Flexural response of aluminium alloy SHS and RHS with internal stiffeners

Tubular profiles, such as square and rectangular hollow sections (SHS and RHS) are widely used in a range of structural engineering applications. Their thin-walled nature means that local buckling is a key design concern, which is usually addressed by adhering to specified slenderness limits. An alternative approach is to employ local plate stiffeners, which can be practically achieved in extruded aluminium alloy sections through the introduction of internal cross stiffeners. The flexural behaviour and design of aluminium alloy SHS and RHS with internal stiffeners is the subject of investigation of the present paper. The primary aims of the study are to generate experimental and numerical data for these new types of cross-section in bending, as well as to assess the applicability of different approaches to their design at cross-sectional and system levels. First, an experimental investigation was performed on aluminium alloy SHS and RHS beams with internal stiffeners subjected to three-point bending, four-point bending and five-point bending (i.e. continuous beams over three supports) of three different configurations. Finite element (FE) models were also developed and validated against the presented test data. Once validated, the models were employed to generate additional structural performance data through numerical parametric studies. Comparisons are then made between the experimental/numerical capacities and the design capacities predicted using a series of international design specifications for aluminium alloy structures, as well as the continuous strength method (CSM). The design strengths predicted by the American and Australian/New Zealand specifications were found to be conservative, while improved predictions are achieved by Eurocode 9. The most accurate and consistent predictions are obtained using the CSM, which was able to capture the significant observed strain hardening at the cross-sectional level and moment redistribution at the global system level.