Seismic behavior of historic square cross-section masonry minarets: The minaret of the Harran Ulu Mosque in Şanliurfa (Türkiye)

The minaret of the Harran Ulu Mosque is one of Türkiye’s most invaluable historical and architectural heritage structures. The site of the Harran Ulu Mosque was included in the UNESCO World Heritage Tentative List in 2000. This study aims to assess the seismic behavior of the masonry minaret of the Harran Ulu Mosque, which sustained damage during the Kahramanmaraş (Pazarcık-Elbistan) earthquakes on February 6, 2023. Despite the relatively low recorded ground motions, the observed damage on the minaret indicates its high vulnerability to seismic actions. An ambient vibration test was conducted to determine the frequency values of the minaret before the earthquakes. The modal parameters obtained from this test were used to calibrate a three-dimensional finite element model of the minaret, developed using ABAQUS software. The first three modal frequencies were identified as 1.24 Hz, 1.29 Hz, and 5.40 Hz from experimental measurements, while the numerical model provided values of 1.17 Hz, 1.19 Hz, and 5.12 Hz. After updating, the maximum discrepancy between experimental and numerical frequencies was reduced to below 5 %. Initially, the seismic behavior of the minaret was assessed through nonlinear static analyses based on the calibrated model. Secondly, a modal pushover analysis was conducted to investigate the influence of higher mode effects on the seismic response of the minaret. Finally, the seismic response of the minaret was evaluated using a simplified limit analysis method. The results obtained from the different analysis approaches revealed a similar damage mechanism, which was found to be consistent with the damage observed in the structure after the earthquake. However, differences in strength and displacement capacities were also observed, which indicate the need for more robust assessment tools for this type of structure. The collapse load factors ranged from 0.12 g (kinematic limit analysis) to 0.15 g (uniform loading), highlighting the varying seismic capacity estimates across the applied methods.