Institute of Engineering Seismology and Earthquake Engineering EPPO ITSAK

Thessaloníki, Greece

Institute of Engineering Seismology and Earthquake Engineering EPPO ITSAK

Thessaloníki, Greece
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Rovithis E.,Institute of Engineering Seismology and Earthquake Engineering EPPO ITSAK | Kirtas E.,Technological Educational Institute of West Macedonia | Bliziotis D.,Geosystems Hellas | Maltezos E.,Geosystems Hellas | And 5 more authors.
Bulletin of Earthquake Engineering | Year: 2017

We present a methodology for a large-scale assessment of soil-structure interaction (SSI) effects on the vibrational characteristics and the seismic loading of structures in a real urban fabric by combining airborne monitoring techniques, field surveys and simple calculations in the realm of structural and geotechnical dynamics. The proposed procedure combines geometrical features of a building stock acquired from a LiDAR-based 3D city model, material and typology data of structures from in situ inspections in representative building blocks, geotechnical data from field surveys and strong ground motion data from seismic hazard and site effects analyses. The integrated data are employed to compute at a first stage the fundamental period of each building in the urban area by means of code-defined formulas for both fixed- and flexible-base foundation conditions, thus treating soil-structure interaction effects in a simplified manner. The seismic action in terms of spectral acceleration at the fundamental period of structures is then computed, following a series of 1D site-specific analyses of soil response under different seismic scenarios. Spatially distributed ratios of structural fundamental periods and spectral accelerations, corresponding to flexible- over fixed-base foundation conditions, are mapped in GIS environment as an index of SSI effects at large-scale. The methodology is implemented in the urban area of Kalochori located west of Thessaloniki in Greece. The examined case study showed that SSI may be significant even for low-amplitude motions and may lead to higher seismic forces compared to the fixed-base case, depending on the dynamic characteristics of the structures, the soil conditions and the shape of the response spectrum. The above may be of importance in microzonation and seismic vulnerability studies at urban-scale when a building-by-building assessment is not feasible and SSI effects are too important to be ignored. © 2017 Springer Science+Business Media Dordrecht

Rovithis E.N.,Institute of Engineering Seismology and Earthquake Engineering EPPO ITSAK | Pitilakis K.D.,Aristotle University of Thessaloniki
Earthquake and Structures | Year: 2016

The 750 m long "De Bosset" bridge in the Cephalonia Island of Western Greece, being the area with the highest seismicity in Europe, was constructed in 1830 by successive stone arches and stiff blocktype piers. The bridge suffered extensive damages during past earthquakes, such as the strong M7.2 earthquake of 1953, followed by poorly-designed reconstruction schemes with reinforced concrete. In 2005, a multidisciplinary project for the seismic assessment and restoration of the "De Bosset" bridge was undertaken under the auspices of the Greek Ministry of Culture. The proposed retrofitting scheme combining soil improvement, structural strengthening and reconstruction of the deteriorated masonry sections was recently applied on site. Design of the rehabilitation measures and assessment of the pre- and post-interventions seismic response of the bridge were based on detailed in-situ and laboratory tests, providing foundation soil and structural material properties. In-situ inspection of the rehabilitated bridge following the strong M6.1 and M6.0 Cephalonia earthquakes of January 26th and February 3rd 2014, respectively, revealed no damages or visible defects. The efficiency of the bridge retrofitting is also proved by a preliminary performance analysis of the bridge under the recorded ground motion induced by the above earthquakes. © 2016 Techno-Press, Ltd.

Morfidis K.,Institute of Engineering Seismology and Earthquake Engineering EPPO ITSAK | Kiousis P.D.,Colorado School of Mines | Xenidis H.,Aristotle University of Thessaloniki
Computers and Concrete | Year: 2014

This paper presents a theoretical and computational approach to solve inelastic structures subjected to overloads. Current practice in structural design is based on elastic analysis followed by limit strength design. Whereas this approach typically results in safe strength design, it does not always guarantee satisfactory performance at the service level because the internal stiffness distribution of the structure changes from the service to the ultimate strength state. A significant variation of relative stiffnesses between the two states may result in unwanted cracking at the service level with expensive repairs, while, under certain circumstances, early failure may occur due to unexpected internal moment reversals. To address these concerns, a new inelastic model is presented here that is based on the nonlinear material response and the interaction relation between axial forces and bending moments of a beam-column element. The model is simple, reasonably accurate, and computationally efficient. It is easy to implement in standard structural analysis codes, and avoids the complexities of expensive alternative analyses based on 2D and 3D finite- element computations using solid elements. Copyright © 2014 Techno-Press, Ltd.

Xenidis H.,Aristotle University of Thessaloniki | Morfidis K.,Institute of Engineering Seismology and Earthquake Engineering EPPO ITSAK | Papadopoulos P.G.,Aristotle University of Thessaloniki
Structural Engineering and Mechanics | Year: 2015

In the present paper a three-dimensional non-linear truss element and a short computer program for the modeling and predicting approximate lateral deflections in thin glass plates by the method of incremental loading are proposed. Due to the out-of-plane large deflections of thin glass plates compared to the plate thickness within each loading increment, the equilibrium and stiffness conditions are written with respect to the deformed structure. An application is presented on a thin fully tempered monolithic rectangular glass plate, laterally supported around its perimeter subjected to uniform wind pressure. The results of the analysis are compared with published experimental results and found to have satisfactory approximation. It is also observed that the large deflections of a glass plate lead to a part substitution of the bending plate behavior by a tensioned membrane behavior which is favorable. Copyright © 2015 Techno-Press, Ltd.

Cultrera G.,Italian National Institute of Geophysics and Volcanology | de Rubeis V.,Italian National Institute of Geophysics and Volcanology | Theodoulidis N.,Institute of Engineering Seismology and Earthquake Engineering EPPO ITSAK | Cadet H.,Sage | Bard P.-Y.,French National Center for Scientific Research
Bulletin of Earthquake Engineering | Year: 2014

The Horizontal-to-Vertical Spectral Ratio from earthquake (HVSR) and from ambient noise (HVN) recordings realistically indicate the fundamental frequency of soil response but, for the majority of the worldwide examined sites, they do not provide reliable amplification curves as calculated by the earthquake standard Spectral Ratio (SSR). Given the fact that HVSR and especially HVN can be easily obtained, it is challenging to search for a meaningful correlation with SSR amplification functions for the entire frequency band and to use the results for the SSR estimate at a further site where only noise measurements are available. To this aim we used recordings from 75 sites worldwide and we applied a multivariate statistical approach (canonical correlation analysis) to investigate and quantify any correlation among spectral ratios. The canonical correlation between SSR and HVN is then used to estimate the expected SSR at each site by a weighted average of the SSR values measured at the other sites; the weights are properly set to account more for sites with similar behaviour in terms of the canonical correlation results between HVN and SSR. This procedure, repeated for all sites in turn, constitutes the basis of a cross validation. The comparison between the inferred and the original SSR highlights the improvements of site response estimation with respect to the use of ambient noise techniques. The goodness and limitations of the reconstruction procedure are explained by specific geological settings. © 2014 Springer Science+Business Media Dordrecht.

Makra K.,Institute of Engineering Seismology and Earthquake Engineering EPPO ITSAK | Chavez-Garcia F.J.,National Autonomous University of Mexico
Bulletin of Earthquake Engineering | Year: 2016

Site effects are one of the most predictable factors of destructive earthquake ground motion but results depend on the type of model chosen. We compare simulations of ground motion for a 3D model of the Mygdonian basin in northern Greece (Euroseistest) using different approximation for this basin. Site effects predicted using simple 1D models at many points inside the basin are compared to site effects predicted using four different 2D cross sections across the basin and with results for a full 3D simulation. Surface topography was neglected but anelastic attenuation was included in the simulations. We show that lateral heterogeneity may increase ground motion amplification by 100 %. Larger amplification is distributed in a wide frequency range, and amplification may occur at frequencies different from the expected resonant frequencies for the soil column. In contrast, on a different cross section, smaller conversion of incident energy into surface waves and larger dispersion leads to similar amplitudes of ground motion for 2D and 1D models. In general, results from 2D simulations are similar to those from a complete 3D model. 2D models may overestimate local surface wave amplitudes, especially when the boundaries of the basin are oblique to the selected cross section. However, the differences between 2D and 3D site effects are small, especially in regard of the difficulties and uncertainties associated to building a reliable 3D model for a large basin. © 2016 Springer Science+Business Media Dordrecht

Rovithis E.,Institute of Engineering Seismology and Earthquake Engineering EPPO ITSAK | Di Laora R.,Parthenope University of Naples | De Sanctis L.,Parthenope University of Naples
Geotechnical Engineering for Infrastructure and Development - Proceedings of the XVI European Conference on Soil Mechanics and Geotechnical Engineering, ECSMGE 2015 | Year: 2015

The effect of soil inhomogeneity on kinematic response of single flexural elastic piles to vertically-propagating seismic SH waves is explored. The system under consideration consists of a fixed-head long pile embedded in a viscoelastic soil layer underlain by a rigid bedrock; soil stiffness is assumed to increase linearly or constant. Both harmonic and real earthquake motions are employed to investigate soil-pile kinematic interaction in frequency and time domain. Pile response in inhomogcncous soil is analysed in terms of kinematic interaction coefficients relating pile-head to free-field soil lateral motion and compared to its homogeneous counterpart. The problem is tackled numerically by means of both rigorous elastodynamic Finite-Element analyses and Beam-on-Dynamic-Winkler-Foundation (BDWF) formulations. The role of model parameters such as pile diameter, rate at which soil stiffness increases with depth and average shear wave velocity VSi30 referring to soil type C or D according to ECS is elucidated. Results indicate that: (a) the horizontal displacement of fixed-head piles under harmonic excitation is essentially governed by a single dimensionless frequency parameter based on an average Winkler wavenumber incorporating pile-to-soil stiffness ratio, pile slenderness and soil inhomogeneity and (b) piles-induced filtering effect tends to increase by increasing the degree of soil inhomogeneity and pile diameter, revealing a substantially reduced seismic demand on the superstructure compared to that pertaining to die free-field motion. The above filtering action although neglected in seismic codes may of importance in pile design practice. © The authors and ICE Publishing: All rights reserved, 2015.

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