## 1 Introduction
Second, test findings on FRP-reinforced columns appear to have been used to construct an equation for predicting the enhanced joint concrete compressive strength owing to confinement, because the column analogy is not relevant for estimating joint shear stress [29]. [PERSON] [20] also developed a method for measuring the shear strength of FRP-strengthened external RC beam-column junctions. Unfortunately, the FRP's effective strain was restricted to 0.4 percent in most situations, which severely understated the FRP's performance. [PERSON] [19] provided an analytical model based on the same technique as [PERSON] [20]. [PERSON]'s methodology for calculating the effective FRP strain is that at the joint panel's peak strength, the FRP comes in effect. According to experimental data on the FRP strengthening of the joint, the usefulness of FRP fibers begins at the junction panel breaking [30]. The [PERSON] [20] model's two flaws were overcome by evaluating FRP effective at the joint panel's first fracture rather than peak strength and not restricting FRP effective strain to 0.4 percent. Both models came up with a formula for the FRP effective strain. Both models' equations were calibrated using test data from RC beam-column sub-assemblages with fiber failure in the literature, i.e.,fiber rupture or fiber debonding only. [PERSON] [20] derived an equation of FRP effective strain for exterior beam-column joints only. An equation for FRP effective strain of internal beam-column joints was not derived because there is a scarcity of test data on interior beam-column sub-assemblages in the literature. Therefore, the expression derived by [19] for the FRP effective strain of the beam-column joints is also limited to the corner beam-column joints. Besides, due to the unavailability of enough experimental test results at that time (i.e., 2010 for [PERSON] [20] and 2015 for [PERSON] [19]), re-calibration and modification of the expression of the FRP effective strain were impossible according to the outlined method. [PERSON] and [PERSON] [31] compared a detailed interior beam-column joint reinforced with FRP sheets or strips to an expanded strut-and-tie model of the exterior and interior RC beam-column connections. However, the technique for adding the tensile strength of FRP and its contribution to the joint's shear strength and diagonal compression strength is not well defined. [PERSON] and [PERSON] [32] developed a technique for estimating the increase in the shear strength of the FRP-strengthened exterior beam-column joints due to FRP composites. A semi-empirical analytical approach was used to assess the shear strength of FRP retrofitted joints. Nevertheless, the model was semi-empirical, and unique empirical factors based on experience were utilized to estimate the shear strength of FRP reinforced beam-column joints. In addition, [PERSON] [33] also used the hierarchy of strength assessment for estimating the capacity of the FRP-strengthened interior and exterior beam-column joints. Nevertheless, the method included empirical coefficients (c1 is empirically reported as c1 = 0.64 by [34] and c2 = 2.0 reported by FIB) [35]. Moreover, the model presented was verified with a limited number of specimens. Given the preceding discussion of current analytical models, it was necessary to develop an analytical model for FRP-strengthened, under-designed interior BCJs that could address the shortcomings of the prior models. The complexity of the procedures, the lack of updated data of experimental results of under-designed RC BCJs, the lack of general equations for interior FRC-strengthened under-designed RC BCJS, the use of empirical equations based on assumptions, and the use of techniques that require high computational efforts to determine the contribution of FRP are all issues that have been identified thus far. As a result, the current study presents an analytical model free of the problems and flaws stated above. The current study suggests a novel and different analytical model free of the issues and flaws stated above.