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Re: uplift in footings

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In this case I go by the letter of the load combinations. Personally, given the "accuracy" applied to the wind and snow provisions of late, I'm a bit surprised they haven't introduced a Dh and Dl for the load combinations. Dh would correspond to a "high" dead load estimate of the system, and used for gravity and lateral seismic loading, and Dl corresponding to a "low" dead load estimate to be used with wind and seismic uplift. I agree that it would seem that 0.6 on a known footing size (and likely a good bit heavier unless the footings were carefully formed) is a bit conservative. The exceptions are exceedingly rare. Besides - if you believe that 7 cy of concrete you order actually gets delivered to the site, there's at least an extra 10%-20% concrete on practically every job I've seen. I'm not aware of a contractor who ordered the exact volume of concrete and ended up with leftovers.


Jim Wilson wrote:
While we're on the subject of footing uplift, why is the 0.6D factor applied to the weight of concrete footings? Isn't this factor primarily intended to cover the unpredictability of future conditions. As long as footings are inspected for size, it can be considered a given fact that the footings will weigh so much and provide so much resistance. Jim Wilson, PE
Stroudsburg, PA

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