Foundation Uplift Resistance
Foundation Uplift Resistance
(OP)
I do not typically get involved in sizing metal building footings, but I have a couple of questions after looking through several sets of foundation plans for metal buildings. When sizing a spread footing to resist an uplift load on a column, do you use the 0.6D + W load combination to determine the resistance to uplift? It seems overly conservative to only be able to use 60% of the footing dead weight.
If the column has a horizontal and uplift reaction and the foundation engineer is using hairpins, does sliding and overturning need to be checked if the column is located in the center of the footing?
If the column has a horizontal and uplift reaction and the foundation engineer is using hairpins, does sliding and overturning need to be checked if the column is located in the center of the footing?





RE: Foundation Uplift Resistance
2. "if the column is located in the center of the footing?".
I don't quite follow your question. Should it be "center of the building"?
RE: Foundation Uplift Resistance
1. Is this a code requirement or is it just typically understood by foundation designers to do this? The drawings that I am looking at appear to use the full footing weight to resist uplift, unless the foundation engineer has also taken into account some of the turn-down at the edge of the slap between footings, as well as a considerable amount of the floor slab.
2. Typically a metal building column will be within a few inches of the edge of the slab. In order for the column to be in the center of a shallow foundation, the column may be on a +/- 1' pedestal and the spread footing may extend past the edge of the slab. For example, for a 6' x 6' footing, maybe 1.5' x 6' will be outside the edge of the slab.
RE: Foundation Uplift Resistance
2. Yes, check on sliding and uplift are required for column pedestal placed either concentrical, or eccentrical with respect to the footing pad, and with, or without shear pin. (Shear pin should be designed for effects from horizontal load with proper safety margin.)
RE: Foundation Uplift Resistance
RE: Foundation Uplift Resistance
RE: Foundation Uplift Resistance
Other codes are similar.
I use the actual dead load of the footing.
RE: Foundation Uplift Resistance
BA
RE: Foundation Uplift Resistance
The geotech reports also usually give us adhesion on the sides of the footings, which helps a lot.
RE: Foundation Uplift Resistance
As for the volume of soil, I usually just take the projected area from the footing. You can argue that shear strength of the soil could be included, you could argue that in cohesionless soils the angle of repose could be used either way (+ or -), and there might be other arguments as well, but it gets down to what you feel you can do professionally to substantiate.