## 1 Introduction
Notably, shear cracks can appear even with modest story drifts, before the yielding of adjacent members, causing a rapid decrease in the connection's load-carrying capacity. The appearance of diagonal shear cracks indicates a considerable reduction in the joint's load-bearing ability. This initial failure may escalate, risking a mechanism that could cause a story collapse if multiple joints fail. Unlike the ductile flexural failures of beams or columns, joint shear failures are brittle and provide little warning, identified by X-shaped cracks, core concrete compaction, and compromised structural integrity at the node connecting frame members. A common failure mechanism involves the deterioration of the bond between reinforcing bars and surrounding concrete in joints, leading to slipping or pull-out of the reinforcement. In older constructions, longitudinal bars of beams and columns often terminate or splice in joint regions without adequate development length or 90\({}^{\circ}\) hooks. Cyclic loading can cause these bars, particularly if they are smooth or surrounded by cracks, to gradually slip within the joint. Bond-slip is often seen in gravity-designed frames and has been identified as a key factor in damage and collapse of reinforced concrete buildings built before the 1970s. As illustrated in Figure 1b, the slipping of longitudinal bars into the joint reduces stiffness, shown by pinched hysteresis loops, and causes premature strength degradation under lateral loads. This results in a \"loose\" beam-column connection, compromising steel anchorage and decreasing moment transfer capacity. Joint shear cracking frequently accompanies anchorage failure; as slip and cracking initiate, the joint's truss mechanism weakens, increasing the load on the concrete strut and potentially leading to failure. Notable indicators of bond-slip failure include bar movements, widening cracks along beam bar paths, and sometimes bar pull-out or hook opening after testing. Inadequate bond anchorage, from insufficient embedment or smooth bars, critically impacts the cyclic performance of beam-column joints. An additional factor contributing to joint distress is an inadequate strength hierarchy within the structural frame. Engineering guidelines advocate for a configuration where columns and joints are robust while beams are weaker. This design ensures that the beam ends yield before the shear capacities of the joints are exceeded, or before column hinging occurs. Many legacy frames, however, overlooked this principle. During seismic events, beams can exert forces on joints surpassing their shear capacity, especially at joints with multiple beam connections. Weak-column scenarios may occur, where columns hinge at the joint, increasing shear demands. This can lead to joint failure even with nominal ties, as the joint may be insufficient for the imposed demand. A notable instance involves connections linking heavily reinforced beams to lightly reinforced columns, causing excessive shear in the joint panel. Experimental studies show that designs violating capacity principles, such as \"weak column-strong beam\", result in joint failure in shear before beam yield, as shown in Figure 1c. Inadequate proportions in dimensions and strength, such as reduced column cross-sections or lack of supporting beams in exterior joints, can force joints to absorb excessive loads, leading to brittle failure. This underscores the need for careful joint geometry and member sizing consideration to avoid joint inadequacies, a common issue in older design practices that led to failures during seismic activities. Figure 1: Examples of beam column joint failures: (**a**) shear failure, (**b**) bond-slip failure, (**c**) weak column-strong beam failure. One effective retrofit technique developed in recent years is the use of buckling-restrained braces (BRBs) [9; 10; 11; 12; 13; 14; 15].