Person: KURTULUŞ, Asli
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Asli
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KURTULUŞ
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ArticlePublication Metadata only A computational workflow for rupture‐to‐structural‐response simulation and its application to Istanbul(Wiley, 2020-10) Zhang, W. Y.; Restrepo, D.; Crempien, J. G. F.; Erkmen, Bülent; Taborda, R.; Kurtuluş, Aslı; Taciroglu, E.; Civil Engineering; ERKMEN, Bülent; KURTULUŞ, AsliScenario-based earthquake simulations at regional scales hold the promise in advancing the state-of-the-art in seismic risk assessment studies. In this study, a computational workflow is presented that combines (i) a broadband Green's function-based fault-rupture and ground motion simulation-herein carried out using the "UCSB (University of California at Santa Barbara) method", (ii) a three-dimensional physics-based regional-scale wave propagation simulation that is resolved at fmax=11.2 Hz, and (iii) a local soil-foundation-structure finite element analysis model. These models are interfaced with each other using the domain reduction method. The innermost local model-implemented in ABAQUS-is additionally enveloped with perfectly matched layer boundaries that absorb outbound waves scattered by the structures contained within it. The intermediate wave propagation simulation is carried out using Hercules, which is an explicit time-stepping finite element code that is developed and licensed by the CMU-QUAKE group. The devised workflow is applied to a 80x40x40 km3 region on the European side of Istanbul, which was modeled using detailed soil stratigraphy data and realistic fault rupture properties, which are available from prior microzonation surveys and earthquake scenario studies. The innermost local model comprises a chevron-braced steel frame building supported by a shallow foundation slab, which, in turn, rests atop a three-dimensional soil domain. To demonstrate the utility of the workflow, results obtained using various simplified soil-structure interaction analysis techniques are compared with those from the detailed direct model. While the aforementioned demonstration has a limited scope, the devised workflow can be used in a multitude of ways, for example, to examine the effects of shallow-layer soil nonlinearities and surface topography, to devise site- and structure-specific seismic fragilities, and for calibrating regional loss models, to name a few.Book PartPublication Metadata only A simplified approach for site-specific design spectrum(Springer, 2018) Ansal, Mustafa Atilla; Tönük, G.; Kurtuluş, Aslı; Civil Engineering; Rupakhety, R.; Ólafsson, S.; ANSAL, Mustafa Atilla; KURTULUŞ, AsliThe design acceleration spectrum requires site investigations and site-response analyses in accordance with the local seismic hazard. The variability in earthquake source and path effects may be considered using a large number of acceleration records compatible with the earthquake hazard. An important step is the selection and scaling of input acceleration records. Likewise, a large number of soil profiles need to be considered to account for the variability of site conditions. One option is to use Monte Carlo simulations with respect to layer thickness and shear wave velocity profiles to account for the variability of the site factors. The local seismic hazard analysis yields a uniform hazard acceleration spectrum on the bedrock outcrop. Site-specific response analyses also need to produce a uniform hazard acceleration spectrum on the ground surface. A simplified approach is proposed to define acceleration design spectrum on the ground surface that may be considered a uniform hazard spectrum.Book PartPublication Metadata only Observations from geotechnical arrays in Istanbul(Springer, 2015-04-16) Kurtuluş, Aslı; Ansal, Mustafa Atilla; Tönük, G.; Çetiner, B.; Civil Engineering; KURTULUŞ, Asli; ANSAL, Mustafa AtillaFew small earthquakes with local magnitude slightly larger than ML = 4 were recorded by geotechnical downhole arrays that have been recently deployed in the west side of Istanbul. Same events were also recorded by Istanbul Rapid Response Network (IRRN) which comprises of 55 surface strong motion stations in the European side of Istanbul. The strongest one of these earthquakes took place on 12/3/2008 in Çınarcık with local magnitude of ML = 4.8. Even though the observed PGAs were not exceeding 0.01 g, an effort is made to model the recorded response at the downhole array sites as well as the at the IRRN stations using the acceleration records obtained by the deepest sensors, i.e. on the engineering bedrock, at the downhole array sites as input bedrock motions. 1D equivalent linear site response analysis that is generally adopted for site-specific response analysis is used for modelling. Observations from the recorded response and results from 1D modelling of ground response have yielded in general good agreement between the observed and recorded soil response at the station sites.Book PartPublication Metadata only Implications of site specific response analysis(Springer, 2018) Ansal, Mustafa Atilla; Tönük, G.; Kurtuluş, Aslı; Civil Engineering; Pitilakis, K.; ANSAL, Mustafa Atilla; KURTULUŞ, AsliDefinition of design earthquake characteristics, more specifically uniform hazard acceleration response spectrum, on the ground surface is the primary component for performance based design of structures and assessment of seismic vulnerabilities in urban environments. The adopted approach for this purpose requires a probabilistic local seismic hazard assessment, definition of representative site profiles down to the engineering bedrock, and 1D or 2D equivalent or nonlinear, total or effective stress site response analyses depending on the complexity and importance of the structures to be built. Thus, a site-specific response analysis starts with the probabilistic estimation of regional seismicity and earthquake source characteristics, soil stratification, engineering properties of encountered soil layers in the soil profile. The local seismic hazard analysis would yield probabilistic uniform hazard acceleration response spectrum on the bedrock outcrop. Thus, site specific response analyses also need to produce a probabilistic uniform hazard acceleration response spectrum on the ground surface. A general review will be presented based on the previous studies conducted by the author and his co-workers in comparison to major observations and methodologies to demonstrate the implications of site-specific response analysis.ArticlePublication Metadata only Interaction of a pile with layered-soil under vertical excitations: field experiments versus numerical simulations(Springer International Publishing, 2017-09) Seylabi, E. E.; Kurtuluş, Aslı; Stokoe II, K. H.; Taciroglu, E.; Civil Engineering; KURTULUŞ, AsliData recorded during a field test involving an instrumented drilled shaft under vertical excitations are examined in order to (1) extract the soil–pile system’s dynamic impedance, and (2) to evaluate the small-strain shear stiffness and material damping properties of the surrounding soil. Numerical simulations of steady-state vibration tests with an axisymmetric finite element model are used for back-calculating the in-situ small-strain dynamic soil properties (i.e., shear stiffness and material damping ratio). Also, a numerically computed impedance function is compared with known analytical solutions and that obtained through direct processing of the field test data. These analyses revealed that the discrete numerical model can successfully reproduce the measured responses of the shaft-soil system, and yield its frequency-dependent impedance function as well as equivalent small-strain dynamic soil properties. The validated numerical model presented here offers a detailed view of the vertical dynamic responses of drilled shafts within the small-strain range, and can be used for design and analysis of future field tests.Conference ObjectPublication Metadata only Microzonation with respect to ground shaking intensity(CRC Press, 2019) Ansal, Mustafa Atilla; Tönük, G.; Kurtuluş, Aslı; Civil Engineering; Silvestri, F.; Moraci, N.; ANSAL, Mustafa Atilla; KURTULUŞ, AsliSeismic microzonation is conducted to assess the seismic hazard on the ground surface with respect to ground shaking intensity. A probabilistic seismic hazard study is conducted to define earthquake characteristics on the rock outcrop. A grid system is generated to divide the investigation area into cells according to geological and geotechnical data. Site characterizations are based on available information to define soil profiles for each cell with soil stratifications and shear wave velocities extending down to the engineering bedrock. Site-specific 1D site response analyses are carried out for all soil profiles, based on the engineering properties of encountered soil layers, selection and scaling of the sufficient number of input acceleration time histories compatible with the regional seismicity and earthquake source characteristics. The microzonation study carried out for Zeytinburnu town on the European side of Istanbul with respect to ground shaking intensity is presented. The importance of the selection of the microzonation parameters for assessing ground shaking intensity is discussed.ArticlePublication Metadata only Regional-scale seismic fragility, loss, and resilience assessment using physics-based simulated ground motions: An application to istanbul(Wiley, 2023-05) Zhang, W.; Chen, P. Y.; Crempien, J. G. F.; Kurtuluş, Aslı; Arduino, P.; Taciroglu, E.; Civil Engineering; KURTULUŞ, AsliUsing results from 57 large-scale physics-based fault-rupture and wave propagation simulations, this research aims to evaluate the seismic risk, loss, and resilience of more than 16,000 reinforced concrete buildings in the Zeytinburnu district of Istanbul, Turkey. For each building and under each earthquake scenario, the spatially varying site-specific simulated ground motions were used for performing three-dimensional nonlinear time-history analyses. The resulting structural responses—such as peak story drift ratios (PSDR) and peak floor accelerations (PFAs)—were utilized to conduct three region-scale tasks: (i) building- and site-specific seismic fragility analysis for both structural and nonstructural components of each building; (ii) intensity-based seismic loss assessment using the FEMA P58 methodology and Monte Carlo simulations; and (iii) resilience evaluation based on the expected time of recovery predicted through FEMA P58. Moreover, both inertial and kinematic soil–structure interaction (SSI) effects were considered using a substructuring method for all three tasks. Site-specific soil properties were utilized to compute the coefficients of soil springs and dashpots, as well as the foundation input motions. The SSI effects were investigated by comparing the fragility, loss, and resilience indices obtained with and without considering SSI.ArticlePublication Metadata only Site specific response analysis for performance based design earthquake characteristics(Springer Science+Business Media, 2014-06) Tönük, G.; Ansal, Mustafa Atilla; Kurtuluş, Aslı; Çetiner, B.; Civil Engineering; ANSAL, Mustafa Atilla; KURTULUŞ, AsliDuring strong earthquakes, seismic waves travelling towards the ground surface alter the engineering characteristics of the soil layers and consequently the characteristics of travelling seismic waves also change with respect to their frequency and amplitude contents. In assessing the site-specific design earthquake characteristics in seismically active zones for performance levels of Collapse Prevention, Life Safety, and Immediate Occupancy that may correspond to 72, 475 and 2475 year return period earthquakes, detailed site characterization and site response analyses may be required. This process may be conducted in two consecutive statistically independent stages. The first stage involves the seismic hazard study to assess the design earthquake characteristics on rock outcrop for selected exceedance levels and the second stage involves detailed site characterization and site response analyses to estimate design earthquake characteristics on the ground surface. The uncertainties arising from the source characteristics need to be taken into account by using a representative number of strong motion acceleration records for site response analyses recorded in locations that are compatible with the seismic hazard with respect to fault mechanism, earthquake magnitude, and source distance. In addition, the strong motion acceleration records should be compatible with respect to peak acceleration and acceleration response spectra levels estimated by the probabilistic or deterministic seismic hazard study. One approach is to use the uniform acceleration hazard spectra and another option is to adopt conditional mean spectrum on rock outcrop estimated in the first stage from the earthquake hazard study for scaling input motions for site response analysis. It was observed that the scaling methodology adopted may play an important role in the calculated earthquake characteristics on the ground surface. A semi empirical procedure was proposed to determine the site specific design earthquake characteristics on the ground surface. A parametric study was conducted to demonstrate the applicability of the proposed methodology based on one dimensional site response analyses using Shake91 and DeepSoil site response codes to evaluate design earthquake characteristics on the ground surface.Conference ObjectPublication Metadata only An investigation of the effects of surface topography on the seismic structural demands for a region of istanbul(CRC Press, 2019) Zhang, W.; Taciroglu, E.; Restrepo, D.; Taborda, R.; Kurtuluş, Aslı; Ansal, Mustafa Atilla; Civil Engineering; Silvestri, F.; Moraci, N.; KURTULUŞ, Asli; ANSAL, Mustafa AtillaIn this study, we provide preliminary results from an ongoing study—funded by The Scientific and Technological Research Council of Turkey, TUBITAK—investigating the effects of site-specific surface topography and soil stratigraphy on dynamic soil-structure interaction (SSI) behavior of structures located within a region of Istanbul. To achieve this, nonlinear time-domain responses of various soil-foundation-structure systems subjected to strong remote earthquake excitations for various site conditions will be investigated. The goal is to transform SSI analyses to consider realistic site conditions. An important part of this effort involves the creation of a map of topography-induced SSI response amplification factors for the south European side of Istanbul by performing 3D simulations using real site topography and soil stratigraphy data, and realistic bedrock ground motions, which are available from previously completed earthquake scenario and seismic microzonation studies. This paper presents preliminary results of large-scale 3D simulations performed for the south European side of Istanbul.ArticlePublication Metadata only A suite of broadband physics-based ground motion simulations for the Istanbul region(Wiley, 2023-04) Zhang, W.; Crempien, J. G. F.; Kurtuluş, Aslı; Chen, P.-Y.; Arduino, P.; Taciroglu, E.; Civil Engineering; KURTULUŞ, AsliPhysics-based earthquake ground motion simulations (GMS) have acquired significant growth over the last two decades, mainly due to the explosive developments of high-performance computing techniques and resources. These techniques benefit high/medium seismicity regions such as the city of Istanbul, which presents insufficient historical ground motion data to properly estimate seismic hazard and risk. We circumvent this reality with the aid of the Texas Advanced Computing Center (TACC) facilities to perform a suite of 57 high-fidelity broadband (8–12 Hz) large-scale physics-based GMS for a region in Istanbul, Turkey. This paper focuses on the details of simulated GMS: (i) validation of the GMS approach against recorded ground motions produced by the 2019 (Formula presented.) Silivri earthquake; (ii) characteristics of 57 different source models, which aim to consider the uncertainties of many fault rupture features, including the length and width, dip, strike, and rake angles of considered fault planes, as well as hypocenter locations and earthquake magnitudes ranging between (Formula presented.) 6.5 and 7.2; (iii) high-resolution topography and bathymetry and seismic data that are incorporated into all GMS; (iv) simulation results, such as PGAs and PGVs versus (Formula presented.) and distances to fault ruptures ((Formula presented.)), of 2912 surface stations for all 57 GMS. More importantly, this research provides a massive database of displacement, velocity and acceleration time histories in all three directions over more than 20,000 stations at both surface and bedrock levels. Such site-specific high-density and -frequency simulated ground motions can notably contribute to the seismic risk assessment of this region and many other applications.