Instability Warning on a Fully Braced Platform

[ronronpcengtips]

I'm designing a fully braced platform (braced vertically on both X and Z directions, beams released for My and Mz, columns having pinned supports). I know that this structure can stand but how can I eliminate the instability warning?

Thanks a lot.

 

[SteveGregory]

Are you analyzing this as a 2-D plane frame or a 3-D space frame?

 

[ronronpcengtips]

It's a 3d space frame. btw.

 

[ronronpcengtips]

Sorry, I didn't mention i'm using staadpro2005. ty.

 

[SteveGregory]

If you have a pinned supports, allow full fixity (no releases) for one member (post) at each of the pinned support joints. I think that will get rid of the instability.

 

[PEStructural]

Whenever I have a pinned support, I use the following support:

FIXED BUT KMX 1 KMY 1 KMZ 1

This is telling STAAD that a VERY small moment can be acheived at the supports. In reality, this is true. You could apply a small moment to a "pinned" support, and have no rotation.

This prevents any instabilities because all degress of freedom are resisted.

Just my $0.02