Climate-aware risk and resilience assessment of urban areas under multiple environmental stressors via-tiered digital city twinning
TwinCity aims to leverage existing tools and services (e.g., climate models, modelling of extreme events and their impacts, EU services, etc.), and develop novel technologies (Layered-Block Models, City Digital Twins) to deliver an integrated socioeconomic resilience assessment platform, addressing multi-hazard risk understanding, better preparedness, faster, adapted and efficient response, and sustainable reconstruction of urban areas. Taking advantage of the unique opportunity offered by the COVID-19 quarantine to calibrate for the effect of business shutdown and recovery, TwinCity offers a robust digital twin of an urban area that accounts for local socioeconomic and business ecosystems to run end-to-end simulations of multiple “what-if” disruption scenarios. The final goal is to offer an open-source basis upon which performance, risk and resilience can be assessed by stake-holders, to be tested with a large-scale pilot study of an island Greek town subject to earthquake and weather/climate hazards.
Project Funding
Hellenic Foundation for Research & Innovation
2nd Call for H.F.R.I. Research Projects to support Faculty Members and Researchers
N. 02515
Collaborators
National Technical University of Athens
Finnish Meteorological Institute
Resilience Guard GmbH
RED, Risk Engineering + Development SpA
Time Period
Feb 2022 – July 2025
Relevant Publications
Spillatura A., Vamvatsikos D., Kohrangi M., Bazzurro P. (2024). Harmonizing Seismic Performance Via Risk Targeted Spectra: State Of The Art, Dependencies, And Implementation Proposals. Proceedings of the 18th World Conference on Earthquake Engineering, Milan, Italy.
Abstract | Structures are typically designed on the basis of ground motion spectral values associated to an “ultimate” limit state of reference, e.g., 10% in 50 years, which gives a measure of the hazard at the site of interest. However, this design approach does not guarantee that the risk will be uniform, even for buildings at sites that share the same design level, as measured, e.g., by the peak ground acceleration, mainly because of differences in hazard curve shape. Aiming to ensure a uniform collapse risk across different sites and buildings, Risk Targeted design maps were first introduced by ASCE7-10 to modify conventional design spectra by employing suitable adjustment factors. As there is more than one approach to define such factors, our objective is to test their effectiveness in matching a specific target risk or, at least, in harmonizing the risk of multiple buildings at different sites with respect to different limit states. To do so, we make use of simplified single-degree-of-freedom structures for several configurations of vibration period and ductility. Although risk matching is shown to be only theoretically possible and unachievable in practice, we claim that harmonization remains a viable and valuable target.
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Karaferis N., Melissianos V.E., Vamvatsikos D. (2024). Seismic Fragility Assessment Of Spherical Pressure Vessels: The Effect Of Fill Ratio Variability. Proceedings of the 18th World Conference on Earthquake Engineering, Milan, Italy.
Abstract | Fragility curves are a seismic risk modeler’s bread and butter, relaying the probability of reaching or exceeding each limit state of interest given the ground motion intensity. Yet, as they convey essential information, they also hide assumptions, especially when used to characterize a group of similar or even seemingly identical structures. Chief among them is the concept that the dynamic properties of such structures are invariable and uncorrelated. However, the latter does not necessarily apply to groups of adjacent “identical” spherical pressure vessels, used for storing gaseous products in industrial facilities. The quantity of product contained within a vessel directly affects its dynamic response. Using an ensemble of four “identical” pressure vessels as a case study, a comprehensive set of fragility curves is developed, each corresponding to a different fill ratio of a single vessel. Then, different approaches are explored to combine said fragilities and assess the group of four. These include full-scale Monte Carlo simulation with or without filling level correlation, as well as the computation of a single “law-of-total-variance” fragility curve. The latter approach is decidedly simpler, yet its use cannot be justified without some knowledge of the facility’s operational profile in terms of day-today fluctuation of the filling level, as it can otherwise lead to unconservative and/or biased results.
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Karaferi E., Kohrangi M., Spillatura A., Tsarpalis D., Vamvatsikos D. (2024). Seismic Risk, Direct, And Indirect Losses For The Historic City Of Rhodes. Proceedings of the 18th World Conference on Earthquake Engineering, Milan, Italy.
Abstract | A risk assessment model is developed for the historic city of Rhodes, Greece, with a focus on the buildings, residential and commercial, that are at risk from earthquakes, the main hazard that the city faces. The structural integrity of the buildings of Rhodes is tested under a stochastic event set of spatially correlated ground motion fields. They are generated with the OpenQuake platform via an event-based probabilistic seismic hazard analysis for 10,000 years using the 2020 European Seismic Hazard Model. All commercial or mixed-use buildings are assigned to corresponding lines of business according to census data and expert opinion, while using data from the 2020 European Seismic Risk Model to determine vulnerability functions, and from HAZUS-MH to assess the related downtime. The assessment takes as input the exposure model, the hazard, and the vulnerability of the assets to return the direct and the indirect losses per line of business. This allows the determination of the direct consequences to the city, translated to the economic losses to rebuild or renovate the damaged buildings. Stemming from the direct losses and especially the downtime, a mesoeconomic model is employed to determine the losses caused by business interruption on an event-by-event basis. By thus providing a comprehensive assessment of the risk faced by the city, the model can be used to develop a socioeconomic impact model and support the development of financial mitigation tools.
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Karaferis N.D., Melissianos V.E., Vamvatsikos D. (2024). Mechanical modeling, seismic fragility, and correlation issues for groups of spherical pressure vessels, Acta Mech, 235:1563-1582.
Abstract | A roadmap is outlined for determining comprehensive seismic fragility curves for (single or groups of) spherical pressure vessel structures commonly found in oil refineries. The developed modeling techniques aim to strike a balance between accuracy and computational efficiency, with a focus on capturing the most pertinent failure modes relevant to these structural types. First, a set of “partial” fragilities is determined based on each vessel’s fill ratio, as the response varies substantially depending on the amount of liquid content. Considering that a seismic assessment process invariably involves simultaneous consideration of such partial fragilities, a Monte Carlo-based approach is employed for their combination. The results naturally depend on the level of correlation employed, but can be almost perfectly matched by simpler analytical methods in the edge cases of full and zero correlation.
Melissianos V.E., Vamvatsikos D., Danciu L., Basili R. (2024). Design Fault Displacement for Lifelines at Fault Crossings: The Code-Based Approach for Europe. Bulletin of Earthquake Engineering, 22: 2677-2720.
Abstract | The earthquake-resistant design of lifelines, such as pipelines, tunnels and bridges, is based on the reliable representation and estimation of the seismic loading. In the case of lifeline–fault crossings, the design fault displacement is typically derived from estimates based on fault dimensions via empirical fault scaling relations for a given “design” scenario event. This approach comes with an unknown level of safety because the fault productivity and the actual distribution of earthquake events are essentially disregarded. To overcome this challenge, a simplified approach is proposed by statistically analyzing the outcome of probabilistic fault displacement hazard analyses (PFDHAs). A selection of faults from the 2020 European Fault-Source Model is used to build the logic tree and to set the range of parameters considered in the PFDHAs. The methodology allows the (mostly conservative) approximation of the fault displacement corresponding to any given return period based on readily available data, namely fault productivity, fault mechanism, fault length, and lifeline crossing location on the fault. The proposed methodology has been proposed and adopted as an informative Annex in prEN 1998-4:2022.
Vamvatsikos D. (2023). Industrial structure design at the edge of the code: A true story of three little pigs. Proceedings of the 10th Hellenic National Conference on Steel Structures, Athens, Greece. (in greek)
Abstract |Three little pigs designed three low-ductility industrial buildings for agricultural usage. Two collapsed under a known extreme hazard. Fortunately, there was no loss of life, but two structures and two livelihoods were destroyed. Was the subpar straw and wood material to blame? Were the designers to be held accountable? History seems to have concluded thus. On the contrary, our recent investigations conclusively show that it was only a case of honest and well-meaning engineers, who were betrayed by an honest and well-meaning design code. They were misled to place their trust on a thought-up q-factor of 1.5 to 2.0 for industrial structure design. This factor was introduced into the code without proper verification, and it could not provide an adequate safety margin for collapse of low-ductility systems under extreme loads. Two, admittedly swine, engineers were framed by the powers that be. Follow us on the journey to uncover one of the greatest misdeeds of history that is still being taught to our children.
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Melissianos V.E., Kazantzi A.K., Karaferis N., Bakalis K., Vamvatsikos D. (2023). Reduced-order models of steel structures for the seismic risk assessment of oil refineries. Proceedings of the 10th Hellenic National Conference on Steel Structures, Athens, Greece.
Abstract | Ensuring the structural and operational integrity of oil refineries in case of an earthquake event is of utmost importance for the society, the environment, and the economy. A potential failure in such critical facilities may trigger a number of undesirable situations, such as fire, injuries, environmental pollution, etc. Hence, improving safety plan and increasing seismic resilience is a necessity that requires the development of reliable models and seismic risk assessment tools. Towards this direction, this paper presents a seismic fragility study of two characteristic steel high-rise stacks encountered in oil refineries, namely a relatively low-rise chimney and a process tower. The developed of reduced-order numerical models, the selection of appropriate engineering demand parameters to capture the seismic response of the structures, the calculation of the fragility curves, and finally the evaluation of the overall seismic response are presented. The results could be exploited in the context of a seismic risk assessment study of an oil refinery, as an integrated system.
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Karaferis N., Vamvatsikos D. (2023). Fragility curve disaggregation examples for localized measures of response. Proceedings of the SECED 2023 Conference, Cambridge, UK.
Abstract | In seismic risk assessment, one is often in need of employing fragility curves that are readily available in literature, rather than developing one’s own. Unfortunately, such fragilities are essentially summaries of the detailed intensity measure (IM) versus engineering demand parameter (EDP) information. When, as usual, the original data is not available, finding a way to disaggregate the fragilities back into the individual IM-EDP record responses can be useful. For example, it would allow converting them to arbitrary IMs. The authors have previously presented an idea of using equivalent single-degree-of-freedom (ESDOF) models to achieve this, showing acceptable results for global EDPs, such as roof drift. These global response parameters are typically governed by the fundamental eigenmode of the structure, and are thus easier to capture by the proposed ESDOF models. To further build upon this concept, different multiple-degree of freedom (MDOF) structure examples are examined, validating the results of fragility disaggregation and IM conversion for limit-states based on more localized measures of response, such as interstorey drifts or peak floor accelerations. The accuracy of the method is therefore further challenged, going after local EDPs via a proxy that discards the effect of higher modes. The target is to specify the limits of the proposed methodology and quantify the potential error
introduced by the method’s assumptions, evaluating its usefulness for such cases.
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Karaferi E., Vamvatsikos D., Kohrangi M., Spillatura A. (2023). Exposure, Vulnerabilities, and scenario seismic risk assessment for the city of Granada. Proceedings of the SECED 2023 Conference, Cambridge, UK.
Abstract | A model is developed for the seismic risk assessment of the city of Granada, Spain, focusing on the building stock. For its implementation, in-house software is coded in the objectoriented programming language Python. Firstly, the assets of interest, in this case the different buildings, are identified and classified according to the taxonomy of the 2020 European Seismic Risk Model, appropriately customized for the characteristics of the local stock. The exposure
model is created using the geographical position of each building and aggregating them per city block. Seismic hazard is determined via the 2020 European Seismic Hazard Model. An eventbased probabilistic seismic hazard approach is employed, generating a stochastic event set for a 10,000 year investigation period, together with corresponding spatially-correlated ground motion fields via the OpenQuake platform. For simplicity, a single intensity measure is employed to characterize all buildings. Suitable vulnerability functions are selected to calculate loss. Results are obtained per block for the damage of buildings in terms of assigning them to different damage states as well as defining the cost of replacement. The resulting consequences are grouped across different functions and lines of business. The focus is on offering a preliminary determination of the disruption caused by each event in support of socioeconomic impact
modelling within the HYPERION EU project.
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Melissianos V.E., Danciu L., Vamvatsikos D., Basili R. (2023). Fault displacement hazard estimation at lifeline–fault crossings: A simplified approach for engineering applications. Bulletin of Earthquake Engineering, 21: 4821–4849
Abstract | Lifelines, such as pipelines, roads, and tunnels, are critical infrastructure and when crossing active tectonic faults, a reliable estimation of the fault displacement in case of an earthquake is required. The first and simplest approach is to use empirical fault scaling relations to compute the design fault displacement, but this may result in an unknown level of safety. Thus, the probabilistic fault displacement hazard analysis (PFDHA) is the appropriate tool to assess the fault displacement hazard within a performance-based framework. Based upon an established PFDHA model, we present a simplified approach for engineering applications focusing on the lifeline–fault crossing along with appropriate simplifications and assumptions to extend its applicability to numerous faults. The aim is to provide a structure-independent approach of PFDHA that can be used when a site-specific study is not required, not possible (e.g., absence of recent sediments for dating past events), or too cumbersome, e.g., for lifeline route selection. Additionally, an in-depth investigation is presented on the key parameters, such as maximum earthquake magnitude, fault length, recurrence rate of all earthquakes above a minimum magnitude, and lifeline-fault crossing site, and how they affect the hazard level. This approach will be the basis for deriving hazard-consistent expressions to approximate fault displacement for use within the Eurocodes. The latter is intended to serve as a compromise between hazard-agnostic fault scaling relations and a comprehensive PFDHA, which requires detailed calculations and site-specific seismological data.
Lachanas C.G., Vamvatsikos D., Dimitrakopoulos E.G. (2023). Intensity measures as interfacing variables versus response proxies: The case of rigid rocking blocks. Earthquake Engineering and Structural Dynamics, 52(6):1722-1739.
Abstract |A comparative study of alternative Intensity Measures (IMs) for structures of rocking response is presented, focusing on the salient characteristics that define the selection of an optimal IM for the problem at hand. An IM may play the role of an interfacing variable, linking hazard with fragility/vulnerability for the risk assessment of structures, or it may only be employed as a proxy for predicting structural response under a given ground motion. In the first case, low conditional variability (high efficiency) and low conditional dependence on seismological parameters (high sufficiency) are needed. For response proxy usage, one may place more importance on the predictive capability of the IM within a simple regression model, favoring high correlation and low fitting errors over an extended range of response. The results showcased that (i) the peak ground acceleration and peak ground velocity, tend to be highly efficient and sufficient in specific regions of rocking response, that is, onset of rocking and overturning, respectively, but not necessarily everywhere; (ii) the average spectral acceleration shows a more consistent performance at the cost of requiring the definition of a proper period range; (iii) magnitude sufficiency is generally more difficult to achieve, compared to the distance from the rupture, and (iv) IMs that may be unsuitable for risk and vulnerability assessment, can still be highly effective as response predictors in statistical models.
Melissianos V.E., Vamvatsikos D., Danciu L., Basili R. (2022). Code-Based Approach for Estimating the Seismic Fault Displacement for Earthquake-Resistance Design of Buried Pipelines. Proceedings of the 5th Panhellenic Conference on Earthquake Engineering and Engineering Seismology, Athens, Greece (in greek).
Abstract | Buried steel fuel pipelines are vulnerable to ground deformations caused by the activation of the crossing seismic fault. In such case, pipelines develop excessive deformations and strains as they follow the ground movement. Ensuring the structural and operational integrity of pipelines, which are critical energy infrastructure, is of utmost importance. In contrast to a typical deterministic design approach, where the seismicity is not taken into account, the performance-based approach can provide the required balance between safety and economy. Towards this path, an approximate methodology for calculating the fault displacement for a given return period was developed. This displacement is suitable for the design of pipelines crossing active seismic faults. using the database of faults in Europe, a lot of probabilistic fault displacement hazard analyses were executed. The statistical processing of these results led to the development of a set of simplified analytical relations that allow the calculation of the design fault displacement based only on data that are available to the engineer, without the requirement of specialized geological and seismological studies. The proposed methodology gas been adopted as an informative annex in the new version of EN1998-4.
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Lachanas C.G., Vamvatsikos D., Vassileiou M.F. (2022). The influence of the vertical component of the seismic excitation on the probabilistic treatment of the seismic response of rocking rigid bodies. Proceedings of the 5th Panhellenic Conference on Earthquake Engineering and Engineering Seismology, Athens, Greece (in greek).
Abstract |
Vamvatsikos D., Lachanas C.G. (2022). Probabilistic distribution of ground motion via observations of rocking rigid bodies. Proceedings of the 5th Panhellenic Conference on Earthquake Engineering and Engineering Seismology, Athens, Greece (in greek).
Abstract |
Lachanas C.G., Vamvatsikos D. (2022). Preliminary seismic risk assessment of ancient columns across Attica for application in decision support systems. Proceedings of the 3rd European Conference on Earthquake Engineering and Seismology (3ECEES), Bucharest, Romania.
Abstract | An approach for preliminary seismic risk assessment is presented for portfolios of cultural heritage assets of classical antiquity. As an example, three ancient columns are considered, located at different sites throughout Attica: The Temple of Aphaia in Aegina, the Temple of Olympian Zeus in the centre of Athens, and the Temple of Poseidon in Sounio. Event-based probabilistic seismic hazard analysis is used for the definition of the seismic hazard via multiple correlated intensity measure fields. The seismic response of the columns is assessed via simplified equations for the prediction of the central value and the dispersion of the lognormal fragility function for rocking blocks. Afterwards, the seismic risk per asset is assessed both in terms of long-term averages, calculating the mean annual frequency of exceeding pre-defined limit states, as well as on an event-by-event basis, calculating the probability of exceeding limit states of interest per asset in scenario events. Overall, a comprehensive tool is offered for supporting decision-making on prioritizing rehabilitation actions for a portfolio of monumental structures.
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Melissianos V.E., Karaferis N.D., Kazantzi A.K., Bakalis K., Vamvatsikos D. (2022). An integrated model for the seismic risk assessment of an oil refinery. Proceedings of the 3rd International Conference on Natural Hazards & Infrastructure ICONHIC 2022, Athens, Greece.
Abstract | Oil refineries play a key role in the energy supply chain. Safeguarding the integrity of such high-importance facilities against natural hazards is crucial because a potential failure may result in a sequence of unwanted events, spanning from business disruption to uncontrolled leakage and/or major accidents. Despite the strict criteria enforced during the design, construction, maintenance, and operation of an oil refinery, Natural-Technological events caused by earthquakes still occur.
Oil refining is a complex process that involves a variety of structural typologies, such as buildings, tanks, chimneys, pipe-racks, pressure vessels, and process towers. These structures have fundamentally different dynamic properties and seismic responses. A comprehensive seismic risk assessment framework is thus required to account for the refinery as an integrated system and provide information about both the structural and operational integrity of the individual assets and the system. In the present study, a virtual crude oil refinery is examined as a case study to demonstrate the steps of a preliminary seismic risk assessment framework, consisting of the seismic hazard calculation, the development of the exposure model, the analysis of the structures at risk, and the damage assessment of the facility. Scenario-based results are presented for the refinery and the critical assets are identified.
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