instability warning and 0 stress result

[peaceatom]

Dear Eng-Tips Forum Members,

I have a RISA 3D model showing a cantilever truss resisting rotation along z axis due to perpendicular wind load.

This model currently shows instability warning and 0 stress for steel code check. Can anyone help with seeing how to fix this? Thank you

Model Detail:

1. construction:
The top glass panels are 6.417' apart adjacent to each other along the structure
These panels are connected to the z purlin, the z purlin connects to the 4" diameter steel tube below.
the steel tubes connects to the WF support at every 20' to 10' apart while these WF rotate freely about the center (z axis).
the WF support at one of the end is fix to hold the 2 pipes from rotating.

2. load path:
one end is fix and the other free.
when wind comes the glass panels are being pushed to rotate about their pivot point 2" below about the z axis (0,0,z).
When the panels wants to rotate due to the wind load, the 4" diameter steel tube are exercising its torsion capacity to resist the angular rotation.

goal:
The purpose of this model is to observe the glass panel stiffness in reducing some of the angular rotation since they are pin connect to the z purlin and to the steel pipe.
I suppose the glass structural support can be ignore or activate by turn on or off the "active" and/or "plane stress" check box

 

[msquared48]

More than likely you have a node that has one too many degrees of freedom designated as unrestrained.

At any node, even pinned, there has to be at least one element designated as fixed in the connection, otherwise the rotation of the node is unrestrained leading to a zero matrix and failure.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com