Browsing by Author "Tönük, G."

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Factors affecting site-specific response analysis
(Taylor & Francis, 2022) Tönük, G.; Ansal, Mustafa Atilla; Civil Engineering; ANSAL, Mustafa Atilla
AbstractThe engineering purpose of a site-specific response analysis is to estimate the uniform hazard acceleration spectrum on the ground surface for a selected hazard level. One of the mandatory components for site response analyses is one or more representative acceleration time histories that need to be scaled with respect to the calculated seismic hazard level for the selected site. The selection and scaling procedures of earthquake acceleration records play an important role in this approach. The effects and differences in using two different scaling approaches are studied: scaling with respect to ground motion parameters and response spectrum scaling. A set of homogeneous ground motion prediction relationships are developed for peak ground acceleration, peak ground velocity, root-mean-square acceleration, Arias intensity, cumulative absolute velocity, maximum spectral acceleration, response spectrum intensity, and acceleration spectrum intensity based on a uniform set of acceleration records for ground motion parameter scaling. The uncertainties associated with site response analysis are considered as epistemic and aleatory uncertainties in source characteristics, soil profile, and soil properties. Aleatory variability is due to the intrinsic randomness of natural systems; it cannot be reduced with additional data (Passeri et al. 2020), however; its variability may be modeled by probability distribution functions. Thus, one possibility is to determine the probability distribution of the acceleration spectrum calculated on the ground surface for all possible input acceleration records, site profiles, and dynamic soil properties. The variability in the earthquake source and path effects are considered using a large number of acceleration records compatible with the site-dependent earthquake hazard in terms of fault mechanism, magnitude, and distance range recorded on stiff site conditions. Likewise, a large number of soil profiles may be considered to account for the site condition variability. The uncertainties related to dynamic soil properties may be considered as possible variability of maximum dynamic shear modulus in site response analyses. A methodology is proposed to estimate a uniform hazard acceleration spectrum on the ground surface based on the probabilistic assessment of the factors involved in site response analysis. The uniform hazard acceleration spectra obtained from a case study are compared with the spectra calculated by probabilistic models proposed in the literature.
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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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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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Probabilistic seismic microzonation for ground shaking intensity, a case study in Türkiye
(Springer, 2023-10) Tönük, G.; Ansal, Mustafa Atilla; Civil Engineering; ANSAL, Mustafa Atilla
The purpose of seismic microzonation is to estimate earthquake characteristics on the ground surface based on a probabilistic approach to mitigate earthquake damage in the foreseeable future for the new buildings, as well as for the existing building stock. The probabilistic analysis and related results are very important from an engineering perspective since the nature of the problem can only be dealt with in a probabilistic manner. The uncertainties associated with these analyses may be large due to the uncertainties in source characteristics, soil profile, soil properties, and building inventory. At this stage, the probability distribution of the related earthquake parameters on the ground surface may be determined based on hazard-compatible input acceleration-time histories, site profiles, and dynamic soil properties. One option, the variability in earthquake source and path effects may be considered using a large number of acceleration records compatible with the site-dependent earthquake hazard. Likewise, large numbers of soil profiles may be used to account for the site-condition variability. The seismic microzonation methodology is proposed based on the probabilistic assessment of these factors involved in site response analysis. The second important issue in seismic microzonation procedure is the selection of microzonation parameters. The purpose being mitigation of structural damage, it is possible to adopt earthquake parameters like cumulative average velocity (CAV) or Housner intensity (HI) that was observed to have better correlation with building damage after earthquakes. A seismic microzonation procedure will be developed with respect to ground shaking intensity considering probabilistic values of the cumulative average velocity (CAV) or Housner intensity (HI).
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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.
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Site characterization for site response analysis in performance based approach
(Springer, 2022) Ansal, Mustafa Atilla; Tönük, G.; Civil Engineering; ANSAL, Mustafa Atilla
The local seismic hazard analysis would yield probabilistic uniform hazard acceleration response spectrum on the engineering bedrock outcrop. Thus, site-specific response analyses need to produce a probabilistic uniform hazard acceleration response spectrum on the ground surface. A possible performance based approach for this purpose requires a probabilistic estimation of soil stratification and engineering properties of encountered soil layers in the soil profile. The major uncertainties in site-specific response analysis arise from the variabilities of (a) local seismic hazard assessment, (b) selection and scaling of the hazard compatible input earthquake time histories, (c) soil stratification and engineering properties of encountered soil and rock layers, and (d) method of site response analysis. Even though the uncertainties related to first two items have primary importance on the outcome of the site-specific response analyses, the discussion in this article focuses on the observed variability and level of uncertainty in site conditions, related to soil stratification, thickness and type of encountered soil layers and their engineering properties, depth of ground water table and bedrock and properties of the engineering bedrock. Thus, one option may be conducting site response analyses for large number of soil profiles produced by Monte Carlo simulations for the investigated site to assess probabilistic performance based design acceleration spectra and acceleration time histories calculated on the ground surface based on 1D, 2D, or 3D site response analysis with respect to different performance levels.
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Site response analysis in performance based approach
(Elsevier, 2024-03) Ansal, Mustafa Atilla; Tönük, G.; Sadegzadeh, Shima; Civil Engineering; ANSAL, Mustafa Atilla
A performance based approach for site response analysis requires a probabilistic approach accounting for the observed variability in soil stratification and engineering properties of the soil layers. The major variability in site-specific response analysis arises from the uncertainties induced by the (a) local seismic hazard assessment, (b) selection and scaling of the hazard compatible input earthquake time histories, (c) soil stratification and engineering properties of encountered soil and rock layers, and (d) method of site response analysis. Even though the uncertainties related to first item, local seismic hazard assessment, has primary importance on the outcome of the site-specific response analyses, the discussion in this article focuses on the possible uncertainties in selection and scaling of the hazard compatible input earthquake time histories, soil stratification, thickness, type and their engineering properties, depth of ground water table and bedrock and properties of the engineering bedrock. One alternative may be to conduct site response analyses for large number of soil profiles generated by Monte Carlo simulations using relatively large number of hazard compatible acceleration time histories to assess probabilistic performance based design acceleration spectra and acceleration time histories calculated on the ground surface with respect to different performance levels. A remaining issue may be considered as the variability induced by 1D, 2D, and 3D site response analysis.
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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.