Buckling strength
Buckling strength
(OP)
I do have a complex structure modeled using shell element (FEMAP with NX-NASTRAN) under a combination of loads in different directions. it is required to have the stresses be less than 80% of the buckling strength of the structure. The question is how to check the buckling strength of the structure (the whole assembled structure) using Finite element. Actually I applied all the loads and run the analysis for buckling and I have the critical buckling factor value (eigenvalue) but I am not sure if this value is valid for a complex struture under a combinations of loads in different direction. I would greatly appreciate any comments in this regards.





RE: Buckling strength
RE: Buckling strength
RE: Buckling strength
RE: Buckling strength
An eigenvalue analysis is not appropriate although it may determine a suitable shape for the initial imperfections. It may be necesary to include large displacements, and yield in the material model depending on the application.
RE: Buckling strength
Which imperfections to select is dependant upon the type of structure one is analyzing. For example, space frames are often thought as being connected with rigid and fixed connectors. This is a theorectical concept. One might consider a fixity factor less than 0.5. For plate components, the displacement pattern resulting from either symmetric or non symmetric loads should be considered. You may want to also consider discontinuity offsets for welded plates. If the structure is a conic, then there are a number of harmonic displacement patterns one needs to consider.
It requires considerable thought as to the selection of imperfection geometry for nonlinear anaysis to be applied correctly. Sometimes adjacent mode patterns can couple and produce lower buckling strengths than those to be considered independently.
RE: Buckling strength
Whether or not you need a non-linear analysis with imperfections depends a lot on the type of structure, the type of loading and how agressive you are with your buckling criteria. If you set a large safety factor on your predicted buckling load using an eigenvalue analysis, then that analysis may be sufficient. A 20% margin on buckling is not very much for most structures, and therefore you probably need to either run a nonlinear analysis or test the structure.
RE: Buckling strength
If you're certain that all the loads apply at the same time then use them, otherwise look for the worst case scenario to remove any doubt.
corus
RE: Buckling strength
An eigenvalue analysis is not appropriate although it may determine a suitable shape for the initial imperfections. It may be necesary to include large displacements, and yield in the material model depending on the application."
I agree with this. Garbage in = garbage out