On the beam and shell modes of buckling of buried pipelines

The paper identifies and analyzes the so-called ‘beam’ and ‘shell’ modes of buckling of buried pipelines. Such failures have occurred as a result of compressive loads induced to pipelines by large ground movements in seismically active areas. In the beam mode of buckling, the pipeline tears through the ground and lifts off in a characteristic Ω configuration. The shell mode of buckling is a more localized failure characteristic of shell type structures. The two types of instability are simulated numerically using appropriate nonlinear kinematics, inelastic material behaviour and approximate modelling of the soil-structure interaction mechanisms. Parametric sensitivity studies are presented. It is demonstrated that initial geometric imperfections can strongly influence the critical loads and strains of both types of instability. Conditions under which the two modes of buckling interact are also discussed.