Kandilli Rasathanesi ve Deprem Araştırma Enstitüsü

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Browsing Kandilli Rasathanesi ve Deprem Araştırma Enstitüsü by Author "Akkar, Sinan."

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    A proposed ground motion selection and scaling procedure for nonlinear response history analysis
    (Thesis (Ph.D.)-Bogazici University.Kandilli Observatory and Earthquake Research Institute, 2016., 2016.) Zengin, Esra.; Akkar, Sinan.
    With the advancement in performance-based earthquake engineering, nonlinear response history analysis of structures has become more common in recent years. The selection and scaling of ground motions for use in nonlinear response history analysis is one of the most critical steps in performance-based seismic assessment procedures. This study presents ground motion selection and scaling procedure that addresses the uncertainty in the spectral demand with the preserved dispersion within the ground motion set. The candidate ground motion sets are constructed based on dispersion statistics about the target spectral demand. The optimum ground-motion set is linearly scaled by using an optimization algorithm that minimizes the error between scaled median and target spectra. The scaling stage ensures that the median record spectrum provides a reasonable match to target median in a previously defined period interval. This procedure allows performing further modification on each scaled ground motion in order to match the target variance of the scenario-based spectrum. In this study, a novel probabilistic framework is presented to propagate the uncertainties in both ground motion intensity and the structural response on fragility curve estimations. To investigate the effects of uncertainties on seismic damage estimations, the results of this study are compared with those obtained by the conventional fragility curve approach.
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    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.
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    Characteristic structural features of tall buildings in Turkey and their dynamic behavior
    (Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2016., 2016.) Odabaşı, Ömer.; Akkar, Sinan.
    High-rise reinforced concrete (RC) shear wall buildings having 10 to 30 stories in metropolitan cities of Turkey are investigated under the systematic framework of Performance Based Earthquake Engineering (PBEE). A building inventory is compiled entailing blueprints of tall buildings in densely populated areas of the cities: Istanbul, Ankara, Bursa and Mersin primarily to represent the tall building stock. These buildings are thoroughly investigated via statistical methods to develop six reference building models. The recently proposed Conditional Spectrum (CS) is used as a tool to scale the selected ground motions which provided the link between the target hazard at the reference site (represents high seismicity) and structural responses. It is concluded that the high-rise RC shear wall buildings designed by Turkish engineering practice in metropolitan areas show satisfactory performance up to 475-year return period ground motions. However, the increase in ground motion hazard (e.g., 2475-year, maximum considered) may result in irreparable and severe damage states for these buildings, which may be mostly critical in terms of economic losses. The results obtained from this study can be used as reference source for future studies on several other research topics on tall buildings such as estimating cost-effectiveness and vulnerability functions of high-rise building stock in earthquake-prone regions of Turkey.
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    Development of Peak Ground Acceleration (PGA) based pre-code reinforced concrete frame building fragilities for Istanbul
    (Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2019., 2019.) Dolağan, İpek.; Akkar, Sinan.
    An important portion of pre-code building stock in Istanbul runs significant earthquake risk. Given a building class, the uncontrolled construction of pre-code buildings in the past leads to a considerable model variability and complicates the prediction of losses for future earthquakes in Istanbul. However, the social and economic loss estimations are necessary for Istanbul to have planned actions to improve the earthquake resilience in the city. At this point, fragility curves; which represent the exceedance probability of a particular damage state are one of the most important components of resilience-based building inventory studies for large building stocks at large metropolitan areas. This study aims to provide fragility curves for pre-code reinforced concrete frame residential buildings in Istanbul. For this purpose, 800 mid-rise frame buildings located in the Zeytinburnu district in Istanbul are compiled and 16 representative building models are developed to account for the model variability of the same building class. The examined buildings do not comply with the code requirements of any period after 1975 and they can be considered as low code. The fragilities are based on Peak Ground Acceleration because such practical ground-motion intensity measures are being popularly used in the loss assessment of large building stocks. Nonlinear building responses are derived from three-dimensional nonlinear response history analysis that are carried out by using OpenSees Software (Open System for Earthquake Simulation). Incremental Dynamic Analysis is performed to determine the statistical distribution of the response parameters. A set of real ground motions, which are consistent with the disaggregation results of a probabilistic seismic hazard assessment for Istanbul are considered in the development of fragilities for each building model. Therefore, the variability in building models of the same building class as well as the record-to-record variabilities are considered in the developed fragilities. The fragility model is a backbone cure with upper and lower bounds covering the model and ground-motion variabilities for mid-rise low-code reinforced concrete frame buildings in the investigated building stock.
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    PGV based no-code mid-rise reinforced concrete frame-type building fragilities in İstanbul
    (Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2020., 2020.) Duran, Halil İbrahim.; Akkar, Sinan.
    16 building models representing a building stock in the Zeytinburnu District in İstanbul that includes approximately 800 mid-rise reinforced concrete (RC) frame buildings are used to develop PGV based fragility models that could partially represent the no-code building vulnerability in Turkey. The 3-D analytical models of the subject frames are modeled with distributed plasticity using the Open System for Earthquake Engineering Simulation (OpenSees) software. The damage states of the fragilities are determined by use of the performance limits of structural members from 2018 version of the Turkish Building Earthquake Code and 2005 version of the Eurocode 8. Peak ground velocity (PGV) is preferred as seismic intensity measure since it has a better correlation with deformation demands. 25 real ground motion pairs are selected using disaggregation results of three different PGV hazard curves determined from three ground motion predictive models that are used in the development of the most recent national seismic hazard maps. Response statistics are kept through incremental dynamic analysis (IDA) to develop fragilities for each model. The fragilities computed from above comprehensive nonlinear response history analyses advocate that consideration of variabilities in (a) structural models, (b) ground motion records and (c) limit states makes a huge impact in the exceedance probabilities of damage states. Therefore, a backbone fragility model, which covers the above uncertainties by up and down scaling of a central model is a must in proper loss assessment of building stocks.
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    Scalar and vector probabilistic seismic risk assessment procedures and their implementation for a simplified mid-rise RC tunnel from building
    (Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2021., 2021.) Curic, Haris.; Akkar, Sinan.
    This thesis implements various scalar and vector methods of probabilistic seismic risk assessment. Methods implemented differ by type of scaling and selection of ground motion records as well as by primary scalar intensity measure (IM) used as ground motion intensity metric. Two different ground motion scaling and selection methods are used, namely stripe scaling and cloud scaling. Conceptual differences between stripe scaling and cloud scaling as well as the differences they produce in risk assessment results are presented and discussed. Different scalar ground motion intensity measures used are fundamental period spectral acceleration (SAT(T1)) and two distinct weighted average spectral accelerations. Weighted average spectral acceleration is a novel intensity measure developed and presented within this thesis. It is shown to be a good predictor of structural response at high intensity levels where structure undergoes intense yielding. Weighted average spectral acceleration enables analyst to set weights to contributions of spectral accelerations at different periods according to their expected importance to structural response. Conditional spectra for ground motion selection are developed for all three considered scalar IMs. Multivariate normal distributions are presented as useful mathematical tools and they are used for various purposes throughout this thesis (conditional spectra, vector IM hazard, structural response modeling, etc.). Maximum likelihood estimation (MLE) based method is also developed for estimation of parameters used for modeling structural response using structural analyses data.