# Assessment of a Substandard Reinforced Concrete Frame's Beam-Column Joint Using Shake Table Testing
## 1 Introduction  
The seismic vulnerability of reinforced concrete (RC) structures, especially those constructed before the enforcement of contemporary seismic design codes, continues to represent a critical area of concern in the field of earthquake engineering. This vulnerability primarily arises due to significant inadequacies in structural detailing, reinforcement practices, and concrete quality. Numerous global seismic events have repeatedly underscored the catastrophic potential of damage to such inadequately designed structures, particularly in regions of structural significance, like beam-column joints. These joints are fundamental elements in structural integrity, effectively governing force transmission between beams and columns, thus critically influencing the overall seismic performance of buildings during earthquakes [1, 2, 3]. Historically, many RC buildings constructed prior to the 1970s neglected adequate seismic considerations, resulting in the widespread occurrence of brittle failure mechanisms at these joints, largely due to deficiencies such as insufficient shear reinforcement, inadequate anchorage lengths, and substandard concrete quality [4, 5, 6, 7]. Hence, the systematic assessment and effective enhancement of these vulnerable elements are imperative objectives for researchers and structural engineers focused on mitigating earthquake-induced hazards. The key factors that influence the seismic behavior of RC beam-column connections under cyclic loading include the shear strength of the joint, the presence of inadequate anchorage, and the aspect ratio of the joint [8]. This type of damage occurs in the most severe scenarios during an earthquake. It contributes to a reduction in the stiffness of the structural element to an unpredictable degree. As such, it is important to exercise special care for this part of the structural system even when microcracks are beginning to form. Damage from cyclic loading at beam-column joints is categorized into three types: corner joint failures, exterior joint failures, and interior joint failures, as illustrated in Figure 1[9]. The primary goal of seismic design is to limit the development of potential plastic hinges at the column faces of a joint while permitting inelastic behavior to be distributed along the beam section. Such developments frequently lead to the spalling of cover concrete and anchorage failures due to the residual deformations at the joint. To thoroughly examine and significantly improve the seismic performance of RC structures, numerous previous studies are explored within four interconnected and highly relevant methodological areas: analytical modeling techniques, experimental investigations conducted in controlled environments, the comparative analysis of various seismic design codes and guidelines, and studies supporting targeted retrofitting strategies. This comprehensive approach not only enhances understanding but also ensures the practical applicability of the findings in real-world scenarios. Recent advancements in analytical modeling have substantially improved our ability to predict the seismic responses of reinforced concrete (RC) beam-column joints. [PERSON] [10] introduced a novel macro-element for analytical modeling, specifically designed for joints with hinges, which proficiently represents the nonlinear characteristics associated with RC beam-column joints. The proposed model accounts for the nonlinear shear response of the central panel, the bond-slip behavior of longitudinal reinforcement bars, and the nonlinear dynamics occurring within plastic hinge zones. [PERSON] et al. [11] proposed a model that exhibits a consistent probability of exceedance at 50%, which is in accordance with the revised provisions for nonlinear beams and columns. Furthermore, it reveals a strong correlation with both the test database and the validation datasets.