Experimental study on seismic behavior of joints connecting precast H-steel reinforced concrete beams and concrete-filled steel tube columns

In this study, a novel joint for connecting hybrid H-steel reinforced concrete (HSRC) beams and concrete-filled steel tube (CFST) columns was proposed, serving as the primary connection type for precast composite frames. This paper presents the findings of an experimental investigation on the developed joints to determine the seismic capacity and key design recommendations. Three full-scale interior test specimens with different connection structures, i.e., untreated, reduced beam section (RBS), and opening in beam web (OBW) cantilever H-steel beams were subjected to cyclic loading tests. The results revealed that the joints exhibited a stable and full hysteretic behavior when the drift ratio was greater than 2%. The specimen connected with the RBS steel beams fully developed the plastic hinge in the RBS zones, which prevented the brittle fracturing of welds. Additionally, the specimen connected with the RBS steel beams showed a favorable ductility, and the total accumulated energy was up to 8.82 times that of the untreated specimen. Therefore, the proposed joint attached to the RBS steel beams could be more applicable to seismically active regions. Nevertheless, the treated specimen connected with the OBW steel beams exhibited insignificant improvement in seismic behavior compared with the untreated specimen. The seismic behavior of the proposed joints was directly influenced by a reduction in the reinforcement ratio of the longitudinal reinforcing rebars that transferred the bending moment between the RC beams and H-steel beams. Thus, a simplified equation was derived and validated through experimental tests to ensure a sufficient nominal area of the bars.