Axial compression tests on hybrid FRP-steel-concrete columns with high-strength steel plates

The applications of high-strength steel (HSS) products to civil engineering structures have been limited by elastic local buckling, by the perceived lack of ductility, and by the perceived difficulties of welding such steels. Against this background, the authors have recently proposed a new hybrid column (i.e. High Strength Steel Plate-Concrete Filled FRP Tube or HSSP-CFFT) consisting of an outer FRP tube, a concrete in-fill and a number of encased high-strength steel plates that are connected to each other by bolted angle brackets at discrete elevations. The new column offers an ideal opportunity for the use of HSS plates in construction, with their high yield stresses being fully utilized and without welding (and therefore without welding residual stresses). In this paper, the rationale for the new column form together with its expected advantages is first explained. Results from a series of axial compression tests are then presented to confirm some of the expected advantages. The results demonstrated that the concrete in the tested specimens was very effectively confined, and that buckling of the steel plates was prevented by the encasing concrete up to and beyond the rupture of the FRP tubes, leading to full structural utilization of the construction materials and very ductile column responses.