I have no issues with my plastic hinge settings, and it converges well in V14. However, when opening the file in V20, it fails to converge. How should I address this?
I have set the hinge overwrites with Relative Length of Line Element at Hinge (0.02) or (0.05) and Limiting Negative Stiffness Ratio (1.0). Both Maximum Total Steps per Stage and Maximum Null (Zero) Steps per Stage are set to fifty thousand steps. However, the results appear as shown in Figure 1 and Figure 2, whereas I intend to achieve the result depicted in Figure 3. How can I resolve this?
Hi yi-ting Lin
The plot shows that the analysis is converging, but the convergence is slow. The unbalanced force is decreasing with displacement, but it is still relatively large.
There are a few things you can try to improve convergence:
- Increase the number of iterations per step.
- Use a different plastic hinge model.
- Increase the limiting negative stiffness ratio.
- Use a displacement-controlled loading scheme.
If you are still unable to achieve convergence, you may need to contact OpenSees support for assistance.
Here are some additional tips for improving convergence:
- Use a consistent mesh density throughout the model. Avoid using sudden changes in mesh density, as this can lead to convergence problems.
- Use a graded mesh around the plastic hinge region. This will help to refine the mesh in the area where the most plastic deformation is expected to occur.
- Check the boundary conditions of the model to make sure that they are correct.
- Check the material properties of the model to make sure that they are correct.
Another thing you can try is to use a different plastic hinge model. The default plastic hinge model in OpenSees is the Ibarra-Medina-Krawinkler model. This model is quite general, but it can be difficult to converge in some cases. Try using a different model, such as the Menegotto-Pinto model or the Concrete Damaged Plasticity model.
You can also try increasing the limiting negative stiffness ratio. The limiting negative stiffness ratio controls how much the stiffness of the plastic hinge can decrease. A higher limiting negative stiffness ratio will allow the stiffness of the hinge to decrease more, which can help to improve convergence.
Finally, you can try using a displacement-controlled loading scheme. A displacement-controlled loading scheme will apply a displacement to the model and calculate the corresponding forces. This can be more stable than a force-controlled loading scheme, especially for models with plastic hinges.
Yousef Bahrambeigi Thank you for your response, but there might be differences between SAP2000 and OpenSees, right? When you mentioned 'Increase the number of iterations per step,' which one is it in the screenshot? Please provide the complete step name. Is it 'Maximum Constant-Stiff Iterations per Step'? I have checked the user manual, but after reading it several times, I still find it challenging to understand. Thank you for your assistance.
Hi yi-ting Lin
- Check the boundary conditions and loads to make sure they are defined correctly.
- Review the material properties to ensure they are appropriate for the analysis.
- Adjust the analysis settings, such as tolerance limits or the maximum number of iterations allowed.
If you're having trouble understanding the user manual, it may be helpful to:
- Look for tutorials or example problems similar to your case.
- Consult with a community or forum where users of the same software share their experiences.
- Reach out to technical support for the software.
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