Experimental behavior of hybrid FRP–concrete–steel double-skin tubular columns under combined axial compression and cyclic lateral loading

• Hybrid double-skin tubular columns (DSTCs) under cyclic lateral loading are studied.
• The effects of concrete strength, axial load, and FRP tube thickness are examined.
• Hybrid DSTCs possess excellent seismic resistance.
• Partial filling of the inner steel tube with concrete enhances seismic resistance.

Hybrid FRP–concrete–steel double-skin tubular columns (DSTCs) are a new form of hybrid columns, consisting of an outer tube made of fiber reinforced polymer (FRP) and an inner tube made of steel, with the space between filled with concrete. In hybrid DSTCs, the three constituent materials are optimally combined to achieve several advantages not available with existing columns, including their excellent corrosion resistance and seismic performance. Although two existing studies have examined the seismic performance of circular hybrid DSTCs, they have been limited to normal strength concrete, small column dimensions, and small void ratios (ratios between the inner diameter and the outer diameter of the annular concrete section). Against this background, this paper presents the first experimental study on hybrid DSTCs filled with HSC subjected to axial compression in combination with cyclic lateral loading. A relatively large column section (with a diameter of 300 mm) was chosen to allow reliable experimental modeling of real columns. The test results indicate that hybrid DSTCs possess excellent ductility and seismic resistance even when high strength concrete with a cylinder compressive strength of around 120 MPa is used; column damage is concentrated in a small plastic hinge region near the column bottom end; and the performance of hybrid DSTCs can be enhanced by filling the inner void in the plastic hinge region. The test results provide valuable data needed for the formulation and verification of a theoretical model for the hysteric behavior of hybrid DSTCs, particularly when they are filled with HSC.