Local buckling and postbuckling strength of extruded aluminium alloy stub columns with slender I-sections

•Stub column tests on 15 extruded aluminium alloy slender I-sections.•Determination of experimental values of local and postbuckling strengths.•Assessment of elastic and inelastic local plate buckling strength predictions.•Evaluation of current design specifications using the obtained experimental results.

A comprehensive experimental programme has been carried out to investigate the local buckling and postbuckling strengths of aluminium alloy I-section stub columns. A total of 15 test specimens made of two heat-treated aluminium alloys (6061-T6 and 6063-T5) were fabricated by extrusion. The material properties were acquired by the tensile coupons cut directly from the extruded cross-sections. The local geometric imperfections in sections were accurately measured prior to the tests. The stub column specimens were tested under axial compression between two fixed end supports, during which the local plate buckling featured visibly for each test specimen before reaching the peak load. The critical local buckling strengths were determined from the measured out-of-plane deflections and surface strains corresponding to the plate elements, which were further compared with the theoretical and analytical values taking into account element interaction and material non-linearity. Based on the obtained experimental postbuckling strengths, the design provisions in current design standards, including the American, Australian/New Zealand, European and Chinese specifications, were all evaluated. It was revealed that the predicted compressive strengths from the four design standards were generally conservative, especially for the cross-sections made of aluminium alloys with pronounced strain hardening properties.