Seismic behavior of I-steel reinforced concrete-filled GFRP tubular columns

To better understand the seismic performance of the steel reinforced concrete-filled GFRP tubular (SRCFGT) columns, this paper presents a low-cycle repeated loading test on twelve I-SRCFGT columns with different parameters including axial compression ratio, diameter-thickness ratio and fiber winding angle. The failure mode, hysteresis curve, skeleton curve, ductility, stiffness degradation, strength degradation and energy dissipation capacity of each specimen are analyzed and discussed. The tests demonstrate the favorable seismic performance of the I-SRCFGT columns. The failure mode consists mainly of fiber fracture and matrix cracking. Besides, results show that an increase in the axial compression ratio from 0.7 to 0.9 leads to greater initial stiffness, but accelerates the stiffness degradation during the loading process, and the ductility index (DI) of the specimen decreases by 3.2 %. Specimens with larger wall thickness of the GFRP tube have higher ultimate bearing capacity, but excessively increasing the wall thickness of the GFRP tube can reduce the ductility of the specimen. The overall displacement ductility of the specimen with a wall thickness of the GFRP tube of 6 mm increased by 3.1 % compared to the specimen with a 4 mm wall thickness of the GFRP tube. However, when the wall thickness of the GFRP tube continued to increase, the DI decreased by 2.6 %. Furthermore, specimens with a fiber winding angle of ±45° perform better in terms of the ultimate bearing capacity and ductility as well as overall seismic performance.