Footing Uplift, new question
Footing Uplift, new question
(OP)
After reading the "Footing Uplift" thread, I have a new question on the subject. When examining a foundation for overturning, I thought that the eccentricity (M/d) was always to be in the center 1/3rd of the footing. Is this a code provision? or a rule of thumb? When checking this, what load combination should be used? 0.6d+1W? 1d+1w? Is this check normally done in addition to the overturning FS check as discussed in the thread "Footing Uplift"?
Another thing that sparked the question is that I am studying for the PE and in the 6 min solutions it has a question that calls for eccentricity in the center 1/3rd. But the solution shows a load combination of 1d+1L+1w, yep, sure enough they show to use live load for this check.
Thanks all.
Another thing that sparked the question is that I am studying for the PE and in the 6 min solutions it has a question that calls for eccentricity in the center 1/3rd. But the solution shows a load combination of 1d+1L+1w, yep, sure enough they show to use live load for this check.
Thanks all.






RE: Footing Uplift, new question
You will have partial bearing when e > L/6. As long as this does not cause your maximum bearing pressure to exceed the allowable, your design should be okay.
You will need to check both D+W and 0.6D+W load combinations for Overturning, stability and allowable bearing pressures.
RE: Footing Uplift, new question
As the previous poster pointed out, if the eccentricity lies outside of the middle third of the footing you will have partial bearing. Some engineers prefer to avoid this situation. This is where the rule of thumb that you mentioned originated. My personal opinion is that partial bearing is acceptable - especially if it is only under short term loading such as WL.
Adam Vakiener, P.E.
RE: Footing Uplift, new question
It may be a rule of thumb for some engineers, but not for others. If the load is outside the kern, you would simply consider a lesser footing dimension with a triangular pressure distribution below it.
If you are concerned about staying within allowable bearing pressure then you should include any loads which contribute to the soil pressure, including live load.
Your question is a misnomer as it is not about footing uplift.
BA
RE: Footing Uplift, new question
RE: Footing Uplift, new question
RE: Footing Uplift, new question
RE: Footing Uplift, new question
RE: Footing Uplift, new question
RE: Footing Uplift, new question