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11.
Dimitrios?RaptakisEmail author Konstantia?Makra Anastasios?Anastasiadis Kyriazis?Pitilakis 《Bulletin of Earthquake Engineering》2004,2(3):301-327
This paper presents results of numerical modelling of site response for Thessaloniki, obtained with two different 2D methods; a finite difference and a finite element method. Ground motion across a 2D model of the subsoil of the city has been simulated for vertically incident SH waves. The predominance of locally generated surface waves is very clear in the synthetic seismograms of a weak event and of stronger ones. These results are then compared with the observations in time domain and frequency domain. The role of the soil formations with high attenuation in the lateral propagation and the effect of the differential motion close to the lateral variations are also pinpointed. The stronger events were finally used to compute strong ground motion in order to reveal and to discuss practical engineering aspects such as peak ground acceleration value, the most familiar indicator in seismic norms, the soil to rock spectral coefficients for the period bandwidth of interest, and the aggravation factor in terms of 2D to 1D response spectra as a useful ruler to account for complex site effects. 相似文献
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Definition of subsoil structure and preliminary ground response in Aigion city (Greece) using microtremor and earthquakes 总被引：2，自引：0，他引：2
P.I. Apostolidis D.G. Raptakis K.K. Pandi M.V. Manakou K.D. Pitilakis 《Soil Dynamics and Earthquake Engineering》2006,26(10):922-940
An extensive campaign—including detailed geologic and geotechnical surveys both existing and news as well as noise measurements—was conducted along a cross-section in order to define both geometry and soil properties (mainly the shear wave velocity) of the main formations in Aigion city. Aigion city is located in the Gulf of Corinth, Greece, a highly seismic region of the Aegean Sea. The main objective of the accurate 2D soil model is its use in site response modeling and in the interpretation of observations from a vertical down-hole accelerograph array. This model revealed a complex geologic structure with a multi-faulted shear zone related to the Aigion fault. The defined subsurface structure offered the possibility for its correlation with estimated site effects, in terms of spectral ratios. Two different data sets, earthquakes recorded at down-hole accelerograph network and noise measurements at 17 sites, were used. To translate the empirical transfer functions with the geologic structure, the 1D estimates were also computed. All these results are consistent, indicating a satisfactory correlation between the soil model and preliminary site response. 相似文献
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The response of laterally loaded pile foundations may be significantly important in the design of structures for such loads. A static horizontal pile load test is able to provide a load–deflection curve for a single free‐head pile, which significantly differs from that of a free‐ or fixed‐head pile group, depending on the particular group configuration. The aim of this paper is to evaluate the influence of the interaction between the piles of a group fixed in a rigid pile cap on both the lateral load capacity and the stiffness of the group. For this purpose, a parametric three‐dimensional non‐linear numerical analysis was carried out for different arrangements of pile groups. The response of the pile groups is compared to that of the single pile. The influence of the number of piles, the spacing and the deflection level to the group response is discussed. Furthermore, the contribution of the piles constituting the group to the total group resistance is examined. Finally, a relationship is proposed allowing a reasonable prediction of the response of fixed‐head pile groups at least for similar soil profile conditions. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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Site effects at Euroseistest—II. Results from 2D numerical modeling and comparison with observations
F.J. Chvez-Garc&#x;&#x;a D. Raptakis K. Makra K. Pitilakis 《Soil Dynamics and Earthquake Engineering》2000,19(1):420
This paper presents results of numerical modeling of site response for Euroseistest. Ground motion across a very detailed model of the subsoil of this valley has been simulated for vertically incident SH waves. The predominance of locally generated surface waves is very clear in the synthetic seismograms. These results are then compared with published studies of observed site effects at this basin and with a detailed analysis of two events in the time domain. It is discussed in which sense it is possible to obtain a good fit between observations and 1D models, even though the real behavior involves locally generated Love waves. For this reason, it can be misleading to rely on an incomplete observation such as empirical transfer functions. Finally, it is stressed that in order to predict ground motion in alluvial valleys the information contained in the phase cannot be neglected. 相似文献
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Olga-Joan Ktenidou Francisco-J. Chávez-García Dimitrios Raptakis Kyriazis D. Pitilakis 《Bulletin of Earthquake Engineering》2016,14(3):623-645
We study site effects using 520 weak motion earthquake records from a vertical array in Aegion, Greece. The array is inside a basin, has four stations in soil, and one in bedrock (178 m depth). The site is marked by high seismicity and complex surface geology. We first use the records to establish the downhole accelerometer orientations and their evolution with time. Then we estimate site effects using empirical spectral ratios with and without a reference site (standard and horizontal-to-vertical spectral ratio). We find significant site amplification which cannot be accounted for by 1D model predictions, along with a significant difference in the amplification level between the two horizontal components. These are indications of 2D effects, namely surface waves generated at the basin edge. The difference in amplification between the horizontal components is maximised when these are rotated with respect to the orientation of the basin edge. The strongest amplification takes place in the direction parallel to the basin edge (SH, or out-of-plane motion), and is up to 2 times higher than in the perpendicular direction (SV, or in-plane motion). This directional effect on the amplification is corroborated by numerical 2D modelling using incident SH and SV waves, with the former possibly generating strong Love waves. In the records, the directionality is clear for windows containing the largest amplitudes of the records (S waves and strong surface waves), while it tends to vanish for coda-wave windows. This directionality is also observed when using response spectral ratios rather than Fourier ratios. We compute soil-to-rock amplification factors for peak ground acceleration (PGA) and find it is significantly higher than what is predicted by current design codes. We attribute this difference to the basin edge amplification, linear soil behaviour, and to the inability of simple scalar values like PGA to describe complex amplification effects. Finally, we analyse the earthquake records at a surface station near the slope crest and do not observe significant topographic amplification. 相似文献
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K. Pitilakis S. Karapetrou D. Bindi M. Manakou B. Petrovic Z. Roumelioti T. Boxberger S. Parolai 《Bulletin of Earthquake Engineering》2016,14(9):2543-2563
This study aims at presenting the analyses of monitoring data that have been used in the context of structural monitoring and Earthquake Early Warning (EEW) for a hospital building in Thessaloniki. Permanent and temporary instrumentation arrays, implemented under the responsibility of Aristotle University of Thessaloniki (SDGEE-AUTH) in close cooperation with German Centre for Geosciences (GFZ) are presented. The ambient noise data recorded at the temporarily installed networks are used for the dynamic characterization of the building based on both vibrational and waveform approaches. Moreover, long-term ambient noise recordings from the permanent array installed within the hospital are used for the investigation of the daily and seasonal wandering of the building resonance frequencies related to environmental effects. The modal identification results are used in a comprehensive framework for the computation of the up-to-date fragility curves representing the actual structural state considering aging effects of the construction materials, possible pre-existing damages and changes in the geometry and mass distribution. The building-specific fragility functions are integrated into two independent EEW systems and rapid damage assessment approaches, namely the PRESTo software and an onsite EEW algorithm on the instruments of the permanent array, to provide the expected level of damage after strong ground shaking at the monitored building. The implemented monitoring networks and the developed operational tools can be used in the context of seismic risk mitigation and preparedness for structural safety assessment under earthquake loading. 相似文献
17.
K. D. Pitilakis S. T. Karapetrou S. D. Fotopoulou 《Bulletin of Earthquake Engineering》2014,12(4):1755-1776
At present, the seismic vulnerability assessment of reinforced concrete (RC) buildings is made considering fixed base conditions; moreover, the mechanical properties of the building remain intact in time. In this study we investigate whether these two fundamental hypotheses are sound as aging and soil-structure interaction (SSI) effects might play a crucial role in the seismic fragility analysis of RC structures. Among the various aging processes, we consider the chloride-induced corrosion based on probabilistic modeling of corrosion initiation time and corrosion rate. Different corrosion aspects are considered in the analysis including the loss of reinforcement cross-sectional area, the degradation of concrete cover and the reduction of steel ultimate deformation. SSI is modeled by applying the direct one-step approach, which accounts simultaneously for inertial and kinematic interactions. Two-dimensional incremental dynamic analysis is performed to assess the seismic performance of the initial uncorroded ( \(\hbox {t}=0\) years) and corroded ( \(\hbox {t}=50\) years) RC moment resisting frame structures, having been designed with different seismic code levels. The time-dependent fragility functions are derived in terms of the spectral acceleration at the fundamental mode of the structure \(\hbox {S}_{\mathrm{a}}(\hbox {T}_{1}\) , 5 %) and the outcropping peak ground acceleration for the immediate occupancy and collapse prevention limit states. Results show an overall increase in seismic vulnerability over time due to corrosion highlighting the important influence of deterioration due to aging effects on the structural behavior. Moreover, the consideration of SSI and site effects may significantly alter the expected structural performance leading to higher vulnerability values. 相似文献
18.
Evaluation of seismic hazard for the assessment of historical elements at risk: description of input and selection of intensity measures 总被引：1，自引：1，他引：0
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