Concrete-Filled Elliptical Hollow Section Beam-Columns under Seismic Loading

Abstract

The seismic behavior of elliptical hollow section (EHS) beam-column members was examined in this study. A comprehensive experimental investigation was conducted on 14 concrete-filled and four bare steel EHS beam-column specimens under combined compression and cyclic bending. The main testing parameters were tube wall thickness, axial load ratio, and bending direction. Among other findings, it was revealed that the bare steel specimens failed in local buckling, whereas the concrete-filled members exhibited more diverse failure modes, including local buckling, a fracture of the steel section following local buckling, and an abrupt fracture of the steel section with no evident local buckling. The failure modes largely depended on the bending direction. Due to the beneficial effects of material hardening and steel-concrete interaction, the moment resistance obtained from the test was consistently larger than the predicted plastic moment resistance. In addition, the specimens exhibited satisfactory ductility and energy dissipation performance, and both characteristics could be effectively improved by either increasing the compactness of the steel section or by applying the concrete infill. The strength, ductility, and energy dissipation characteristics of the specimens subjected to biaxial bending fell between the cases of major-axis and minor-axis bending. Based on the test results, the existing design methods for predicting the moment resistance of the considered members were evaluated. A preliminary design equation for ductility prediction was also proposed.