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Dear STKO team,
Thank you very much for developing such a convenient SKTO software, which has been very helpful for my modeling work.I will always keep an eye on the development of the STKO software and recommend it to my classmates.
Firstly, I want to simulate the seismic response of a RC joint using STKO. The detailed introduction of this joint is shown in the following figure.


Below, I will send you two model files that I have already created. These two files are almost identical, except that the Joints use Joint2D element and BeamColumnJoint element respectively.
The model with Joint2D element can achieve perfect results, but the model with BeamColumnJoint element cannot. I don't know where the problem lies, I hope you can help me take a look. In addition, I have found an issue where the calibration of spring elements in the Joint element uses the moment- rotation response curve instead of the stress-strain response curve, otherwise it will not converge. As shown in my attached model, I'm not sure if you have the same understanding.

Finally, I would like to ask how to output the response curves of the specified springs of BeamColumnJoint Element and Joint2D Element during the loading process. For example, I want to know the respective rotations of bar-slip springs and shear-plane springs.

Looking forward to your reply. Wishing you a happy life.

Hi, There is no figure attached in your post. Anyway, uniaxial stress-strain relationship can be used in case of assigning physical property in material point but not for capturing section response. Only integrated responses, such as axial force-displacement, moment-rotation, shear force-displacement are assigned in the zeroLength elements of the Joint2D element. Because of this, moment-rotation, instead of stress-strain relationships, are used in the Joint2D element.

For force-displacement (moment-rotation) output, you need to enable "material.stress" and "material.strain" in MPCO recorder. The results can be seen from the post-processor Gauss plot. Each zeroLength element has one Gauss point, which can been seen at the location of zeroLength element.

Dear kesavapraba,
Thank you very much for your reply. Here is the figure of the joint model. Now I am attaching the two Joint models that I have built, where the model with Joint2D Element has a perfect result, but the model with BeamColumnJoint Element does not give the correct results. I don't know if there is an error in the BeamColumnJoint Element settings in my model. Looking forward to your help in looking at the models.

Here is the file of the two joint models. In addition, you said “For force-displacement (moment-rotation) output, you need to enable "material.stress" and "material.strain" in MPCO recorder. The results can be seen from the post-processor Gauss plot. Each zeroLength element has one Gauss point, which can been seen at the location of zeroLength element.” However, I checked the MPCO recorder option and select the material stress-strain output, but the Joint center point will not show the Gaussian integration point in post-processing, and I still can't select it to output the moment-rotation response of the Joint plane.I wonder if you could help me try it, I would appreciate it! Very much looking forward to your reply and hope you have a great life!

These models are a bit difficult to use and poorly documented.

Regarding the Joint2D model:

• Pay attention to the node numbering. I think you are putting nonlinear rotational springs on the column side only.
• You are doing DisplacementControl analysis so you should not be able to record reactions on the beam dofs. The only reason you can with the Joint2D is because it internally use a MP constraint (without including it in the reactions) so that you can read reactions on the node between the beam and the joint

Regarding the beamColumnJoint. It's hard to tell what is going on. Try to use the example they provided and check whether it gives the expected results or not. At least, you can understand if it's a bug or a modeling error

Thank you very much for your answer, I will keep trying. Have a nice life.

You're welcome