RE: Instability at Joint

Don't pin all your members in torsion (MX in STAAD.pro), that's just asking for a trouble as the members can spin about their own axis when connected members and/or supports are not rigid.

For more on solving instabilities check these posts:

• communities.bentley.com/.../staad.pro-instability-and-zero-stiffness
• communities.bentley.com/.../ram-instability-in-finite-element-analysis.aspx