March 17, 2010

Do You Ever Get the “LOCKED” Message on a Simple Beam Model?

Do you get an instabilities warning when you’re trying to do a simple 2D model in RISA-3D?

Instability warning

Below is the easiest way to test and fix the instability:

  • Open the Node Reactions spreadsheet, and see which joint is unstable.
  • In the Boundary Conditions spreadsheet, apply a Reaction to the joint in the degree of freedom that was LOCKED.
  • Re-run the model and examine the Node Reactions.

If the reaction that is restraining the instability is showing a ZERO force or moment, then the instability is inconsequential to the results. Also, if the reaction that is restraining the instability is showing a non-zero force or moment, then you have a problem with the model that must be corrected for you to get valid results.

Tags: RISA-3D Instability

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