## Factor of Safety for overturning of footing with load in 2 directions

## Factor of Safety for overturning of footing with load in 2 directions

(OP)

I have a footing that has overturning in 2 directions and I'm wondering about meeting the factor of safety requirements for overturning. I have the footing.xls spreadsheet from Alex Tomanovich which I've used in the past for non-concentric foundations and found to be very accurate. It appears when overturning moments are applied in 2 directions it checks the FS in both directions using the full resistance load but wouldn't that be "double dipping" to use the same load to resist forces in both directions? I've always found the Tomanovich spreadsheets to be very accurate so maybe it's acceptable. The spreadsheet indicates that it's based on "Analytical Approach to Biaxial Eccentricity" by Eli Czerniak which was published in an ASCE journal in the 60's. I've tried finding a copy of that article but haven't had any luck.

In the past when I've had footings with biaxial bending I've use a proportion of the resistance load to resist the overturning in each direction. I was comfortable with this approach because it's conservative but for this particular case there could be large cost implications and design challenges so I'm looking for confirmation that it's ok to use the full resistance load to resist the overturning in both locations is acceptable.

Thanks.

In the past when I've had footings with biaxial bending I've use a proportion of the resistance load to resist the overturning in each direction. I was comfortable with this approach because it's conservative but for this particular case there could be large cost implications and design challenges so I'm looking for confirmation that it's ok to use the full resistance load to resist the overturning in both locations is acceptable.

Thanks.

## RE: Factor of Safety for overturning of footing with load in 2 directions

One way to look at this is to assume that the two loads have a singular resultant which should be used with the dead load (once) and with the "odd" shape of the footing in the resultant direction.

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## RE: Factor of Safety for overturning of footing with load in 2 directions

I'd think that'd inform the stability of the x-y loads?

f-d

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## RE: Factor of Safety for overturning of footing with load in 2 directions

## RE: Factor of Safety for overturning of footing with load in 2 directions

I've looked at a couple hypothetical conditions using the resultant overturning moment and if you calculate the resistance moment to the corner than the SF isn't any worse than looking at it in the 2 orthogonal directions which may be way some people just do that.

## RE: Factor of Safety for overturning of footing with load in 2 directions

## RE: Factor of Safety for overturning of footing with load in 2 directions

Dik

## RE: Factor of Safety for overturning of footing with load in 2 directions

## RE: Factor of Safety for overturning of footing with load in 2 directions

Dik

## RE: Factor of Safety for overturning of footing with load in 2 directions