## 1 Introduction
They analyzed the strength ratio of the horizontal stiffener to the beam flange and the strength ratio of the vertical stifterer to the beam flange. Three types of failure modes were obtained: horizontal stiffeners failure, vertical stiffener failure, and beam failure. Their results showed that the connections reinforced with T-stiffeners having 130% of strength to beam flanges presented stable hysteretic behavior and good ductility. [PERSON] et al. [20] conducted a series of cycling load tests for a proposed new design of bolted beam-to-column connections for CFT. In their design, the beam-to-column connection was of bolted type. Their results showed that bolted connections had superior seismic resistance in stiffness, strength, ductility, and energy dissipation mechanisms. They also showed that although the story angular drift reached 7%, the structure still stood with all the connections presenting plastic angular displacements of more than 5%, thus, meeting the specifications for seismic resistance. [PERSON] et al. [21] proposed and analyzed the seismic behavior of a connection for circular CFST column-to-steel beam composite structures. The connection was characterized by an extended endplate welded to a steel beam and bolted to a CFT column using high-strength steel rods. The experimental results indicated that the presence of floor slabs contributed to the strength of joints significantly and reduced beam sections were effective in moving the buckling zone away from the welds. More importantly, the connection exhibited good ductility and energy-dissipation capability, meeting the requirements recommended by AISC. [PERSON] et al. [13] tested four different connections with steel beams and CFT columns, under cyclic displacement-controlled load. Square and circular steel tubular columnswere considered with two different types of connections: (i) shop welded, flat and curved extended endplates bolted to the CFT column with steel rods passing through the column, and (ii) a through beam connection type, where the beam passes through the joint and is connected with an additional bolted bracket without using any welding between the beam and the column. The experiments demonstrated that all the subassemblies performed in a ductile manner to large displacements with no apparent signs of local distress in the tube wall. [PERSON] et al. [17] investigated the cyclic behavior of composite joints consisting of (CFST) columns, steel beams, and through-bolt connections. A total of ten specimens, including five specimens with square CFST columns and five specimens with circular CFST columns, were tested under lateral cyclic loading with horizontal displacements imposed at the top of the column. The hysteretic curves of the connections indicated very good energy absorption capacity, showing the potential to be used in earthquake-prone regions. [PERSON], [PERSON] and [PERSON], [PERSON] [22] conducted research on the seismic behavior of novel steel-concrete composite beam-to-column connections reinforced by outer-annular-stiffener. This type of connection consisted of beams with varying depths in opposite sides, and a CFST column. Four cruciform connection specimens with varying beam depth ratios were tested under monotonic and cyclic loading protocols to investigate shear capacity, hysteretic behavior, deformation capacity and failure modes within the irregular joint panel zone. All the tested specimens demonstrated good plastic deformation and energy dissipation capacity. [PERSON] et al. [23] evaluated the seismic performance of a damaged tolerant steel frame. In this steel frame, a composite ultra-high-performance concrete (UHPC) joint and friction damper were applied at the beam-to-column connection. The results showed that the UHPC joint provided excellent crack resistance and deformation capacity, while the friction damper resisted the moment in normal service and dissipated energy under earthquake conditions. [PERSON] et al.