I am modeling a simple RC Beam in Ansys with Perfect Bond between steel rebar and concrete. This is being done by going to menu item Prepocessor -> Coupling/Ceqn -> Coincident Nodes and in the menu I selected "All Appropriate".
I am getting the following error in the log file when I run the analysis:
"There are 25 small equation solver pivot terms (e.g., at the UZ degree of freedom of node 2776). Please check for an insufficiently constrained model."
Can someone please guide me where am I going wrong?
Dear Muhammad,
As Ayman explained, the pivot error is because of insufficient constraint 99% of the time and has nothing to do with mesh. The error you are getting is because of lacking of enough constraint, therefore, software can't solve the equation for calculating displacement at the specified node.
If you just change the mash and use even very fine mesh is not going to help resolving the issue and just the node number that ansys got problem will change. I suggest that you double check the constraint and rerun the model.
Hi Muhammad,
This "Solver Pivot Error" you are getting is probably due to the insufficiently constraints at the steel rebar node. Try to constraint the twist "rotation about the bar local axis" while keeping other two rotational degrees of freedom free as well as translational degrees of freedom. I hope this will solve your problem.
Good luck!
Thank you sir for your response.
I figured out the problem with my model was the mesh and I have now been able to develop what looks like a good mesh but the problem still persists BUT now the error is for 1 solver pivot term (instead of 25 earlier). The node on which this error is coming is on the top surface of beam (screenshot attached).
Dear Muhammad,
As Ayman explained, the pivot error is because of insufficient constraint 99% of the time and has nothing to do with mesh. The error you are getting is because of lacking of enough constraint, therefore, software can't solve the equation for calculating displacement at the specified node.
If you just change the mash and use even very fine mesh is not going to help resolving the issue and just the node number that ansys got problem will change. I suggest that you double check the constraint and rerun the model.
Thank you sir for your response.
I have additionally constrained my model in the UZ direction and the solver pivot error has been resolved.
Thanks for your help.
Hi, I have had the same problem recently.
- Ensure that model is adequately constrained. Constrain the Z - axis too of all supports.
- If this doesn't work, check that the element in use allows these degrees of freedom eg UX, UY, UZ
Cheers
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