Behaviour and design of structural stainless steel members under concentrated transverse forces

Abstract

Stainless steel is gaining increasing use in structural engineering applications due to its corrosion resistance, low maintenance costs, high recyclability, aesthetic appeal, excellent fire resistance and favourable structural properties. The stress-strain behaviour of stainless steels differs fundamentally from that of carbon steel: stainless steel has a more rounded response with no clear yield point and significant strain hardening. This has a profound effect on the structural behaviour of stainless steel elements. The aim of this work is to investigate the behaviour of stainless steel I-sections under concentrated transverse loading and to develop design rules that reflect the particular characteristics of the material. Concentrated transverse loading is a load case where a force acts perpendicular to the flange of a girder over a relatively small area, causing local failure of the web beneath the load and flange bending. The current design code for structural stainless steel elements, namely Eurocode 3: Part 1.4, adopts the same design expressions for stainless steel as for carbon steel for such loading conditions. A comprehensive experimental and numerical investigation has therefore been conducted to evaluate the existing provisions and propose new design rules. A total of 34 member tests and over 500 finite element simulations have been performed covering three types of concentrated transverse loading – internal one-flange, internal two-flange and end one-flange loading, three stainless steel grades – austenitic, duplex and ferritic and a range of the key influential parameters. The results showed that the existing design recommendations are conservative and that there is considerable scope for the development of more economical design guidance. The new design equations offer 10% - 20% improvements in capacity predictions over the current design formulae. An alternative design approach, based on numerically generated reference loads, namely the elastic buckling and plastic collapse load under concentrated loading, in conjunction with strength curves, has also been proposed. This required the development of a consistent method for the numerical determination of plastic collapse loads, which is known to be challenging for the complex failure modes associated with localised loading. The reliability of both proposed design approaches have been verified by means of statistical analyses in accordance with EN 1990.