Rotation of dispBeamColumn element

[niloufar]

Hi
I want to obtain the rotation of dispBeamColumn element during nonlinear timehistory analyses, and I used the below command:

recorder Element -file Data/chordDeformation1.txt -time -ele 1 plasticDeformation

but the results of plastic rotation are too small (that is numbers like 1.24e-11)
I know that the model has no problem, but I can not obtaine the coorect plastic rotation of elements. would you please help me.
I am so confused
Looking forward to your guidance
Thanks so much

[vesna]

Many OpenSees users reported the same problem which makes me think that there is a bug in that recorder type. I would avoid using it. Instead you can recorde curvatures and from curvatures you can calculate plastic rotations.

[niloufar]

Thanks so much dear vesna for replying
would you please tell me how can I recorde curvatures of an element? which command should I use? (My model is a 3-D model of a steel building)

Thanks again
Looking forward to your guidande

[niloufar]

Dear Vesna
would you please help me?

[niloufar]

how can i calculate curvature to obtain plastic rotation? would
you show me an example please?

[vesna]

To record the curvature you need to record section deformation.

recorder Element -file Curvature.out -time -ele 1 section 1 deformation

[niloufar]

Thank you dear vesna
I have 2 questions:
which column of output file indicates the curvature of section?
how can I calculate the plastic rotation of section from the curvature?
would you please give me an example?
looking forward to your guidance
best regards

[niloufar]

Dear vesna
I need your help

[Tas]

I would propose an answer and then wait for Vesna to confirm it (or not).

1. The plastic rotation in a point (-section) of an element, that corresponds to an integration point, is given by: the difference between the value of curvature obtained from the section deformation recorder and the curvature’s value that represent the yielding value (that is not given directly by the program) * Lp (that is user defined).

2. The columns that are viewed in the recorder output file correspond to the terms of the section that is used to model the element, if for instance is an aggregation section that “couples” axial and bending behavior (actually it just adds and it doesn’t couples) then the file contains a column for axial strains and a second column for curvatures.

3. Question: Does this “manual” way of obtaining plastic rotations concerns all kind of beam-column non linear elements: DBE, FBE and Beam with Hinges Elements?? or the recorder Element -file Data/chordDeformation1.txt -time -ele 1 plasticDeformation can be used for FBE and/or for Beam with Hinges Elements ??

Thank you niloufar and Vesna.

[vesna]

Thanks Tas for your responses to previous questions. I agree with both of your answers. I would just add one more comment. To see what are the columns of your output file, record them in -xml format rather that by using -file option.

3. DBE does not have such recorder option. So far, users were only complaining about FBE. It may work for the beamWithHinges element as the plastic hinge length is directly specified by users. However, you will have to test it to see if it works or not.

[niloufar]

Thank you tas and vesna
I have one more question:
I used dispBeamColumn elements, now how can I calculate the curvature value that represent the yielding value of the section * Lp ?
whould you please give me an example?
thanks you again and looking forward to your guidance.

[Tas]

Hi,

The value that is multiplied with Lp is equal to the difference between the value of curvature obtained from the section deformation recorder and the curvature’s value that represent the yielding value (and not just the last one..).

For how to obtain the yielding curvature you can read the topic: "Plastic hinges and forceBeamColumn elements"

[niloufar]

Dear Tas
thanks so much for your guidance

[niloufar]

I could obtain the curvature of the elements at both ends of them (including plastic and yielding curvature).
But the problem is that, I can't obtain the plastic curvature apart from the yielding curvature.
would you please give me an example to obtain the yielding curvature apart from the plastic curvature?

[amir70007]

Hi niloufar

Do you think that I can compare curvature results (deformation recorder) to FEMA criteria?
FEMA considers teta @ teta plastic with chord rotation.