M.S. Theses
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Browsing M.S. Theses by Author "Çaktı, Eser."
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Item Characteristics of the dynamic response of the Sultan Ahmet Mosque (Istanbul) to earthquakes(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2021., 2021.) Dönmez, Kökcan.; Çaktı, Eser.The 400-year-old Sultan Ahmet Mosque is located southwest of the ancient hippodrome in Istanbul's historical peninsula. This historic structure, which has survived from the Ottoman period, experienced many damaging earthquakes in the North Anatolian Fault, especially in the fault segments within the Marmara Sea, since its construction was completed in 1617. The mosque is prominent as a cultural heritage element in the city. Therefore, its primary structural system has been monitoring since 2012. The Structural Health Monitoring system deployed in the mosque consists of ten triaxial (two horizontal, one vertical) accelerometers functioning at a sampling rate of 200 Hz. Sensors were installed as four at the main dome, four at the upper galleries of the pillars, one at the ground level, and the last one on the basement floor. Over two hundred recorded earthquakes between October 2012 and November 2020, whose magnitudes ranging from minor to strong, were processed and assessed through scripts coded on MatLab. Used criteria such as sensor completeness of an event and the signal-to-noise ratio of a recording initially reduced the number of earthquakes. Hence in this thesis, the final catalogue of 103 events was analysed in time- and frequency-domain after evaluating the catalogue statistically as functions of magnitude, distance, and azimuth. In the time domain, acceleration, velocity and displacement peaks were obtained and assessed individual- and group-based. Their various relations with earthquake magnitude and amplitude were also examined. In frequency domain analyses employing modal approaches, the dependence of dominant frequencies on time, temperature, earthquake magnitude, and ground motion amplitude was investigated. Particle motions and mode shapes for the selected largest-amplitude events were identified and depicted. Finally, the existence of soil-structure interaction and the rocking vibrations in the structure were investigated.Item Dynamic response characteristics of the Fatih mosque in Istanbul estimated from earthquake data(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2017., 2017.) Tongut, Ayşe.; Çaktı, Eser.Structural Health Monitoring (SHM) enables continuous recording of the dynamic response of a structure and analysis of its time-varying dynamic characteristics for condition and ultimately damage assessment. SHM is increasingly used for the estimation of dynamic behavioral characteristics of historical structures, which is vital for conservation, repair and strengthening. For the preservation of the architectural heritage, a crucial element in our present-day culture, the historical constructions need to be identi ed both in terms of their structural system and present damages. The Fatih Mosque in Istanbul is part of a larger complex. The rst mosque was built soon after the conquest of Constantinople between the years 1463 and 1470. After 1766 earthquake the rst mosque collapsed. The present mosque built in 1771 and is one of the most signi cant monuments in the city. In this study, the four-year monitoring data (2013-2016) recorded by the Fatih Mosque Structural Health Monitoring System is analyzed. The vibration monitoring system in the Fatih Mosque consists of thirteen three-component accelerometers and four two-component tilt-meters.During the four year period, the mosque experienced more than 160 earthquakes whose magnitudes varied between 2.1 and 6.5 in the Richter scale. A database of recordings suitable for further analysis is created by applying selection criteria for number of recording stations, signal to noise ratio, epicentral distance and earthquake magnitude. The data is uniformly processed using computer codes developed in MATLAB. Time domain and frequency domain characteristics of structural response are studied with the help of recorded earthquakes in the structure. Additionally presence of soil-structure interaction and rocking; and variations in wave travel times are investigated.Item Estimation of the high frequency decay parameter (k) and anelastic attenuation factor (Q) for Istanbul(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2018., 2018.) Süleyman, Hakan.; Çaktı, Eser.In this study we attempt to estimate parameters that are related to path and near-surface effects, due to earthquakes that occurred in northwestern Turkey, by drawing on data from the Istanbul Earthquake Rapid Response System (IERRS) that is operated by the Department of Earthquake Engineering at Boğaziçi University’s Kandilli Observatory and Earthquake Research Institute. Our data set includes over 4677 strong motion recordings from 115 stations of the IERRS. The records are associated with events having local magnitudes ranging within 4.0Item Experimental evaluation of natural vibration frequencise of un-damaged and damaged reinforced concrete buildings with laser vibrometry(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2021., 2021.) Ertürk, Sefer Ömercan.; Çaktı, Eser.In this study, a laser vibrometer recently acquired with the support of the Boğaziçi University Scientific Research Projects Fund is tested and validated in laboratory and field conditions. It has been used in a survey carried out in Istanbul about fundamental frequency assessment of 103 tall buildings. The records obtained are analyzed, and a fundamental frequency – building height relationship for tall reinforced concrete buildings in Turkey is proposed. Furthermore, the laser vibrometer has been used in a survey for the assessment of fundamental frequencies of damaged and undamaged buildings in İzmir following the 30.10.2020 Samos-Sığacık earthquake. The records taken from 38 buildings are analyzed, and characteristics of fundamental frequencies of buildings in different damage states are discussed.Item Long-term dynamic response of Hagia Sophia in Istanbul to earthquakes and atmospheric conditions(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2015., 2015.) Dar, Emrullah.; Çaktı, Eser.The effects of atmospheric factors on structural behavior have gained more importance due to climate change as result of global warming in recent years. In this thesis, the effects of ground motions and atmospheric variations on the modal parameters of Hagia Sophia in Istanbul, which is one of the most prominent structures created in the history and is in the UNESCO world heritage list, are examined. Firstly, the frequency variation of Hagia Sophia due to atmospheric conditions such as temperature, wind speed, humidity and precipitation has been assessed. For this purpose, acceleration records are divided into half-hour segments and the Fourier amplitude spectra of each segment are calculated using short-time Fourier transform. In this way, an annual frequency variation of the structure is achieved by combination of frequency values obtained from these spectra. Afterwards, the frequency variation of Hagia Sophia is compared with the variation of atmospheric conditions and the results are assessed individually. Secondly, the dynamic behavior of the Hagia Sophia during different earthquakes is analyzed. The modal parameters and mode shapes of the structure are determined. The decrease associated with the first two modal frequencies of the structure during each earthquake is calculated. Finally, the effect of maximum acceleration and duration of strong ground motion on modal frequencies of the structure is investigated.Item Stochastic simulation of the January 24, 2020 Elazığ,-Sivrice earthquake(Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2023., 2023) Acar, Şükran.; Çaktı, Eser.This thesis focuses on the application of stochastic ground motion simulation methodology to the 24 January 2020 Mw 6.8 Elazığ-Sivrice earthquake, which occurred on the P¨ut¨urge segment of the East Anatolian Fault in Turkey. In this context, the dynamic corner frequency-based stochastic finite fault method was used to simulate the ground motion fields generated by the 24 January 2020 Elazığ-Sivrice earthquake earthquake. Input parameters for the simulations are derived from regional sources and seismic parameters to ensure the reliable production of synthetic ground motions. The model parameters are evaluated by comparing the real records of the Elazı˘g- Sivrice earthquake with synthetic records and preferred models are selected accordingly. Moreover, the synthetic records have been compared with regionally suitable ground motion models (GMMs). The stochastic ground motion simulation methodology is used together with the extended fault model, evaluating both random and earthquake specific slip distribution options. Alternative models or values are considered for the stress drop, geometric spreading, Q and duration models as well as for site amplification. A combination of models that yield the lowest error terms both in frequency and time domain parameters is proposed as the preferred model for this study. As a result of this study, it is seen that the simulations of the Elazı˘g- Sivrice (Mw 6.8) event give reasonable results for frequency ranges higher than 1 Hz and the determined parameters can be further developed and used as input to other studies evaluating seismic hazards in related regions.Item The use of laser scanning in civil and earthquake engineering(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2017., 2017.) Ercan, Tülay.; Çaktı, Eser.Laser scanning technology is one of the most e cient solutions for generating three-dimensional data. Besides its use in areas such as archaeology, biology, geology, architecture, it has been used for various purposes in civil engineering. While conventional methods are limited in describing the current state of a structure as they mostly involve point speci c measurements, the geometry of a structure can be rapidly described by analyzing three-dimensional point clouds to a high precision. Laser scanners can be also used as a tool for structural monitoring. Structural deformations/damage caused by earthquakes, or due to other static or dynamic mechanisms can be monitored. Moreover, realistic structural models re ecting the actual geometry can be created for engineering purposes. In this study, the results of the laser scanning survey carried out in the Edirnekap Mihrimah Sultan Mosque are presented. Mihrimah Sultan Mosque was built in the period of 1562-65 by Architect Sinan and has a special importance among his work because of its exceptional geometry. The rst laser scanning survey of the mosque was performed in 2015 and has been repeated annually since then. The current deformation/damage state is investigated with the help of the point cloud data. Three-dimensional structural model of the dome of the Mosque was created from point cloud data and results are presented. It is believed that this study will positively contribute to the use of laser scanning in civil/earthquake engineering and to the preservation of this important architectural heritage building.