Civil Engineering

Permanent URI for this collectionhttps://hdl.handle.net/10679/312

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Now showing 1 - 17 of 17

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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 comparison study between 1D and 2D site response analyses based on observed earthquake acceleration records
(Springer, 2023) Shamekhi, Shima; Ansal, Mustafa Atilla; Kurtuluş, Aslı; Civil Engineering; ANSAL, Mustafa Atilla; KURTULUŞ, Asli; Shamekhi, Shima
The objective of the present work is to evaluate the necessity of 2D site response analysis based on the comparison among the peak ground and spectral accelerations recorded by Istanbul Rapid Response Network and Istanbul vertical array stations during the Mw = 6.5 24/5/2014 Gökçeada and Mw = 5.9 19/5/2011 Kütahya earthquakes with the calculated accelerations by 1D and 2D site response analyses. The shear wave velocity profiles determined based on in-situ geophysical and geotechnical measurements and laboratory tests within the Istanbul Microzonation Project are revaluated adopting a revision scheme to obtain the best fits between the recorded and calculated spectral accelerations by 1D site response analysis. These modified shear wave velocity profiles are later used for 1D and 2D site response analyses performed in North–South and East–West directions to model peak ground and spectral accelerations on the ground surface. Finally, by modelling different distances around boreholes the influence of variation of the soil profile in horizontal direction is investigated by 2D analyses.
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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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Implications of site specific response analysis
(Springer, 2018) Ansal, Mustafa Atilla; Tönük, G.; Kurtuluş, Aslı; Civil Engineering; Pitilakis, K.; ANSAL, Mustafa Atilla; KURTULUŞ, Asli
Definition 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.
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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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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, Asli
Seismic 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.
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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 Atilla
Few 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.
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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 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, Asli
The 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.
Open Access
Site response from Istanbul vertical arrays and strong motion network
(Earthquake Engineering Research Institute ( EERI ), 2014) Ansal, Mustafa Atilla; Kurtuluş, Aslı; Tonuk, G.; Civil Engineering; ANSAL, Mustafa Atilla; KURTULUŞ, Asli
In the framework of Istanbul Microzonation Project for the European side, the investigated region was divided by a grid system of 250m×250m and site investigations were performed for each cell based on borings and in-situ seismic wave velocity measurements for defining representative soil profiles with shear wave velocity values extending down to the engineering bedrock. Geological and geotechnical laboratory and field testing data with measured seismicwave velocities enabled to determine the engineering properties of the soil and rock layers encountered in all the cells. There have been limited number of earthquakes within 100km range of Istanbul with local magnitude in the range of ML=4-5 and few more distant and more stronger earthquakes that were recorded by the existing three vertical arrays as well as by the Istanbul Rapid Response Network (IRRN) strong motion stations. Even though the maximum PGA were similar, the observed spectral response were different indicating the importance of the distance and source magnitude concerning the frequency content and predominant soil period ranges. Even though the level of ground shaking intensity is relatively low, efforts were made to evaluate the variation of the recorded accelerations with depth in vertical arrays located at Ataköy, Zeytinburnu and Fatih. Attempts were also made to model the recorded acceleration time histories at the triggered IRRN stations using the acceleration records obtained at the bedrock level from the vertical array stations in the case of the recent 19.5.2011 Mw=5.7 Kütahya earthquake that took place approximately 185km away.
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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, Asli
During 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.
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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.

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