Ambient vibration testing and empirical relation for natural period of historical mosques. Case study of eight mosques in Kermanshah, Iran

Eight historical mosques of Kermanshah constructed in 18th or 19th century CE are investigated with ambient vibration tests on their sites and buildings. Conventional peak picking technique is used for determination of structures’ fundamental frequencies and spectral ratio of horizontal to vertical components along with ellipticity inversion of Rayleigh waves are considered to identify the natural frequency of ground and shear wave velocity profile to define the site conditions according to the national codes of Iran and Italy. The recorded motions on the buildings are used to calculate the fundamental frequencies of the structure. Afterward, buildings are modeled by macro-element method and material properties are tuned in the way that the fundamental frequencies from the modal analyses match with the measured values from AVTs. Finally, more modal analyses are performed by the calibrated models to present an empirical relation between the natural period of the mosques, the geometrical characteristics of the buildings, and the mechanical properties of the construction materials. The results show that the natural periods of the masonry buildings of the mosques are different from the values of empirical relations in the national codes. Meanwhile, the proposed empirical relation presents the natural periods of the buildings of this study reasonably well and can be used for other masonry buildings of similar architecture and materials.