Collapse and post-collapse behavior of steel pipes

Full text: Steel pipes under external pressure plus bending may reach their load carrying capacity due to two failure modes: (i)global buckling: in this case the pipe structure buckles in a 'column mode'; (ii) localized collapse: in this case the pipe structure collapses with its sections loosing their round shape. In many engineering applications such as the design of pressure vessels or the design of marine pipe lines it is very important to be able to determine the collapse pressure of steel pipes subjected to external pressure and bending; besides it is very important to also be able to quantify the effect of imperfections such as ovality, eccentricity or residual stresses on the collapse pressure. The determination of the post-collapse equilibrium paths is also very important in order to be able to assess on the stability of the post-collapse regime; that is to say in order to assess if a collapse will be localized in a section or will propagate along the tubular structure. It is also important in this case to analyze the effect of the imperfections on the post-collapse regime. In a previous publication we presented finite element models that we developed for studying the influence of the above described imperfections on the collapse behavior of steel pipes under external pressure; in that publication we also presented the experimental qualification of the numerical models. Our purpose in the present paper is to extend the study to the post-collapse regime and to the loading case of external pressure plus bending. We present the finite element models developed using shell elements, we discuss the validation of those models and then we use the validated models to perform parametric studies in order to investigate the significance of the different imperfections in load cases that combine external pressure with different degrees of bending. Refs. 3 (author)