How to force a Buckling / Eigenvalue analysis to ignore beam offsets? 1

[jean15paul]

Hi everyone. I'm trying to run a buckling analysis on a model that has a lot of stiffened plates, where the plates are modeled with CQUAD4's and the stiffeners are CBEAM's with offsets.

When I try to run the linear buckling solution (SOL 105), I get a fatal error for each offset element that says:

*** USER FATAL MESSAGE 6174 (EBEMD)
BEAM ELEMENT (EID=1141) WITH OFFSETS ARE NOT SUPPORTED IN DIFFERENTIAL STIFFNESS
OR NONLINEAR ANALYSIS. REMODEL WITHOUT USING BEAMS WITH OFFSET.

At my last job we used NX Nastran, and there was a command to force Nastran to ignore beam offsets. I'm pretty sure it was "SYSTEM(463)=0" in the File Management section. Unfortunately it's not working for me now, possibly because at my new job we're using MSC Nastran. I "SYSTEM(463)" doesn't appear in my MSC Quick Reference Guide.

Does anyone know of a way to run a buckling analysis on a model that includes element offsets?

FYI, I search this forum and the only thread I found was this one, but it didn't get answered. Any help would be GREATLY appreciated. thread825-259152

 

[stresscalcs]

Hi

Beware, MSC used to tell you that buckling analysis results should not be relied upon when using elements with offsets. I think the message is telling you that.

You do not explicitly say what versions of anything you are using but with MSC Nastran 2010 things appear to have changed. See

http://www.scribd.com/doc/42790341/33/Offsets-for-Beams-and-Shells.

Richard

 

[jean15paul]

Thanks for the reply stresscalcs. I'm using Patran 2012 and MSC Nastran 2012.

In the time since I posted this I found some information on the new capability in MSC Nastran to correctly consider offsets in buckling and nonlinear analysis. It's done through the use of the MDLPRM card, specifically MDLPRM, OFFDEF, <option>. This capability was added in MSC Nastran 2010

There appear to be a few different options that instruct Nastran on how to handle offsets, and I need to read up to understand them. But from what I've read so far it appears that MSC Nastran can now correctly use element offsets in differential stiffness or nonlinear analysis.