Equivalent local imperfections for FEM-based design of welded box sections

Abstract

Nowadays, significant research activities are running parallel and focusing on the development of equivalent geometric imperfections applicable for GMNI analysis which provides safe-sided and reliable buckling resistance using FEM-based design. The currently available local buckling-type imperfection given in EN1993-1-5, which is widely used by researchers and designers, has been developed based on the Winter-type buckling curve. Many researchers criticized this buckling curve in the past for overestimating the local buckling resistances of square welded box section columns. Therefore, an improved buckling curve has been developed and calibrated in the past, fitting the experimental and numerical results with adequate safety. To this new buckling curve, the magnitude of the equivalent geometric imperfection has been adjusted by the authors. The current research aim is to validate this new imperfection magnitude and to check if it accurately represents the improved local buckling curve and satisfies the safety requirement of EN1990. Furthermore, the current study aims to provide a constant value imperfection representing the improved buckling curve, which satisfies the mentioned safety requirements for welded square box section columns made of normal strength steel (S235, S355, and S460). The proposed imperfection factor can be used as an alternative to the currently adopted imperfection factor given in the EN 1993-1-5 for GMNI analysis.