The power of wind

[Don_P]

I went to a seminar last week where one of these guys spoke. It's a ~4 meg file of wind and tornado damage pics and descriptions.
http://www.forestprod.org/durability07martin.pdf

Notice the one slide at the % of F1-F3 tornados, we can build to protect the occupants in the majority of these. Notice the foundation failures as well. A pier and beam foundation very likely won't weather an F1 or a strong wind. Something to think about as you plan and budget. The other lesson for me was that I'll try very hard to never build another attached garage. The door blows out and then the walls and roof are a lever to tear the house apart.

[MountainDon]

Interesting stuff. 




I'm glad I don't live in any of the extreme wind areas.

[Beavers]

Thanks for sharing DonP,  great photo's.  It's crazy to see the photo's of some houses almost untouched, while the house next door is completely gone!

Based on the photo's it also seems like you can't expect toe nailed rafters to stay on your house for long in a tornado. 

[Don_P]

I helped clean up after one went over our house while I slept. It touched down a couple of miles away. While I was helping to cut into one place I couldn't figure out why the second floor was gone and the first was untouched. Till I got to the oak tree in the backyard with the upside down motorhome in it. Wasn't even their camper  .

[glenn kangiser]

Very interesting.  I like a foot and a half of dirt on my roof.

200lbs x 2000 sq ft = 400,000 - that should hold it.. not all is covered though and not all is 1 1/2 feet thick.  Likely only 200,000 lbs hold down weight.

[desimulacra]

Glen I'm not pulling your tail and would rather be in your home than mine in case of a strike but I have been thru 3-5 tornadoes dependent on how you look at it??? There are few truly safe homes, just safer homes. While I agree that an under ground home is one of the safest style homes,  I have seen underground homes that were destroyed and pics of pavement and concrete pads yanked out of the ground. I remember from somewhere where a large tornado can generate 400 PSI on a structure. 2000 sf x 400 = 800,000 pounds of force.

[glenn kangiser]

I have thought of the same thing- a tornado is not likely on the mountain - it should kill it, but any opening can be pressurized with relation to the other side of the building  so - right - I agree - nothing is really totally safe - maybe one of the underground septic tank structures - unless a tree or something lands on the entrance - flood etc. 

[MountainDon]

It's not possible to be 100% safe at all times and in all endeavors.








...and still no diversion from "power of wind" to "farts" 

[glenn kangiser]

I have been working pretty much full time with breaks only while my client is readying the next building, and am rather slow lately.

I have been taking care of my backed up local jobs during breaks and just got another brushing job with the Bobcat through another good customer.

After last years fire, people are thinking of "The Power Of Wind" during the next fire also.  This job is in a tinderbox area and I don't think any residence in that area will survive the next fire if brushing is not taken care of.  It is just past where the fire was stopped and the fire teams knew it would be pretty unstoppable if it got to that point.

[Don_P]

This cycle of rain keeps shutting us down, I'm sure we'll be crying about drought in a month or two though. I hear you on wind and fire, my wife had one get away from her and stopped it at the woods line, 5 more feet and the ridge road above us would have been the only option. She scrambled the guys on Superbowl Sunday, I made a big donation  .

Mountains do tend to break up tornados but not always. There is one clear swath not too far from here from years ago. The eye of Hurricane Hugo also passed over us spawning small twisters and heavy shears, the highest mountain in the state is in our county. Ridgetops and gorges get their own high winds. There is actually nowhere in the country outside of the 90 mph zone. You can check chapter 3 of the codebook for wind maps and building design forces.

Although it is not possible to be safe at all times it is not smart to be reckless, especially with the lives of others. Notice in the pictures that almost all of the failures were avoidable, most were easily avoidable. There is no need to lose your home or your life in a moderate wind event. 80-90% of tornados are moderate or less. A house built to coastal standards would make it through most high winds and tornados as well. The AWC High Wind Guides are available here;
http://www.awc.org/Standards/wfcm.html
Notice they hand off foundation design to code standard.

I'm still trying to read and digest another part of the seminar, and the reason I drove 8 hours to attend. Post Frame construction uses a similar foundation to what you all are trying to promote but does it to withstand these events. It requires either proper bracing or utilizing the walls and diaphragms of the structure to keep the properly embedded foundation posts from failing. It is a direction that would be good to research further. Dr Manbeck's powerpoint from part of the lecture is here, it may be greek without him explaining, to be honest the architects at my table were lost.
http://www.woodworks.org/files/PDF/Presentations/WSF_Atlanta/Manbeck_-_Post_Frame_building.pdf
The shallow pier standard I'm working on understanding now is here, good stuff but I have a number of books open with pulled hair in each   
http://bse.wisc.edu/bohnhoff/Publications/Copyrighted/EP486_1.pdf