Electric_Steel
Structural
- Oct 30, 2023
- 6
(Apologies for a repost, but trying again in the general group to hopefully reach more eyes)
Hello all,
Long time reader, but first time posting a question on Eng-Tips. I have a project with significant seismic forces (PGA.m > 2.0) and we need to support a quite heavy piece of equipment (~400kips) on a reinforced concrete mat slab. Currently we are trying to avoid deep foundation elements if possible and economize where it makes sense. As you might expect, overturning and sliding (i.e. - stability) is controlling the size of the slab.
ASCE 7-16 section 12.4.2.2 seems to allow the engineer to exclude vertical seismic effects during foundation design, but we are trying to determine how far does this exception goes, and if this can be applied to overturning/sliding checks. This exception would certainly help us economize the design, but several folks in my office are hesitant to rely on this code section. I think there are at least a few reasons for this reticence:
1) The commentary doesn't explain the "why" behind this section. If we understood the logic of this exclusion for foundation design, we could better use our engineering judgement. Does anyone have any insight into the "why" of this exception?
2) The section states that vertical seismic may be neglected for the purposes of "determining demands on the soil-structure interface of foundations". What exactly is meant by "soil-structure interface"? This term is not clearly defined in Section 11 (as far as I can tell interface is different from soil structure interaction). Should we be interpreting this section to only apply to some foundation checks and not others? Perhaps this exclusion is just when determining contact pressures (i.e. - bearing capacity checks)?
Let me know what you think or if I might have overlooked a good resource. Always curious to hear others' perspectives. For the client's sake, I'd like to get more comfortable with this section and leverage this exclusion if possible.
--Cheers!
Hello all,
Long time reader, but first time posting a question on Eng-Tips. I have a project with significant seismic forces (PGA.m > 2.0) and we need to support a quite heavy piece of equipment (~400kips) on a reinforced concrete mat slab. Currently we are trying to avoid deep foundation elements if possible and economize where it makes sense. As you might expect, overturning and sliding (i.e. - stability) is controlling the size of the slab.
ASCE 7-16 section 12.4.2.2 seems to allow the engineer to exclude vertical seismic effects during foundation design, but we are trying to determine how far does this exception goes, and if this can be applied to overturning/sliding checks. This exception would certainly help us economize the design, but several folks in my office are hesitant to rely on this code section. I think there are at least a few reasons for this reticence:
1) The commentary doesn't explain the "why" behind this section. If we understood the logic of this exclusion for foundation design, we could better use our engineering judgement. Does anyone have any insight into the "why" of this exception?
2) The section states that vertical seismic may be neglected for the purposes of "determining demands on the soil-structure interface of foundations". What exactly is meant by "soil-structure interface"? This term is not clearly defined in Section 11 (as far as I can tell interface is different from soil structure interaction). Should we be interpreting this section to only apply to some foundation checks and not others? Perhaps this exclusion is just when determining contact pressures (i.e. - bearing capacity checks)?
Let me know what you think or if I might have overlooked a good resource. Always curious to hear others' perspectives. For the client's sake, I'd like to get more comfortable with this section and leverage this exclusion if possible.
--Cheers!
