The proposed static analysis does not converge.

[DMY0119]

Please help me. This is a two-storey masonry structure built using the equivalent frame modelling approach. When performing gravity analysis and proposed static analysis to obtain the hysteresis curve of the structure, the gravity analysis works fine, but the results of the proposed static analysis always show no convergence. I'd like to know exactly what is causing the non-convergence. There is an associated model scd file below.

[kesavapraba]

This issue arises due to non-invertibility of system matrix. Near zero (perfect plastic) material can be one of the reasons. You can try using Concrete02 (assigning a low tensile strength, for instance 0.1 MPa) instead of Concrete01 (which has perfect zero for tensile strength). Zero stiffness in the tension zone of concrete01 might cause issue for forcebeamcolum while doing the matrix inversion. Similarly, check other material definition as well.

[DMY0119]

Firstly, thank you for your help. However, after I changed the material in it to "concrete02", the result of the proposed static analyses is almost unchanged and still does not converge. Below are the screenshots of the parameters of concrete02 and the results of the analysis.

[kesavapraba]

Ok, I would suggest you to try doing linear elastic analysis first, by assigning elastic properties and elasticBeamColumn element for all piers and spandrels. Once linear elastic analysis runs fine, subsequently you can assign forceBeamColumn element to a single pier with nonlinear material properties and debug where the problem arises.

[DMY0119]

Thank you for your answer. I have used the method you mentioned, but it seems that I cannot find the source of non-convergence. I would like to know if this non convergence is caused by the model parameters of pinching4, incorrect use of rigidlink, or the method of establishing rigid regions.

[kesavapraba]

Ok, Please share the recent linear elastic model with one nonlinear element that you tried. I will try to debug the cause of convergence issue.

[DMY0119]

Here is my final model file. Thank you very much for your help.

[STKO Team]

There are 2 sources for the convergence issue:
1) Your concrete does not have any tensile strength and since you don't have any reinforcement, it can quickly become unstable. Can you try the DamageTC1D uniaxial material?
2) Your shear material has softening. In a force-beam column you have several integration points, but constant shear so it's hard for the force-beam column to find convergence after softening.
3) Regarding the reference load for disp-control, make it larger (possibly of the order of magnitude of the expected base shear), otherwise the load-multiplier (unknown of the disp-control) is far from the solution
4) Pay attention to your stiff elements. Make sure they are not too stiff