M.S. Theses

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Mitigation of earthquake hazards of medium-rise buildings by using different soil improvement methods
(Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2023., 2023) Gültekin, Furkan.; Edinçliler, Ayşe.
Earthquakes can be hazardous to occupants and their assets, especially in some regions such as Turkey, Japan, Chile, and the United States of America etc. Nowadays, some regulations were published to mitigate the hazards occurring in buildings during earthquakes. Besides, the hazards can be mitigated by making use of different soil improvement methods such as Geotechnical Seismic Isolation (GSI) Systems which earthquake loads transferred from ground to structure are decreased using geotechnical materials. Gravel and Gravel-Rubber Mixtures (GRM) can be alternative materials for the GSI system because they provide more bearing capacity, less earthquake-induced settlements and high permeability. The aim of this thesis is to evaluate the effectiveness of the proposed Gravel and Gravel Rubber Mixtures (GRM) materials on the seismic performance of low-to medium rise buildings by means of 1/10 scaled 3 and 5- story building models by shaking table tests. The shaking table experiments were conducted by considering different rubber content, thickness of GSI and the number of stories under various seismic motions. Within the scope of this thesis, all improved cases were compared with unimproved cases. This study showed that surrounding building foundations with Gravel or Gravel Mixtures plays a key and favorable role in the mitigation of earthquake hazards by dissipating earthquake energy inside the soil.
Effectiveness of foundation reinforcement on seismic performance of retaining walls
(Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2023., 2023) Demirel, Muhammed Taha.; Edinçliler, Ayşe.
Soil reinforcement is a widely studied improvement method to improve the strength and stiffness of the soil. The primary goals of soil reinforcement are to increase the bearing capacity and decrease the settlement of the soil along with improving the strength of the soil. Geosynthetic soil reinforcement is founded on the idea of taking advantage of the characteristics of geosynthetic materials like the tensile strength of geosynthetic materials, the pressure distribution potential of geosynthetic materials, and the interlocking mechanism between soil and geosynthetic materials. Many studies in the literature focus on using geosynthetic materials in slopes, embankments, or soil foundations below footings. However, there is not any study focusing on the use of geosynthetic reinforcement under retaining walls. This study aims to investigate the effectiveness of geogrid-reinforcement on the seismic performance of the retaining walls under different earthquake motions by shaking table tests. The effects of the length of reinforcement (L) and the number of reinforcement layers (N) on the seismic performance of the retaining walls constructed on geogrid reinforced sand under the different earthquake motions were investigated.
Consideration of structural ageing in the development of analytical fragility functions
(Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2023., 2023) Çevik, Onur.; Hancılar, Ufuk.
This study investigates the ageing effects led by the corrosion of structural materials on the fragility functions analytically derived for reinforced concrete momentresisting frame type buildings which is the predominant typology in T¨urkiye. First, in situ and laboratory material testing results for 175 reinforced concrete buildings located in Istanbul, constructed between 1962 and 2004 with different heights and plan features are examined in order to better understand the level of corrosion and its spread in structural members. The level of corrosion and different ways it occurs is then implemented in structural analyses by altering the mechanical properties and constitutive models of materials with the data obtained from the experimental and numerical results in the literature. For this purpose, three-dimensional finite element models for lowand mid-rise buildings designed in accordance with the provisions of the 1975, 1997 and 2018 Turkish earthquake codes are elaborated. The responses of pristine and aged buildings are studied through nonlinear dynamic analyses under strong ground motion acceleration recordings selected and scaled to represent the level of seismic hazard in Istanbul. Multiple- stripe analysis and maximum likelihood method are implemented for the derivation of fragility functions. The results show that the behavior of structures aged by the effects of corrosion is a significant reduction in structural capacity and thus yields higher damage probability estimates by the derived fragility curves.
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.
A study on fling steps in the Turkish strong ground motion dataset
(Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2023., 2023) Adanır, Emrecan.; Tanrıcan, Gülüm.
In this study, the existing methodologies on fling step calculation from strong ground motions have been investigated and improvements on the most recent data processing scheme eBASCO (Schiappapietra et al., 2021) have been proposed. Capability of the proposed scheme is verified through comparison of permanent displacements that obtained on the processed records and those derived from the co-located GPS data both from Türkiye and worldwide earthquakes. For the first time, Türkiye permanent displacement inventory is created through processing both horizontal and vertical components of the Turkish strong motion dataset. For this purpose, 288 recordings (Rjb ≤ 50 km) of 20 shallow crustal earthquakes (Mw ≥ 6) occurred between 1983-2023 are utilized. In addition, 36 recordings of the 2023 Kahramanmaraş (Mw 7.7) earthquake are also processed and included in this thesis. Performance of evaluation of two global prediction models for fling amplitudes (Kamai et al. (2014) and Burks and Baker (2016)) are performed using Turkish permanent displacement inventory. Then, fling step prediction model of Burks and Baker (2016) is adjusted and the Türkiye-adjusted equation has been further compared with the recordings of the 6 February 2023 Kahramanmaraş (Mw 7.7) earthquake. Lastly, the permanent displacements in vertical components from Turkish strong motion database and NESS 2.0 database are inspected. Performance of the Kamai et al. (2014) prediction equation for this component is evaluated through residual analyses. In addition, based on the empirical dataset, a new predictive model for this component is proposed. This study will contribute to both seismic design of new structures and more accurate evaluation of existing structures in the vicinity of faults. The presented inventory will greatly help to identify the fling containing ground motion records to be used in the seismic design of the structures through selecting and scaling procedures. Furthermore, the presented fling inventory will augment to fling values of normal and strike-slip earthquakes in the worldwide fling database by 22% and 33%, respectively.
Development of empirical fragility functions after the 2020 earthquakes in and around Türkiye
(Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2023., 2023) Açıkgöz, Nurullah.; Hancılar, Ufuk.
In 2020, two major earthquakes occurred that caused life losses and severe damages to the built environment in Türkiye: On January 24 an earthquake of moment magnitude 6.8 in the East Anatolian Fault Zone nearby Elazı˘g (Sivrice) province and, an earthquake of moment magnitude 6.6 on the North Samos Fault in the Aegean Sea offshore Izmir (Seferihisar) province on October 30. Immediately following these devastating ground shakings, the Turkish Ministry of Environment, Urbanization and Climate Change conducted large-scale and detailed post-earthquake damage surveys in both regions. The observational damage data collected by the technical staff of the Ministry consisted of 92,800 structures in Elazı˘g and 213,776 structures in Izmir. This thesis aims to construct comprehensive empirical fragility functions from these two damage datasets by employing statistical methods. In order to examine the uncertainties, fragility curves are produced using different ground motion models and local soil information from different sources, and to consider these effects a ground motion model using a logic tree approach is proposed. Fragility curves for reinforced concrete moment-resisting frame type structures and unreinforced masonry structures, which are the predominant typologies in T¨urkiye, are proposed with their confidence intervals. Comparisons with the fragility functions for similar structures available in the literature are provided.
Development of a seismic damage prediction model by using machine learning classification algorithms with an artificial dataset
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2023., 2023) Atici, Ali Talha.; Hancılar, Ufuk.
Assessing the potential damage to buildings due to a possible earthquake in a region and taking measures, such as strengthening or reconstruction of vulnerable structures, is critically important to minimize social and economic losses that are likely to occur. Evaluating the seismic performance of structures is a comprehensive and time-consuming process. However, using well-trained machine learning prediction models instead of traditional structural performance analyses can significantly reduce computation time. This thesis focuses on developing a damage prediction model using classification-based machine learning algorithms, utilizing a two-dimensional reinforced concrete frame system dataset that represents low to mid-rise, non-ductile buildings. The structural features forming the dataset are obtained from a comprehensive literature review on building stock characteristics in the Marmara region. Nonlinear time-history analyses are conducted using actual earthquake records with the OpenSeesPy framework. The maximum inter-story drift ratio is used as an engineering demand parameter to classify the damage state of buildings. Reliable machine learning models are developed with a balanced dataset. Twenty-four models are created using six variant ground motion intensity measures and four classification algorithms: k-Nearest Neighbors, Support Vector Machine, Decision Tree, and Random Forest. The best-performing model is determined by comparing performance metrics and the confusion matrix. In conclusion, the model developed with a dataset incorporating peak ground velocity and utilizing the Random Forest classification algorithm demonstrates the most effective performance with 92% prediction accuracy.
The use of machine learning algorithms to derive fragility curves for MID-RISE reinforced concrete buildings
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2023., 2023) Ülkü, Onur.; Hancılar, Ufuk.
The occurrence of an earthquake does not necessarily indicate that there is a seismic risk. The existence of risk depends on having three components, which are hazards, exposures, and fragility together. Assessing the risk of existing buildings is a building-specific task that may be tremendously time- consuming and computationally burdensome. Moreover, determining the risk of each structure can be complicated when investigating a portfolio or a group of buildings. Developing fragility curves for buildings provides a possible and undemanding method to estimate damage likelihood. Machine learning algorithms are one of the novel approaches that are implemented for estimating potential structural damage. Well- trained machine learning algorithms provide to speed up processing, cut down the cost of computation, and produce reliable fragility curves. This thesis focuses on developing fragility curves for generic building inventory spread over the Marmara region by predicting the probability of maximum inter- story drift ratio intervals via five various machine learning algorithms, which are Random Forest, Stochastic Gradient Boosting, Na¨ıve Bayes, Decision Tree, K-Nearest Neighbors. Information on the characteristics of pre-dominant building typologies in the Marmara region available in the literature is utilized for creating an artificial inventory dataset of mid- rise RC buildings. The data for the machine learning was gathered by designing and analyzing 2-D frame systems under non-linear time history analysis with OpenSeesPy. The machine learning algorithms are trained considering different intensity measures and buildings’ characteristics. Machine learning algorithms are evaluated when generating fragility functions by comparing those produced by fitting log-normal distribution with the maximum likelihood estimation method.
Time - dependent seismic hazard assessment for the north and east Anatolian faults
(Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2022., 2022) Koca, Cem.; Şeşetyan, Karin.
Until now, many probabilistic seismic hazard assessment (PSHA) studies have been performed for Turkey. However, except in a limited number of cases, character istic fault source modeling was not used. Since the North and East Anatolian Faults (NAF and EAF) have a tendency for rupturing in characteristic earthquakes, the first objective of this research is to develop a sound hybrid characteristic recurrence model for the NAF and EAF. The so-called hybrid model involves a composite characteris tic model (i.e., an exponential part for the smaller and a characteristic part for larger magnitudes) developed for each segment combined with a characteristic recurrence pro posed for multi-segment ruptures. Two different hybrid earthquake recurrence models with time - independent (or Poissonian) and time – dependent (or renewal) character istics are developed. By means of the renewal hybrid model, the effect of some seismic gaps along the NAF and EAF on seismic hazard is assessed, which is the primary purpose of the thesis. On the other hand, these two models have also given the oppor tunity to evaluate the results of the fully exponential model of the NAF and EAF. The comparison between different earthquake recurrence models developed for the NAF and EAF yields interesting results. Fully exponential model usually produces over estimated seismic hazard compared to the Poissonian hybrid – characteristic model. Slip deficits on some fault segments can increase the seismic hazard dramatically if the results of renewal hybrid model are considered. Although the overestimated results of fully exponential fault source model can compensate the high hazard based on renewal hybrid model, depending on the amount of slip deficit, the time – dependent hazard may exceed the hazard obtained by the fully exponential model. In cases where there is a considerable amount of slip deficit on a fault, a time - dependent seismic hazard model should be developed to deal with the worst-case scenario.
Epistemic uncertainty in the analytically derived fragility functions : multiple stripe analysis versus cloud analysis
(Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2022., 2022) Önder, Zeynep Eda.; Hancılar, Ufuk.
This study aims to examine the effects of epistemic uncertainty arising from dif ferent analysis approaches on the derived fragility functions. To this end, fragility functions are developed by using two different methods namely multiple stripe analysis (MSA) and cloud analysis, and compared for low-rise and mid-rise (3 and 6-story), re inforced concrete (RC), moment-resisting frame (MRF) buildings designed as per the Turkish Seismic Codes (TSC) published in 1975 and 2018. Each building’s prelimi nary design complies with the minimum requirements specified in the relevant seismic codes. A total of four buildings are studied considering different heights and different seismic codes. The OpenSees Program (the Open System for Earthquake Engineering Simulation) is used to perform nonlinear dynamic analyses of the structures. While spectral displacement (Sd), spectral acceleration (Sa) and peak ground acceleration (PGA) are chosen as intensity measures, maximum inter-story drift ratio (MIDR) and top displacement (Dtop) are selected as engineering demand parameters. For the dam age state definitions through threshold values on the EDPs, nonlinear static (pushover) analyses are conducted to pick the limit values of top displacements from the idealized pushover curves whereas limit values for MIDR are drawn from the Hazus MR4 Tech nical Document. For MSA, 11 stripes and 22 pairs of earthquake records for each stripe are used, while 44 sets of record pairs are used for cloud analysis. Fragility functions for the aforementioned buildings are developed by using two methods and compared to account for the epistemic uncertainty in the derivation of fragility functions.
Numerical modelling of ground motions in Eskişehir basın
(Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2022., 2022) Akpunar, Lütfü İhsan.; Tanrıcan, Gülüm.
Eskişehir basin is located at the boundary of central and western Anatolia tectonic regions. Between two active faults it extends in EW direction with two open ends. So far deep velocity structure of the basin has not been well constrained however, average shear wave velocity for the top 30 m and sedimentary thickness estimations are available at various locations of the basin (e.g.,T¨un et al. (2016); Yamanaka et al. (2018); Ozel et al. (2020)). Number of strong motion recordings is rather limited due low seismicity of the region. The largest magnitude event that has ever been recorded within 150 km is the 2011 Simav Earthquake (Mw 5.9). Eskişehir city, with a popula tion close to a million people, has been expanding towards to this sedimentary basin. Long period ground motion is the concern of large scale structures that will be built at this region. Here we first present observed features of strong ground motions of this event recorded in the Eski¸sehir basin. Firstly, we observed that ground motion from the 19.05.2020 Mw 5.9 earthquake is governed by Rayleigh waves at periods longer than 0.5 s. Retrograde motion is visible almost at all basin- recordings. Among recorded waveforms, PGA and PGV of a basin- edge station (#2610 AFAD station) are formed by Rayleigh waves at periods 1 s. The longest significant duration of recordings is as high as 53 sec. Recorded spectral acceleration for 5% damping at spectal periods longer than 1 s is much higher than the one predicted by region specific ground motion prediction models. In the second phase, we showed formation of an experimental basin geometry utilizing linear interpolation of predominant frequencies at 95 measurement points. Dimensions of the model are 43 km \ 27 km \ 15 km. Basin layer continues across the entire model in EW direction, but bordered by northern and southern hills to mimic the geographical environment. Maximum depth is about 600 m. In the last phase we investigated the 3D wave propagation of small magnitude events, 17.01.2015 Mw 4.3 and 18.09.2015 Mw 3.7, occurred at northwestern part of the region and center of the basin, and compared with observed recordings for a possible validation of the velocity model. The computer code utilized in simulation relies on a finite difference modelling using staggered grids with nonuniform spacing. Ground motion simulation of the Mw 4.3 event reveals that the current velocity model overestimates the velocities in the eastern part of the basin in the NS direction, where E-W direction synthetics are generally smaller than the observed ones. On the other hand, synthetic velocities agree with observed ones at basin-center stations in the west. These findings suggest that more careful definitions of basin boundaries are necessary for the future models. Comparison of 1D and 3D simulation results also suggest that a 3D velocity model may produce longer and -more realistic- duration ground motions. The final step is to perform a blind simulation for the 20 February 1956 Mw 6.5 earthquake. The source was modeled by considering the ambiguities in the source parameters. The previous research was compiled to deal with unknown information about the mechanism and location of this event for consensus. We have compared the simulation outcomes with GMPEs models. The numerical simulation results yielded higher outcomes than estimated spectral ordinates by GMMs.
Effects of site improvement technique on seismic performance of geotechnical structures
(Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2022., 2022) Demirtaş, Bilge Sultan.; Edinçliler, Ayşe.
Earth-retaining structures are widely used in the man-made environment and compose the significant constituents of infrastructural systems worldwide. Besides, they have been constructed broadly in seismically active regions. Earthquakes can cause a lot of damage to geotechnical structures. The prevention of failures in these structures is an important issue. Cost effective remedies can be applied to retaining structures in order to prevent them from failing under seismic loading. The use of lightweight materials behind the wall as a cushion layer is one of the methods to improve the seismic performance of the retaining system. The objective of this thesis is to investigate the effects of cushion type on the seismic performance of retaining walls by performing shake table tests. The experiments were carried out with a 1/25 scaled retaining wall model with or without a cushion layer. In the experimental study, the cushions were considered as EPS geofoam and a mixture of tire crumb and sand. Additionally, various parameters, such as cushion thicknesses, EPS geofoam densities, mixture ratios of sand-tire crumb mixture, and input characteristics, are also evaluated. The results were examined by comparing the cases having a cushion layer with the case without a cushion layer depending on mentioned parameters. The evaluation of the results indicates that the seismic performance of the retaining wall is very sensitive to cushion type. It is observed that the EPS cushions are more effective than the sand-tire crumb mixtures to improve the seismic performance of the wall. Additionally, the use of cushion layer with higher thickness can be an effective solution to improve the seismic performance of the retaining wall, prevent the future failure of the retaining structure, and mitigate earthquake hazards.
Seismic evaluation of Bolu viaduct 1
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake research Institute, 2006., 2006.) Candan, B. Tolga.; Aydınoğlu, M. Nuray.
A thesis is presented on the seismic evaluation of a viaduct using non-linear analysistechniques. The Bolu viaduct is a 2-3 km long seismically isolated structure with two parallelbridges each with a span length of 39.2 m and pier height of maximum 49 m that was nearly complete when it was struck by the 1999 Duzce earthquake in Turkey. With the design basedon AASHTO standards, it suffered complete failure of the seismic isolation system andnarrowly avoided total collapse due to excessive superstructure moment. After investigationsthe retrofit of the viaduct had been decided due to the study carried out by Michele Calvi and J. Nigel Priestley. This thesis concentrates on the retrofitted structure of Viaduct 1 by non-linear time historyanalysis.
Investigation of failure modes and mechanisms of Alibey Earth Dam by solid-fluid coupled nonlinear dynamic finite element simulation
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2006., 2006.) Parker, Ahmet Alper.; Siyahi, Bilge.
In this study, earthquake resistance of Alibey Earth Dam was investigated. Darn was modeled with four node plane-strain finite elements and displacement-pore pressure coupled finite element analyses were performed. Nonlinear material models such as pressure dependent and independent multi yield materials were implemented during the analyses. Transient dynamic finite element analyses were performed with Newmark method. Newton-Raphson solution scheme was adopted during the solution of the equations. Liquefaction and/or cyclic mobility effects were considered during the analysis. For the finite element analyses OpenSees (Open System for Earthquake Engineering Simulation) framework was adopted.
Strain based performance evaluation charts for rectangular reinforced concrete columns in nonlinear analysis of structures
(Thesis (M.S.)- Bogazici University. Kandilli Observatory and Eartquake Research Institute, 2005., 2005.) Şadan, Oğuz Bahadır.; Aydınoğlu, M. Nuray.
Several methods and criterion are being used recently in determination of the deformations occurred in structural elements of a building and performance evaluation of these structural elements under earthquake motion using nonlinear analysis. Performance evaluation of structures under nonlinear earthquake loading using material strains, rather than the rotations as commonly used in other seismic codes (FEMA356, ATC40, EUROCODE8 etc.) is the basic subject of this study. Performance evaluation using material strains is also being mentioned in Chapter 13 of New Turkish Seismic Code Dra3. For performance evaluation using member strains, Strain Based Performance Evuluation Charts for rectangular reinforced concrete columns have been formed which bring easiness by omitting several cross sectional analysis in order to transform rotations into strains. These Strain Based Performance Evaluation Charts are intended to be very useful for the structural engineers who will practice nonlinear analysis using New Turkish Seismic Code in the future. However it should be noticed that these charts are formed only for rectangular reinforced columns with limited concrete-steel grade combinations. Therefore further studies should be performed for other combinations and beams.
Seismic performance evaluation of public school buildings in İstanbul metropolitan area
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2005., 2005.) Ekser, Burç.; Yüzügüllü, Özal.
Earthquake resistance of school buildings deserves special attention with respect to seismic safety because of their occupancy characteristics and their importance to immediate and long-term earthquake disaster relief and recovery efforts. The aim of the study is that the seismic performance evaluation of public school buildings in Istanbul. According to this, in Istanbul, three different types of projects are practiced and evaluated for public schools constructed due to different number of stories and different earthquake zones. besides, these kinds of porjects were analyzed in terms of 1975 and 1998 Turkish Codes. In addition to the seismic performance evaluation of public schools, a preliminary screening procedure was carried out in that study. To eliminate the losses caused by earthquakes, the earthquake resistance of the school building must be examined by quick and easy method which is Rapid Visual Screening Procedure prepared by Applied Technology Council. Actually, the method which was carried out, is classified the earthquake resistance resistance of the public schools and determined a detailed evaluation is required or not.
Development of fragility functions for code conforming low-rise reinforced concrete buildings
(Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2021., 2021.) Şenol, Erkan.; Hancılar, Ufuk.
In this study, fragility functions are developed and compared for low-rise (2 and 3-story), reinforced concrete (RC), moment-resisting frame (MRF) buildings, which are designed per the Turkish Seismic Codes (TSC) released in 1998 and 2018, at eight different locations in Istanbul, Turkey. In the preliminary design of each building, the minimum conditions defined in the corresponding seismic code are followed. Moreover, the capacity design principles are taken into consideration as defined in the seismic codes. To increase the representa tiveness of the dimensions (i.e., footprint, structural member dimensions, story height) of the buildings, the past studies about the characteristics of the low-rise buildings in Turkey, and the structural drawings belonging to the existing buildings designed per the corresponding seismic codes are examined and used. Considering eight different locations, two different story numbers, and two seismic codes, a total of 32 buildings are designed and analyzed. The nonlinear analyses of the buildings are conducted by using the OpenSees Software (Open System for Earthquake Engineering Simulation Pacific Engineering Research (PEER) Center Version 3.0.3). The structural elements (beams and columns) are modeled with frame elements. The distributed plasticity (fiber) is considered for the columns whereas lumped plasticity (plastic hinge) is considered for beams. To generate the fragility functions for the buildings, multiple stripe analysis (MSA) together with the maximum likelihood estimation (MLE) method is utilized. Spectral displacement (Sd) and spectral acceleration (Sa) are selected as the intensity measure (IM) parameters whereas the maximum inter-story drift ratio (MIDR) and top displacement (Dtop) are used as engineering demand parameters (EDP). The fragility functions are developed for four damage states which are slight damage, moderate damage, extensive damage, and complete damage. While deciding the limit values of the EDPs for each damage state, we perform pushover analysis to decide the limit values of top displacements from the idealized pushover curves. With regards to the limit values of MIDR, they are taken from Hazus MR4 Technical Manuel, which is defined for low-rise, high-code MRF structures. For MSA, eleven intensity measure levels (stripes) are defined, and for each stripe, 22 pairs of ground motion records are selected and used. To select the ground motion records for each stripe, a code-based target response spectrum is developed for each IM level. By making use of the devel oped response spectra for each IM, 22 pairs of ground motion records are selected from PEER Ground Motion Database for each IM level (stripe). The fragility functions based on the different types of IMs (Sa and Sd) and the different types of EDPs (MIDR and Dtop) are developed and compared for the 2 and 3-story low-rise RC buildings designed per TSC1998 and TSC2018.
Pipeline damage assessment through Monte Carlo simulation
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2021., 2021.) Bingöl, Ali Osman.; Hancılar, Ufuk.
Earthquakes are one of the most catastrophic events among all the disasters. They affect societies in many aspects including life losses and economic losses. Besides the life losses, a lot of people get injured and become disabled due to earthquakes. As being parts of the lifeline systems in a city, potable water systems, wastewater systems, electricity systems, etc. are vital for human life. The impediments in the serviceability of these lifeline systems, put people’s lives in danger even after an earthquake. Studies to reduce the negative effects of earthquakes and guess the serviceability of a lifeline system after an earthquake has gained major importance. In this study, algorithms to predict the number of damages on the water pipeline system due to an earthquake suggested by both HAZUS-FEMA (2003) and the Ameri can Lifeline Alliance (ALA-2001) are compared. Moreover, the Monte Carlo simulation technique is introduced to these two methods and the results of these methods through Monte Carlo simulation are also compared. To perform the analyses, a generic study of the Zeytinburnu potable water system in Istanbul is examined with four different pipe material types, namely, concrete, bellmouth concrete, steel, and polyethylene under a scenario earthquake generated by ELER software. Concrete and steel pipes have large diameters, whereas bellmouth concrete and polyethylene pipes have small diameters in this study. With these different pipe material types, the effects of being brittle and being ductile materials on pipe failures are also evaluated and compared.
A study on the fragility modeling of mid-rise tunnel form RC buildings for Turkey
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2021., 2021.) Özen, Uğur.; Akkar, Sinan.
The mid-rise tunnel form RC buildings in metropolitan cities in Turkey and their dynamic behavior against earthquake action are investigated by deriving a representative model. First of all, the compiled blueprints of the tunnel form RC building inventory are categorized into four different groups and their fundamental features are studied statistically. The first group, which is the focus of this study represents general features of mid-rise tunnel form buildings in Turkey. Secondly, the nonlinear structural model of this building is developed based on the code requirements and guidelines to perform push-pull and pushover analysis for obtaining its simplified SDOF version in the MSc thesis of Curic (2021). The results of these two theses will complete and augment each other in a near-future collaborative work. Then, the ground motions selected and scaled to the target conditional-response spectra developed in Curic (2021) are used together with the provisions in the 2018 Turkish Building Earthquake code, 2004 Eurocode, and 2017 ASCE code to assess the structural performance of the model building (through damage states) for developing fragility curves. The observations from this study show that the performance of mid-rise tunnel form buildings can be called as satisfactory under the requirements dictated by the national and international standards. Another observation is that different engineering demand parameters give different performance assessment results. Hence, novel global and local performance demand parameters should be investigated by studying other categories (mid- and high-rise) tunnel form buildings. The variabilities in (1) engineering demand parameters, (2) structural properties such as story number, types of vertical elements, and mathematical model, and (3) the definition of limit states in both local and global performance levels have a significant effect on the fragility curves. These variabilities are taken into account for performance based assessment.
Epistemic uncertainties in probabilitic earthquake hazard models and their effects on the results :|the case of Marmara region
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2021., 2021.) Perdıbuka, Hülya Yüksel.; Şeşetyan, Karin.
Throughout the history and also in the not too distant past, Marmara region has been a center that hosted several of the most destructive earthquakes around the World. Considering the density of population and building stock and the concentration of economic activities, the performance of comprehensive earthquake hazard assessment studies is one of the essential steps towards the mitigation of the seismic risk in the Marmara region. The seismicity and the earthquake characteristics of this region have been studied extensively in the last decades, and various hazard maps have been created. In the light of the increasing amount and quality of data and new studies on seismotectonic and the developments in the earthquake hazard calculation methods, the need for a regular updating of the earthquake hazard estimates for regions with high seismic activity arises. Therefore, new earthquake hazard maps for specific regions or regions covering many countries are being generated continually. In today’s practice, the use of the probabilistic earthquake hazard assessment method has become a common implementation in the preparation of earthquake hazard maps. However, as opposed to site-specific assessments, large scale regional studies usually investigate the effects of epistemic uncertainties only in a limited way, and in most cases, only the mean hazard outputs are reported. Nonetheless, analysis of epistemic uncertainties in the hazard assessment and reporting of the uncertainty ranges associated with the ground motion estimations can provide valuable insights towards a better understanding of the seismic hazard and consequently of the seismic risk. Starting from this point of view, developing an earthquake hazard assessment model specific to the Marmara region, dealing specifically with the uncertainties associated with the modelling approaches, is quite meaningful when the earthquake history of the region is also considered. In this thesis, in order to examine the effects of uncertainties on probabilistic earthquake hazard analysis results specific to the Marmara region, the Turkish Seismic Hazard Map developed within the scope of the “Update of seismic hazard maps of Turkey (UDAP-Ç-13-06)” project was evaluated. Alternative models were included in the earthquake hazard calculations by obtaining uncertainties related to the data and modelling parameters and combining them in a logic tree structure. Accordingly, hazard maps are obtained for PGA and 5 % damped Spectral Accelerations at T = 0.2 s and 1.0 s for 475 and 2475 years return periods, and uncertainty ranges for the computed ground motion parameters are presented. The sensitivity of the results to the uncertainties associated with different modelling parameters is investigated. The results indicate that, even for the Marmara region, which is one of the best-studied regions in terms of seismic activity and geological structure, the seismic hazard models can be associated with large uncertainties.

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