workbench buckling results 1

[romanm40]

Hi,
When analyzing a structural truss for buckling under multiple loads I try to get a load multiplier to be equal one by changing one of the loads as explained by manual. By achieving this I assume the loads as critical. Performing stress analyses of the same truss under critical loads I found that compression stresses in critical members much higher than allowable. I would appreciate it if someone explained what the problem is

 

[Drej]

There is no problem. Probably. My guess is that:

1/ you've probably performed a linear buckling analysis to obtain the critical loads

2/ then performed a linear static analysis to find the (compressive) stresses in the members

and the reason you are seeing much higher stresses (higher than say your "allowable - whatever that is) is because of the Euler buckling theory used in the linear buckling analysis. Euler analysis gives NON-conservative values for the buckling load - in other words, it calculates a critical load(s) which is normally higher than the ACTUAL critical load for the structure. This is perfectly normal Euler behaviour. To obtain much better critical loads use the critical loads found by Euler and carry out a non-linear static analysis. Look in the help file for the points to consider when doing this type of analysis (Structural Guide> Chapter 7. Buckling Analysis>). Remember, for example, that in your real structure your geometry/materials/etc. will not be perfect, which will also reduce the buckling load - your non-linear buckling model will be very sensitive to these sorts of things.


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