NONLINEAR STRUCTURAL MODELING OF HAGIA SOPHIA IN ISTANBUL

Gülen Uncu

(Thesis Supervisor: Prof. Dr. Eser Çaktı)

ABSTRACT

Hagia Sophia in Istanbul is one of the most iconic architectural and engineering achievements in history. Constructed in the sixth century, the structure remained standing for over 1500 years, despite being exposed to numerous destructive earthquakes that caused significant damage, including partial collapses. Its location in a high seismic hazard zone makes the evaluation of its structural performance essential. Since the 1990s, studies on Hagia Sophia have mostly relied on linear analyses and idealized geometries, largely neglecting long-term deformations. This thesis focuses on the evaluation of the level and extent of the present-day deformations on the structure; the creation of a finite element model based on the actual geometry rather than the idealized one; the assessment of the contribution of permanent deformations to the static and dynamic structural response; nonlinear static and dynamic modeling to understand the structure’s present and future earthquake behavior; and the assessment of potential collapse mechanisms of the structure. The deformed geometry of the building was obtained using three-dimensional laser scanning and converted into a mesh. A model with ideal geometry was first developed in SAP2000 and then updated to reflect the observed deformations. Both deformed and undeformed models were transferred to ANSYS and subjected to static and dynamic analyses. Real earthquake records were used in linear dynamic analyses. The nonlinear modeling was carried out using calibrated material definitions based on recordings from the Mw 6.1 Silivri earthquake on April 23, 2025. Additional analyses were performed using both real and synthetic ground motion records. The results were evaluated in terms of structural response and collapse mechanisms, with a particular emphasis on the influence of geometric deformation.