Ph.D. Theses
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Browsing Ph.D. Theses by Author "Çaktı, Eser."
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Item Constraining source properties of the 1509, 1766 and 1894 Istanbul earthquakes(Thesis (Ph.D.)-Bogazici University.Kandilli Observatory and Earthquake Research Institute, 2022., 2022) Yenihayat, Nesrin.; Çaktı, Eser.; Şeşetyan, Karin.In this thesis, stochastic simulations were performed for the 10 September 1509, 22 May 1766, and 10 July 1894 Istanbul earthquakes to constrain their source parame ters with a detailed characterisation and classification of associated damages and their distributions. Damage information was obtained as spatial distributions of observed data assembled from various sources and interpreted on the MMI scale. Using a finite fault simulation approach, numerous scenarios were modeled with calibrated and validated source, path and site parameters. In calibration, simulations were performed for 59 recordings of the 26 September 2019 Silivri (Mw=5.8) earth quake. In order to test our model on a larger Marmara earthquake recordings obtained at 19 stations of the 17 August 1999 Kocaeli (Mw=7.4) earthquake were also simulated. Through an iterative selection of source parameters and comparison of simulation based synthetic intensity distributions with intensities assessed from actual damage, evaluations of source parameters of three earthquakes were made. Findings indicated that most likely the magnitude of the 1894 Istanbul earthquake was Mw=[6.8 to 6.9], and its epicenter was either at the midpoint of the Prince Islands segment with a 42 km rupture or at the intersection of the Prince Islands segment with the Izmit segment as a 60 km total rupture. The 1766 earthquake likely had a rupture length of about 80 km along the Central Marmara Fault with a magnitude of Mw=[7.0 to 7.1]. Our findings suggested that the 1509 earthquake most probably occurred as a combined rupture of the Prince Islands segment and the Central Marmara Fault, and created a 120 km rupture with a magnitude of Mw=7.6.Item Real-time structural health monitoring using statistical methods(Thesis (Ph.D.)-Bogazici University.Kandilli Observatory and Earthquake Research Institute, 2023., 2023) Dar, Emrullah.; Çaktı, Eser.The detection of structural damage relies on understanding the long-term variation of modal parameters and their relationship to changes in atmospheric conditions. This thesis aims to address this challenge by developing a real-time algorithm for structural health monitoring systems, which are becoming increasingly important. The algorithm uses statistical models developed by analyzing four years of modal frequencies, damping ratios, and mode shapes of Hagia Sophia, a UNESCO World Heritage structure, and their correlation with atmospheric parameters such as temperature, humidity, and wind speed. The algorithm uses four different regression models to predict the modal frequency as a function of the atmospheric conditions and selects the most suitable one. It then compares the predicted and measured frequencies to identify structural anomalies. The algorithm also employs the Modal Assurance Criterion (MAC), Coordinate Modal Assurance Criterion (COMAC), and Enhanced Coordinate Modal Assurance Criterion (ECOMAC) methods to examine the long-term variation of mode shapes. The algorithm is implemented in a user interface software called “AISHM,” which displays the modal parameters and the 3-D animation of the structure in real-time. The software also has the capability to track earthquakes and analyze the structural response in real-time. In summary, this thesis presents a comprehensive approach to real-time structural health monitoring using statistical models and advanced analysis techniques, which can have significant implications for maintaining and preserving historical structures.Item Use of distinct element method in the assessment of earthquake behavior of masonry structures(Thesis (Ph.D.)-Bogazici University.Kandilli Observatory and Earthquake Research Institute, 2014., 2014.) Saygılı, Özden.; Çaktı, Eser.There are a number of masonry structures in Istanbul and in other cities of Turkey that suffered severe damage from earthquakes. As they will continue to get affected by the earthquakes, more research is needed to assess their seismic dynamic behavior particularly in the states of large deformations/damage and collapse. This still remains as a challenge in spite of significant developments in understanding factors affecting the seismic resistance of masonry structures. The present thesis deals with non-linear dynamic analysis of masonry structures modelled through distinct element methodology. First, a masonry mosque has been built at 1:10 reduced scale and tested by subjecting it to a sequence of earthquake excitations on the shake table in three phases: test of the base-isolated model, of the model as it is and that of the strengthened model. The results of these three phases were used in the calibration/validation of the numerical model developed by distinct element approach. It has been concluded that the methodology and the elements developed in this stage are good enough to be employed in the investigation of real masonry structures. In the second stage, three masonry minarets in Istanbul were studied under sine waves (velocity amplitude range: 10 cm/s – 100 cm/s; frequency range: 0.1 Hz – 13 Hz) and under real and simulated earthquake ground motion. The deformation levels and patterns induced in the minarets and the energy balance in the system are investigated to analyze the damage processes.