Impact of stepped footing on calculation of sliding
Impact of stepped footing on calculation of sliding
(OP)
We have a DSA plancheck comment that insists on the fact that the overall sliding of the building is reduced at areas where we have stepped footings.
Our geotechnical engineers disagrees with the plan checker, but Mr plan checker is asking him to prove via existing publication that there is no sliding reduction due to the stepped footing.
Does anyone know of such publication? Have any of you run into this issue? Is the plan checker right? Is my geotechnical engineer right?
I can see a potential reduction in one direction (towards the hill), but not in the other (see attachment)...
http:/ /files.eng ineering.c om/getfile .aspx?fold er=8632527 b-cfb1-4b2 0-a430-c74 581b2d784& amp;file=s liding.pdf
Our geotechnical engineers disagrees with the plan checker, but Mr plan checker is asking him to prove via existing publication that there is no sliding reduction due to the stepped footing.
Does anyone know of such publication? Have any of you run into this issue? Is the plan checker right? Is my geotechnical engineer right?
I can see a potential reduction in one direction (towards the hill), but not in the other (see attachment)...
http:/





RE: Impact of stepped footing on calculation of sliding
RE: Impact of stepped footing on calculation of sliding
I agree with hokie. I have only done one sloped footing and it was sufficient. I haven't done the calcs, but I'd bet that the stepped footing is more stable.
RE: Impact of stepped footing on calculation of sliding
RE: Impact of stepped footing on calculation of sliding
If the sliding is reduced, HOW MUCH is it reduced by?
I don't think it is right to completely ignore the friction in the stepped area (and sliding won't work anymore).
Do you guys know of any litterature that quantifies the reduction?
Why is there a reduction downhill? Isn't friction acting the opposite direction as the force, as I sketched out in the attachment?
RE: Impact of stepped footing on calculation of sliding
Regards,
DRG
RE: Impact of stepped footing on calculation of sliding
Thanks for your post.
RE: Impact of stepped footing on calculation of sliding
RE: Impact of stepped footing on calculation of sliding
RE: Impact of stepped footing on calculation of sliding
For seismic considerations, it is either sliding FS or bearing capacity or earth pressures. For sliding FS, you can reduce FS to 1.5/1.33 or to FS = 1.1 For B.C., you can increase allowable by 1/3 rd. For earth pressures, if walls are shorter than 12 ft, they don't apply & for taller walls you can use the inverted seismic triangle but then you can reduce all your F.S. to 1.1
I have to agree with your Geotechnical engineer.
RE: Impact of stepped footing on calculation of sliding
RE: Impact of stepped footing on calculation of sliding
If you replaced the foundation soils with strong rock cut in stairsteps, all the movement would be translational, with no decrease in sliding resistance. Since the foundation soil is not 'stronger than dirt' (BigH is old enough to remember those detergent ads), the reduction might be to account for shearing through the soil that allows the footing to move downhill as well as horizontally. It might be the checker's way of accounting for the global stability issue.
KPFFIRVINE - Ask the plan checker for a written explanation of why the reduction occurs and how much it should be. We have a divergence of opinion here, and we might do better if we knew where he's coming from (soil mechanics or outer space
RE: Impact of stepped footing on calculation of sliding