Post-earthquake damage assessment of a historic masonry fortress: Ravanda castle after the 2023 Kahramanmaraş earthquakes

The 6 February 2023 Kahramanmaraş earthquakes caused severe damage to numerous historical masonry structures in southeastern Türkiye. Ravanda Castle, a medieval fortified complex with a history of nearly 1000 years, experienced significant structural deterioration, particularly in its towers, curtain walls, and vaulted systems. This study presents a comprehensive damage assessment and seismic performance evaluation of the castle through an integrated approach combining field surveys, digital twin modeling, image processing, and three-dimensional finite element analysis. The digital twin model enabled the identification of damage in inaccessible regions, while crack patterns and out-of-plane displacements were documented through multi-scale assessment methods. Nonlinear time-history analyses revealed significant tensile damage concentration and out-of-plane instability, especially in the K6 tower and Y4 vaulted structure. Based on the observed damage, different intervention strategies were proposed, including mechanical steel stitching for the K6 tower and partial reconstruction for the Y4 system. The results show that the strengthening strategy reduces maximum displacements by approximately 25–50% and relative displacement demands by 30–35%, while reconstruction increases load-carrying capacity by 20–30%. Overall, the interventions improve structural performance by limiting tensile damage and enhancing load transfer, while preserving the historical integrity of the structure.