overturning stability for footing with biaxial moment
i have a footing with biaxial moment. how do i go about finding a "toe" or moment arm distance for calculating my resistance to overturning? thanks
check out our whitepaper library.
see this thread javascript
penindex(450,450,'
let's try that again.
i'm not sure if i'm missing something in that thread. i've gone through my process of calculating my effective area and found my maximum soil pressue. now i want to satisfy my overturning stability. for footing with single eccentricity i take my overturning moment about my "toe" or the outermost edge where the footing will actually overturn. like i said maybe i missed something in that thread but where does that location occur with two way eccentricity?
i just calculate the otm safety factor independently about each axis. if they are both good, then i consider the overall footing to be good.
i suppose you could calculate the stability ratio about a line perpendicular to your eccentricity which starts at the corner of your footing.... that might end up being more accurate. but, i've never seen anyone do it that way.
with two way eccentricity, there are two toes, one for mx and one for my. if the footing is square, you need only consider the maximum moment. but if the footing is rectangular, you must consider both.
best regards,
ba
simple enough. thank you.
take a look at the thread referenced by strucuraleit. the sixth post is mine and contains an attached pdf of a mathcad file i wrote for footings with biaxial moments. sheet 3 has an interaction formula for overturning stability. i wrote this interaction myself so you won't find it in any literature. it combines the overturning effects in the two directions. ignore the "0.75" factor in the test to the right of the interaction formula as it no longer applies.
miecz,
i do not understand your last comment. please elucidate.
best regards,
ba
miecz,
okay, sorry i was not able to find the file you were talking about. now i have found it. and, having found it, i still don't understand it. so far as i am concerned, it is a pile of garbage.
overturning may occur in either the x of the y direction. the expression given in your file for safety factor on overturning has no merit whatever!
best regards,
ba
ba,
the expression that i wrote for overturning safety is not based on experimental test. so, i agree, it has little merit. that's why i didn't offer it up at the beginning of this thread.
having read the other responses, i see that none of them are based on experimental evidence, or come from the literature. so, as i see it, we're into the realm of measured opinion here.
when i imagine a footing with overturning moment in one direction with some safety factor against overturning, and then add a force in the other direction, i feel that there is a reduced safety against overturning resulting from the additional moment. so, i don't believe the safety factors are independant.
the formula is my attempt to quantify the interaction. constructive criticism is always welcome.