The effect of shear wall joint and column jacket on structuralperformance in buildings with low concrete strength designedaccording to the 1975 earthquakes code

On February 6, 2023, a pair of devastating earthquakes, referred to as the "Disaster of the Century," struck along the East Anatolian Fault with epicenters in the Pazarcık and Elbistan districts of Kahramanmaraş, registering moment magnitudes of 7.7 and 7.6, respectively. Following these events, the question of whether to retrofit older buildings within the existing building stock or, in cases where they fail to meet current codes, the effectiveness of such retrofits and their contribution to the structural system, has become a widely debated issue, serving as the primary motivation of this study. In this context, a 30-year-old, four-story reinforced concrete building without a basement, located in Yeşilyurt district of Malatya and classified as slightly damaged after the earthquakes, was investigated through both field surveys and numerical analyses. The performance assessment of the existing structure was conducted, and retrofit alternatives were evaluated. Three different retrofit models were developed, including shear walls with and without boundary elements, as well as jacketed exterior columns with and without shear walls, in order to assess the contribution of boundary elements and column jacketing to the ductility and load-bearingcapacity of substandard reinforced concrete structures. The study was carried out in two stages. In the first stage, field investigations included preparing measured drawings, extracting cores, exposing reinforcement in columns and walls, identifying foundation type, and conducting soil surveys. In the second stage, the as-built structure and the retrofit alternatives were modeled in Seismobuild, followed by modal analysis and nonlinear static pushover analysis in both transversal and longitudinal directions using Seismostruct. Subsequently, nonlinear dynamic analyses were performed using four ground motion records from the Kahramanmaraş earthquakes. The results indicate that while boundary elements significantly enhanced the ductility in the transversal direction, their effect was less pronounced in the longitudinal direction. Additionally, jacketed exterior columns improved ductility and contributed to moment–rotation capacity. However, they were not as effective as shear walls in reducing interstory drifts. The findings highlight the crucial role of boundary elements in the retrofitting process of deficient reinforced concrete buildings.