Shallow Foundations
Shallow Foundations
(OP)
When is the weight of the footings themselves applied to the soil in bearing pressure calculations?
My understanding is that for ASD allowable bearing pressures, you do not include the weight of the footing as part of the pressure on the soil because that is factored in as part of the safety factor. Is that correct?
Reading a design manual this weekend, the foundation design was based on LRFD ultimate soil bearing capacity, and the weight of the footing was included. Is that correct?
My understanding is that for ASD allowable bearing pressures, you do not include the weight of the footing as part of the pressure on the soil because that is factored in as part of the safety factor. Is that correct?
Reading a design manual this weekend, the foundation design was based on LRFD ultimate soil bearing capacity, and the weight of the footing was included. Is that correct?






RE: Shallow Foundations
Our geotech reports typically give net allowable bearing pressures for which I neglect the weight of the footing competely (admittedly in contradiction with my idea above). As for LRFD combinations (I'm assuming used for the footing checks and not the soil checks), I would not include the footing weight as this isn't a concentrated load like the applied column load and won't cause any bending in the footing.
Both of the above statements are true only for gravity footings or lateral footings with no moment. If you have moment at the top of the footing, then I add the weight of the footing (if I need to) to help with overturning.
RE: Shallow Foundations
RE: Shallow Foundations
If I am using a soils report frequently the soils report says that the weight of the footing can be ignored.
The concrete is generally around 150 pcf, and is replacing soil that is around 110 pcf. If I ever really wanted to get something to work I suppose I could justify just adding the difference of the concrete weight - soil weight as that is the net increase to the soil bearing, but I've never done this yet, and it does not seem to be the standard of practice for the engineers I've been around.
RE: Shallow Foundations
RE: Shallow Foundations
Depends on what data the bearing pressure is based on.
RE: Shallow Foundations
RE: Shallow Foundations
RE: Shallow Foundations