05.20: Modified Ayrton‐Perry formula for flexural buckling of HSS welded box sections

Abstract

The residual stress in steel structural elements has significant influence on the flexural buckling behaviour of compressed members. This phenomenon causes that hot-rolled, cold-formed and welded sections with the same geometry have different flexural buckling behaviour and resistance. Previous research results showed that the residual stress pattern of members made from high strength steel (HSS) is different than for normal strength steel (NSS) structures, which results in different flexural buckling behaviour. The current design rules of the EN 1993-1-1 [1] for column buckling resistance is based on the Ayrton-Perry type formula taking the effect of the residual stress and geometric imperfections as generalized imperfections into account. The effect of the residual stress magnitudes is not implemented directly in the method, therefore its implementation could result a more precise column buckling curve, which can differentiate between hot-rolled, coldformed and welded sections, as well as NSS and HSS structures. The current paper introduces a method, which implements the effect of the residual stress pattern of welded box section columns into the Ayrton-Perry type formula. This new formulation results in a revised and improved column buckling curve. This new buckling curve is compared to the general buckling curves of the EN 1993-1-1 [1] and also compared to recent experimental and numerical results conducted by the authors. The parameters of the improved buckling curve are studied and evaluated in the details. The effect of the magnitude of the residual stress on the buckling resistance is studied and compared to the numerical results. Based on a detailed experimental and numerical research program an improved formulation of the Ayrton-Perry formula is proposed, which is validated for welded square box sections applicable for NSS and also for HSS grades.