Field Study and Evaluation of Buckling Behaviour of Steel Tanks under Geometric Imperfections

Abstract

Shells are among the most frequent structural components which are used in construction and industrial projects. Shell structures are composed of shell bearing elements and mainly used in oil and gas tanks, offshore marine platforms, silos, funnels, cooling towers, ship and aircraft body, etc. Despite the frequent use of steel cylindrical shells, their construction and assembling process has caused main problems. In these structures, there is no possibility for the integrated construction due to their large shell extent and they are built using a number of welded curved panel parts; hence, some geometrical imperfections emerge. Most of these imperfections are caused by the process of welding, transportation, inappropriate rolling, as well as installation and implementation problems. These imperfections have a direct impact on the structural behavior of shells during the buckling and external compressive load. Since in most shell tanks during operation, there is high possibility for the suction (vacuum) state, compressive forces in their thin wall cause buckling and failure. In this research, the imperfections made in steel cylindrical tanks being constructed in one of the refinery site are introduced and evaluated using a field study. Relying on the statistical inference, they are classified and then, by studying the effective factors and origin in their generation, the common imperfections are identified. Later, the impact of common imperfections on the buckling behavior is experimentally evaluated under uniform external pressure. Then, nonlinear numerical analysis of the test specimens is performed. Finally, experimental results, finite element and analytical relations are compared.