Browsing by Author "Taciroglu, E."

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Blind identification of site effects and bedrock motion from surface response signals
(Elsevier, 2018-04) Ghahari, S. F.; Abazarsa, F.; Jeong, C.; Kurtuluş, Aslı; Taciroglu, E.; Civil Engineering; KURTULUŞ, Asli
A method for blind identification of site effects from two nearby ground surface response signals is presented. The proposed approach makes use of ground surface accelerations from two nearby stations to back-calculate the transfer functions of both sites and their common bedrock motion. Seismic analysis of structures cannot be carried out accurately unless site effects are taken into account. Moreover, presently available empirical attenuation relationships for predicting ground surface motions are only useful if site effects are considered. While an extensive collection of analytical and numerical techniques is available to analyze ground responses induced by bedrock motions, their accuracy depends on a priori knowledge of site properties and the availability of bedrock motions. There are techniques based on direct/indirect measurements—such as spectral analysis of surface waves (SASW), and material testing of borehole samples—however, responses predicted by their output do not necessarily reflect site behavior during strong motions. As such, the estimation of site response from acceleration data recorded on the ground surface during real-life events is a key capability. In the method proposed herein, the site response is identified from recorded ground surface accelerations at two nearby stations through a blind identification technique, under the assumption that the unknown bedrock motion is identical for both stations and those two stations have different transfer functions. Most of the existing site response identification methods rely on a strategically chosen reference station, and the present approach obviates this limitation. We demonstrate the performance of this new approach using a synthetic, but adequately realistic, example.
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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, Asli
Scenario-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.
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A cost-benefit analysis of sensor quality and spatial density for rapid regional post-event seismic damage assessment: Application to Istanbul
(Elsevier, 2022-12) Cheng, Q.; Liao, W.; Fei, Y.; Tian, Y.; Lu, X.; Zhang, W.; Ghahari, F.; Kurtuluş, Aslı; Taciroglu, E.; Civil Engineering; KURTULUŞ, Asli
A quantitative evaluation of the influence of sensor quality and spatial density on the results of rapid regional seismic damage evaluations of buildings can provide an important reference for the deployment of a strong-motion network. However, the influence of sensor quality and spatial density on seismic damage assessment is still unclear. Therefore, a cost-benefit analysis framework of sensor quality and spatial density for rapid regional post-event seismic damage assessment is proposed. In this framework, a simulation method for sensor-recorded ground motions and an interpolation-based ground motion field refinement method are used to consider the influence of the quality and density of the sensor network. The accuracies of seismic damage assessments with different sensor layout schemes were compared using the time-history analysis-based regional seismic damage assessment method, through which the influence of sensor quality and spatial density on the seismic damage assessment can be quantitatively evaluated. Finally, the Zeytinburnu district of Istanbul was selected as an example for illustrating the proposed framework. The main conclusions are as follows: (1) the spatial density of the sensors used is more significant for improving the accuracy of a seismic damage assessment than the quality of the sensors used; (2) the influence of population density can be considered using the proposed framework; and (3) the proposed framework can quantitatively consider the influence of sensor quality and spatial density on the rapid regional seismic damage assessment of buildings, which provides an important reference for the deployment of a strong-motion network for a given budget.
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Influence of accelerometer type on uncertainties in recorded ground motions and seismic damage assessment
(Springer, 2022-07) Liao, W.; Fei, Y.; Ghahari, F.; Zhang, W.; Chen, P. Y.; Kurtuluş, Aslı; Yen, C. H.; Cheng, Q.; Lu, X.; Taciroglu, E.; Civil Engineering; KURTULUŞ, Asli
Strong motion data recorded by strong-motion networks are essential for preventing and mitigating earthquake disasters, such as earthquake early warning and earthquake emergency responses, and the type of accelerometer can significantly influence the quality of recorded ground motions (GMs) and the subsequent usage. Different types of accelerometers vary significantly in both the price and the quality of collected data, because cheap accelerometers generate non-negligible self-noise and reduce the quality of the collected GMs. However, the effects of the accelerometer type and spatial density on the accuracy of GM-based seismic damage assessment are still unknown. The present study attempts to quantify these effects comprehensively at a regional scale. First, a method to simulate recorded data from different quality sensors is devised, using characteristics of existing low-, medium-, and high-quality accelerometers. These simulations use input data from either the Pacific Earthquake Engineering GM database or from a high-fidelity fault rupture and regional wave propagation simulation. Subsequently, the simulated sensor data are used to assess the seismic damage to typical buildings at a city scale. The results indicate that low-quality sensors found in most smartphones are currently insufficient for assessing seismic damage. Medium-quality accelerometers (MEMS-based instruments), on the other hand, can provide feasible solutions for cost-effective city-scale deployment and may offer deployment options that are superior to sensor networks with high-quality accelerometers.
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Influence of sensor density on seismic damage assessment: A case study for istanbul
(Seismological Society of America, 2022-08) Cheng, Q.; Fei, Y.; Lu, X.; Liao, W.; Zhang, W.; Chen, P. Y.; Kurtuluş, Aslı; Ghahari, F.; Vela, V.; Taciroglu, E.; Civil Engineering; KURTULUŞ, Asli
The strong ground motions (GMs) recorded by strong motion networks are significant to increase the accuracy of seismic damage assessment. However, the influence of sensor density on seismic damage assessment remains unclarified. Therefore, a workflow is proposed in this study to quantitatively analyze the influence of sensor density on seismic damage assessment. The scenario-based earthquake simulation method is first used to provide the time history of GM at each location as the ground truth of the analysis. Subsequently, a GM prediction method, namely the interpolation method, is adopted to predict GMs at locations without sensors using measuring data from the limited sensors. Finally, the building scale and region scale seismic damage under different sensor densities are compared to quantitatively analyze the influence of sensor density on seismic damage assessment. A detailed case study for Zeytinburnu District, Istanbul, Turkey, is performed to demonstrate the proposed methods. The findings of this study can provide an important reference for seismic damage assessment and the deployment of strong motion networks.
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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, Asli
Data 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.
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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 Atilla
In 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.
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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, Asli
Using 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.
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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, Asli
Physics-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.
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Velocity pulse effects of near-fault earthquakes on a high-speed railway vehicle-ballastless track-benchmark bridge system
(Taylor & Francis, 2022-09-02) Chen, L. K.; Kurtuluş, Aslı; Dong, Y. F.; Taciroglu, E.; Jiang, L. Z.; Civil Engineering; KURTULUŞ, Asli
The near fault (NF) line waves send out signal envelopes that oscillate over lengthy periods of time with periodic impulses. Like train bridges, train tracks demonstrate comparable track-bridge (TB) motion dynamics. Using these coupling dynamics, are the high-speed train-track-bridge (HSTTB) system designs sensitive to those parameters? This research incorporates a Finite Element Analysis (FEA) technique developed for simulating the dynamic reactions of the coupled TB system when faced with simultaneous NF lateral and vertical ground motions (GMs). For the first time, data from the pre-commissioning field testing of the Beijing-Shanghai high-speed train are utilized to validate the Train-Track-Bridge Dynamic Analysis (TTBDA) test. As a matter of fact, the current research has concentrated on the running safety of the high-speed train's operations, as well as the possible derailment mechanism of the high-speed train, in light of the far-field (FF) earthquakes. This analysis reveals that the NF GMs in the bridge structure's seismic reactivity are considerable. Many high-speed train derailments are due to frequent wheel displacement, elevated wheels, and significant lateral motion. The data discovered in the field may give engineers vital information for calculating relevant situations and railroad engineering projects.