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[KevinEleven]

I'm just a curious Aussie builder. Is there someone in the mid-west where tornadoes are common that can answer a few simple questions from an interested spectator half a globe away.
1. Are the buildings we see disintegrating on TV just old ones that aren't designed to withstand high wind forces or aren't builders required to build to a standard that will resist high wind forces?
2. Why aren't your caravans & trailer homes anchored to concrete blocks in the ground?

When Yasi went through North Queensland earlier this year, homes built in the recent past only sustained superficial damage. That's wind speed up to 290kph (180mph)
On our northwest coast buildings have to be designed to withstand much higher wind forces.

[KevinEleven]

And do they do an assessment of the damage & make any recommendations for changes in building practices? like here?
http://www-public.jcu.edu.au/news/JCUPRD1_071493

[Flowers232]

I'm just a curious Aussie builder. Is there someone in the mid-west where tornadoes are common that can answer a few simple questions from an interested spectator half a globe away.
1. Are the buildings we see disintegrating on TV just old ones that aren't designed to withstand high wind forces or aren't builders required to build to a standard that will resist high wind forces?
2. Why aren't your caravans & trailer homes anchored to concrete blocks in the ground?

+1 I would like to know also.

[FynrDzynr]

Don't expect a response any time soon. I've asked similar questions over the years & never got an answer. Makes one wonder if generally Americans are just too proud to admit their shortcomings.
Funny here in Oz that a few years ago designers were being criticized for designing above the minimum mandated standard because we were contributing to the "decline in affordable housing". But since Larry, Yasi and a few floods nothing more has been said.
Merv

[Les]

I'm from Oklahoma.  Only 180 mph.  We should be so lucky.

The tornadoes around here have winds from 150 to 300+ MPH winds.  I've seen well built homes disappear with only the bottom plate left bolted to the slab.  There's a school bus from a nearby town they still haven't found.  They believe it's in the lake 4 miles away.

Most would probably like to anchor their mobile homes, but the fact is alot of people can't afford to.  Trailer homes that were anchored to a foundation have been torn apart and nothing recognizable left.  There are quite a few concrete homes near where I live.  My home has all the hurricane clips, solid sheathing, braces, bolts and anything else I read about or thought of, but it's not concrete.  I don't think it would make it thru an F4 or F5.  But that's why I have a safe room that is concrete on 5 sides.

Sounds like your  mandated standard for your average home isn't much different than ours. 

Beefing up the coast line!!  I'll send that idea to Florida.  Don't think they've considered that yet.  Can you send information on how to conduct a study of construction practices?  I don't think we have ever thought of that.  Someday I'll come down and talk to you all and take alot of notes.  I hear you have indoor plumbing down there to.  That's too cool.  After I get all this information I'll be rich up here and won't have to draw house plans anymore.

And what are all those extra boards for in frame view in Env.  I usually just use the elevation and nail a bunch of stuff together, then we take chain saws and cut away everything that doesn't look like the house and slap a little paint on it.

Talk to you guys later  
Les


 

[KevinEleven]

Hi Les,
In cyclone areas reinforced concrete masonry still tends to be the structure of choice. Its resistance to flying debris is probably the prime factor. The performance of lightweight construction can be severely impacted once the external fabric is punctured.
Can you link to an image of a hurricane clip? All our buildings are bolted down from roof battens right through to footings. Corrugated steel sheet roofing even has its special screws.

What do you mean by "Beefing up the coast line!!  I'll send that idea to Florida"

[Les]

Hi Kevin,

By Beefing up the coastline (just funning around), I meant
^{buildings have to be designed to withstand much higher wind forces}
They have done that on the coast.  It is older construction that gets blown away.

The performance of lightweight construction is severely impacted and the external fabric punctured when your trees or car ends up in your living room.

What do you mean by "all our buildings".  On the coast, all houses, commercial buildings or the whole country anything thing that's built.  Because here there is a wide range.  From no codes in some areas way out in the country to very strict in others.

There have been several studies of areas hit hard by tornadoes and recommendations made, books written, guidelines published, but the codes have not changed much that would make recommendations mandatory.  All comes down to cost.  People that can afford too spend more can have a safer home.

You're right, can't beat concrete.  That's where I feel safe. I have had 2 pass over my house that weren't quite on the ground.(before we had a safe room)  Worst sound ever, like your laying under a train.  

http://www.strongtie.com/ftp/catalogs/c-hw09/C-HW09-p25.pdf
http://www.strongtie.com/ftp/catalogs/c-hw09/C-HW09-p12.pdf
http://www.strongtie.com/ftp/catalogs/c-hw09/C-HW09-p38-p39.pdf

Do you guys get many tornadoes?    

F1  Weak: 73-112 mph winds: Roofs damaged, mobile homes moved off foundations, trees snapped, moving autos pushed off roads.

F2  Strong:113-157 mph winds: Roofs removed from frame houses, large trees snapped or uprooted, mobile homes destroyed, boxcars overturned.

F3  Strong:158-206 mph winds: Walls removed from well-constructed houses, cars overturned, most trees leveled.

F4  Violent: 207-260 mph winds: Well-constructed houses destroyed, cars thrown.

F5  Violent: 261-318 mph winds: Well-constructed houses lifted up and disintegrated, automobile-sized structures thrown over 100 meters, steel-reinforced concrete badly damaged.


Les

[FynrDzynr]

I meant buildings have to be designed to withstand much higher wind forces
They have done that on the coast.  It is older construction that gets blown away.

That's what I wanted clarified.

What do you mean by "all our buildings".  On the coast, all houses, commercial buildings or the whole country anything thing that's built.  Because here there is a wide range.  From no codes in some areas way out in the country to very strict in others.

Generally Aust is divided into Geographical regions then each site is assessed according to Terrain Category, Shielding & Topography. Design Wind Loads are derived from these. Any remodelling work or rebuilding work (eg post-disaster) has to comply with the current standards.

There have been several studies of areas hit hard by tornadoes and recommendations made, books written, guidelines published, but the codes have not changed much that would make recommendations mandatory.  All comes down to cost.  People that can afford too spend more can have a safer home.

You're right, can't beat concrete.  That's where I feel safe. I have had 2 pass over my house that weren't quite on the ground.(before we had a safe room)  Worst sound ever, like your laying under a train.  

http://www.strongtie.com/ftp/catalogs/c-hw09/C-HW09-p25.pdf
http://www.strongtie.com/ftp/catalogs/c-hw09/C-HW09-p12.pdf

D1 & D2 We have looped straps that wrap around the top plates, up & over the truss/rafter then back down & wrapped around the top plates again
D3 we'd have a J-bolt cast into the bond beam of concrete masonry to hold the nailing plate down. Better still we eliminate the plate altogether & have fish plates threaded onto the reo in the bond beam spaced such that a truss can just fit between each pair. Then a 16mm (5/8") bolt goes through each fishplate & the nailing plate of the truss.

http://www.strongtie.com/ftp/catalogs/c-hw09/C-HW09-p38-p39.pdf

Do you guys get many tornadoes?

   
Yes, but not high frequency like your area. I've spent most of the last 30 years on Brisbane's southside. In that time I think we had 3. First was Nov3 1973. iirc this was prior to the establishment of the cyclone testing centre at James Cook Uni in Townsville. Yes, highset houses were lifted off their stumps, a flat roof off a block of units opposite the pub ended up a kilometre away in the forest. Also saw a length of 4x2 hardwood punched clean through a 9" brick wall in Macgregor. Brickwork didn't even crack!

F4  Violent: 207-260 mph winds: Well-constructed houses destroyed, cars thrown.

F5  Violent: 261-318 mph winds: Well-constructed houses lifted up and disintegrated, automobile-sized structures thrown over 100 meters, steel-reinforced concrete badly damaged

I'm not aware of any equivalent here, thankfully
Merv

[KevinEleven]

Merv, you forgot to provide a link to Online Conversions so he can convert the kN's in the tables above to whatever they use over there.