ACI318-14 Special Moment Frame Column Transverse Reinforcement Detail

[JTM2020]

Hi, this is my first post.
Please guide me if I'm doing anything wrong, or similar question is already posted somewhere.

I'm designing special moment frame column detail.
According to ACI318-14, "18.7.5 Transverse reinforcement", column needs special detailing (closely spaced confinement) at plastic hinge zone (within L0). I'm bit confused and appreciate if someone can help me understanding the following questions.

1) Is this special detailing of confinement only required for columns where flexural yielding is likely to occur? or all column needs this detailing regardless of having flexural yielding or not?

2) Is satisfying the "Strong Column-Weak Beam" requirement as in 18.7.3 enough to prove that column will not have flexural yielding? hence special detailing is not required for these columns.

3) If question 2) is "NO", is non-linear-static-push-over-analysis be accepted to identify the hinge locations?

Thanks in advance.

 

[HTURKAK]

Hi JTM2020, i looked to your profile and you joined Eng-Tips Forums today (on July 1, 2021).. so, as per the forum rules you must be forum member to write thread.

I will try to respond your questions acc. to my best knowledge,

- No.. all columns of SMF's needs this detailing regardless of having flexural yielding or not.. Gravity only columns could be exempted..

- No.. satisfying the "Strong Column-Weak Beam" requirement as in 18.7.3 is not enough to prove that column will not have flexural yielding. Consider storey mechanism vs sway mechanism.. eventually plastic hinging may develop at columns starting with 1st floor columns ..

- IMO , yes ... push over analysis is very useful to see the sequence of plastic hinges developing.. (The procedure is , the user locate the pushover hinges on the model and assign them with hinge properties , then the user can review the pushover displaced shape and sequence of hinge formation on a step-by-step basis ..)

I will suggest you to look the following doc. and worked examples ..

 

[JoshPlumSE]

1) Is this special detailing of confinement only required for columns where flexural yielding is likely to occur? or all column needs this detailing regardless of having flexural yielding or not?
**The purpose of the detailing is that the confinement allows the column to undergo more ductile post-yield behavior. So, conceptually it is only required in the columns that are part of the moment frame itself and in the locations near where a plastic hinge is anticipated to form. It's about ductility in the area near the hinge and increasing the column to experience this extra strain without losing its gravity load carrying ability.**

2) Is satisfying the "Strong Column-Weak Beam" requirement as in 18.7.3 enough to prove that column will not have flexural yielding? hence special detailing is not required for these columns.
**Definitely not. That provision helps, but it doesn't guarantee anythiing. In fact tests and non-linear models often show building that obey SC/WB relationships still have plasting hinging in the columns too. Not as much as building that don't obey SC/WB relationships, of course.**

3) If question 2) is "NO", is non-linear-static-push-over-analysis be accepted to identify the hinge locations?
**I don't think so. NL pushover is more about retrofit than it is about design. To me, it's never been all that difficult to identify where in the column the confinement reinforcing should go. So, I'm a bit confused by the question.**