Experimental study of U-shaped steel-concrete composite beam to square CFST column joints

Abstract

Concrete-filled steel tubular (CFST) columns and U-shaped steel-concrete composite (USCC) beams have received extensive attention because of superior mechanical performance over steel and reinforced concrete members. In this study, an innovative cost-effective and construction-effective USCC beam to CFST column joint configuration with T-shaped internal diaphragms is proposed. Four beam-column joint specimens were designed according to the proposed design provisions, and were tested under combined constant axial compression and cyclic lateral loading, including one specimen with T-shaped diaphragms in strong direction, two specimens with T-shaped diaphragms in weak direction, and one control specimen with conventional internal diaphragms. Test results revealed that the specimens with T-shaped diaphragms exhibited similar cyclic behavior, moment-bearing capacity, ductility, stiffness, and energy dissipation capacity to the specimen with conventional internal diaphragms. The primary failure modes were fracture and buckling of bottom flange of the U-shaped steel in the connection vicinity, leading to a remarkable pinching effect in the cyclic behavior. All specimens were tested up to a story drift ratio of 4%, showing good elasto-plastic deformation capacity. The specimens have a superior bearing capacity under negative moment and a lower one under positive moment due to premature fracture of bottom flange. All specimens were classified as the semi-rigid and partial strength joint under positive moment, semi-rigid and full strength joint under negative moment. Additionally, the contributions to story drift were analyzed theoretically and the results via the proposed calculation formulas were found to be in good agreement with the measured story drift.