Deprem Mühendisliği

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A comparison and evaluation of different soil-structure-interaction approaches for bridges
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2019., 2019.) İnci, Oytun.; Şafak, Erdal.; Önem, Göktürk.
During the last fifty years, bridge construction has increased extensively throughout the world, including on areas with bad soil conditions, to meet the transportation needs of expanding urban areas. Although Soil-Structure-Interaction (SSI) procedures for performance-based design of buildings have been introduced in design guidelines, seismic provisions are not clearly stated for bridges. There are two main approaches to include SSI in performance-based design of the bridges; direct method and substructure method. In the direct method, bridge and soil systems are analyzed as a single system under seismic shaking, defined at bedrock. As an alternative, the substructure method is introduced to solve the system as substructures in two stages, called kinematic interaction and inertial interaction. The nonlinear response of piled foundation systems of bridges are subjected to kinematic interaction; whereas, the nonlinear response of superstructure is subjected to inertial interaction. In this study, first, he linear design of two different bridges are introduced by considering their geometry and the number of spans. Bridge-I has three spans with uneven pier heights, and Bridge-II has four spans with identical piers and the geometry. Both bridges are designed based on a response spectrum created according to site response analysis and used in the performance-based design of the bridges. 19 different records are selected and scaled according to the criteria given in AASHTO LRFD Bridge Design Specifications Article 4.7.4.3.4 (AASHTO, 2012) Seismic Design Guidelines. Seismic records are categorized with respect to soil parameters, chosen for both strength-based and performancebased design of bridges. Secondly, using the direct method, the Nonlinear Time History (NTH) analyses are performed for both bridges to investigate the behavior of structural elements. The nonlinear responses of the bridges are re-calculated by using the substructure method, including the kinematic and inertial interactions. Responses of the structural elements are combined according to commonly-used combination rules. Finally, results of these methods are compared with each other, as well as the linear response of the structures, to underline how the behavior of the structures vary according to different analysis methods.
A method to calibrate analytical models of multi-story buildings from earthquake records
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2014., 2014.) Kocakaplan, Sedef.; Şafak, Erdal.
For multi-story buildings, the standard approach to develop analytical models from earthquake records is to match the modal characteristics (i.e., modal frequencies, damping ratios and mode shapes) of the model with those identified from the data. Typically, the response of the building is recorded in the basement, roof and a few intermediate floors. When the number of the instrumented floors is less than the total number of floors, an analytical model cannot be constructed uniquely. In other words, more than one model can match the recorded response. This study presents a new method based on the transfer matrix formulation of the response. The method requires that vibration time histories are known at every floor. Since they are typically not recorded at every floor, we first present a methodology to estimate vibration time histories at non-instrumented floors from those of the instrumented floors. We assume that, at each modal frequency, the mode shape of a multi-story building can be approximated as a linear combination of the corresponding mode shapes of a shear beam and a bending beam. We determine the combination factors by using the least-squares approximation to the mode shapes identified from the records. The accuracy of the methodology is tested by using recorded motions from two buildings that have instruments at every floor. Assuming that only a few floors had instruments, the vibration time histories at other floors are calculated and compared with the recorded time histories. The results of the methodology are also compared with those from other approximation techniques, such as linear or cubic interpolations, and found to be much superior. Once the vibration time histories are known at every floor, we present a new approach to calibrate analytical models of multi-story buildings based on the transfer matrix formulation of the response. The methodology utilizes top-to-bottom spectral-ratios at each story and shows that these spectral ratios are not influenced by any structural changes in the stories below. Thus, starting from the top story, the stiffnesses of each story can be determined uniquely by matching the dominant frequencies of the spectral ratios, assuming that the mass of each floor is known or estimated. A numerical example is presented to confirm the validity of the approach. The study proves that the story stiffnesses of a multi-story building can be determined uniquely by using vibration records taken from only a few floors.
A parametric study for the characterization of site amplification
(Thesis (Ph.D.)-Bogazici University.Kandilli Observatory and Earthquake Research Institute, 2020., 2020.) Fercan, Nazife Özge.; Şafak, Erdal.; Ansal, Atilla.
In earthquake engineering, the approximation of site amplification by using practical ways has been an important issue. Various site parameters were proposed and applied in the engineering practice. Among these, time averaged shear wave velocity for the top 30 m, Vs30, and fundamental frequency, f0, have been used widely. In this study, we investigated the reliability of Vs30 parameter, and the performance of alternative time averaged shear wave velocities (e.g., Vs40, Vs50, etc.) and shear wave travel times (Ttz) at various depths for the estimation of site amplification. For the same bedrock depth, we considered 17 shear wave velocity profiles, changing from convex (i.e., the velocities changing faster near the surface and slower near the bedrock) to concave (i.e., the velocities changing slower near the surface and faster near the bedrock). We divided the soil media, first into layers with equal thickness, and then into layers with equal wave travel times. For each layering type and soil profile, we calculated the site amplification factors and fundamental frequencies, and studied their correlations with time averaged shear wave velocities (Vsz) and wave travel times (Ttz) for different depths, z. We have also investigated the correlation of site amplification factors, surface PGAs (Peak Ground Accelerations), and fundamental soil frequencies (f0) for each case. We have identified the optimal averaging depths for the averaged shear wave velocity and the wave travel time to characterize site amplification. The study showed that there is a sharp change in the correlations when switching from convex to concave profiles. By gradually increasing the bedrock acceleration levels, we have also studied the nonlinear soil response and its correlations with linear soil response. We presented guidelines to estimate nonlinear soil amplification factors and fundamental frequency from the linear ones. Considering that the linear fundamental frequency and amplification can easily be calculated from field tests (e.g., ambient noise measurements for f0 detection), these guidelines provide a useful tool to estimate nonlinear ones.
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.
A seismic vulnerability analysis procedure for urban loss assessment
(Thesis (Ph.D.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2008., 2008.) Tüzün, Cüneyt.; Aydinoğlu, M. Nuray.
The assessment of seismic vulnerability of buildings in seismically active urban areas is of great importance in terms of engineering, economical and social aspects. In this study an analytical procedure has been developed in order to obtain the vulnerability functions of existing buildings. The building information included over all geometry of the structure, as-built dimensions and configuration of the structural members, complete with reinforcement details of beams and columns, which are extracted from the design dossiers available in the Bolu municipality archives. Totally 120 buildings, 20 from each class, are classified depending on their number of stories ranging from 2 to 7 story and nonlinear response history analysis has been performed in order to obtain damage distributions by using 20 spectrum compatible ground motions. In the first chapter a brief explanation of the role of loss estimation studies in urban planning, urban disaster management and mitigation has been given. In the second chapter, existing building vulnerability relationships have been evaluated and particular examples of studies that have made important contribution to the development are briefly cited. In the third chapter, basic steps of a standard derivation of analytical vulnerability functions are identified and the importance of each step in the process has been explained. In the fourth chapter, the procedure based on real building data has been explained in detail including the ground motion characterization, properties of building data, analytical methods used in the analysis, damage definition and quantification, statistical process and the determination of the vulnerability parameters. Results are presented in the form of lognormal vulnerability curves with respect to spectral acceleration or spectral displacement. In the fifth chapter, the conclusions are presented and the contribution of the study to the existing knowledge in the field has been evaluated
A simplified non-linear soil-structure interaction (SSI) model for the earthquake response of surge vessels resting on shallow foundations
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2017., 2017.) Turandan, Kenan.; Uçkan, Eren.
In this study, earthquake response of a surge vessel which consists of 8 interconnected tanks is studied. This HPV unit is located in western Saudi Arabia with 600.000 m³/day desalination capacity. The focus of this study is to see and evaluate the response of the structure under soil structure interaction effects. Therefore the properties of the superstructure are kept the same for all the analysis. SSI parameters and earthquake input motions are changed in order to represent the various properties of soil and earthquake motions. The comparisons of analyses results to earthquake codes are made. Some suggestions are made to overcome the existing weakness and increase the performance of the structures. SSI model is developed and various non-linear analyses are conducted and the results are evaluated and compared. Also the difference in response of the structure is compared with and without SSI considered. In the first chapter of this study, the scope of the work and general information about the surge vessel is given. In the second chapter, the methodology is explained. In the third chapter modelling and analyses are explained. Modelling and analyses are not kept as separate chapters in the name of being compatible with the development flow of the study. And the analyses results are evaluated and comparisons are made along with the development. In the fourth and final chapter conclusions are presented and suggestions for improving this study are proposed.
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.
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.
Acceleration - displacement response spectra (ADRS) for design of seismic isolation systems in Turkey
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2018., 2018.) Yolcu, Aslıhan.; Tanrıcan, Gülüm.; Tüzün, Cüneyt.
Nonlinear Response History Analyses (NLRHA) have been frequently used in seismic isolation system design since the displacement at long period end of the codebased spectra is limited to a certain value and may not accommodate larger displacement demands. The NLRHA is a practical tool to determine the maximum displacement of the system based on prede ned values of e ective period, e ective damping and base shear transmitted to superstructure which are internally connected and requires an iterative process. In order to reduce the process, the methodology which is called as Acceleration-displacement response spectra (ADRS) approach is proposed by Whittaker and Jones (2013, 2014). In this study, ADRS approach is extended considering the new Turkish Building Seismic Design Code (TBSDC, 2018) that will come into force in 2018. Series of nonlinear response history analyses are performed for several isolation system parameters and seismic hazard levels. Displacement spectra are obtained by using bi-linear hysteresis curve model. E ective and robust ADRS graphs which facilitate the preliminary design stage of the seismic isolation systems are obtained in terms of acceleration and displacement demands of earthquakes. The e ects of di erences in fundamental seismic isolation system parameters and ground motion selection criteria on the preliminary design of seismic isolation systems are examined and represented in graphical forms. ADRS graphs provide the base shear and displacement limits of seismic isolation systems in the region under maximum considered earthquake (DD1) and design basis earthquake (DD2) design levels. Shaking levels are obtained from New Probabilistic Seismic Hazard Map of Turkey (TDTH, 2016). The design spectra composition is formed using two site categories (NEHRP C and NEHRP D) and two hazard zones (high and moderate hazard) at each design level. For each design spectra, eleven horizontal ground motion pairs are selected and linearly scaled using the geomean spectral ordinates. Analyses are performed using a combination of eight site-speci c design spectra in total, six e ective isolation system periods and ve yield levels. Evaluation and discussion of the ADRS graphs are provided to develop an overall understanding about the base shear and displacement limits of a seismic isolation systems in the region.
Advance modelling and collapse risk estimation of a highway bridge
(Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2013., 2013.) Görk, Serkan.; Şafak, Erdal.; Aydınoğlu, M. Nuray.
In this study, collapse risk of a highway bridge is estimated analytically using advance mathematical model. The concentration of this study is on advance modeling of the bridge, including linear sticks of beams, nonlinear modeling of piers and abutments with their shear capacities, inelastic connecting members, inelastic foundations and inelastic soil springs. The structural data including all geometry and dimensions, configuration of structural members and connecting elements, reinforcement details for piers, and material properties are taken from ‘as-built’ drawings of the bridge from contractors. Two different mathematical models have been constructed with different foundation conditions for nonlinear response history analyses with enough numbers of earthquake records. Collapse fragility curves are obtained in terms of spectral acceleration corresponding to dominant natural period of the bridge. The integration of collapse fragility curves of models and corresponding hazard curve gives the collapse risk of the bridge. In the first chapter of this study, the scope of the work and general information about the bridge has been given. In the second chapter, the methodology of estimating collapse risk in an analytical way has been introduced. The steps of collapse risk estimation have been explained. In the third chapter, mathematical modeling of the structure has been given in details. Materials, nonlinear load-carrying members, beams, connecting elements, foundation and soil properties have been given in detail. In the fourth chapter, analysis objectives, modal analysis results, the earthquake records and hazard curves have been presented. In the fifth chapter, fragility curves are developed and the collapse risk has been calculated for these two models. In the last chapter, the conclusions are presented and suggestions for improving this study are proposed.
Alternate representations of dynamic properties and loading
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2014., 2014.) Gülenç, Caner.; Tanırcan, Gülüm.; Aydınoğlu, M. Nuray.
This study covers three main topics, which are directly related to dynamic behaviour of structures, namely, representation of mass, damping and loading. These three properties of equation of motion are generally represented by widely accepted approaches. In this thesis, such representations are discussed via comparisons with infrequently used representations and viability of them is investigated. For case study, 50-story core wall structure is chosen. First topic discussed here is mass representation. Indisputably, the most accepted assumption for mass representation is lumped mass approach, which is very practical to construct the matrix or, at least, easy to understand the concept of. Another representation, not common one, consistent mass approach derived by a similar procedure in the method for derivation of stiffness coefficients. Consistent mass matrix has off-diagonal terms as distinct from lumped mass matrix. Since the core wall has a continuous form, it is reasonable to represent its mass distribution with consistent mass approach, which takes into account coupling terms. Effects of consistent mass representation on dynamic response of a 50-storey core-wall tall building are investigated. Second one is damping property which may be evaluated as one of the most controversial aspects of structural dynamics. As it is not possible to derive a damping matrix from the element cross section properties and material properties directly, proportional viscous damping matrix is generally used instead, which is defined in terms of modal damping ratios at certain anchor frequencies. However, viscous damping model has a significant deficiency associated with the energy mechanism. Studies based on experimental data show that dissipated energy per cycle of an oscillating system is essentially independent of the excitation frequency as opposed to dependency inherent in the viscous damping model. Such damping model is called rate-independent or structural damping, which is conveniently modelled in the frequency domain through complex stiffness matrix. One of the aims of this study is to observe the effects of such an alternate damping model on the linear seismic response of a tall building. To this end, a 50-story core-wall tall building system is investigated. Drift and total acceleration response characteristics for a set of earthquake records are obtained from the analyses conducted through Fourier Transform. Last concept, probably the most innovative idea of this study, is related to loading part of equation of motion. It has been long applied that ground accelerations are used directly as force by multiplying floor masses, eventually, relative response quantities are obtained. The underlying idea of this loading concept is based on pseudo-static transmission assumption, which presumes that base displacement, in any time instant, is transmitted throughout building statically and naturally, such movement does not deform the structure. One of the aims of this study is to investigate viability of this concept. The motivation is based on the idea that if the building is tall enough, is it possible to be transmitted of base displacements throughout the building without generating any significant deformation? For this reason, absolute response and relative response quantities of the 50-story core-wall are obtained by using acceleration and displacement loading concepts respectively. Comparative results are given at the end.
An evaluation of the behaviour of RC bridge piers under vertical and horizontal components of earthquake ground motion
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2019., 2019.) Abanuz, Cem.; Hancılar, Ufuk.
Reinforced concrete (RC) bridges with single piers have been used extensively in Turkish highways. During the past earthquakes in Japan, USA and New Zealand extensive damages occurred in the single piers indicates the inadequacy of seismic design. In the design of the concrete bridge piers, generally horizontal earthquake forces are taken into consideration. An additional P-∆ effect occurs when the horizontal earthquake effect and the vertical earthquake effect act together on the bridge piers with a large beam cantilever width. The effect of additional P-∆ effect under the effect of vertical earthquake may increase the bending moment and shear forces values in the columns and the piers supporting the bridge may experience damage. Another circumstance encountered in large-scale projects is the use of filler material as a dump / storage area under bridge piers. This causes a certain part of the bridge pier heights to remain under the soil filling material and shortens the free pier height. For a single column pier of a conventional bridge maximum moment and shear values occur at the bottom of the column under seismic forces. This region where the maximum stress occurs is designed to be the plastic hinge region of the column. Maximum shear and longitudinal reinforcement used in the plastic hinge region to provide the conditions is stated in the regulations. When the part of the column is buried under the soil, maximum moment and shear force values of the bridge columns may not occur at the bottom of the column but at the upper end of the buried height. Therefore, the critical section of the column will be above the bottom of the column which was not considered in the seismic design. The amount of longitudinal and shear reinforcement may also be inadequate than the required reinforcement to resist the seismic forces which may cause the flexural and shear failure. In this study, a single 30 m-tall RC pier of a conventional bridge is examined under horizontal and vertical components of three separate earthquake records for three different deck to pier flexural stiffness ratios. Conventional bridges are constructed with movement joints and connections. The pier has a monolithic 15m-wide cap beam. The height of the cap beam is increased to provide different flexural stiffness ratios between column and cap beam. As the flexural stiffness of the cap beam is increased, the change in the column shear force and moment due to additional P-Δ effect of vertical component of earthquake is investigated. As a result, only the horizontal impact of the earthquake and the effect of both horizontal and vertical earthquakes are compared for the column forces. Secondly, the single pier of the conventional bridge with the same geometric properties is investigated for the cases that it is buried under 5 m, 10 m and 15 m of earth fill. The horizontal components of the same earthquake records are used in the analysis. Forcedeformation relation of the soil is represented by non-linear p-y springs for the buried cases.
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.
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.
Characterization of response spectra for near field conditions by earthquake ground motion simulation
(Thesis (Ph.D.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2007., 2007.) Şeşetyan, Karin.; Erdik, Mustafa.; Madariaga, Raul.
Strong ground motion estimation tools such as empirical ground motion prediction equations rely mostly on recorded data. Good quality strong motion data became available mostly in recent years and are still sparse for near field conditions. Strong ground motion records on the other hand contain them several characteristics such as source, path and especially local site effects. These features can sometimes be hardly differentiated when one is willing to study only one of them. As such, realistic simulation of the 3D wavefield generated by a fault rupture in a heterogeneous medium becomes critical for the study of strong ground motion. Particularly features such as intra-event and inter-event spatial and temporal variability of ground motion can be studied in detail. With increasing computational power and newly emerged methods such simulations become increasingly feasible. In this study I use kinematic simulation with 3D Staggered Grid Finite Difference method to study the characteristics of near source effects of strong ground motion. I also aim to prove that kinematic simulation with 3D Staggered Grid Finite Difference method (3DFD) is a useful tool to analyze and estimate the characteristics of long period strong ground motion. For this purpose first a simulation model has been set for the 2004 Mw=6.0 Parkfield earthquake. Making use of the available 3D crustal velocity structure of the region and several slip models of the earthquake over 40 near source recordings produced by the event have been simulated. Encouraged by the very good agreement between observed and simulated waveforms, 3DFD has been used for the characterization of directivity effects in the near source region. Eleven earthquakes covering a magnitude range from 6.0 to 7.4 have been modeled using one or more slip models for each of them. Eight of these events had a strike-slip mechanism whereas the remaining ones were dip-slip events. Resulting spatial distributions of fault parallel, fault normal and average response spectral accelerations at longer periods have been analyzed to derive general formulations for the modification of the response spectral values found from earthquake hazard analysis to include near source directivity effects. With recently emerging structural design methods, engineering studies concentrate more and more on the long period characteristics of strong ground motion. The present study validates kinematic simulation tools, particularly the 3DFD method used herein as a useful method for the simulation of low frequency strong ground motion in realistic earth media for engineering purposes.
Collapse risk estimation of reinforced concrete buildings
(Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2013., 2013.) Beyazoğlu, Tamer İzzet.; Şafak, Erdal.; Aydınoğlu, M. Nuray.
In this study, collapse risks of five-storey RC frame buildings are estimated analytically using advance mathematical model. The concentration of this study is on advanced nonlinear analysis of the building including nonlinear modeling of columns and beams with their shear capacities. Collapse fragility curves are obtained in terms of spectral acceleration corresponding to dominant natural period of the building. The collapse risk of the building is obtained through integration of collapse fragility curves of models and corresponding hazard curve. In the first chapter of this study, the scope of the work and literature survey have been given. In the second chapter, the methodology of estimating collapse risk in an analytical way has been introduced. The steps of the proposed methodology for collapse risk estimation have been explained briefly. In the third chapter, mathematical modeling of the buildings has been given in details in terms of non-linear material properties, lump and distributed plasticity approach for structural members. In the fourth chapter, objectives of the analysis, the strong ground motion records and hazard curves used in the analysis phase have been presented. In the fifth chapter, fragility curves are obtained and the collapse risk has been calculated for each building under consideration. In the last chapter, the conclusions are presented.
Comparative evaluation of codes and regulations in Turkey for earthquake performance assessment of existing buildings
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2020., 2020.) Dede, Şahin Özdoğan.; Hancılar, Ufuk.
New Turkish Building Seismic Code published in 2018 has been officially in force since January 1, 2019. The new code introduces significant changes not only in the countrywide seismic hazard maps but also in structural modeling and analysis issues for the design of new buildings as well as in the definition of performance objectives and assessment methodologies for existing buildings. In this study, a comparative earthquake performance assessment of a reinforced concrete building in Istanbul is presented. The building, which was constructed in 2006, has four stories rising above a basement floor. The lateral load-carrying system consists of moment-resisting frames with two shear walls around the staircase. Although it is assumed that the building was designed according to the provisions of the Turkish Building Seismic Code-1998, it was identified as a risky building last year based on the simplified guidelines by the Ministry of Environment and Urbanization (Riskli Yapıların Tespit Edilmesine İlişkin Esaslar-2013). Earthquake performance of the study building is evaluated for the requirements of the new Turkish Building Seismic Code (2018) and of its previous version (2007) as well. For this purpose, a three-dimensional finite element model of the building is elaborated on the basis of the blueprints. Geometrical and material characteristics are further verified by the reports on in situ measurements and field tests. Linear and nonlinear static and dynamic analyses procedures are implemented, and a detailed assessment of the building against the performance criteria by each code is performed. Additionally, the building is assessed on the basis of the updated guidelines by the Ministry of Environment and Urbanization (Riskli Yapıların Tespit Edilmesine İlişkin Esaslar-2019). Outcomes of the earthquake performance assessments are presented comparatively, and the differences/changes among the codes and guidelines are highlighted.
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.
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.
Correlations between ground motion intensity measures and structural response parameters through nonlinear dynamic analyses
(Thesis (Ph.D.)-Bogazici University.Kandilli Observatory and Earthquake Research Institute, 2009., 2009.) Hancılar, Ufuk.; Durukal, Eser.

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