Only tension elements for bracing problem
Hi @Anonymous
The same problem you face here is explained in the Autodesk Webinair: Instability warnings during model analysis by Mr. Artur & Mr. Rafal exactly at the 5th minute of the video, you can watch it here: https://www.youtube.com/watch?v=5CCLzG12JQ4&list=PLY-ggSrSwbZqow_60fiqJwS69mg1nQMzk&index=16
He said that you should make the diagonals and posts as truss members and the upper and lower chord should be continuous (one piece) and make a release to it (pinned pinned release) not truss bar.
Note: truss bars shouldn't have releases too.
That method from the webinair would solve the instability but causes a moment in the upper and the lower chords.
So, i have another approximate to solve both of that and won't affect the results much.
As you can see in the picture:
I have made the diagonals and the posts as truss members, roof and wall bracing too.
But, fot the upper and lower chord members i have made a custom release for them as an elastic release with partial stiffness coefficients in Mx (start), My (start & end) and Mz (start & end).
Then, i have made that partial elastic pinned pinned release to every member of the chords.
As i design the purlines as continuous, i have made a release to it's start and end only (at the 1st and last truss).
That will solve your instabilities.
Hi @Anonymous
The main problem is the 2 purlins at the top of the roof. I deleted one row of them then the model converge.
Set all cases that don't act alone as auxiliary
Set upper and lower chord as simple bares (not truss)
Set roof diagonals as "neglected" so as not to interfere with load distribution
Model attached
M. Agayr
Did you find this post helpful? Feel free to Like this post.
Did your question get successfully answered? Then click on the ACCEPT SOLUTION button.