Mat footing eccentricity within middle third, Overturning always OK?
Mat footing eccentricity within middle third, Overturning always OK?
(OP)
If I model a mat foundation on soil using finite element and no tension (eccentricity within middle third), is it safe to assume it wont fail in moment overturning check?
The reason i ask is because overturning check is not checked using finite element software spmats. It does check soil bearing pressure.
And i was wondering if I could skip the separate rigid analysis for overturning.
The reason i ask is because overturning check is not checked using finite element software spmats. It does check soil bearing pressure.
And i was wondering if I could skip the separate rigid analysis for overturning.






RE: Mat footing eccentricity within middle third, Overturning always OK?
RE: Mat footing eccentricity within middle third, Overturning always OK?
BA
RE: Mat footing eccentricity within middle third, Overturning always OK?
Mike McCann
MMC Engineering
RE: Mat footing eccentricity within middle third, Overturning always OK?
RE: Mat footing eccentricity within middle third, Overturning always OK?
Mike McCann
MMC Engineering
RE: Mat footing eccentricity within middle third, Overturning always OK?
can i assume overturning is also ok.
anyway, i decided to check overturning manually also.
RE: Mat footing eccentricity within middle third, Overturning always OK?
RE: Mat footing eccentricity within middle third, Overturning always OK?
RE: Mat footing eccentricity within middle third, Overturning always OK?
This check is especially important for corner of edge columns.
RE: Mat footing eccentricity within middle third, Overturning always OK?
RE: Mat footing eccentricity within middle third, Overturning always OK?
Back then(before the program automated that calculation), I drew up a quick image to help people get an intuitive feel for OTM safety factor based on the soil pressure diagrams. I have attached that image.
This image is perfectly accurate when the footing is considered rigid (and mats are not usually rigid). Even so, the goal was to give our users an approximate, intuitive and visual way to go from soil bearing to overturning safety factor.
FWIW: The most instructive aspect of this image is that if 50% of your mat is in compression then that approximately corresponds to a 1.5 safety factor for overturning. As long as you achieve that, you are usually in good shape.... I hope this helps.
RE: Mat footing eccentricity within middle third, Overturning always OK?
p = (D+L)/A^2 ± M/S where p is the pressure at the edge of footing.
If the load is at the kern, then M = (D+L)S/A^2 = (D+L)A/6.
Overturning moment = M
Stabilizing Moment = 0.6D*A/2 = 0.3D*A
0.3D*A = (D+L)A/6 (equating stabilizing moment to overturning moment)
D/(D+L) = 0.556
If dead load is less than 0.556 (D+L), overturning will govern the design.
A similar argument could be made for the mat.
BA
RE: Mat footing eccentricity within middle third, Overturning always OK?
If D < 1.25L (or L > 0.8D) then overturning wil govern the design.
BA