Design of hot-finished tubular steel members using a stiffness reduction method

Abstract

A stiffness reduction method (SRM) for the design of hot-finished tubular steel members is presented in this paper. Stiffness reduction functions that fully capture the adverse influence of imperfections and plasticity on member stability are developed. The proposed SRM is implemented by (i) reducing the flexural stiffness (EI) of the member using the developed stiffness reduction functions, (ii) performing elastic Linear Buckling Analysis (LBA) and Geometrically Nonlinear Analysis (GNA) of the member with reduced flexural stiffness and (iii) making cross-section strength checks and ensuring that the lowest buckling load amplifier from LBA is greater than or equal to 1.0. Owing to the full allowance for the spread of plasticity, residual stresses and geometrical imperfections through stiffness reduction and instability effects through LBA and GNA, the proposed approach offers an enhanced and more direct assessment of structural behaviour relative to traditional design where structural analysis is accompanied by member design equations, effective lengths and the notional load concept. The proposed method is verified against nonlinear finite element modelling for a large number of tubular steel members. Comparisons of the proposed approach against the methods recommended in the European structural steel design code EN 1993-1-1 for the design of tubular members are also provided.