Seismic performance of circular concrete-filled FRP tubes consisting of H-steel with shear studs: Experimental study and numerical modelling

Existing studies about concrete-filled FRP tubes (CFFTs) are generally focused on their behaviour under axial load, which have demonstrated their excellent compressive ductility. For their applications in regions with seismic risk, longitudinal reinforcements should be provided for CFFTs in order to ensure their ability to resist bending moments. In published literatures, longitudinal reinforcements for CFFTs were mostly steel rebars or FRP rebars, while only limited studies were about CFFTs reinforced with profiledsteel. Against this background, 6 circular large-scale CFFTs consisting of H-steel with shear studs (HS-CFFTs) were investigated experimentally under combined axial load and lateral cyclic load to study their seismic behaviour. These HS-CFFTs were designed with a total height of 2150 mm and a concrete diameter of 300 mm, and the testing parameters included the FRP thickness (tfrp = 4.0 mm - 6.0 mm), the axial load ratio (n = 0.2 - 0.33), as well as the area ratio of Hsteel (rho = 4.54% - 5.67%). Test results indicated that, (1) HS-CFFTs exhibited rounded hysteretic curves with ample energy dissipation capacity; (2) the H-steel experienced no local buckling due to the effective concrete support and the sufficient FRP confinement; (3) the FRP tube thickness was positively correlated with the peak lateral load and the ductility of HS-CFFTs; compared with HS-CFFTs with tfrp = 4 mm, HS-CFFTs with tfrp = 6 mm had a higher peak load FP (7.3% - 7.4% higher) and a larger ductility index 14 delta (3.4% - 11.7% higher); (4) increasing the H-steel ratio could effectively improve the seismic performance of HS-CFFTs; HSCFFTs with rho = 5.67% had higher peak load (2.5% - 10.0% higher) compared with those with rho = 4.54%; (5) the ductility of HS-CFFTs would decrease obviously as the axial load ratio increased; the ductility index 14 delta for HSCFFTs with n = 0.33 was smaller (14.1% - 25.0% lower) than the counterparts with n = 0.2. A numerical model incorporating with "NonlinearBeamColumn" elements as well as specific constitutive models for the FRP tube, the H-steel and the concrete core was established on the OpenSees platform. The proposed numerical model provided a simple, computationally efficient and reasonably accurate approach for simulating the hysteretic behaviour of HS-CFFTs.