Structures are not ideal - Challenges of buckling analyses

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The linear buckling analysis is widely used for determining the load level at which the structure loses its stability. In reality, structures may be sensitive to even small imperfections in their shape, which is accounted for by applying large factors of safety when using the linear buckling analysis. The geometrically nonlinear analysis describes the buckling behavior more accurately, thus giving better confidence on the performance of the design. This gives means for achieving more robust designs while at the same time minimizing the weight.

In some cases, like in the axially loaded thin-walled column shown below, stability is lost suddenly and the structure collapses. In other applications, like in a simply supported flat panel, the structure may have long post buckling region in the load-deformation curve, as depicted by the nonlinear analysis model. The pitfall of the nonlinear analysis model is, though, that it cannot capture the buckling of an ideal symmetric flat panel or an ideal tube under axial compression. Introducing geometric imperfections in the structure overcomes the problem.

 

 

 Stuctures are not ideal

The image illustrates how the load-deflection curve depends on the magnitude of the imperfection size "a".

 

The upcoming ESAComp 4.4 version introduces geometrically nonlinear static analysis which is essential for reliable buckling analyses. A common practice is to generate disturbances in the model to account for the geometrical imperfections. In ESAComp this is handled in a user-friendly manner: The shape of the imperfection can be generated with linear buckling analysis. For cylindrical shells the distorted shape can be based on analytical formulas as well. The new capability makes it possible to apply the nonlinear buckling analysis in the early phases of the project where important decisions are made for the design.

Further reading: ESAComp Example Case – Imperfections in Cylindrical Shells