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    Full-scale structural evaluations of Iskenderpas,a minaret
    (Elsevier Science Inc, 2023) Aymelek, Abdullah; Yanik, Yusuf; Demirtas, Betul; Yildirim, Omer; Calik, Ismet; Turker, Temel
    Nowadays, innovative methods have been used for observing and structural evaluating of historical structures. In this paper, it is presented the full-scale structural assessments of a minaret after a Finite Element model calibrating according to vibration test results. Also, the structural behaviours under earthquake and wind loads were identified by considering the environmental effects on the selected masonry minaret of Iskenderpas,a Mosque. First of all, modal analysis was executed on the three-dimensional Finite Element model created according to field survey in ANSYS Workbench. In-situ vibration tests were implemented at different intervals by using developed vibration measurement system. The experimental modal parameters were attained from collected signals. The experimental results were used as reference values in model calibration of this minaret to reflect the existing structural behaviour. Model calibration process was carried out on the initial model both by changing of material properties of masonry wall and by taking into account the interactions with mosque walls and ground. Full-scale structural evaluation was carried out under earthquake and wind loads on both the initial and the calibrated models in the weak direction of this minaret. The top displacements, drift ratios, principal stress values and their distributions were determined. It was shown that the analyses on the calibrated model produce more realistic structural behaviour.
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    Investigation of environmental effects through long-term vibration monitoring on the structural behavior and seismic performance assessment of the Hagia Sophia Bell Tower
    (Pergamon-Elsevier Science Ltd, 2025) Yanik, Yusuf; Turker, Temel; Ozturk, Hasan Tahsin; Demirtas, Betul; Aymelek, Abdullah; Yildirim, Omer; Calik, Smet
    This study presents development and application of a high-precision, multi-channel vibration measurement system to monitor structural behavior of Hagia Sophia Bell Tower. The research focused on assessing the dynamic characteristics of the tower, both through experimental measurements and numerical simulations. The study began by conducting an in-depth analysis of the tower's dynamic properties using finite element (FE) models, enabling the identification of experimental frequencies. Long-term monitoring was carried out using the newly developed vibration measurement system, complemented by a digital sensor that enabled simultaneous recording of environmental conditions such as temperature and humidity. These parameters were continuously monitored to assess their potential impact on the frequencies and dynamic responses of the tower. Subsequently, regression analyses were performed to establish the relationship between environmental factors, and the tower's structural behavior. The experimental data were used to update FE models, ensuring a more accurate representation of the tower's actual behavior under varying conditions. Earthquake analyses were also conducted on the FE models to evaluate the seismic performance. The results of the study confirmed that vibration testing, combined with environmental monitoring, was a highly effective method for detecting changes in structural behavior. The findings highlighted the significant influence of environmental factors on the dynamic characteristics, with frequency variations reaching an average of 3.6%. These effects should be considered in ongoing monitoring. It was demonstrated that updating FE models reduced numerical errors below 2.5%. These findings gave importance of integrating long-term monitoring with FE model updating, providing more accurate protection and assessment strategies.
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    Modal testing and full-scale seismic evaluation of a historical minaret according to 2023 Kahramanmaraş earthquake and TBEC 2018 design spectrum
    (Emerald Group Publishing Ltd, 2025) Demirtas, Betul; Yanik, Yusuf; Aymelek, Abdullah; Turker, Temel; Yildirim, Omer
    PurposeMinarets, which were constructed from different types of materials, are slender and tall structures. Minarets could vary in terms of the construction technique, geometry and material. The seismic vulnerability and dynamic behavior of minarets could be different because of these reasons. Full-scale evaluation of minarets includes both experimental and numerical investigations. Experimental methods provide knowledge on the in situ conditions. The structural analysis and performance evaluation can be performed by using numerical methods. In this paper, full-scale structural evaluation of the Trabzon Fatih Mosque Minaret was presented by using experimental and numerical methods.Design/methodology/approachFirstly, the finite element (FE) model of the minaret was generated by ANSYS software. Then, experimental measurements were carried out under environmental vibrations with newly developed vibration system. Afterwards, the initial FE model of the minaret was updated by using manual updating method according to the experimental measurement results. For the seismic performance assessment of the historical minaret, the time history and response spectrum analyses were performed on the initial and updated FE models using the acceleration records of 2023 February Kahramanmaras earthquake and TBEC 2018 codes. The results were evaluated comparatively, revealing that the nonlinear analyses produced higher values compared to other methods. Additionally, variations were observed in the updated FE model results compared to the initial FE model. Finally, it was seen that the minaret did not have sufficient strength against Kahramanmaras earthquake load, so it could collapse under such an earthquake.FindingsBy employing model updating method, the average absolute difference was substantially reduced from 9.12% to 2.11%. The maximum displacements increased with the effect of model updating in all analyses. It was also seen that the spectrum analyses results had lower values than the time-history analyses results and the displacement of the updated FE model was found to be approximately 8% greater than that of the initial FE model in the nonlinear analyses. The maximum/minimum principal stresses decreased in the updated model in the linear analyses. Also, it was determined that the equivalent stresses were higher in linear analyses. It was seen that the cracks occurring in the nonlinear analyses were concentrated more intensely at the bottom region, the transition segment and around the balcony of the minaret. The concentration of damage in these regions suggested that special attention was needed to increase structural durability. The drift ratios were calculated as 0.0056 and 0.0076 for the initial and updated FE models in the linear analyses, respectively. The initial FE model remained the CD limit, but the updated model reached the limit in CP. The drift ratios were calculated as 0.0087 and 0.0093 for the initial and updated FE models in the nonlinear analyses. Both the FE models reached the CP limit. It could be concluded that the minaret did not have sufficient strength against Kahramanmaras Earthquake, so it could collapse under such an earthquake. The drift ratios were calculated as 0.0041 and 0.0043 for the initial and updated FE models in the spectrum analyses. Both the FE models remained within the CD limit.Originality/valueThis paper aimed to evaluate effects of FE model updating on the dynamic and seismic behaviors of the historical Fatih Mosque Minaret in Trabzon. Structural behavior of the minaret was investigated using both experimental and numerical methods. For this purpose, 3-D FE model generated with ANSYS software of the minaret was updated according to the ambient vibration test results. Ambient vibration tests were conducted by measurement system, which was developed by our research team. The manual model updating method was utilized to minimize the differences between numerical and experimental results by varying the material properties. The linear-nonlinear time history analyses and response spectrum analyses were carried out to evaluate the seismic performance of the initial and updated FE models using the acceleration records of 2023 February Kahramanmaras Earthquake records and TBEC 2018 codes.
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    Variations of natural frequencies of masonry minarets due to environmental effects
    (Springer Heidelberg, 2024) Yanik, Yusuf; Aymelek, Abdullah; Yildirim, Omer; Demirtas, Betuel; Turker, Temel
    It is very important to distinguish the reason of change in natural frequencies of structures either caused by a possible damage or environmental conditions (temperature and humidity). In this study, the changes in the dynamic properties of masonry and reinforced concrete minarets under environmental effects, such as temperature and humidity, were investigated. The masonry minarets of Iskenderpasa, Haci Kasim, and Tavanli Mosques and the reinforced concrete minarets of Karadeniz Technical University, Dilaveroglu and Papatya Mosques in Trabzon were monitored by ambient vibration test method, and the relationship between natural frequencies and temperature and humidity was tried to be determined. For this purpose, the natural frequencies of these minarets were measured at certain intervals under different temperature and humidity conditions over a period of approximately 6 months. The vibration measurement system which was developed by our research team was used in the measurements. From the data collected by these measurements, the variation intervals of the natural frequencies (the smallest and the highest values), the percentages of change and their relations with temperature and humidity were revealed. This relationship was determined using linear-non-linear simple and multiple regression analyses. From this study, it was found that the natural frequencies change under environmental effects, such as temperature and humidity, and this rate of change was approximately 7%. There was moderate correlation in Tavanli, Dilaveroglu, and Papatya Minarets, and strong correlation in Haci Kasim Minaret.