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Wind load needed to topple a storm shelter

  1. Mar 20, 2012 #1
    I am planning on building an above ground storm shelter that will be 16' x 16' by 8'. The footers will be 24" W by 12" D with 4-#4 rebar. Insulated Concrete Forms (ICFs) will be used for the walls then a 5" floor slab. Concrete space of the ICFs is 6.5" or 8" or 10" defending on someones response to my questions. The ceiling will be 6" Concrete reinfored with rebar and wire web. The walls will have rebar every 16" in both directions. Now the question. With a 16' x 8' cross section of wall, on normal level ground what wind speed would it take to topple the building for each wall thickness? I would guess you can leave out the affect of the ground holding down the slab/footings unless you can calculate that as well. I want to avoid having to dig down or pile dirt around this building if possible. My thought is that the weight of the building built with 6.5" concrete walls would be enough to provide safety up to 200 MPH but, I would like to know for sure. I want to thank you in advance for you help with this question
    Ken
     
  2. jcsd
  3. Mar 20, 2012 #2
    Definitely one could calculate and determine the wind load that the wall could sustain, and you could find applicable equations in that regard via internet search. But since you are talking about 200 mph winds, your building would be subject to either a hurricane or a tornado, in which case the inside/outside pressure differential has also to be taken into account, so that your building does not blow up so to speak, or the roof lift and blow off. Even though you are making your building out of concrete which you think is strong and heavy, air can have tremendous force when the pressure differential is great enough. I do not think PF can give realistic advice on whether your building would be safe in a tornado or hurricane.
     
  4. Mar 21, 2012 #3

    jim hardy

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    I dont know where you are so excuse if this sounds obvious..
    That sounds very similar to construction of quite a few houses in Liesure City Fla built shortly after WW2. They still remembered the Sep 15 1945 storm that was comparable to hurricane Andrew(Aug 92).
    Those houses did great in Andrew but some lost windows.
    Opinion is still divided on just how much wind was in those two storms.
    Officially 145mph but some old-timer meteorologists believe gusts went to 200 in both. (Anecdotal, from a retired hurricane forecaster)

    Sounds like you're tying everything together vertically? Make sure walls are okay in tension, roof gets lift if front door blows open and ram effect pressurizes structure.
    In that wind there's plenty of heavy flying debris. Rocks from fields pepper houses like machine guns. Roof shingles slice into plywood like a thrown knife. So use good doors.

    andrew-damage-1a.jpg
    photo from: http://www.unsolvedmysteries.com/usm483355.html?t=Human Interest
     
  5. Mar 21, 2012 #4
    Thanks for the replys. In answer to those questions FEMA requires a steel door & frame with three point dedbolts and heavy duty hinges. The door blowing open should not be an issue. Venting is via two small 4" vent pipes and should not provide enough venting to cause blowout. I am more concerned with the chances the building could be rolled over and sent tumbling down the road. I would think the mass of all that concrete would not let that happen but I wanted to see if there was someone who could tell me what MPH force would be required using the 16' x 8' wall hit straight on. If it would help I can provide the total yardage of concrete that will be used in the building to be used as the dead weight.
    Thanks
    Ken
     
  6. Mar 21, 2012 #5
    Howdy Folks,
    I calculated to total weight of the building using just the weight of the concrete which should be close enough for what I want. I can build with walls that have concrete thickness of 6.25", 8" or 10". Seems like uniform weight distribution should be ok as well.

    Building with 6.5" Total Weight: 89,700 lbs
    Building with 8" Total Weight: 100,230 lbs
    Building with 10" Total Weight: 112,710 lbs

    Thanks
    Ken
     
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