Axial compressive behaviour of rectangular DCFSST stub columns

In this paper, a new type of rectangular double-opening concrete filled sandwich steel tube (DCFSST) is devel-oped. This new type of composite section can keep the inner steel tubes away from the cross-sectional centroid axis through the reasonable configuration. In order to assess the structural behaviour of rectangular DCFSST members, a pilot research on stub columns under axial compression was conducted. A total of 10 specimens, including 5 with double steel square hollow sections (SHSs) and 5 with double steel circular hollow sections (CHSs), were tested with the various offset rate of inner tube (e0) and opening ratio (phi). The experimental ob-servations indicate that, generally, e0 and phi have moderate effect on the failure process and failure modes of the specimens, and the failure modes of the specimens include outward local buckling of outer tube, crushing of the sandwiched concrete and inward local buckling of inner tubes. In addition, phi has significant influence on the load-deformation curves, axial capacity and axial compressive stiffness of the specimens; however, e0 has no obvious effect on the above performance. Moreover, nonlinear finite element (FE) simulation on the behaviour of axially compressed rectangular DCFSST stub columns was carried out using the ABAQUS software, and the typical performance of new composite members was further analyzed by the verified FE model. Finally, the formulae to calculate the axial capacity of rectangular DCFSST stub columns were also developed based on the FE simulation results and test results.