Papers by Kyriazis Pitilakis
Bulletin of Earthquake Engineering, 2020
In this study, the nonlinear seismic response analysis of five sites with deep boreholes in Bucha... more In this study, the nonlinear seismic response analysis of five sites with deep boreholes in Bucharest (Romania) is performed. A ground motion database consisting of recordings obtained during several Vrancea intermediate-depth earthquakes is compiled for the analyses. The results of the nonlinear site response analysis show that significant longperiod spectral amplifications occur for all five sites and that the level on input peak ground acceleration influences in a significant manner the spectral amplifications, both as median value and variability. In addition, the differences in terms of site amplification factors between the five analysed sites also increase with the level of the input peak ground acceleration levels. The median site amplifications decrease with the increase of the peak ground acceleration for spectral periods of up to 2.0 s, while for longer periods the median site amplifications increase. The results of the nonlinear site response analysis were also validated by using real ground motions recorded in the same area during recent Vrancea intermediate-depth earthquakes.
Bulletin of the Geological Society of Greece, Jul 27, 2017
Strong motion data recorded during the 15-year operation of the CORinth Gulf Soft Soil Array (COR... more Strong motion data recorded during the 15-year operation of the CORinth Gulf Soft Soil Array (CORSSA) in the highly seismic region of Aegion have been homogenized and organized in a MySQL database. In the present work we describe the contents of the database and the web portal through which these data are publicly accessible. CORSSA comprises one surface and four downhole 3-D broadband accelerometric stations. It was installed in 2002, in the framework of European project CORSEIS, aiming at gathering data for studying site effects, liquefaction, and non-linear behaviour of soils, as well as earthquake source properties. To date, the array has recorded 549 local and regional events with magnitudes ranging from 1.1 to 6.5. Although the vast majority of the recorded events caused weak ground motion at the CORSSA site, the scientific value of the data set pertains to the sparsity of this kind of infrastructure in most parts of the world.
ASTM International eBooks, Oct 1, 2011
This paper examines the strain-dependent dynamic properties (G/G O-logc-DT curves) of dry and sat... more This paper examines the strain-dependent dynamic properties (G/G O-logc-DT curves) of dry and saturated sand-recycled rubber mixtures in a range of shearing strain amplitudes from (5 Â 10 À4) % to (6 Â 10 À1) % using a fixed-free torsional resonant column device. The effect of the rubber content on the pore water pressure buildup and volumetric threshold strain c v t of saturated mixtures, as well as the effect of specimens' geometry on the experimental data, are also presented and discussed. Based on a comprehensive set of experimental results, a modified hyperbolic model, frequently used in practice, has been proposed. An increase in the rubber content leads to a more linear shape of the G/G O-logc and DT-logc curves and a reduction in the pore water pressure buildup. Damping is expressed in terms of DT-DT O , which eliminates the effect of the rubber content and the mean confining pressure. The final aim is to propose appropriate design G/G O-logc-DT curves for sand-rubber mixtures currently used in practice.
The definition of the geometry and dynamic soil properties of a complex geological structure is o... more The definition of the geometry and dynamic soil properties of a complex geological structure is of main importance for site effect empirical and theoretical analyses. The case of Mygdonia sedimentary basin where the EUROSEIS test site was developed is a long time, in operation since 1993, large scale laboratory in physical conditions. Mygdonia basin belongs to the closest active seismic zone that affects the city of Thessaloniki and was the epicentral area of the strong 1978 earthquake (Ms=6.5). The construction of the 3D model is based on old and recent geological, seismological, geophysical, and geotechnical data. This dataset includes microtremor measurements (at 200 points), local and regional earthquake records from temporary networks, seismic reverse profiles using big explosions, electrical surveys, geotechnical boreholes and tests. All these data have been analyzed using many different techniques, from a geophysical and seismological point of view (refraction, surface wave inversion, HVSR, SSR and GIS spectral ratios). The synthesis of all results led to a preliminary 3D model proposed in terms of site response analysis.
ASTM International eBooks, Oct 1, 2011
The paper examines the small-strain dynamic properties of mixtures composed of sandy soils with r... more The paper examines the small-strain dynamic properties of mixtures composed of sandy soils with recycled tire rubber. For this purpose, the experimental results stemming from a torsional resonant column testing program on twenty four [24] saturated and dry specimens are analyzed. The percentages of rubber used range between 0 and 35 % by mixture weight. G O values increase whereas DT O values decrease systematically as the content of rubber decreases and the mean confining pressure increases. Based on the experimental results we propose an analytical relationship for the estimation of G O , which is expressed in terms of an equivalent void ratio that considers the volume of rubber solids as part of the total volume of voids, along with an analytical relationship for the estimation of DT O. Finally, the effect of the specimen's size and the duration of confinement on the initial shear modulus and damping ratio of the mixtures are also discussed.
ASTM International eBooks, Oct 1, 2011
Journal of Astm International, 2012
This paper examines the strain-dependent dynamic properties (G/GO-logγ-DT curves) of dry and satu... more This paper examines the strain-dependent dynamic properties (G/GO-logγ-DT curves) of dry and saturated sand–recycled rubber mixtures in a range of shearing strain amplitudes from (5 × 10−4) % to (6 × 10−1) % using a fixed-free torsional resonant column device. The effect of the rubber content on the pore water pressure buildup and volumetric threshold strain γtv of saturated mixtures, as well as the effect of specimens’ geometry on the experimental data, are also presented and discussed. Based on a comprehensive set of experimental results, a modified hyperbolic model, frequently used in practice, has been proposed. An increase in the rubber content leads to a more linear shape of the G/GO-logγ and DT-logγ curves and a reduction in the pore water pressure buildup. Damping is expressed in terms of DT-DTO, which eliminates the effect of the rubber content and the mean confining pressure. The final aim is to propose appropriate design G/GO-logγ-DT curves for sand–rubber mixtures currently used in practice.
COMPDYN 2009 - 2nd International Conference on Computational Methods in Structural Dynamics & Earthquake Engineering, 2009
Proceedings of the 6th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2015), 2017
Loess Plateau of China is one of the most representative geomorphologic regions for loess around ... more Loess Plateau of China is one of the most representative geomorphologic regions for loess around the world due to the deep covering layer and wide distribution area. Many catastrophic disasters induced by earthquake had been identified in this area. This study examined systematically the small-strain stiffness and damping of loess in Lanzhou, Northwest of China, through the laboratory resonant column (RC) test method and the field down-hole test method. On the basis of the analyses of test results, it was found that the smallstrain shear modulus G 0 of loess was more sensitive to water content than the small-strain damping D min. A linear relationship between log(G 0) and log(σ′ m) was observed for loess, while the corresponding slope in log-log coordinates decreased with water content increasing. Similarly, log(D min) decreased linearly with log(σ′ m) as well. G 0 of undisturbed loess was much higher than reconstituted ones at low water content and this difference could be negligible for saturated loess. The similar phenomenon was observed for D min too. The pattern of correlation between G 0 and σ′ m for loess accorded well with the findings in literature but in the present study, higher values of G 0 could be expected, which may be ascribed to the different device used. In comparison with the down-hole test results, there was a good agreement between RC results and laboratory results for G 0 of loess. Finally, the correlations between G/G 0 and γ/γ 0.85 could be normalized perfectly for Lanzhou loess,
Bulletin of Earthquake Engineering, 2021
On October 30th 2020, a M7.0 earthquake occurred in the Aegean Sea close to Samos Island (Greece)... more On October 30th 2020, a M7.0 earthquake occurred in the Aegean Sea close to Samos Island (Greece) and the western coast of Turkey that had a strong impact on the city of İzmir, about 70 km away from the epicenter. 116 people were killed, several hundreds were injured and about 4% of the structures sustained damages, including buildings that totally collapsed. Strong amplification of ground motion within Bornova basin (İzmir) where severe damages were observed, has been reported among the detrimental factors that may have contributed to such earthquake losses. This study is devoted to providing evidence that the reason of the observed intensity of ground motion in Bornova basin is mainly related to site effects and in particular to what is referred to as basin effects. The evaluation of observations for basin effects is based on a analysis with empirical techniques in frequency domain as well as with time–frequency analyses to reveal the contribution of different wave types in the response. Empirical findings are correlated with the particular geological structure of the Bornova basin, the latter being enhanced with a representative deep VS model using surface wave inversion on strong motion recordings. Furthermore, empirical findings are validated with 2D numerical analyses of a simplified basin model. Building characteristics and structural damages are also discussed in an attempt to comprehend the relation between them and basin effects. Noting that basin effects are not explicitly included in any modern seismic code, an approach is proposed to introduce the extra amplification due to basin effects in design practice.
Soil Dynamics and Earthquake Engineering, 2018
The paper presents an alternative site classification scheme and associated intensity dependent s... more The paper presents an alternative site classification scheme and associated intensity dependent spectral amplification factors, aiming to contribute to the ongoing revision of Eurocode 8. The new classification scheme, introducing among the main classification parameters the fundamental period T 0 of the site, is an evolution of the recent work by Pitilakis et al. (2013) [1], while the main features of the amplification factors and the new seismic design actions are summarized in the use of two anchoring spectral values, for short (0.2-0.3 s) and intermediate (1.0 s) periods, instead of only one of the present version of Eurocode 8 (i.e. effective ground acceleration), and the scalar intensity variation of site amplification factors to account for soil nonlinearity. The work is based on a comprehensive analysis of a worldwide database of strong ground motion records from sites which dispose a very well-documented soil profile down to the seismic bedrock (Vs > 800 m/s).
Soil Dynamics and Earthquake Engineering, 2016
The Euroseistest Verification and Validation Project (E2VP) is part of a series of complementary ... more The Euroseistest Verification and Validation Project (E2VP) is part of a series of complementary benchmarking exercises launched to better assess the ability of numerical simulation to accurately predict seismic ground motion. E2VP targeted more specifically the current, most-advanced numerical methods applied to realistic 3D, linear models of sedimentary basins through a quantitative comparison of the recorded and numericallysimulated ground motions. The target site, located within the Mygdonian basin near Thessaloniki, Greece, has been thoroughly investigated for two decades and a detailed, realistic 3D model has been derived from geological, geophysical and geotechnical investigations, while a dedicated instrumentation provided a significant number of surface and borehole recordings. Verification and validation tests up to a frequency of 4 Hz, much beyond the 0.4 Hz fundamental frequency of the deepest part of the graben, have been performed for a set of 19 local, small to moderate magnitude events. For careful and accurate enough computations, the model-to-model differences are smaller than the model-to-observations differences, the latter being controlled by uncertainties primarily in the crustal propagation model and source properties, and secondarily in the shallow structure. It is therefore recommended to prefer distant and/or deep events (R > 10-20 km, Z > 8-10 km) for validation exercises. Additional sensitivity tests illustrate the ability of carefully verified numerical simulation tools to provide an instructive insight at the structure of the so-called "aleatory" variability of ground motion, for both its within-and between-event components. The between-event variability is shown to be very sensitive to hypocenter location errors (even as low as ± 2 km), and to uncertainty in magnitude estimates. It explains the increase of aleatory variability for small magnitude events and emphasizes the usefulness of dense seismological networks. The within event, single-site variability is shown to be associated to an "epistemic" dependence of the 3D site response on the event back-azimuth, distance and depth, and calls for caution when interpreting singlestation variabilities derived from a too small number of events.
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Papers by Kyriazis Pitilakis