Flexural performance of concrete-filled circular 6061-T6 aluminium alloy tubes fabricated by friction stir welding: Testing, simulation and design

Concrete-filled aluminium alloy tubular (CFAT) members provide a lightweight, corrosion-resistant and structurally efficient composite solution for sustainable infrastructure. However, their application in large-scale structural members is limited by the restricted extrusion capacity of aluminium alloy tubes, particularly for large-diameter circular sections. Friction stir welding (FSW) offers a practical fabrication route for such members by enabling circular aluminium alloy tubes to be assembled from plates, yet the flexural behaviour of FSW concrete-filled circular aluminium alloy tubular (FSW-CFCAT) members remains insufficiently investigated. This study addresses this gap through the testing, simulation and design investigation of FSW-CFCAT beams subjected to pure bending. A total of four concrete-filled circular 6061-T6 aluminium alloy tubular beams fabricated by FSW were tested under four-point bending, and their failure modes, moment–deflection responses, strain development and composite action were examined. An advanced finite element model was developed and validated against the corresponding test results, followed by parametric studies on weld width, weld yield strength, diameter-to-thickness ratio, concrete strength and weld position. The design predictions from Eurocode (BS EN 1994-1-1) (2004) and Chinese Code (GB 50936) (2014) were evaluated, indicating that BS EN 1994-1-1 (2004) underestimated the flexural resistance by 10.5% on average, whereas GB 50936 (2014) overestimated it by 8.8% on average. Modified design methods incorporating concrete confinement and plastic development effects were then proposed, and a provisional reduction coefficient of 0.98 was introduced from FE calibration to account for the most unfavourable weld positions, leading to improved accuracy and consistency in predicting the flexural resistance of FSW-CFCAT beams.