Methods and tools innovations for seismic risk assessment
The proposed project intends to translate research to practice through rigorous and efficient methodologies and tools to assess seismic safety of NPP. It also has the aim to innovate current practice by supporting simulation results with experimental data and experience feedback in the framework of Bayesian approaches and machine learning. The research will develop methods to improve the predictability of (non linear, best-estimate) beyond design analyses (design extension earthquakes). The refined seismic PSA provides meaningful support in the decision making process and could be useful for real time expertise of plant safety in case of temporary unavailability of safety relevant equipment or structures. It is also proposed to develop efficient tools to identify major contributors to risk such that efforts to increase safety and resistance are focused on relevant equipment. The outcome will thus increase the reliability of the analyses and in turn increase confidence in the probabilistic and deterministic safety assessment results. The results of this project will then help nuclear operators in their periodic safety reviews and to respond to the high-level EU-wide safety objectives of the amended EURATOM nuclear safety directive (stress tests). The considered accident scenarios will provide input for updating severe accident management guidelines (SAMG).
Project Funding
European Commission – Nuclear Fission and Radiation Protection Research
Horizon 2020
NFRP-2019-2020-03
Collaborators
Electricite De France
EDF Energy R&D UK Centre Limited
Limited Liability Company Energorisk
Fondazione GEM
Helmholtz Zentrum Potsdam Deutschesgeoforschungszentrum GFZ
GDSIS
Unstitut de Radioprotection et de Surete Nucleaire
Instituro Univeritario di Studi Superiori di Pavia
LGI Consulting
National Technical University of Athens – NTUA
State Enterprise State Scientific and Technical Center for Nuclear and Radiation Safety
Technische Iniversitaet Kaiserslautern
Univerza V Ljubljani
Geo-Research Institute
North Carolina State University
Pacific Earthquake Engineering Research Center
Time Period
Sept 2020 – Aug 2024
Relevant Publications
Melissianos V.E., Karaferis N.D., Bakalis K., Kazantzi A.K., Vamvatsikos D. (2024). Operational status effect on the seismic risk assessment of oil refineries. International Journal of Disaster Risk Reduction, 113: 104842.
Abstract | The operational status of an oil refinery (type and scale of operations that take place at any time instance) largely determines the amount of fuel produced, circulated within the facility, and stored in tanks. This status is affected by seasonality, periods of peak or low demand, as well as periods of routine maintenance. However, it is an aspect that is typically neglected even though it stands out among the factors that determine the seismic performance of several critical industrial assets, such as the storage tanks, as well as the consequences of any potential failure. An open-source refinery testbed is employed herein to demonstrate the effect of the refinery’s operational status on the seismic risk estimates. Alternative realistic operational scenarios are developed following typical industry practices and are arranged over a time period between two refinery major maintenance shutdown events. The most probable damage state is selected for each asset to identify the most vulnerable ones. Based on the type and importance of the impacted assets, the potential consequences are determined at the facility level. Resulting estimates are very different if an earthquake strikes during a regular/high/low-demand period, or a maintenance period. The framework can be utilized to identify the locations within the refinery that may trigger cascading failures and secondary damages, should their assets be damaged by a seismic event. The outcomes can be exploited by stakeholders, risk engineers, and emergency action planners for developing customized and businesslike procedures to enhance the seismic resilience of the facility.
Melissianos V.E., Karaferis N.D., Bakalis K., Kazantzi A.K., Vamvatsikos D. (2024). Hazard, exposure, fragility, and damage state homogenization of a virtual oil refinery testbed for seismic risk assessment. Earthquake Spectra. 2024;0(0).
Abstract | A virtual mid-size oil refinery, located in a high-seismicity region of Greece, is offered as a testbed for developing and testing system-level assessment methods due to direct impact from seismic shaking and without considering geohazards, such as liquefaction and surface faulting. Its characterization is offered in a dedicated repository (https://doi.org/10.5281/zenodo.11419659) and it comprises (a) a comprehensive probabilistic treatment of seismic hazard tied to an open-source seismological model; (b) a hazard-consistent set of ground motion records; (c) a full geolocated exposure model with all pertinent critical assets, namely tanks, pressure vessels, process towers, chimneys, equipment-supporting buildings, and a flare; (d) the corresponding record-wise asset demands and summarized fragilities derived via nonlinear dynamic analyses on reduced-order numerical models. Background information is provided on all refinery assets to delineate their role in the refining process. Furthermore, an explicit homogenization of the damage states is proposed, translating them from the asset level to the refinery system level considering the importance of each asset on the overall operational and structural integrity of the refinery. The results can form the basis of any follow-up study that seeks to characterize the effects of cascading failures (fires, explosions), mitigation measures, seismic sequences, and operational constraints on the functionality, risk, and resilience of refining facilities.
Karaferis N., Gerontati A., Vamvatsikos D. (2024). From PGA To Anything: Fragility Curve Conversions For Nuclear Power Plant Applications. Proceedings of the 18th World Conference on Earthquake Engineering, Milan, Italy.
Abstract | There has been a lot of discussion on intensity measure optimality for conventional structures, touting the advantages of novel metrics of ground motion intensity to improve upon the efficiency and fidelity of seismic assessment. Yet, somehow this revolution of sorts has not transitioned to nuclear power plant assessments, which cling to the time-honored tradition of the peak ground acceleration (PGA). They do so for the simple reasons of stiffness and mass. That would be stiffness in the assets themselves, typically leading to periods of the order of 0.1 to 0.2sec for both the structures and their nested components, but also in the rigidity of regulations in an understandably ultra-cautious industry. Adding the mass (and cost) of engineering effort required to reassess already established fragilities for hundreds of standardized components, it is no wonder that there is too much inertia to allow moving away from PGA. Would it not be great if someone came along and offered a minimal-error approach for converting existing fragility curves from PGA to any intensity measure of choice? Interestingly, the response characteristics of nuclear power plants may actually favor an equivalent one/two-degree-of-freedom-model based procedure that allows disaggregating existing fragilities back into ground-motion-level constituents and reconstructing them anew with the desired intensity measure parameterization. There is little doubt that safeguarding the integrity of nuclear power plants would still require massive computations rather than rely on shortcuts, yet such an approach can give novel intensity measures a fighting chance to prove that they are worth the trouble for nuclear engineering.
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Gerontati A., Karaferis N., Vamvatsikos D., Bazzurro P., Droszcz C. (2024). A Bare-Bones Nuclear Power Plant Case Study To Test Uncertainty Propagation And Correlation Effects. Proceedings of the 18th World Conference on Earthquake Engineering, Milan, Italy.
Abstract | The safety of a nuclear power plant is influenced by both aleatory randomness and epistemic uncertainty, as well as the potential inter-component and intra-component correlations. Aleatory randomness arises from inherent variability in the data, while epistemic uncertainty stems from limitations, or incomplete knowledge in models or data. Component correlation refers to the extent to which the properties of various components within a Nuclear Power Plant (NPP) are interdependent and how they may co-vary within a single component (intra-component correlation) or among similar/identical ones (inter-component). Evaluating their effects to completion is a non-trivial operation that requires a full model of the power plant and its components, as well as the overall fault tree. When the goal is the evaluation of alternative approaches to safety assessment, one need not set the bar so high. In this, we offer a pared-down model, comprising simplified models of the reactor building and of one or more non-structural components, together with a simplified fault tree that leads to loss of core cooling capacity. As an example, three alternative cases of perfect, partial, and no correlation are employed to test common causes of failure. Uncertainty is propagated using a Monte Carlo simulation with either classic or progressive Latin hypercube sampling, using the simplified model as an efficient benchmark for NPP-compatible applications.
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Lachanas C.G., Vamvatsikos D., Causse M., Kotha S.R. (2024). The Effect Of Ground-Motion Characteristics And Intensity Measures On The Sliding Of Rigid Bodies. Proceedings of the 18th World Conference on Earthquake Engineering, Milan, Italy.
Abstract | The sliding response of rigid bodies is investigated under multiple suites of ground-motion records having different inherent characteristics: Ordinary (no-pulse-like, no-long-duration), near field, pulse-like versus spectrally-matched non-pulse-like twins, and long-duration versus spectrally-matched short-duration twins. A basic Coulomb friction model of a rigid block resting freely on a flat surface is used as a testbed, applying incremental dynamic analysis to assess response statistics under the different suites at multiple levels of intensity. Alternative intensity measures are employed, including the peak ground acceleration, the peak ground velocity, and variants of average spectral acceleration—defined as the geometric mean of spectral accelerations over a range of periods. As engineering demand parameters, both the maximum absolute displacement and the absolute residual displacement are employed. The results indicate a non-trivial sensitivity to duration and pulsiveness, and suggest as well that some intensity measures perform considerably better than others in suppressing sensitivity to such peculiar ground-motion characteristics.
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Kazantzi A.K., Karaferis N., Melissianos V., Vamvatsikos D. (2024). Seismic Reliability Of Acceleration-Sensitive Ancillary Elements In The New Generation Of Eurocodes. Proceedings of the 18th World Conference on Earthquake Engineering, Milan, Italy.
Abstract | The seismic performance of nonstructural/ancillary elements plays a decisive role in the seismic resilience of both ordinary buildings and critical industrial and infrastructure facilities, since damages that are likely to be sustained by such components can undermine the functionality and safety of an otherwise structurally intact structure. Owing to the above, the new generation of Eurocodes invests a great deal of effort towards prescribing appropriate provisions for delivering anchoring systems of acceleration-sensitive nonstructural components that can withstand the (often greatly) amplified floor accelerations with respect to the ground ones. In particular, prEN 1998-1-2:2022 offers a very detailed methodology for estimating the acceleration that is eventually imposed at the component level, accounting for several dynamic attributes of the primary system and the nonstructural component, which are yet not always trivial to determine with an appropriate level of confidence. This paper investigates to what extent the reliability of a code-conforming nonstructural component can be affected by the uncertainties associated with the assumptions made during design. The focus is on the relation of the period of the component to the period of the supporting building using a typical industrial building-type structure as a case-study. On account of the findings that revealed a rather significant sensitivity of the final design product to these uncertainties, the study extended its scope towards reviewing two alternative design methodologies that are offered in prEN 1998-4:2022 for the design of ancillary elements. These two latter approaches are shown to be less sensitive to the designer’s input and can offer more robust designs for the anchorage systems of nonstructural components that are close to tuning with the frequencies of the primary structure.
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Gerontati A., Karaferis N., Sipcic N., Vamvatsikos D., Bazzurro P., Droszcz C. (2024). A Minimalistic Computational Testbed For Evaluating Fragility Assessment, Record Selection, And Intensity Measure Optimality For Nuclear Powerplants. Proceedings of the 27th International Conference on Structural Mechanics in Reactor Technology (SMiRT27), Yokohama, Japan.
Abstract | Recent advances in Performance-Based Earthquake Engineering (PBEE) have followed their own revolutionary path over the past two decades. Focusing on the assessment of conventional buildings and infrastructure, several innovative proposals on improving fragility assessment have appeared over the years, focusing on record selection, improved intensity measures, as well as novel uncertainty propagation approaches. Whether these are also useful for nuclear powerplant assessment remains a question. Partially owing to the well-established practice and guidelines, introducing novelty in such procedures faces significant hurdles in terms of modeling, computational power, and complexity. In an effort to overcome said difficulties in the context of the METIS Euratom project, we propose a minimalistic computational testbed comprising simplified models of a building, one or more components, and a bare-bones fault tree
to tie them together and propagate uncertainties. The METIS simplified testbed is realized in open source, using Python and OpenSees to offer a fast assessment platform, whereby one can test any number of ideas in a setting that resembles a real case study. Among them are important questions, such as the influence of aftershocks, or clustered seismicity in general, new uncertainty propagation techniques, the use of hazard consistent record selection approaches in place of selection based on the uniform hazard spectrum, as well as the use of new intensity measures that can potentially reduce the aleatory uncertainty in the estimates of risk. Focusing on the latter, we present an example of application of the testbed and its results.
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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.
Kazantzi A.K., Karaferis N.D., Melissianos V.E., Vamvatsikos D. (2024). Acceleration-sensitive ancillary elements in industrial facilities: alternative seismic design approaches in the new Eurocode. Bulletin of Earthquake Engineering, 22: 109-132.
Abstract | The Eurocode 8—Part 4 approaches, per their December 2022 update, are presented for the design of acceleration-sensitive industrial ancillary components. The seismic performance of such nested and/or supported ancillary elements, namely mechanical and electrical equipment, machinery, vessels, etc. is critical for the safety and operability of an industrial facility in the aftermath of an earthquake. Of primary importance are the structural characteristics of the supporting structure and the supported component, pertaining to resonance, strength, and ductility, and whether these are known (and to what degree) during initial design and/or subsequent modifications and upgrades. Depending on the availability and reliability of information on the overall system, the Eurocode methods comprise (a) a detailed component/structure-specific design accounting for all pertinent component and building characteristics, equivalent to typical building design per Eurocode 8—Part 1–2, (b) a conservative approach where a blanket safety factor is applied when little or no such data is available, and (c) a ductile design founded on the novel concept of inserting a fuse of verified ductility and strength in the load path between the supporting structure and the ancillary element. All three methods are evaluated and compared on the basis of a case-study industrial structure, showing how an engineer can achieve economy without compromising safety under different levels of uncertainty.
Lachanas C.G., Vamvatsikos D., Kazantzi A.K. (2023). Intensity measures for assessing the rocking response of server racks in steel buildings. Proceedings of the 10th Hellenic National Conference on Steel Structures, Athens, Greece. (in greek)
Abstract | Alternative seismic intensity measures (IMs) are examined for the case of non-structural rocking building contents and in particular for the case of server racks standing freely on the higher floors of steel buildings. Observations following recent earthquakes in developed countries have revealed that most of the damages after a seismic event consider non-structural building contents of high value. On the other hand, the selection of a robust
IM is a basic requirement in the context of the performance-based earthquake engineering framework for assessing the seismic risk and the consequential loss/damage of engineering structures or non-structural contents with high fidelity. Hence, a bunch of alternative IMs are tested in terms of efficiency and sufficiency as potential IMs for rocking vulnerability studies. The simple planar rocking block model is employed for running nonlinear dynamic analysis with a set of 34 floor motions that were recorded during past earthquakes on the roof of instrumented steel buildings. Rocking blocks of various shapes and sizes are analyzed that resemble two-dimensional analogues of server racks. After analysis, efficiency and sufficiency of the examined IMs are compared aiming to propose optimal IMs for the case of rocking contents in the different stages of rocking response from rocking uplift to overturning.
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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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Vamvatsikos D., Lachanas C.G. (2023). Stranger things in seismic response and statistical tools to resolve them. Proceedings of the SECED 2023 Conference, Cambridge, UK.
Abstract | Demogorgons, monsters, and mythical creatures do not appear only in Soviet research labs, secretive government facilities or just plain Hawkins, Indiana. They frequently cross-over to earthquake engineering in the form of questions that conform to the paradigm of “Does X matter in seismic response?”. X can be a seismological characteristic, such as duration, vertical component, incident angle, or near-field directivity; it can also be a structural property, such as building period, rocking block size, or plan asymmetry. We, as investigative structural engineers, are vastly more familiar with the latter set of queries and we are clearly better equipped to handle them. We can sometimes even provide definitive answers that most, if not all of us, would agree upon. Instead, questions involving seismological characteristics seem to leave us baffled and stuck in an Upside Down world that resembles structural engineering but is not exactly the same. Wading through its murk, it is good to have some investigative tools and processes that will help us find our way home. In the end, though, we may end up equal parts enlightened and confused, as most questions of whether something of the seismologist world matters for the structural one are nearly-universally answered by uttering “It depends”.
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Melissianos V.E., Karaferis N.D., Kazantzi A.K., Bakalis K., Vamvatsikos D. (2023). Towards seismic resilience of industrial facilities: the case study of an oil refinery. Proceedings of the SECED 2023 Conference, Cambridge, UK.
Abstract | Crude oil refineries are high-importance infrastructure that play a key role in the energy supply chain. Securing the operational and structural integrity of refineries in the aftermath of an earthquake is crucial for avoiding the undesirable consequences of a Natural-Technological (NaTech) incident, such as injuries, environmental pollution, business interruption, and monetary losses. Refineries are designed, constructed, maintained, and operated under a strict framework of standards and regulations. Still, seismic-related NaTech incidents are occurring. Thus, to assess with more confidence and consequently improve, if needed, their seismic resilience, a coherent performance-based framework needs to be utilised, that accounts for the refinery as an integrated system comprising a variety of structural typologies, such as buildings, tanks, and high-rise stacks. These structures have very diverse dynamic properties and hence seismic responses. Towards this objective, a virtual crude oil refinery is examined herein as a case study. The aim is to showcase the steps of a seismic risk assessment framework when applied to such infrastructures, focusing on the evaluation of the seismic hazard, the development of the exposure model, the numerical analysis of the structures, and the preliminary damage assessment of the facility using different earthquake scenarios.
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Kazantzi A., Karaferis N., Melissianos V.E., Vamvatsikos D. (2023). Design of acceleration-sensitive ancillary elements under uncertainties in the new eurocode. Proceedings of the SECED 2023 Conference, Cambridge, UK.
Abstract | The overall seismic safety and operability of industrial building-type structures located in critical infrastructure facilities, largely depend on the seismic performance of their nested and/or supported ancillary elements, namely mechanical and electrical equipment, machinery, vessels, etc. Hence, on account that (a) no or minimal direct structural damages are anticipated in the equipment-supporting structures per se during moderate or even strong earthquake events since such structures are typically overdesigned and (b) the sustained structural damages are mostly due to the inferior seismic performance of the nested ancillary elements that could trigger a series of adverse cascading incidents (e.g., uncontrolled fires, explosions), significant effort has been
invested towards developing a design framework that could deliver safe designs for the latter. Despite the significant advancements in the relevant field, the development of a robust design framework is often undermined by several uncertainties that come into play in the evaluation of the capacity and demand of such nonstructural components. In particular, critical information that is needed for the design of the ancillary elements, such as the dynamic characteristics of the component and the supporting structure, are often abstract and/or require substantial effort for being retrieved with certain confidence. On that basis, the new Eurocode 8, offers three distinct design options that allow for adjustments in the conservatism that is induced in the design of the acceleration-sensitive ancillary elements according to the availability and reliability of information on the overall system. This study investigates, by means of a case study industrial structure, the extent to which the seismic reliability of an otherwise code-compatible component designed to comply with each one of the three alternative Eurocode design routes, is likely to be undermined for small discrepancies of the assumed properties from their actual values.
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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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Lachanas C.G., Vamvatsikos D., Dimitrakopoulos E.G., (2023). Rocking intensity measures: From interface variables to response proxies. Proceedings of the SECED 2023 Conference, Cambridge, UK.
Abstract | In the context of the performance-based earthquake engineering (PBEE) framework an intensity measure (IM) is the interface (or interfacing) variable that links the seismic hazard with the structural fragility/vulnerability for the risk assessment of structures. On the other hand, from the standpoint of structural dynamics, an IM may be used as a proxy for predicting the structural response under a specific ground motion. Hence, depending on the usage per case, different criteria of optimality should be employed. An interface variable needs to be efficient (low conditional dispersion) and sufficient (low dependence on seismological parameters), whereas also its hazard needs to be assessable via available ground motion prediction equations. For the case of a proxy, hazard computability is not necessary, whereas the most important criterion is the capability of the IM to predict the engineering demand parameter (EDP) within a (simple) regression model. Thus, a response proxy needs mainly to offer high correlation and low fitting errors within IM-EDP regression models. Herein, after addressing these two different cases of IM usage, a comparison of alternative IMs for rocking structures is presented, mainly focusing on their use within a PBEE framework for risk assessment. Simple rocking bodies are employed for running incremental dynamic analysis with a set of 105 ordinary (no-pulse-like, no-long-duration) natural ground motions. It is shown that some well-established IMs are both efficient and sufficient for the case of rocking bodies. Still, due to the nature of rocking response, some (e.g., peak ground acceleration) tend to be optimal only in specific regions of response (e.g., rocking initiation). Moreover, dependence on the magnitude of the earthquake is found to be higher than for the distance from the rupture. Finally, IMs that are inefficient and insufficient for risk assessment can be at the same time very effective when used as response proxies.
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Gerontati A., Vamvatsikos D. (2023). The effect of intensity measure selection and epistemic uncertainties on the estimated seismic performance for non-structural components of nuclear powerplants. Proceedings of the SECED 2023 Conference, Cambridge, UK.
Abstract | The seismic performance of a structure/component is influenced by aleatory randomness and epistemic uncertainty, but also by the intensity measure (IM) selected for the assessment. Aleatory randomness results from natural ground motion record variability, while epistemic uncertainty corresponds to modelling assumptions, parameter variability, omissions or simplifications. IM selection, though, depends on the analyst and the data available. Potential
candidate IMs are the peak ground acceleration (a nuclear industry standard), spectral acceleration at a fundamental period of the structure (the relative newcomer), and average spectral acceleration in the range of short periods (the novel option). Their performance in quantifying uncertainty for short-period nuclear powerplants is not given, nor is it necessarily obvious given the sizeable uncertainties involved. To provide a basis for discussion, a singledegree-of-freedom non-structural component in an AP1000 reactor building is used as casestudy. Three alternative uncertainty propagation approaches are employed: (a) Monte Carlo simulation with classic Latin hypercube sampling, (b) Monte Carlo simulation with progressive Latin hypercube sampling and (c) a first-order second-moment method, representing different compromises between speed and accuracy. The resulting fragility curves of the non-structural component are compared in terms of efficiency for assessing its performance, offering evidence in support of optimizing IM selection.
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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.
Gerontati A., Vamvatsikos D. (2022). A comparison of three scalar intensity measures for non-structural component assessment of nuclear powerplants. Proceedings of the 3rd European Conference on Earthquake Engineering and Seismology (3ECEES), Bucharest, Romania.
Abstract | Three candidate intensity measures are compared in terms of efficiency and sufficiency for assessing the non-structural performance of nuclear powerplant components. These are the peak ground acceleration, the spectral acceleration at the fundamental period of the structure, and the average spectral acceleration in the range of short periods. To do so, single-degree-of-freedom non-structural components of different periods and capacities are considered at different locations within an AP 1000 reactor model. Incremental dynamic analysis is performed for a set of 30 records. The spectral floor accelerations of each SDOF component are monitored and capacity exceedances are recorded to assess the lognormal parameters of component fragility curves. The numerical results demonstrate that average spectral acceleration would be the most useful intensity measure in both efficiency and sufficiency, regardless of location, period or capacity, with the obvious exception of the ground surface. Nevertheless, the conventional choice of the peak ground acceleration remains a very close contender, as it leads to results of low dispersion and little bias for such stiff structures and short-period components.
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Karaferis N., Vamvatsikos D. (2022). Intensity measure transformation of fragility curves for 2D buildings using simplified models. Proceedings of the 3rd European Conference on Earthquake Engineering and Seismology (3ECEES), Bucharest, Romania.
Abstract | Seismic fragility curves are an essential tool for any risk assessment endeavour. While there is a wealth of studies that have provided high quality fragilities for many different types of structures, these curves are typically presented in terms of a single intensity measure (IM). To keep using such valuable data, an analyst is either forced to adopt the same (potentially suboptimal) IM, or completely discard them and restart with a new one. Instead, we propose a simple method for transforming a fragility curve to any IM of choice by using an equivalent single-degree-of-freedom model and its incremental dynamic analysis results to disaggregate the fragility to its constituent record-level results. Validation results from two complex 2D building hint that there is promise to this approach, offering nearly-error-free transformations of global-response fragilities at the cost of a few response history analyses of a nonlinear oscillator.
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Goldschmidt K., Sadegh-Azard H., Sevbo O., Richard B., Garcia P., Bazzurro P., Vamvatsikos D. (2022). Innovative approaches for seismic fragility analysis within METIS project. Proceedings of the 26th International Conference on Structural Mechanics in Reactor Technology (SMIRT-26), Berlin, Germany.
Abstract | The building and structure related part of the Euratom funded Project METIS (metis-h2020.eu) is focused on the evaluation of fragility curves, giving failure probabilities for increasing ground motion intensity, intensity measure selection, uncertainty quantification and bayesian updating of fragility curves. While METIS improves the methodologies for the seismic assessment of NPPs, work package 6 (WP) focuses on the structural part of the project delivering the methodologies for specific, detailed fragility curves and applying these to the case study. The work will finalize in guidelines for the application of the developed methodologies. In the following, first work within the fragility analysis part of the project and future topics will be presented.
METIS Members
