Instability type 3 - and partial stiffness coeff.

[Anonymous]

I have a question regarding instability type three. During the design of steel structure which there are many releases defined in it. Can I solve the instability type 3 by defining a partial stiffness coeff. If yes, what is the optimal values recommended, and how these values will affect the calculation of the results?

[Krzysztof_Wasik]

Hi @Anonymous 

In some cases instability type 3 can be ignored. Please refer to 

https://knowledge.autodesk.com/support/robot-structural-analysis-products/troubleshooting/caas/sfdcarticles/sfdcarticles/Can-instability-type-3-error-be-ignored-in-Autodesk-Robot-Structural.html

If extensive displacements/rotations are caused by too many releases define small elastic coefficient instead of fully released degrees off freedom in releases. It should stabilize model (block unexpected nodes rotation).

Smaller elasticity defined in releases , smaller influence on force distribution will be obtained.

When elastic releases are used DSC algorithm should be set in Tools >Job Preferences >Structure Analysis.