Seismic behaviour of FRP-concrete-steel double-tube columns with shear studs: Experimental study and numerical modelling

FRP-concrete-steel double-tube columns (i.e., double-tube concrete columns or DTCCs) are a novel type of structural members composed of two concentrically-placed tubes (i.e., an outer FRP tube and an inner steel tube) with all the space inside the two tubes filled with concrete. Shear studs on the inner steel tube are recommended to increase the composite action when DTCCs are subjected to large bending moments. The optimized section configuration of DTCCs allow the three constituent materials in the columns to deliver their respective advantages and to avoid their respective shortcomings. The limited existing studies on DTCCs have been focused on their compressive behavior. These studies have demonstrated the excellent ductility of DTCCs, an important advantage for their potential applications in regions with seismic risk. However, the seismic behaviour of DTCCs has not been systematically investigated. Against this background, this paper presents a combined experimental and numerical study on the seismic behaivour of DTCCs, where the experimental part included a series of largescale DTCCs tested under combined cyclic lateral loading and constant vertical compression, while the numerical part included the development of a finite element model incorporating beam-column elements and specific stress-strain models to consider the unique behaivour of the two parts of concrete in DTCCs (i.e., the concrete core inside the inner steel tube and the concrete ring between the two tubes). The experimental results revealed that: (1) the increase of FRP thickness had a positive effect on their hysteretic behavior; (2) when the steel ratio was constant, the peak lateral load of DTCCs increased with the steel tube diameter; (3) the concrete core not only enhanced the lateral load capacity and the ductility of DTCCs, but also provided efficient suppression on the buckling of the steel tube. The numerical model, established using the OpenSees platform, is able to provide reasonably accurate predictions of the hysteretic behaviour of all specimens.