Failure to analyze after adding zero-length elements

[shiRo]

Dear STKO team.
I am trying to model the analysis of RC columns under cyclic loading and have successfully obtained force-displacement curves. Then I am trying to simulate bond slip using zero length element but the model is not working properly, can you help me to check my model, thanks a lot!
Best regards

[kesavapraba]

Hi, I identified two issues in your model: a missing connection between the column and the bottom fixed node, and unnecessary points defining the zero-length element. I rectified these errors and adjusted some analysis settings, and the model now runs successfully. Please check the attached model.

[shiRo]

Hi, I identified two issues in your model: a missing connection between the column and the bottom fixed node, and unnecessary points defining the zero-length element. I rectified these errors and adjusted some analysis settings, and the model now runs successfully. Please check the attached model.

First of all thank you very much for checking it out for me and helping me modify it, it now runs properly for analysis.
However the force-displacement curves of the vertices I got from checking the running analysis don't seem to be quite normal, the graph below is the result I got before I added the zero-length element, and they are so different from each other, can you help me again to see what the problem is? Thank you again!
best wishes
ShiRo

[kesavapraba]

Hi, To better understand your analysis, I'd appreciate some additional explanation on how you compared the numerical results. Providing details on the comparison criteria and, if possible, a visual representation like a figure or chart, would be immensely helpful.

[shiRo]

Hi, To better understand your analysis, I'd appreciate some additional explanation on how you compared the numerical results. Providing details on the comparison criteria and, if possible, a visual representation like a figure or chart, would be immensely helpful.

Sure. To start with an example, Figure 1 below shows two hysteresis curves, where the black curve takes into account bond slip between the reinforcement and the concrete, and the gray curve does not take into account bond slip.
My goal is the same, to use zero length elements to make a comparison of the hysteresis curves of my columns before and after taking bond slip into account, the hysteresis curves before adding the zero length elements are above where I have attached them.
The hysteresis curve I got after running the model you modified for me was anomalous, and although I made some adjustments to it later, the results were not satisfactory, attached is a plot of the anomalous analysis results.
Finally, I am attaching the model without the zero-length element added.

[STKO Team]

There is a mistake in how you are interpreting the zero-length element for bond-slip.

First, it doesn't make sense you use a uniaxial material in the global X direction (shear for the beam). If you using only 1 phenomenological model, it should be a moment-rotation, thus it should go into the appropriate DOF (not the first 1).

Another, more accurate, approach is to use the material you are using (Bond_SP01). But this material is for steel. So you need to put it into a Fiber-section, similar to the section you have for the column.

Now you need to choose:
If the steel parameters you use for slip are DISPLACEMENTS (as you did), you need to make the concrete for that section with infinite fracture energy (no softening). And this fiber section (that now represents stress VS displacement) MUST go into a ZeroLengthSection!

The other option is to convert the slip displacements into strain, and use it inside the column itself, at the end zones, smeared along the plastic hinge length, using a Hinge integration scheem

[shiRo]

There is a mistake in how you are interpreting the zero-length element for bond-slip.

First, it doesn't make sense you use a uniaxial material in the global X direction (shear for the beam). If you using only 1 phenomenological model, it should be a moment-rotation, thus it should go into the appropriate DOF (not the first 1).

Another, more accurate, approach is to use the material you are using (Bond_SP01). But this material is for steel. So you need to put it into a Fiber-section, similar to the section you have for the column.

Now you need to choose:
If the steel parameters you use for slip are DISPLACEMENTS (as you did), you need to make the concrete for that section with infinite fracture energy (no softening). And this fiber section (that now represents stress VS displacement) MUST go into a ZeroLengthSection!

The other option is to convert the slip displacements into strain, and use it inside the column itself, at the end zones, smeared along the plastic hinge length, using a Hinge integration scheem

Hi，I apologize for not being able to work on this one recently due to some other reasons, I tried to understand your suggestion and I wasn't able to come up with a clear way to fix the model, I then studied #06 in Advanced E-learning Courses and tried to improve on my previous model but once again I had convergence issues. Would you be able to help me check if I have followed the correct steps to build the model and find the reason why the calculations are not converging? Thanks a lot!

[kesavapraba]

Hi, the solution given in the response by STKO_Team is different from the one you followed in the model. I have modified your model following the solutions provided by STKO_Team. Please check if the results make sense. Attached is the revised model.

[shiRo]

Hi, the solution given in the response by STKO_Team is different from the one you followed in the model. I have modified your model following the solutions provided by STKO_Team. Please check if the results make sense. Attached is the revised model.

Thank you very much for your help, I still have a question, how to realize "the concrete with infinite fracture energy (no softening)" in STKO Team's suggestion?

[kesavapraba]

Hi,. For concrete02 material, the ultimate strain should be changed to match the fracture energy.