Instability of shells

A hull subjected to compressive stress is likely to bend transversely when the stress reaches a critical value: this phenomenon is known as "buckling". Buckling is a sudden deformation of the hull, generally exhibiting a number of waves in the circumferential and meridional directions. Since the loading is generally due to the weight carried by the hull, buckling will, in most cases, cause a sudden and total collapse. Hull shear generates principal compressive stresses and can therefore also cause instability when this shear reaches a critical threshold.

The load-bearing capacity of a hull is strongly influenced by geometric imperfections, which play an extremely unfavorable role. Buckling resistance is also governed by the material's yield strength. Determining the load-bearing capacity of hulls by analytical methods is only possible for hulls that are simple in geometry and loading.

The development of high-performance computers and highly efficient numerical methods now make it possible to calculate a shell structure, whatever the complexity of the geometry, the importance of the effect of imperfections and non-linear behavior. These numerical models are used not only by scientific researchers, but also – in the form of commercial FEM (Finite Element Method) software – by project engineers.

Today, more than ever, the project designer's main task is to correctly model and convert the numerical results into the characteristic buckling resistance of a "real" hull, in order to achieve a reliable and cost-effective project.

This dossier briefly discusses calculation methods for verifying a hull's resistance to buckling.