, 45 degree, so take "30 to 45" row.

Roof is divided into zones E-H relative to wind direction (you consider all directions and take th worst-case).

The -negative- signs mean UP-lift.

I have to design for 3 to 8 psf UP-lift on parts of the roof. (Since wind can be any direction, pretty much the whole roof.)

Southerners like flatter roofs, take 20 degree. Any part of the roof must withstand 7 to 14 pounds square foot up-lift.

Since a southern roof may be designed for 20PSF down-load, and may weigh less than 10PSF, a 14PSF up-lift has to be pondered in design.

Small areas like parapets and porch roofs may have to be designed for higher spot-loads. There's also a section "Components and Cladding".

At 130MPH nominal wind speed an overhang can have 45PSF of up-lift.

There's more. Wind is turbulent and you may not have to design for 7-14PSF on the *whole* roof at the same time, some areas are likely neutral or down-force. You still have to plan each sheet of plywood for the whole force, but you may not need 7,000+ pounds of pull through wall plates.

These are obviously approximations based on simplified conservative assumptions. There's more pages to control you if you want to do more-exact computations to maybe save a buck.