RAM Elements - Huge Displacements

RE: RAM Elements - Huge Displacements

Nik — Mon, 07 Nov 2022 21:45:02 GMT

I am encountering the same issue. I checked the rotation at each node and they are a max of 5", which I am unable to track the node. (It does not display the node number). I am not sure what is causing the warning to pop-up! Any advise regarding this? Thanks in advance!

RE: RAM Elements - Huge Displacements

Warren Negron — Thu, 18 Aug 2022 13:38:26 GMT

Hello Seth,

Thank you for providing your expertise. This was indeed the solution to my problem. I appreciate all your help

RE: RAM Elements - Huge Displacements

Seth Guthrie — Wed, 17 Aug 2022 22:53:29 GMT

Your model is set to run as a 3D frame, but it's a 1D beam and there no RX restraint so it can spin. If you look at the analysis results you might see large RX rotations. You can restrain RX at one end to easily avoid the issue (or both ends, or use an RX spring). Alternatively you can limit the analysis DOF to 2D frame, but don't use that approach where you are applying twist forces as you have here.

RE: RAM Elements - Huge Displacements

Warren Negron — Wed, 17 Aug 2022 21:34:02 GMT

Similar to Stephani's issue. I am getting a "Huge displacements, structure is not stable." error message for a simple ram elements model. I checked the deflection and the magnitude is 1/2" way under 1". I am not sure what is going on. I do however, need to account for torsional moment affects due to an eccentric load combined with weak-axis bending from lateral wind load. Any help on what could be wrong in the model would be appreciated. Also, see attached the link to the model and a sketch of what I am describing.

communities.bentley.com/.../22116_5F00_03_5F00_08.17.22_5F00_Girt-Design.zip communities.bentley.com/.../Ram-Elements-Question.pdf

RE: RAM Elements - Huge Displacements

Karl G — Fri, 02 Oct 2015 17:51:46 GMT

Stephani,

Thank you for posting your file.

Some of the columns (look at Members 9, 11, 12, 17, 27, 32, and 62) are pinned at the base (TX, TY, TZ restraint) and have only pinned beams framing into them. These column are free to twist about their own axes without restraint. This rotation is the cause of the large displacement. Fixing RY (torsion) at the base of these columns will resolve the problem. You will find that there will be no torsional moment reaction at the base.

You can omit the RY restraint at the columns that have a horizontal brace framing into them, since the horizontal brace provides some torsional resistance.

Karl

RE: RAM Elements - Huge Displacements

Karl G — Fri, 02 Oct 2015 14:44:54 GMT

The large displacement may be a large rotation and associated with a torsional instability.

If you would like us to review the model, please share it using the Secure File Upload link in the bottom left corner of this web page and post the file name after it is uploaded.