## 2 _Introduction_
The results of experimental and numerical studies revealed that when the joints in an RC frame are reinforced by CFRP, at that moment, the capacity increases by 37%, whereas a maximum of 18% decrement of joint rotation is observed [14; 15]. The results of the test for the RC joints retrofitted by hybrid CFRP sheets consequently suggest that this scheme may efficiently ameliorate the stiffness and rehabilitate the joint capacity efficiently [16]. The effectiveness of near-surface-mounted carbon-reinforced polymer ropes for enhancing interior-reinforced concrete (RC) beam-column joints was investigated. The X-shaped rope, implemented with two ropes on each side of the beam and two on each side of the column, imparted the best effectiveness on stiffness and yielding load, and the stiffness increased by 236.7% compared to the control beam-column joint [17]. Thereafter, a full-scale 3D exterior beam-column joint, lacking shear reinforcement but externally shear-strengthened with CFRP sheets, was investigated with respect to its behavior under both gravity and lateral cyclic loadings. The results revealed enhancements in lateral load-bearing capacity, energy dissipation, and secant stiffness [18]. Meanwhile, the effects of externally strengthened connections by utilizing several kinds of composites have been experimentally studied, and the results revealed that the simultaneous use of CFRP and glass fiber-reinforced polymer (GFRP) is capable of resolving the issues of lacking ductility and shear strength of problematic joints [19]. The effect of a set of parameters related to the contribution of CFRP sheets that were externally attached to the joint was numerically investigated. The obtained results confirmed the effectiveness of the CFRP-strengthening technique with respect to a relatively wide range of considered parameters [20]. An investigation detailing RC beam-column joints strengthened with steel-reinforced polymer (SRP) systems and their seismic performance has been presented by [PERSON], and the results of an experimental campaign performed at the Laboratory of Materials and Structural Testing of the University of Salerno, Italy, have been published [21]. In the research, the outcomes of cyclic tests performed on SRPstrengthened joints have been examined via a comparison against those obtained from a prior experimental program. They include companion specimens otherwise not provided with transverse beam stubs and strengthened by CFRP systems. Parallel to the above work, another scholarly attempt by [PERSON] and [PERSON] has tested some scaled joints modified by using CFRP [22]. In particular, either partial or full debonding of composites has been identified as the dominating factor across the test results. Nonetheless, the work has shown that a 20% increment in strength and energy dissipation and a 100% increase in stiffness are both possible. Additionally, the analytical prediction of shear strength carried out was in decent agreement with the experimental results. Thereafter, to evaluate the joint performance, CFRP-retrofit methods were applied to fortify RC joints and results revealed that the use of appropriately increasing composites can considerably enhance the ductility and strength of joint samples laterally [23]. Moreover, another numerical study concluded that the extent of the effectiveness of the CFRP web-bonding of joints toward the relocation of a hinge is used in order to yield a seismically enhanced performance of an RC structure [24]. Here, comparisons have been made accordingly between the results of frame retrofitting at the joints' webs using CFRP sheets and steel braces [25]. The numerical model for RC joints with CFRP-cover has been developed and nonlinear analyses have been conducted. As a result, the numerical model proposed in the work is capable of predicting the experimental work with precision [26]. The investigation on the method of web-bonded strengthening in the case of deficient RC joints with CFRP confirmed its ability to restore and further upgrade the strength of the system [27].