## 2 _Introduction_  
The use of carbon fiber-reinforced polymers (CFRPs) is to repair and retrofit reinforced concrete members, and this has lately given rise to an extreme eagerness and interest expressed by researchers and engineers alike [1; 2; 3]. The rehabilitation of such frames can be carried out locally by strengthening individual elements such as beams, columns, and beam-column connections, or globally by including shear-resisting elements such as shear walls or braces. Various strengthening methods for RC frames, which were not designed for seismic loads, were proposed by employing carbon fiber-reinforced polymer (CFRP) to enhance the collapse-resistant capacity of the joints. The experimental test results showed that the proposed reinforcement designs could effectively increase the load resistance capacity of the joint but failed to reduce the severe softening behavior [4]. The response of non-ductile, heat-damaged reinforced concrete (RC) beam-column joints was investigated through some experimental research works. The findings proved a considerable improvement in the cyclic performance of the joints strengthened with a hybrid CFRP system [5]. In an experimental study, the behavior of three-dimensional reinforced concrete joints under combined lateral and gravity loads was tested via the strength method with CFRP composite sheets on two reinforced samples, which showed an increase in strength of 9% to 23% [6]. Many studies were carried out on the strengthening of 3D external RC beam-column joints without transverse bars in their common core using CFRP. The results indicated that strengthening prevents the diagonal shear failure at the column in the transverse beam connection point, and also increases the lateral load capacity by 11-15%, energy absorption by 10-20%, and energy loss by 2.2 times [7]. Thereafter, the seismic response of a beam-column connection with a shear deficiency (BCJ) reinforced with UHPFRC and/or CFRP was investigated. The results revealed that the synergistic action of UHPFRC and CFRP can increase the structural stiffness, strength, and energy dissipation capacity of the BCJ compared to other strengthening techniques [8]. In general, beam-column connections are a vital component of the structure not only in terms of stability but also in terms of seismic performance. By strengthening a basic building model, one can witness the bending effects of improving accuracy and reducing computational effort, and this method is effective for the earthquake-resistant design of frames [9]. In particular, shifting the formation location of plastic hinges off the column toward the beam interval is a useful method geared toward increasing the beam-column connection capacity, which can further enhance the overall seismic structural performance. To effectively relocate a plastic hinge, different retrofitting plans can be positioned, for example, web- and flange-bonded approaches and simultaneous web-flange-bonded approaches [10; 11]. Literature-wise, much of the bulk of research in this area in recent years has focused on the former. The experimental assessment of RC beam-column connections, either internally with steel bars or externally via CFRP sheets, has proven its capacity for noticeable joint enhancement through this strengthening technique [12]. In particular, the work has emphasized joint behavior under reverse cyclic loading to assess deformation capacity and strength. As a result, the findings have indicated that the bearing capacity and ductility of the connections are closely related to the original element condition and strengthening application. Furthermore, several rehabilitation schemes concerning joints with CFRP composites have been evaluated, whereby their configurations in the forms of U and X can be exemplified accordingly [13]. Therefore, it is reported that all schemes selected can successfully modify the mode from joint non-ductile shear failure to ductile-flexural.