A fast and practical approximations for fundamental period of historical Ottoman minarets

Minarets were built in various forms by different civilizations throughout the history. In the Ottoman period, since the minarets suffered significant damage during devastating earthquakes, geometric forms and construction techniques of these structures were progressively improved and they became indispensable components of a mosque in the residential regions of the Ottoman Empire. In this study, firstly dynamic characteristics and structural properties of eighteen Ottoman minarets located in Bursa were investigated with experimental and numerical techniques. Ultrasound tests and ambient vibration tests were performed in situ while modal analysis was applied to numerical models of the minarets. Results of frequencies compared modal test with the simulation and numerical models updated for further structural analyzes. The investigation is also carried out on power of the relationship between first period and each parameter effected the period. Consequently, two empirical formulas were developed to estimate the first period of historical Ottoman minarets by using results obtained from eighteen minarets. Although there are a few approximation including a method by authors in predicting fundamental frequency of the minarets, the current study shows that these methods may fail and cause misleading results. The results also include the comparison of the results from these methods with the suggested approximation on this study. •This study includes modal and material tests, FEM modeling and modal updating for Ottoman minarets.•The first mode of Ottoman era minarets generally are dominant in each direction.•Two empirical formulas for fundamental period of the minarets were suggested for use in seismic assessment of historical minarets.•These formulas can be used to check each other or determine material properties of the minarets.