## 2 Beam-Column Joints of Composite Frames Under Seismic Loads
### Beam-Column Joints of Composite Frames Under Seismic Loads: State-of-the-Art
[PERSON] et al. (2021) [7] explored a new type of joint between a reinforced concrete-filled steel tube column and a beam. Four specimens with varying characteristics were tested under cyclic loading. The results showed that slipping between the concrete and steel caused pinch phenomena in the joint's hysteretic curves. Increasing the size of the middle steel tube improved stiffness and energy dissipation but had little effect on strength. Transfer sleeves played a crucial role in limiting stiffness and strength degradation while enhancing energy dissipation. [PERSON] et al. (2022) [8] focused on evaluating the seismic behaviors of different connections in steel residential buildings, including endplate, side plate, and hot-rolled T-shaped connector (HTC) connections. The experimental findings revealed that both the connections of lateral plate and HTC connections exhibited favorable cyclic response characteristics. These included consistent force-displacement patterns, a gradual reduction in rigidity, adequate ductility, and effective energy absorption capacity. In contrast, the connection of the endplate suffered an untimely rupture at the welded interfaces between the endplate and the side plates. Furthermore, the suggested HTC connections not only demonstrated satisfactory seismic performance but also required no additional stiffeners and had a minimal impact on indoor space, making them easily concealable within partition walls. [PERSON] et al. (2022) [9] presented an experimental study on the behavior of connections between T-shaped CFT columns and U-shaped steel-concrete composite beams. Five different connection details were tested, with all showing favorable seismic performance with plastic hinge failure occurring at the beam-ends. The joints demonstrated good ductility and energy dissipation capacity, meeting Eurocode 3 requirements for rigid joints in braced frames. They concluded that their proposed joint design with vertical ribs is seismically feasible and provides recommendations for practical applications. [PERSON] et al. (2023) [10] introduced a new manufactured steel beam (H-shaped) to a CFT column joint design. This system aims to improve construction efficiency and structural performance by eliminating welding in column connections. The joint employs embedded threaded steel bars for column segments and outer annular stiffeners for beam connections. They tested four joint specimens under cyclic loading, examining parameters, such as column tube thickness, sleeve distance, and steel strength, and their results showed good flexural capacity, deformability, and energy dissipation. [PERSON] et al. (2014b) [11] examined the performance of a new through-beam connection between reinforced concrete beams and CFT columns. Tests showed different failure modes and demonstrated good seismic performance, load capacity, and ductility. Finite element modeling validated the results, and this new connection type simplifies construction without sacrificing structural integrity and offers valuable considerations for future CFST column-to-RC beam connections. Moreover, [PERSON] et al. (2017) [12] introduced and tested a novel moment-resisting connection called a \"through rib stiffener beam connection\" for I-beams and concrete-filled circular steel tubular columns. Four cruciform specimens were experimentally examined to evaluate the behavior of the connections under seismic loading. The new connection involved vertical rib stiffeners welded to the beam flanges, passing through pre-slotted holes in the column. It was found that the new connection exhibited rigid moment-resisting behavior, good ductility, and energy dissipation capacity. The connection appears to satisfy seismic design requirements and is practical and cost-effective. [PERSON] et al. (2017) [13] introduced a refined finite element model for predicting the behavior of composite steel-concrete welded joints under earthquake loads.