Behavior of gravity columns in seismic event

[compe_ad]

Hi all! Can you please help me to understand the behavior of gravity columns in seismic event?
After reading section 18.14 of ACI, I understood that it is okay for gravity columns to go to yielding under seismic event. If the demands on gravity columns exceeds the capacity during seismic event, we change the detailing not the DESIGN (we do not change original size of column which it get by designing columns based on gravity loads only. Doesn't the failure of gravity column in seismic event can be catastrophic and shouldn't we have to ensure it doesn't fail in seismic event as well.
Shouldn't there be check to limit to what degree the failure of column is accepted? Lets say for induced forces in seismic event, the demand to capctiy ratio for column is 3. Isn't this a serious issue and don't this indicate we may need to increase column size?

 

[jayrod12]

Did you not get the answers you were looking for in the last thread you started about this?

 

[compe_ad]

Yes I didn't get the answer I was looking for

 

[jayrod12]

For anyone looking, this is the previous thread thread507-520423.

Unfortunately I don't practice with the ACI manual, where I am we use the CSA manual. That being said, my comments from the other thread still apply as far as I understand things, you need to check gravity columns accounting for the lateral drift (not lateral loads) induced by a seismic event and ensure it still works. So unless the ACI is drastically different than CSA (which I've never thought they were that different) I believe you may be mis-interpreting that code clause.

But I'd love for someone with more experience with the ACI manual to weigh in.

 

[driftLimiter]

Is says design them for the load combo 1.2D + 1.0L + 0.2 S or 0.9D AND acting simultaneously with the design displacement.

Your columns must have a UC < 1.0 for this scenario. Or else you will need to satisfy all the requirements of 18.14.3.3 (in ACI 318-14).

This detailing will allow for seismic behavior akin to a special moment frame (i.e. ductile).

The thing to consider here, is that the column is already designed for the same gravity loads with no lateral displacement from your vertical design, for this condition it has a UC less than 1.0.

If your seismic displacement is pushing you way beyond 1.0 then something feels off to begin with, but you definitely need to detail the thing for more displacement ductility.
Is the displacement very large? Is your column already at a High UC just from gravity?? Something about either of those scenarios feels wrong and needs to be investigated. I would strive to get UC < 1.0 including design displacement.