The location of plastic hinges

[Ameri]

Hi all,

I do not know how it is possible to find the location of plastic hinges made in beams and columns of a 3D RC frame, and how to figure out in which order they take place after performing a time history analysis. Could anybody help me about the question please?

Thanks for your time.

[vesna]

How did you model beam and column elements?

[Ameri]

Dear vesna,
The beams are modeled as "nonlinearbeamcolumn" element, while the columns are considered to be "dispbeamcolumn".
I really appreciate your consideration.

[vesna]

you will need to write a script that will do it for you. You basically need to record curvature at two integration points that encompass the plastic hinge region. Using this curvatures you can calculate plastic hinge rotations. Plot them as a function of time for plastic hinges. Calculate rotation at yielding for each plastic hinge and use it to establish initiation of yielding.

[Ameri]

Dear Dr. Vesna,

I would be grateful if you could tell me which of the following recorders might be more suitable and reliable to capture the plastic hinges formed in a building during a time history analysis:

1) recorder element -file $filename.out -time -ele $elementnumber basicDeformation
2) recorder element -file $filename.out -time -ele $elementnumber plasticDeformation
3) recorder element -file $filename.out -time -ele $elementnumber ChordDeformation
4) recorder element -file $filename.out -time -ele $elementnumber plasticRotation
5) or any other recorders I am not aware from!

If I draw a comparison between the results obtained from the appropriate recorder, and the acceptance criteria recommended in FEMA, would it be helpful for indication of the plastic hinges formed in a building-frame due to earthquakes?

I appreciate your tolerance toward my frequent questions.

[Ella]

i am also interested in this topic.

[vesna]

I am not familiar with FEMA acceptance criteria and can not comment on that one.

basicDeforamtion and ChordDeformation create the same output and are better option than plasticDeformation or plasticRotation. Several users reported problems with plasticDeformation recorder. However, I think that the best way to capture formation of plastic hinges is by recording the curvature (as I explained in my previous post).

[Ella]

dear prof. vesna
could you please tell us that do you mean the best way we should use is use of these two recorders
recorder Element -time -file startele1.out -ele 1 section 1 deformation
recorder Element -time -file endele1.out -ele 1 section $lastsectionnumber deformation
to obtain the curvatures at the start and end points of beams and then multiple it by the length of beam to find rotations?
thanks a lot

[Ameri]

Dear Dr. Vesna,

Many thanks for your generous help. I wonder if you could tell me how can I figure out whether the captured rotations reveal formation of a plastic hinge or not? I mean when we record the rotations, maybe they are very small and no plastic hinge would occur. Therefor, there might be some criteria to recognize if the rotation is large enough to result in a plastic hinge. Actually I know how IDARC defines plastic hinges (it uses plastic moment formula proposed by Park et al. In 1984, and checks the elements for locations having a moment bigger than Mp), but I have no idea about the limitations regarding the rotation of plastic hinges. I would be grateful if you could help me to cope this problem. And as always, your help is greatly appreciated.

[vesna]

Ella,
You need to record the curvature at two integration points that approximately encompass the plastic hinge region, not the first and the last integration point of the beam.

Ameri,
You need to calculate rotation at yielding for each plastic hinge and use it as a trigger to trace plastic deformations within plastic hinges.

[Ameri]

Dear Dr. Vesna,

Thanks a lot for your wonderful help. You made everything clear and easy to follow. I hope someday return your kindness.

Kind regards

[Ella]

dear prof vesna,
thanks for your nice help.

[Georgia]

It seems this discussion is going to be the most informative topic debating on plastic hinges in opensees! thank you professor vesna ...

[liaopengzhan]

Very useful !