Hi,
I need some help with my model. I have uploaded a secure file.
Why is there an instability at node 16?
When I fix the node and run the model and look at load combination S6 = DL + 0.6WLZ, the members 7 and 8 do not come up with the same results. The nodal displaces at the top of the columns are also different in Tz.
Am I missing a nodal release somewhere? Thanks!
The instability occurs because all members framing into the node have moment releases. As a result, Node #16 is free to spin without restraint about its own axis about the global x-axis. To eliminate the instability fix the end of one of the members (suggest Member 14) into the node.
More on this type of instability can be found on this page. The sections titled "Pinning the Free End of a Cantilever" and "Beam, Column, and Brace Intersections" apply to the instability errors and warnings in your model