Seismic Performance Assessment of a School Building Strengthened With External Shear Walls During an M L 6.4 Earthquake in Taiwan

Taiwan's National Center for Research on Earthquake Engineering conducted field reconnaissance after an M L 6.4 earthquake on January 21, 2025. A junior high school building, over 50 years old and seismically strengthened in 2010, sustained moderate damage. The retrofit involved adding external shear walls to the outside of the corridor. Observations showed that the added shear walls remained intact, but some columns of the original frame were unevenly damaged. Additionally, slight cracks appeared around the ends of beams connecting the existing frame to the external shear walls. Using simplified numerical models, this study conducted a parametric study and nonlinear response history analysis to investigate the cause, pattern, and extent of damage, and to assess the seismic performance of the school building, which lacked instrumentation for recorded response data. The results indicate that the relative lateral stiffness of the load‐transfer mechanism between the existing frame and the external shear wall is critical. Based on the ground accelerations recorded at two nearby strong ground motion stations, the building likely experienced the maximum inter‐story drifts of 0.011 and 0.017 rad, respectively. The corresponding displacement ductility demand (i.e., the maximum displacement divided by the yielding displacement) reached 1.7 and 2.6, respectively. In addition to increasing the relative lateral stiffness of the load‐transfer mechanism, this study proposes two strategies to improve the seismic performance of typical Taiwanese school buildings retrofitted with external shear walls: limiting the distance between adjacent external shear walls, and placing a single external shear wall in the middle of the outside of the corridor.