"Non convergence of nonlinear problem" for simple load cases in model with unidirectional supports, releases, or soil (uplift allowed) in Robot Structural Analysis

Autodesk Support

Dec 4, 2024

Products and versions covered

Issue:


"No convergence of nonlinear problem" reported for simple load cases (for example wind load case), while all combinations are convergent, in a model with unidirectional (UZ+ or UZ-) supports, unidirectional releases, elastic soil (in a panel thickness definition) or where bracings have been declared as 'Tension only' bars.
No convergence error 

Causes:

The load applied in divergent load cases causes the model to either move 'upwards' or rotate about its outer edge.


 

Solution:

As simple loads don't act alone, but together with other load cases (especially self-weight included).
Their results can be disregarded, as long as all defined combinations converge. In nonlinear models load scenarios are represented by combinations only.

Simple load cases should be excluded form being calculated by setting them as "Auxiliary load cases".
Follow the steps:

  1. Open Analysis > "Analysis type".
  2. Select non convergent load case.
  3. Click "Change analysis type" button.
  4. Check "Auxiliary"
  5. Button OK.

In case of non convergence of combinations in such model refer to "No convergence of nonlinear problem" during analysis in Robot Structural Analysis 

Note:

  • Divergent results should be ignored for some types of load cases (for example. Equivalent Lateral Force Method for seismic load generation cannot be set as auxiliary as they include automatic load generation),
  • The model should be designed for (converged) combinations with this (not converged) simple load case being one of their components.


 

Products:

Robot Structural Analysis Products;

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