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ANSAL, Mustafa Atilla

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Mustafa Atilla

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Now showing 1 - 10 of 27
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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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    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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    Characterization of site amplification by a parametric study
    (Taylor & Francis, 2023) Fercan, N. O.; Şafak, E.; Ansal, Mustafa Atilla; Civil Engineering; ANSAL, Mustafa Atilla
    The reliability of Vs30 and the performance of alternative time averaged shear wave velocities (Vsz) and shear wave travel times (Ttz) at various depths, z, were investigated for the estimation of site amplification and fundamental frequency (f 0) characterization by considering the linear and nonlinear soil behavior. The study revealed that alternative parameters performed better than Vs30 and the best performing z parameters changed by switching from convex to concave theoretical profiles and by increasing ground motions. For a practical usage in site investigations, guidelines to estimate nonlinear soil amplification factor and fundamental frequency from the linear ones were presented.
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    2D non-linear seismic response of the Dinar basin,TURKEY
    (Elsevier, 2016-10) Khanbabazadeh, H.; Iyisan, R.; Ansal, Mustafa Atilla; Hasal, M. E.; Civil Engineering; ANSAL, Mustafa Atilla
    Local geological conditions generate significant amplification of ground motion and concentrated damage during earthquakes. The highly concentrated damages at the edges of the Dinar basin during occurred earthquakes at regions close to rock outcrop bring up the effect of the inclined bedrock effect on the dynamic behavior of the basin with 2D geometry. In this study, first the idealized 2D model of the basin based on the results of the underground explorations and geologic investigations is proposed. Results show that Dinar basin has an asymmetric 2D geometry with two different bedrock angles at edges. Then, a numerical study using finite difference based nonlinear code which utilizes appropriate static and dynamic boundary conditions, and includes hysteresis damping formulation based on the user defined degradation curves is conducted using real earthquake motions of different strength and frequency content. The constructed model is subjected to the collection of 16 earthquakes with different PGA's of 0.1, 0.2, 0.3 and 0.4 g, four motions for each PGA. It was seen that the dynamic behavior of the basin is broadly affected by the two dimensional bedrock. The results indicates the higher effect of the 6° bedrock inclination at east part on the amplification with respect to the steeper 20° bedrock slope at the west. Also, the results show the insignificant effect of the bedrock at the depth more than 150 m on the amplification of the east edge. While the effect of the 6° bedrock angle at the east part continues until 1500 m from the outcrop, it affects the amplification until 700 m from the outcrop at the west part with 20° bedrock angle.
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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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    Nonlinear dynamic behavior of the basins with 2D bedrock
    (Elsevier, 2018-04) Khanbabazadeh, H.; Iyisan, R.; Ansal, Mustafa Atilla; Zulfikar, C.; Civil Engineering; ANSAL, Mustafa Atilla
    Resonance due to impedance contrast, focusing due to subsurface topography, conversion of the body waves to surface waves and subsurface topography are among the factors influencing the amplification specification of the sites, which can only be considered by the application of suitable nonlinear analysis method. In this study, using the fully nonlinear analysis method, along with a hysteretic-type model and no extra damping, the effects of the basin edge on the dynamic behavior of the basins is investigated in more accurate manner. To make the results useful at engineering affaires, the investigated basins are classified into sandy, clayey and layered basins. Special degradation curves for each of the (soft, medium plasticity and stiff) clay and (loose, medium dense and dense) sand types have been extracted and fitted to the continuous functions which is used by the nonlinear method's hysteretic-type damping scheme. The results exhibit the differences in the amplification behavior of the basins with different soil types under the different excitation levels. Also, the sensitivity of the different parts of the basin surface with 2D geometry to different period levels is investigated. This finding can be used at dynamic structural design of the buildings on basins with 2D bedrock inclination.
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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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    A comparison study between 1D and 3D site response analyses based on observed earthquake acceleration records…
    (National Technical University of Athens, 2023) Shamekhi, Shima; Ansal, Mustafa Atilla; Civil Engineering; ANSAL, Mustafa Atilla; Shamekhi, Shima
    The characteristics of the site conditions have a very significant influence on the variation of building damage during earthquakes, thus, it is essential to evaluate and analyse the effects of site conditions. One option is to conduct site-specific response analysis to calculate the response of the soil layers by using estimated acceleration records on rock outcrop, shear wave velocity profiles, shear modulus reduction, and damping ratio curves as inputs for the encountered soil layers. The objective of the present work is to evaluate the necessity of 3D 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 24/05/2014 Gökçeada and Ml=5.7 26/09/2019 Silivri earthquakes with the calculated accelerations by 1D and 3D 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 an optimization scheme to obtain the best fits between the recorded and calculated accelerations by 1D site response analysis. These modified shear wave velocity profiles are later used for 3D site response analyses performed taking into consideration the three components of the recorded acceleration time histories in all three directions at the bedrock level to model peak ground and spectral accelerations on the ground surface.
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    Numerical modeling of the offshore wind turbine monopile foundation under environmental loading
    (CRC Press, 2019) Fard, Maryam Massah; Erken, A.; Erkmen, Bülent; Ansal, Mustafa Atilla; Civil Engineering; Silvestri, F.; Moraci, N.; FARD, Maryam Massah; ERKMEN, Bülent; ANSAL, Mustafa Atilla
    Prediction of dynamic performance of an offshore wind turbine requires consideration of many different design parameters. Beside the superstructure, foundation also plays an important role both functionally and financially in their design. In this study, numerical dynamic analysis of an offshore wind turbine with a monopile foundation is performed under wave action that may lead to liquefaction around pile diameter due to the cyclic stresses induced by the pile displacements. The effects of foundation characteristic such as monopile diameter and its embedment depth are investigated. The results in terms of displacements, excess pore water pressure, and inertial forces are presented and discussed. Findings are considered to give better estimation of the dynamic performance and liquefaction susceptibility of the offshore wind turbines foundations under cyclic loads induced by the pile displacements.
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    Local site conditions and seismic risk assessment of historic buildings
    (2013) D’Ayala, D.; Ansal, Mustafa Atilla; Civil Engineering; Bilotta, E.; Flora, A.; Lirer, S.; Viggiani, C.; ANSAL, Mustafa Atilla
    The objectives of the Istanbul Seismic Risk Mitigation and Emergency Preparedness Project are to improve Istanbul’s preparedness for a potential earthquake. Within this framework “Risk Assessment of Cultural Heritage Buildings” was designed to address the vulnerability of cultural assets, specifically buildings with global cultural heritage value. One of the components of the project was the vulnerability and risk assessment of 170 historic buildings of varied age, value and state of conservation, distributed over several square miles. Many of these buildings have public functions such as museums or education establishments. Among the most famous are Topkapı Palace and Hagia Irene museum. After a discussion of the choice of the most appropriate earthquake scenario, the methodology used for assessing the effects of local site conditions on the seismic performance of selected cultural heritage buildings is presented. The purpose is to estimate the earthquake characteristics on the ground surface based on the probabilistic and deterministic hazard studies. The site specific elastic design spectra for each site are then manipulated to obtain site specific nonlinear displacement spectra, so that these can be directly compared with capacity curves for the buildings obtained by using mechanism approach limit state analysis. The procedure for obtaining the capacity curves is described and the choice of the most appropriate level of ductility and the equivalent reduction coefficient are discussed. A procedure to evaluate performance points and to define safety factors based on lateral acceleration, drift or expected damage level, is presented. The process of arriving at a risk evaluation and hence recommendation for strengthening or otherwise, is finally highlighted with respect to four comparable case studies.