Seismic Strengthening Design and Post-Intervention Capacity Evaluation of a Low-Rise Masonry Building

This study investigates the seismic strengthening of a three-storey unreinforced masonry building located in Tirana, Albania. The structure was originally built in the 1940s and later modified by adding an extra storey, which introduced stiffness irregularities and reduced lateral capacity, particularly in the transverse direction. Initial capacity assessments using spectrum-based analysis and nonlinear pushover procedures confirmed a high level of vulnerability. Based on these findings, a strengthening strategy was designed in accordance with Eurocode 8 – Part 3. The intervention scheme consists of new reinforced concrete (RC) columns at critical locations, RC jacketing of selected masonry walls, diaphragm strengthening, and foundation enhancement using tie-beams. Post-intervention pushover analyses were performed to quantify performance improvements. The results indicate significant gains in lateral resistance, overall stiffness, and deformation capacity. For a 95-year return period, the retrofitted building remains within the Damage Limitation state; for a 475-year event, it reaches the Significant Damage state without approaching Near Collapse. The adopted strengthening approach successfully mitigates the key deficiencies and complies with Eurocode 8 performance requirements. The findings also provide a practical reference for the retrofit of similar pre-code masonry structures in Tirana and other Albanian urban areas.