This work is concerned with the influence of the boundary conditions on the instability of circular cylindrical shells subject to axial forces and bending. Actually, it is well known that the major deformation characteristic of the response of such shells to bending consists in the progressive flattening of the cross section and this fact leads to a limit value of the carried load. However, in the case of thinner shells subject to loads inducing also axial stresses, the onset of short wavelength rippling followed by sudden collapse can precede the limit load. In any case for such shells, even in the absence of a catastrophic collapse, it is found that the rippling influences the value of the limit load. In the present paper it is shown that some boundary conditions, such as stiffening rings, which are commonly employed in submarine pipelines as buckling arrestors, can substantially influence the stress distribution in the circular shell and, consequently, the ultimate load that can be withstood.
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