On the dynamic response of square tunnels in sand

The paper investigates the seismic response of square tunnels in sand by means of dynamic centrifuge testing and numerical analysis. A series of dynamic centrifuge tests, conducted at the University of Cambridge on a square aluminium model tunnel embedded in dry sand, are initially presented. The tests, which were designed to investigate the seismic response of flexible tunnels, are analyzed numerically by means of full dynamic analysis of the coupled soil-tunnel system, using different soil and soil-tunnel interface models. Numerical predictions are compared to the experimental data, so as to better understand the response mechanism and validate the numerical modelling. The validated numerical models are then used to investigate the effect of lining rigidity on the soil-tunnel system dynamic response. The experimental and numerical results reported herein, indicate a non-negligible rocking deformation mode for the tunnels during seismic shaking coupled with racking distortion. The significant effects of the lining rigidity, soil-tunnel interface characteristics and soil yielding on the dynamic earth pressures and the shear stresses developed around the perimeter of the tunnel, as well as on the dynamic lining forces, are also reported and discussed.The research leading to these experimental results has received funding from the European Community’s Seventh Framework Programme [FP7/2007-2013] for access to the Turner Beam Centrifuge, Cambridge, UK, under grant agreement no. 227887 [SERIES: Seismic Engineering Research Infrastructures for European Synergies; www.series.upatras.gr/TUNNELSEIS].This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.engstruct.2016.07.01

Impact on loss/risk assessments of inter-model variability in vulnerability analysis

Fragility curves (FCs) constitute an emerging tool for the seismic risk assessment of all elements at risk. They express the probability of a structure being damaged beyond a specific damage state for a given seismic input motion parameter, incorporating the most important sources of uncertainties, that is, seismic demand, capacity and definition of damage states. Nevertheless, the implementation of FCs in loss/risk assessments introduces other important sources of uncertainty, related to the usually limited knowledge about the elements at risk (e.g., inventory, typology). In this paper, within a Bayesian framework, it is developed a general methodology to combine into a single model (Bayesian combined model, BCM) the information provided by multiple FC models, weighting them according to their credibility/ applicability, and independent past data. This combination enables to efficiently capture inter-model variability (IMV) and to propagate it into risk/loss assessments, allowing the treatment of a large spectrum of vulnerability-related uncertainties, usually neglected. As case study, FCs for shallow tunnels in alluvial deposits, when subjected to transversal seismic loading, are developed with two conventional procedures, based on a quasi-static numerical approach. Noteworthy, loss/risk assessments resulting from such conventional methods show significant unexpected differences. Conventional fragilities are then combined in a Bayesian framework, in which also probability values are treated as random variables, characterized by their probability density functions. The results show that BCM efficiently projects the whole variability of input models into risk/loss estimations. This demonstrates that BCM is a suitable framework to treat IMV in vulnerability assessments, in a straightforward and explicit manner

Systemic seismic vulnerability and risk assessment of urban infrastructure and utility systems

The seismic vulnerability and risk assessment of infrastructure and utility systems are essential to prevent or mitigate sufficiently the negative consequences, implement resilience management strategies, and recover efficiently after a major earthquake. In a complex urban environment, having multiple interacting and interdependent infrastructures becomes even more important. Earthquake hazards not only affect a single asset, but also their impact is much greater because of the inter- and intra-dependences among various infrastructure, utility systems, and lifelines. Therefore, we urgently need efficient tools to quantify and assess the systemic vulnerability and risk of urban infrastructure and utility systems. This is a challenging topic that is nowadays receiving more attention from the research community, the industry domain, and the policymakers. This paper aims to review the available modelling approaches and tools for the seismic risk analysis of interconnected systems, including advantages and limitations. It focuses in particular on the European funded SYNER-G project that encompasses interdependencies, delivers a holistic methodology, and implements a comprehensive framework based on the Object-Oriented Modelling paradigm. The capacities of the SYNER-G framework are illustrated through a selected application regarding the seismic risk analysis of interconnected infrastructure and utility systems in the city of Thessaloniki, Greece. Among other aspects, the paper discusses hazard modelling issues of the two common approaches, the probabilistic and the scenario-based procedure and illustrates in a specific example the impact of mitigation strategies, based on their effect on the performance of the interconnected systems and the overall loss reduction. The integration of interdependencies into the risk analysis and resilience strategies facilitates a better understanding of critical infrastructure operation and enables well-informed proactive and reactive decision-making and efficient disaster risk management, by infrastructure owners and operators, insurance companies, consulting agencies, and local authorities.The present work has been done in the framework of grant agreement No. 813137 funded by the European Commission ITN-Marie Sklodowska-Curie URBASIS-EU project. Also, we would like to acknowledge all the contributors to the SYNER-G project that was funded from the European Community’s 7th Framework Program under grant No. 244061

Calibration of Strain Gauged Square Tunnels for Centrifuge Testing

© 2016, Springer International Publishing Switzerland. A series of dynamic centrifuge tests were conducted on square aluminum model tunnels embedded in dry sand. The tests were carried out at the Schofield Centre of the Cambridge University Engineering Department, aiming to investigate the dynamic response of these types of structures. An extensive instrumentation scheme was employed to record the soil-tunnel system response, which comprised of miniature accelerometers, total earth pressures cells and position sensors. To record the lining forces, the model tunnels were strain gauged. The calibration of the strain gauges, the data from which was crucial to furthering our understanding on the seismic performance of box-type tunnels, was performed combining physical testing and numerical modelling. This technical note summarizes this calibration procedure, highlighting the importance of advanced numerical simulation in the calibration of complex construction models

3d numerical modelling of the seismic response of the thessaloniki urban area the case of the 1978 volvi earthquake

This study aims at showing the numerical modelling of earthquake ground motion in the Thessaloniki urban area, using a 3D spectral element approach. The availability of detailed geotechnical/geophysical data together with the seismological information regarding the relevant fault sources allowed us to construct a large-scale 3D numerical model suitable for generating physics based ground shaking scenarios within the city of Thessaloniki up to maximum frequencies of about 2 Hz. Results of the numerical simulation of the destructive MW6.5 1978 Volvi earthquake are addressed, showing that realistic estimates can be obtained. Shaking maps in terms of ground motion parameters such as PGV are used to discuss the main seismic wave propagation effects at a wide scale

Seismic wave amplification: Basin geometry vs soil layering.

International audienceThe main purpose of the paper is to analyze seismic site effects in alluvial basins and to discuss the influence of the knowledge of the local geology on site amplification simulations. Wave amplification is due to a combined effect of impedance ratio between soil layers and surface wave propagation due to the limited extent of the basin. In this paper, we investigate the influence of the complexity of the soil layering (simplified or detailed layering) on site effects in both time and frequency domain. The analysis is performed by the Boundary Element Method. The European test site of Volvi (Greece) is considered and 2D amplification in the basin is investigated for various soil models. Seismic signals are computed in time domain for synthetic Ricker signals as well as actual measurements. They are analyzed in terms of amplification level as well as time duration lengthening (basin effects) for both SH and SV waves. These results show that the geometry of the basin has a very strong influence on seismic wave amplification in terms of both amplification level and time duration lengthening. The combined influence of geometry/layering of alluvial basins seems to be very important for the analysis of 2D (3D) site effects but a simplified analysis could sometimes be sufficient. In the case of Volvi European test site, this influence leads to (measured and computed) 2D amplification ratios far above 1D estimations from horizontal layering descriptions

THESSALONIKI SEISMIC HAZARD ASSESSMENT: PROBABILISTIC AND DETERMINISTIC APPROACH FOR ROCK SITE CONDITIONS

Within the framework of four research projects (RISK-EU, EUROSEISRISK, SRM_LIFE and LESSLOSS) extensive calculations were carried out assessing the seismic hazard in the Thessaloniki and surrounding area. The main results were derived from probabilistic and deterministic approaches taking into account rock site conditions for each examined site in the Metropolitan area of Thessaloniki. The expected strong-ground motions were calculated applying different methodologies. Two different groups worked for the assessment of the seismic hazard, the first one constituted of the INGV (Istituto Nazionale di Geofisica e Vulcanologia, Italy) and LSMF (Laboratory of Soil Mechanics and Foundation Engineering, Thessaloniki, Greece) and the second one of LSMF and ITSAK (Institute of Engineering Seismology and Earthquake Engineering, Thessaloniki, Greece)