Interaction of local and global buckling of box sections made of high strength steel

While there are precise analytical model available to assess the calculation of critical and ultimate load for global and local buckling separately, the interaction of both modes prove to be difficult as membrane effects and imperfections are of major impact. In an experimental programme, thirteen tests on columns with high b/t-ratio were carried out on square welded box sections made of S500 and S960 steel material, varying the global slenderness. The experiments were re-calculated with the Finite-Element-programme Ansys. The calibrated numerical model was subsequently used for parametric studies. The study at hand provides additionally an analytic approach to determine a slenderness depending reduction factor to design box sections prone to coupled instability. This approach, subsequently denoted as “generalised slenderness approach (gs)” is still orientated on the Ayrton-Perry format, which is also the basis of the Eurocode design procedure. Local effects are not included by omitting parts of the cross-section in the gs-approach, but by adding an additional equivalent global imperfection. The amplitude of this imperfection is based on the effective width method, but design charts for box sections are developed to ease the application.