Roof without walls- How to design for wind? - Page 2
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  1. #21
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    there is a lot of steel hay barns built out here. basically the roof space your talking about, open sided, a pole every 12' of wall length though and a 6x6x2 concrete footer for lack of proper terminology under each. just for wind lift.

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  3. #22
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    Its just a pole barn for goodness sake, if you are really worried about it put some large roof panels on hinges so in the off chance it does try to come off the ground the trap doors open and let the pressure through. Be sure to have a cable on hem so they can not fold over backwards.
    Better yet, just a large ridge vent with plenty of free area with a large enough overhang that rain wont get in. Any pressure build up just exits the ridge vent

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    It isn't pressure so much as vacuum. I don't work on open buildings, but it gets a mite windy down here sometimes in the fall. We design for 137 in town. I caculated uplift on a corner of a metal building gymnasium, it was over 100psf.
    I would not worry too much about holding the frame down, spanning that deck 13'-4? It will fail long before the frame gets lifted.

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    Quote Originally Posted by Rudd View Post
    It isn't pressure so much as vacuum. I don't work on open buildings, but it gets a mite windy down here sometimes in the fall. We design for 137 in town. I caculated uplift on a corner of a metal building gymnasium, it was over 100psf.
    I would not worry too much about holding the frame down, spanning that deck 13'-4? It will fail long before the frame gets lifted.
    Three trusses would be spaced about 12' apart. 35'-40' pan deck sheets attached so they overhang a bit.

    I don't think that's pushing it for 20 gauge pan deck.

  7. #25
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    Those flaps don't kill lift. They simply turn it upside down.



    Quote Originally Posted by gustafson View Post
    YOu would think there would be some clever trick aside from making it weigh more than the lift generated by 'x' speed wind to keep it from flying away. Like those flaps on nascar roofs that kill lift when you are suddenly going 180 mph backwards.

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    They make a big deal about how airplane wings work via the air flowing over them having a longer path and creating a low pressure there, but a vacuum by itself can do nothing. If it could all the planets would quickly or slowly explode into space.

    It is the combination of the higher pressure below the wing and the lower pressure above it that creates the lift. It is the difference between the two. So, yes the air flowing across the bottom of the wing really is pushing it up. When the wing is not moving, the pressure above it is equal to that below and there is no net force.



    Quote Originally Posted by boslab View Post
    I suppose downforce could be generated by having a flat top roof and a curved under face so the air has further to go under it than over it, like an airfoil or upside down wing, I might have got that completely wrong btw as I don’t know a great deal about aerodynamics, I’m sort of applying fluid flow from college years ago, I still find venturimeters fascinating ( big pipe, transition small pipe reverse transition big pipe, then we got to fabricate one and weld it, I enjoyed that)
    Would an upside down wing push down or suck down or whatever the heck they do, do wings get sucked up or pushed up, is it lift or suck that gets planes up in the air, still undecided, are the falling if they fly upside down, or it could be magic
    Mark

  9. #27
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    Like I said, 1 1/2" 22 ga. B deck is good for 5' span in these parts.

    https://vulcraft.com/catalogs/Deck/V...al-Aug2018.pdf

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    I would hesitate in designing such a roof as an upside down wing with the lift is downwards. What worries me is that the air flowing below it will be pinched between the roof and the ground at the lowest spot in the roof. This could also act to create a higher pressure, not at that central point, but around the "leading edge". This could result in a torque with that leading edge under a lifting force while the central and rear areas are being forced downward. Once the leading edge is ripped off the supports, it would cascade.

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  12. #29
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    You could make it by using concrete "Double Tees".
    No concerns of it flying away.
    Or burning down......

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    Quote Originally Posted by digger doug View Post
    You could make it by using concrete "Double Tees".
    No concerns of it flying away.
    Or burning down......
    A friend of a friend had an 80ft+ long by 10+ ft tall post tensioned concrete beam I could have. I don't know what it weighs, but I expect once I moved it I would have a different set of challenges to building a roof structure out of it.

    It did cross my mind though.

    I believe I have solved my roof becoming a sail problem. I just put a deposit on a bunch of 4200 bushel grain bin silos. My shop looks like a huge barn anyway so I'll add a wall of silos to the prevailing wind side of this roof and I think we'll be in good shape.

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    Quote Originally Posted by Garwood View Post
    A friend of a friend had an 80ft+ long by 10+ ft tall post tensioned concrete beam I could have. I don't know what it weighs, but I expect once I moved it I would have a different set of challenges to building a roof structure out of it.

    It did cross my mind though.

    I believe I have solved my roof becoming a sail problem. I just put a deposit on a bunch of 4200 bushel grain bin silos. My shop looks like a huge barn anyway so I'll add a wall of silos to the prevailing wind side of this roof and I think we'll be in good shape.
    ...and they are taxed less or none....

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  17. #32
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    Quote Originally Posted by Garwood View Post
    A friend of a friend had an 80ft+ long by 10+ ft tall post tensioned concrete beam I could have. I don't know what it weighs, but I expect once I moved it I would have a different set of challenges to building a roof structure out of it.

    It did cross my mind though.

    I believe I have solved my roof becoming a sail problem. I just put a deposit on a bunch of 4200 bushel grain bin silos. My shop looks like a huge barn anyway so I'll add a wall of silos to the prevailing wind side of this roof and I think we'll be in good shape.
    dam that's a hell of a totem poll

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    Quote Originally Posted by 1yesca View Post
    dam that's a hell of a totem poll
    Bridge beam that got bumped/dropped and a corner chunked out.


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