Flexural behaviour of concrete-filled double skin aluminium alloy tubes

Concrete-filled double skin structural members, comprising of two metal tubes and concrete infill between them, have been gaining popularity in structural engineering because of their high strength, large stiffness, good ductility and easy maintenance. The use of aluminium tubes in these members can further enhance their performance, as aluminium alloy offers lightweight and good corrosion resistance. This study presents experimental and numerical investigations on the flexural behaviour of concrete-filled double skin aluminium alloy tubular (CFDSAT) members under in-plane bending. A total of 10 CFDSAT beams, including 3 specimens with square outer and inner tubes, 2 specimens with square outer and circular inner tubes and 5 specimens with circular outer and inner tubes, were tested. The failure modes, flexural strength and bending moment versus mid-span deflection curves obtained from the experiments are reported. Finite element (FE) models of the CFDSAT beams were developed and validated against the experimental results. The validated FE models were adopted to carry out a parametric study to examine the influence of cross-section slenderness of inner and outer tubes, hollow ratio, concrete compressive strength, cross-section shape and composite action on the flexural behaviour of CFDSAT beams. In the absence of design rules for CFDSAT beams, a design methodology, which is based on the Eurocode 4 framework, is proposed to determine the flexural strength of square and circular CFDSAT members. Moreover, slenderness limits for square and circular CFDSAT cross-sections are proposed based on the data obtained from the experiments and FE analyses.