Can the buckling load be much greater than collapse load?

[hoodzhj]

I am doing buckling and collapse analysis of a tank structure by FEA software. The results show that the buckling load is much bigger than the collapse load, is it possible? or there are somethings wrong in my model?

Thanks

 

[corus]

Buckling is elastic behaviour. Use large displacements and allow for imperfections in the geometry or load to get the true buckling behaviour.

corus

 

[dik]

For short compression elements, the buckling load is generally greater than the failure load by compression.

Dik

 

[rb1957]

your FE code could be giving you an Euler result for "buckling" ... which tends to infinity as l/rho tends to zero ... but this sounds a bit "dumb", you should check how your code is calculating the "buckling" load. if you have "short" columns (L/rho < 50) you should be using the Euler-Johnson method (which adds a plasticity correction to Euler, so that the column stress doesn't exceed fcy).

not quite sure what the collapse load is , maybe everything working at fcy.

you may want to look into crippling of your section, usually only a problem on thin gage members, thick, narrow flanges are stable in compression, and so can work up to fcy.

 

[MSDw]

The relation between the load causing buckling is independent from the load causing collapse. As the first is defined at which total tangent stiffness matrix of the whole structure vanishes ( NON-linear analysis) while the former is defined at which the number of plastic hinges that develope in the sturcture exceeds by one the number of statically indeterminancy of the same structure. in BOTH cases a major assumption is that equilibrium and yield criteria are NOT violated.

MSDw