1,721,020 research outputs found
3D physics-based numerical modeling as a tool for seismic risk assessment of urban infrastructural systems: the case of Thessaloniki, Greece
No full textThe aim of this paper is to develop a seismic risk assessment study of urban infrastructural systems relying on state-of-the-art tools for the prediction of earthquake ground motion as well as the assessment of vulnerability. The proposed approach makes use, on one hand, of 3D physics-based numerical simulations of source-to-site wave propagation problems to provide an accurate description of spatial variability of ground shaking and, on
the other hand, of systemic approaches for the evaluation of the vulnerability of complex, interconnected urban systems. The city of Thessaloniki, in Northern Greece, is taken as case study and the physical damage and loss of performance for the main water supply system are estimated based on connectivity based performance indicators. A couple of rupture scenarios with magnitude MW equal to 6.5 and 7.0, breaking two major hazardous
faults around the city are used. The results indicated that 3D simulations can efficiently and accurately account for near-source conditions, geological and site conditions at local scale as well as for spatial and cross-correlation of ground motion. The risk estimates are compared with the ones obtained using a standard approach based on Ground Motion Prediction Equations (GMPEs), accounting for the spatial variability of ground motion.
It was concluded that the GMPEs based approach can be used for a preliminary and faster seismic loss estimation. However, the results shed light on the main advantages of a full 3D numerical modeling for seismic risk assessment in large urban environments and spatially distributed systems. A major advantage is the more accurate estimation of spatial correlation of ground motion, which is location- and earthquake- specific
Capturing geographically-varying uncertainty in earthquake ground motion models or what we think we know may change
Get PDFOur knowledge of earthquake ground motions of engineering significance varies geographically. The prediction of earthquake shaking in parts of the globe with high seismicity and a long history of observations from dense strong-motion networks, such as coastal California, much of Japan and central Italy, should be associated with lower uncertainty than ground-motion models for use in much of the rest of the world, where moderate and large earthquakes occur infrequently and monitoring networks are sparse or only recently installed. This variation in uncertainty, however, is not often captured in the models currently used for seismic hazard assessments, particularly for national or continental-scale studies. In this theme lecture, firstly I review recent proposals for developing ground-motion logic trees and then I develop and test a new approach for application in Europe. The proposed procedure is based on the backbone approach with scale factors that are derived to account for potential differences between regions. Weights are proposed for each of the logic-tree branches to model large epistemic uncertainty in the absence of local data. When local data are available these weights are updated so that the epistemic uncertainty captured by the logic tree reduces. I argue that this approach is more defensible than a logic tree populated by previously published ground-motion models. It should lead to more stable and robust seismic hazard assessments that capture our doubt over future earthquake shaking
Structural health monitoring for seismic protection of structure and infrastructure systems
No full textStructural Health Monitoring (SHM) of civil-engineering structures is becoming more and more popular both in Europe and worldwide mainly because of the opportunities that it offers in the fields of construction management and maintenance. More precisely, SHM offers several advantages in terms of reduction of inspection costs, because of a better understanding of the behavior of both structures and infrastructures under dynamic loads, seismic protection, observation in real or near real-time, of the structural response and of evolution of damage. Therefore, it is possible to produce post-earthquake scenarios and support rescue operations. In this context, this paper provides a review of different technical aspects of SHM summarizing some sensor validation methodologies for SHM. Following that, recent progresses on SHM of buildings subjected to seismic actions and relevant ways to detect damage are recalled. Moreover, some aspects of SHM of tunnels and bridges are covered. Some related applications that use sensor networks designed by the University of Trento and a startup are described, pointing out the solutions adopted to build reliable SHM systems. Finally, concluding remarks and promising research efforts are underlined
Experimental and numerical investigation on the seismic response of rectangular underground structures
No full textLAUREA MAGISTRALELa grande importanza rivestita dalle opere in sotterraneo, nel trasporto e nell'industria,
è altamente in contrasto con la mancanza di una procedura di progettazione antisismica
regolata e dettagliata. Le strutture in sotterraneo, rispetto a quelle superficiali,
hanno mostrato prestazioni migliori in occasione di eventi sismici. Tuttavia, l’alto
rischio associato al loro danneggiamento o collasso incrementa la loro vulnerabilità: il
funzionamento di un’ampia rete potrebbe essere fortemente compromessa e ridotta,
in queste eventualità.
Il comportamento sismico delle strutture in sotterraneo è abbastanza complesso da
capire e da descrivere. Innanzitutto, la natura stessa di queste strutture è unica:
esse presentano un’interazione continua con il terreno circostante, lungo tutta la loro
superficie esterna. Perciò, la progettazione antisismica di strutture in sotterraneo è
molto sensibile a qualunque ipotesi semplificativa, fatta per tenere in considerazione
l’interazione terreno-struttura (SSI). Lo stato di sforzo-deformazione osservabile nel
rivestimento è influenzato da tre fattori cruciali: i comportamenti meccanici (non
lineari) di terreno e struttura, la flessibilità relativa terreno-struttura e le caratteristiche
meccaniche dell’interfaccia. Anche le caratteristiche intrinseche dell’evento
sismico e le particolarità geologiche sito-specifiche influenzano la performance strutturale.
Nella maggior parte dei casi, le opere sotterranee hanno una geometria 3D
non trascurabile (e.g. tunnel di grandi estensioni longitudinali), che aumenta il
grado di complessità dell’analisi.
Il progetto antisismico di opere in sotterraneo viene spesso trascurato, per la mancanza
di regolamenti o linee guida e anche perché, come detto, tali strutture sono
considerate meno vulnerabili nei confronti carichi sismici. Inoltre, è necessario notare
che questi tipi di infrastrutture richiedono estesi sistemi di monitoraggio e il
loro possibile danneggiamento è difficilmente riconoscibile. Ad oggi, è presente una
case-history limitata, mentre permane un gran numero di incertezze e problemi irrisolti.
E’ recentemente iniziata una serie di campagne sperimentali che sfruttano
i grandi progressi fatti nel campo della modellazione in scala, attraverso la centrifuga
geotecnica, anche se i risultati richiedono ancora molta attenzione nell'essere
interpretati.
Questo studio si propone come obiettivo quello di chiarire alcuni aspetti relativi
al comportamento sismico di strutture sotterranee, mettendo a confronto risultati
sperimentali (i.e. quelli provenienti da un test effettuato in centrifuga geotecnica,
all'interno del progetto TUNNELSEIS) con quelli provenienti da analisi numeriche.
In particolare, si è investigato il comportamento di un segmento di tunnel a sezione rettangolare. Per quanto riguarda le simulazioni numeriche, si è fatto uso del metodo
degli elementi finiti, attraverso il software ABAQUS. Le analisi sono state effettuate
alla scala del prototipo, in condizioni plane strain. A differenza del rivestimento, il
cui comportamento meccanico è stato considerato elastico, il comportamento non
lineare del terreno, durante la fase di scuotimento, è stato modellato in maniera
semplificata, facendo uso di un criterio Mohr-Coulomb, accoppiato ad una legge di
flusso plastico non associativa. I parametri del modello sono stati calibrati facendo
uso di curve G-gamma-D fornite da letteratura. L’interazione terreno-struttura è stata
tenuta in debita considerazione e modellata adeguatamente. Nei capitoli successivi
viene presentata un'analisi parametrica, per verificare gli effetti causati da una serie
di fattori sui risultati finali, come le condizioni rottura per la sabbia (i.e. di picco o
critiche), le caratteristiche meccaniche dell'interfaccia, le deformazioni plastiche. Infine,
sono state valutate le forze interne al rivestimento, in accordo con forme chiuse
disponibili, comunemente utilizzare nelle fasi preliminari di progettazione, e confrontate
con i dati sperimentali e con le predizioni numeriche. Le analisi numeriche
riproducono in maniera ragionevole buona la risposta sperimentale. Le discrepanze
tra dati sperimentali e risultati numerici vengono principalmente attribuite alle semplificazioni di cui si è fatto uso nei modelli processati e soprattutto alla
differenza tra proprietà meccaniche reali e presunte del terreno, nonché alla loro
evoluzione durante il procedere dell'esperimento.The great importance of underground facilities in terms of transportation and industrial utility is highly in contrast with the lack of a detailed and ruled seismic design procedure. Compared to above-ground structures, the underground ones have shown better performances in seismic events. Nevertheless, the high risk associated with their damage or collapse increases their vulnerability: the serviceability of wide network may be strongly affected and reduced in those eventualities.
Seismic behaviour of underground structures is quite complex to understand and to describe. First of all, the nature of those structures itself is unique: they present a full interaction with surrounding geo-materials, along their whole external surface. Thus, design of underground structures, in the seismic stage, is highly sensitive to any simplified assumption, made to take into consideration soil-structure interaction (SSI). Stress-strain field observed in the lining is influenced by three crucial features: soil and structural constitutive models (non-linear), soil-structure relative flexibility and interface strength properties. Earthquake characteristics and geological site-specific features also affect structural performance. In most cases, underground facilities have a significant 3D geometry (e.g. tunnels of great longitudinal extension), which increases the degree of complexity of the investigation.
Seismic design of underground structures has been often neglected, for the lack of specific codes or guidelines and also because, as mentioned above, underground structures are considered less vulnerable to earthquake loading. Moreover, it must be noticed that those kind of facilities are very difficult to be monitored and possible damaging is hard to be detected in detail. A poor case-history is available nowadays, while a great number of uncertainties and open problems still remains. Experimental campaigns has recently started, exploiting the great progresses made in scale-modelling, through geotechnical centrifuge facilities, even though their outcomes still require extreme care to be correctly interpreted.
This study is intended to clarify some aspects related to seismic behaviour of underground structures, comparing experimental results (i.e. geotechnical centrifuge test performed within the project TUNNELSEIS) with numerical predictions. In particular, the behaviour of a segment of rectangular lining has been investigated. For the numerical simulation, the finite element method is implemented, using ABAQUS. The analyses have been performed on prototype-scale models under plane strain conditions. While the tunnel behavior is assumed to be elastic, the soil non-linear behavior during shaking is simply modeled using a Mohr-Coulomb failure criterion, coupled with a non-associative plastic flow-rule. The model parameters are adequately calibrated using common G-gamma-D
curves, available in literature. The soil–tunnel interface is also accounted and simulated adequately. A parametric analysis is presented in the ensuing chapters, testing the role of different features on final outcomes, such as sand state conditions (i.e. peak or critical), interface strength properties, plasticity. Finally, the internal forces of the tunnel lining are also evaluated with available closed form solutions, usually used in the preliminary stages of design and compared with the experimental data and the numerical predictions. The numerical analyses can generally reproduce reasonably well the recorded response. Differences between the experimental data and the numerical results are mainly attributed to the simplification of the used model and to differences between the assumed and the actual mechanical properties of the soil and the tunnel during the test
SEISMIC PERFORMANCE OF A SYSTEM OF INTERDEPENDENT LIFELINE AND INFRASTRUCTURE COMPONENTS
No full textThe aim of this research is to develop a generic procedure for the assessment of the serviceability of a system
(single system or system of systems) if one or more interacting components of the system are damaged by an earthquake.
The system serviceability (functionality) is evaluated starting from the expected degree of damage of the single
components (direct physical damage estimated using appropriate fragility functions) and accounting for their functional
interaction (functional system architecture and single or by-directional interactions among components). Through the
evaluation of the components’ non-functionality, the overall serviceability of the system is assessed, possibly in the form
of a “system serviceability curve”, for different levels of seismic input intensity. Aleatory and epistemic uncertainties are
treated using a Bayesian inference. The applicability of the proposed approach is established through an illustrative
example. It is shown that the methodology is quite general and applicable to real systems with diverse degrees of
complexity and knowledge of system and components details.PublishedTokyo Institute of Technology4.1. Metodologie sismologiche per l'ingegneria sismicarestricte
Evaluation of the systemic vulnerability and risk of interconnected systems at urban scale
No full textLes conséquences des tremblements de terre ont un impact sur l'ensemble de l'environnement bâti et ses entités sont de nature systémique.L'interaction et les relations entre les différents composants d'un système et entre les différents systèmes de l'infrastructure critique sont cruciales, ce qui est généralement frappant après un événement extrême tel qu'un tremblement de terre. Afin de hiérarchiser les actions et les interventions post-événement visant à atténuer le risque sismique, l'évaluation des risques liés aux infrastructures au niveau du système doit impérativement être réalisée à l'échelle mondiale et à grande échelle. Par conséquent, l'un des principaux objectifs de ce travail de recherche est de calculer et d'évaluer le risque systémique et la vulnérabilité des systèmes d'infrastructures critiques à l'échelle urbaine. Il a été observé que l'évaluation des risques des infrastructures critiques présente des lacunes majeures au niveau mondial, ce qui limite son exécution à quelques endroits seulement dans certains pays. Cela est dû en partie à la complexité et à la rareté des données, des méthodes et des mesures, ainsi qu'à l'absence d'outils adéquats, ouverts, utilisés à l'échelle mondiale et efficaces pour l'évaluation systémique des risques liés à l'interaction des infrastructures. Pour cela, nous visons à améliorer et à développer le cadre méthodologique avec des métriques pertinentes en tirant parti de la force des études précédentes, et à l'intégrer à une plateforme ouverte contemporaine puissante, à savoir l'outil OpenQuake, qui présente plusieurs avantages pour une utilisation étendue et globale. C'est l'une des principales originalités de la thèse qui a en même temps un impact pratique significatif. La méthode et l'outil développés dans OQ ont été largement évalués et validés par l'analyse des risques sismiques de plusieurs types de réseaux de démonstration et par le banc d'essai des systèmes de transport et de services publics d'une grande ville comme Thessalonique. En plus de l'utilisation globale, cette mise en œuvre peut également contribuer à une analyse plus sensible des différents aspects de l'exposition, du danger et de la fragilité à l'effet de la performance globale du système d'infrastructure qui n'a pas été bien abordée dans les études précédentes. En ce qui concerne le modèle de site local, cette recherche étudie également la précision des conditions du site local dans l'évaluation du risque systémique du système d'infrastructure critique à l'échelle urbaine.En outre, la performance du système d'urgence, tel que le système de soins de santé, est l'un des aspects inévitables de la gestion des risques de catastrophe. La performance du système de santé ne dépend pas seulement de la vulnérabilité des bâtiments hospitaliers ou de la disponibilité du personnel, mais aussi de l'approvisionnement en services publics à partir de systèmes tels que l'approvisionnement en eau et en électricité ou de l'accessibilité des blessés à travers le réseau routier. Cependant, l'identification et la quantification complètes des interdépendances complexes entre les systèmes de soins de santé et les infrastructures critiques présentent une lacune notable. L'incapacité à prendre en compte efficacement les interdépendances externes des infrastructures cruciales constitue un obstacle important à l'évaluation des performances de l'ensemble du système de soins de santé, ainsi qu'à l'étude des vulnérabilités inhérentes aux hôpitaux. À cette fin, en identifiant les différents types d'interdépendances, nous avons développé un cadre méthodologique et de nouvelles mesures pour évaluer la performance systémique du système de soins de santé. En outre, nous avons également démontré l'importance d'intégrer les interdépendances de second ordre, ce qui n'a pas été fait dans les études précédentes. Ceci a été illustré par une application étendue à l'étude de cas du système de soins de santé de Thessalonique à l'échelle urbaine.The aftermath effect of the earthquakes impacts the whole built-up environment, and its entities are systemic in nature. Interaction and interrelationships between the various components within a system and between various systems of the critical infrastructure are crucial, which is generally vivid after an extreme event like earthquake. In order to prioritize actions as well as the post-event interventions to mitigate the seismic risk, infrastructure risk assessment at the system level is vital to be carried out globally and extensively. Therefore, one of the main objectives of the research work is to compute and evaluate the systemic risk and vulnerability of critical infrastructure systems at urban scale. It has been observed that the risk assessment of critical infrastructures possess a major global gaps restricting it to be done only at few places of some countries. This is partially because of the existing complexity and scarcity of the data, methods and metrics and absence of adequate, open, globally used and efficient tool for systemic risk assessment of interacting infrastructures. To this, we aims to upgrade and develop the methodological framework with relevant metrics leveraging the strength of previous studies, and to integrate it to contemporary powerful open platform, namely the OpenQuake tool, which presents several advantages for extensive and global usage. This is one of the main originality of the thesis having at the same time a significant practical impact. The method and the tool, that has been developed in OQ, has been extensively evaluated and validated through the seismic risk analysis of several types of demo networks and the test bed of utility and transportation systems of a large city like Thessaloniki. Addition to the global usage, this implementation can also further aid for more sensitivity analysis of the various aspects of the exposure, hazard, and fragility to effect of overall performance of the infrastructure system which has not been addressed well in previous studies. In terms of local site model, this research also investigates the precision of local site conditions in the systemic risk assessment of critical infrastructure system at urban scale.Furthermore, the performance of the emergency system, such as healthcare system is one of the inevitable aspects of disaster risk management. The performance of healthcare system doesn’t only rely on vulnerability of the hospital buildings or the availability of the staff, but also on the supply of the utilities from the systems like water supply and electric power or the accessibility of the injured through the road network. However, there lies a notable gap in the comprehensive identification and quantification of the complex interdependencies of healthcare systems to the critical infrastructures. The inability to effectively account for external interdependencies from crucial infrastructures presents a substantial obstacle to evaluating the performance of the entire healthcare system, in addition to studying hospitals' inherent vulnerabilities. To this end, identifying the various types of interdependencies, we developed the methodological framework and novel metrics for assessing the systemic performance of the healthcare system. Moreover, we also demonstrated the importance of incorporating the second order interdependencies which has not been carried out in past studies. This has been illustrated by applying extensively to the case study of the healthcare system of Thessaloniki on an urban scale. This contribution provides an operational tool and essential insights into the functional level of the healthcare system on an urban scale ensuring an emergency response system within a resilient systemic perspective. Its applicability can be extended to address a spectrum of other hazards and emergency systems considering interdependencies at urban and regional scales
Seismic Analysis and Fragility Curves of Gravity Waterfront Structures
Get PDFThe aim of the study is to propose adequate fragility curves for waterfront/ retaining structures for ground shaking without the presence of liquefaction, using available data from past earthquakes’ damages in Europe and worldwide and numerical analysis of typical cases. Existing fragility curves and damage states are evaluated and their shortcomings and/or limitations are assessed. Typical waterfront structures, with different geometry, foundation soil conditions and seismic excitations, are studied using appropriate numerical modeling. The corresponding damage levels are estimated with respect to the induced residual displacements and the seismic response of the soil-structure system. Considering aleatory uncertainties of the parameters involved, analytical fragility curves are then constructed for the different types of waterfront structures and foundation conditions. The computed analytical fragility curves are compared with the validated empirical ones, in order to propose fragility functions and corresponding damage levels for gravity waterfront/ retaining structures based on European distinctive features
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