Seismic Performance of Embedded GFRP Tube-Concrete Composite Exterior Beam-Column Joints

To address issues such as construction congestion， concrete casting defects， and shear-induced brittle failure in the core region of traditional concrete beam–column joints under severe earthquakes， this study proposes a novel joint system incorporating glass fiber-reinforced polymer （GFRP） tubes combined with high-ductility hybrid fiber-reinforced engineered cementitious composite （HECC）. This system is designed to replace stirrups in the joint core and improve interfacial bonding performance. Four exterior beam-column joint specimens were designed， with the core material （normal concrete （NC） or HECC） and GFRP tube fiber orientation （±45° or ±60°） as the main test variables. Quasi-static cyclic loading tests were conducted to evaluate and compare the seismic performance of the joints， including bearing capacity， ductility， energy dissipation， and stiffness degradation. The results demonstrated that the confinement provided by the GFRP tubes significantly enhanced joint ductility. Specimens with ±45° fiber-oriented tubes exhibited a 9.3% improvement in energy dissipation compared to those with ±60° tubes. Moreover， due to the lateral confinement provided by the GFRP tubes， which helps resist diagonal principal tensile/compressive stresses， and the improved reinforcement-to-matrix bond and crack propagation inhibition offered by the HECC， the joint combining GFRP tubes and HECC in the core region showed comparable ductility and stiffness retention to the conventional concrete joint， along with a 1.3% increase in bearing capacity and an 8.8% improvement in energy dissipation.Compared with traditional concrete joints， the proposed composite joint significantly reduces stirrup usage and construction difficulty， thus offering a viable solution for designing high-performance beam-column joints with minimal transverse reinforcement.