Analytical and numerical study of the lateral buckling of an imperfect pipe accounting for torsional effects

The stability problem of pipelines under high temperature and high pressure in terms of lateral buckling has been largely concerned recently. Owing to the complex conditions encountered in the sea bottom, many factors affect the structural behavior of pipelines resting on the seabed, such as initial imperfections and unexpected torsion. This paper thus focuses on the mechanical response of imperfect pipes (with a fixed length) under uniaxial compression, in presence of torsional effects. The problem is addressed first in an analytical way. The classical governing equations of a beam lying on the seabed are adjusted, introducing extra terms accounting for initial imperfections and twisting effects. The cases of imperfect pipes with free and fixed torsion at both ends are investigated, and closed-form analytical solutions are obtained in most cases. Furthermore, non-linear finite element computations are performed. Results include force–displacement response curves and buckled deformed shapes. A detailed comparison is conducted between numerical results and analytical solutions, accounting for various lateral stiffness densities, and different imperfection types and amplitudes. A general good agreement is achieved, at least within a small deformation domain. However, the numerical calculations sometimes lead to unexpected phenomena that analytical solutions cannot capture due to geometric non-linearities.