How To Resist Uplift Load for Metal Building

[lumbee]

I have the drawings from a manufacturer for a 40' x 40' metal building. Looking at the worst case scenario(115 mph winds), the uplift would be 7 kips. Won't this make the footing have to be oversized greatly to counteract the uplift force? I am thinking about using a buried spread footing and pedastal combination. This would allow me to use soil to help hold down the footing and minimize the concrete. Does anyone have any suggestions? Can this load be reduced because of it being a wind load?

 

[JedClampett]

All you have to do is engage a portion of the footing and/or slab and/or grade beam equivalent to 7000 lb. I would advise using the code equations and only using 60% of the weight. It doesn't take very much concrete to weigh 7000 lb. If your footing is buried, you can use the weight of the soil above it.
Figure out the area of floor slab or in the case of a grade beam, length, required. Make sure it can span without any soil supporting it and you've designed for uplift, assuming the anchors are designed.
Don't forget to add hairpin bars to take lateral forces.

 

[UcfSE]

You can't reduce it because it is wind load. You also need to know if that is the net uplift. Metal building footings can get large because the buildings are so light. There isn't a lot of dead load to help resist the uplift so more of the resistence has to come from the weight of the footing. For details such as whether to use a pedastal you should probably see what others in your area do.

 

[SlideRuleEra]

Be sure to make a suitable economic comparison between your alternatives. The extra concrete cost in a simple mass footing may be less expensive than the added labor, forms, & construction time needed for a spread footing/pedestal (or similar elegant solution).

http://www.SlideRuleEra.net

 

[bylar]

In IBC: Where the alternate basic load combinations are used, only two thirds of the minimum dead load likely to be in place during a design wind event shall be used.

 

[DRC1]

At 150 pcf 7,000# is 1.8 cu. yds., which is not a lot for foundation concrete. A 3ft x3ft x 1.5ft footing with a 1ft sq x 3ft stem is .6 cyds, with 2.5 ft of soil the wt per footing would be around 4,000 pounds.
So.. I would look at using simple spread footings to resist the net uplift.