Two aspects of seismic performance of structural systems are examined. The first relates to curre... more Two aspects of seismic performance of structural systems are examined. The first relates to current measures of seismic intensities. It is shown that fragilities corresponding to ground acceleration processes that have the same peak ground acceleration or ordinates of response spectra can differ significantly. The second aspect relates to life-cycle cost. A method is developed for calculating the probability distribution function of structural life-cycle cost rather than just its expectation. The expected life-cycle cost can be used during the design, construction and retrofit/rehabilitation decision making. Expected losses can also be used in insurance application to calculate appropriate premiums to cover cost of damage from probable earthquakes. On the other hand, the probability law of the cost is essential in risk transfer for the catastrophic events, which generally deals with tail of the distribution, i.e., the probability of cost exceeding a critical value. Developments in t...
Catastrophe (CAT) modelling is a field that combines science and engineering to assess natural an... more Catastrophe (CAT) modelling is a field that combines science and engineering to assess natural and man-made catastrophe risk to allow the risk-takers to better understand and manage their risks. CAT modelling has an essential role in the (re)insurance industry, in which probabilistic models are used to quantify the risk of perils, such as earthquakes. The purpose of this paper is to analyse whether the implementation of vibration-control systems can reduce the seismic risk. The CAT modelling framework described in this paper is for a hypothetical settlement, located in a seismic zone. Three main components are essential in CAT modelling: the hazard, the exposure, and the engineering parts, each modelled, in this paper, using simplified approaches. The seismic hazard is described by a probabilistic model for earthquakes characterized by two parameters, the moment magnitude and the epicentral distance. The exposure is represented by a deterministic distribution of buildings idealized ...
Extreme earthquakes may produce significant financial damage and affect a large number of people,... more Extreme earthquakes may produce significant financial damage and affect a large number of people, due to direct and indirect damage to structures and infrastructure. Transportation networks are essential parts of infrastructure, which can cause significant financial loss and downtime for large communities, as a result of extreme seismic events. An accurate risk assessment and high-performance risk reduction methods are essential tools for preparedness and resilience in case of catastrophic events. This study focuses on the assessment and reduction of the seismic risk of cable-structures, such as cable-stayed bridges, which could be indispensable but vulnerable components of critical transportation networks. Cables are slender structures with low inherent damping, exposed to a wide range of day-to-day and extreme excitation. The seismic risk assessment is achieved through estimating seismic fragility for cables, which is a widely-used measure for structural reliability. The seismic r...
The evaluation of the seismic risk relies on the vulnerability of structural systems as functions... more The evaluation of the seismic risk relies on the vulnerability of structural systems as functions of seismic intensity measures, such as the spectral acceleration. For these intensity measures to be sufficient, they need to fully define the response of the structural systems. This is possible only under the assumption that the response of complex structural system can be accurately approximated by the response of linear single-degree of freedom systems. Usually, these extreme events are often characterized by large magnitudes and relatively short epicentral distances. The response of structures subjected to such extreme excitation is highly non-linear, which exhibits a weak dependence between values of the spectral acceleration and the demand parameters. The correlation between ground-motion parameters and the structural demand must be analyzed using metrics of their statistical dependence. It is proposed to use directly parameters of the seismic process itself, such as the moment m...
Abstract This paper has a twofold aim: to assess the performance of tuned-inerter dampers (TIDs) ... more Abstract This paper has a twofold aim: to assess the performance of tuned-inerter dampers (TIDs) to reduce vibrations in cable structures subjected to seismic ground motions; and to extend an existing TID-design method for cables to a practical scenario of multiple cables in a cable-stayed bridge. In this study, TIDs are installed between the cables and the bridge’s deck, the cables being excited at both their ends by the response of the bridge’s deck and pylon to seismic ground motions. The seismic hazard is described in a general manner by rates of earthquakes and synthetic ground-motion time histories with respect to their moment magnitudes and epicentral distances. Two approaches that use an existing deterministic method to design TIDs to reduce vibrations in cables are discussed. The first one, perhaps more effective but impractical, assumes that each cable’s response is reduced by its own independently-designed TID. The second approach, more realistic and practical, proposes the design of one single TID for all cables to reduce their mid-span response in an optimal way. Numerical results are shown for cable models in the Evripos Bridge in Greece, for which a unique TID is designed for all cables in the bridge, subjected to a hypothetical seismic-hazard scenario. It is shown that the TID-controlled cables have generally a better response, that is a lower average maximum absolute mid-span displacement for most of the cables, and lower variability in the response.
Proceedings of the 6th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2015), 2017
Seismic fragility is the main tool used in the performance-based earthquake engineering, and repr... more Seismic fragility is the main tool used in the performance-based earthquake engineering, and represents the probability of a dynamic system to enter a damage state for a given intensity measure (IM). The most commonly-used seismic IMs are the peak ground acceleration (P GA), which is the absolute maximum of the ground acceleration, and the spectral acceleration (SA), which characterizes well the response of simple linear systems, but shows large uncertainties in the characterization of the seismic response of complex non-linear systems. The main assumption that underlies the basis of the selection of P GA or SA as IMs is that they correlate satisfactorily with the demand parameters (D) of realistic structures, i.e., nonlinear, complex dynamic systems. Statistics and tools of random vibrations are employed to quantify the dependence relations between seismic IMs and structural demand parameters, for non-linear systems subjected to seismic ground-motion records.
Abstract A large number of ground-motion time histories is required for a reliable probabilistic ... more Abstract A large number of ground-motion time histories is required for a reliable probabilistic seismic-hazard analysis. However, insufficient ground-motion records has been a major issue in earthquake engineering even in high-seismicity areas. Stochastic and seismological ground-motion models are used to simulate time histories in order to overcome this issue. Many times these models require a large number of records for calibration, are available only for regions with a wealth of data, or fail to characterize well specific sites. The current paper introduces a novel stochastic ground-motion model that allows simulation of realistic non-stationary, non-Gaussian time histories that are statistically consistent with data even at sites with very low numbers of records. This goal is achieved by combining the prior knowledge from a seismological model, calibrated to global data, with the site-specific data within a Bayesian framework. The proposed model uses the specific barrier model as the seismological model and numerical results consistent with records from a nuclear powerplant site in Romania are presented.
Civil and mechanical engineering systems are often subjected to vibrations which could alter thei... more Civil and mechanical engineering systems are often subjected to vibrations which could alter their behaviour or even lead to their damage or failure. Generated either by man-made processes, such as traffic or equipment, or by natural processes, such as seismic or ocean waves, vibrations may be represented by stochastic processes defined over certain ranges of frequencies. Vibration-control systems have been developed to reduce the undesired response of systems subjected to random vibrations. The aim of the current paper is to compare comprehensively the performance of three popular passive vibrationsuppression devices installed in linear single-degree-of-freedom (SDOF) systems subjected to Gaussian and non-Gaussian random vibrations with general frequency content, characterised by a power-spectral density function. The vibration-control systems analysed in this study are the viscous dampers (VD), the tuned-mass dampers (TMD) and the tuned-inerter dampers (TID), and their performance is assessed in terms of reliability metrics, such as the probability of failure and the first passage time. The twofold goal of this study is reached through (1) the development of explicit analytical relations of the controlledsystems' responses to the Gaussian input; and (2) Monte Carlo simulation estimates of the reliability metrics for the systems subjected to the non-Gaussian loads.
Two methods based on stochastic reducedorder models (SROM) are proposed to solve stochastic stabl... more Two methods based on stochastic reducedorder models (SROM) are proposed to solve stochastic stable nonlinear ordinary differential equations. One general method available for the probabilistic characterization of the response of nonlinear systems subjected to random excitation is Monte Carlo (MC), wherein the response of the nonlinear system must be calculated for a large number of samples of the input, which can be very computationally demanding. Random vibration theory is also inadequate for calculating response statistics for both linear systems under non-Gaussian inputs and nonlinear systems subjected to any kind of excitation. The two methods proposed are based on SROM, i.e., stochastic models with a finite number of optimally selected samples. The first method uses a SROM model for the random input. The second method is based on a surrogate model for the response of the nonlinear system defined on a Voronoi tessellation of the input samples. The newly proposed methods are applied for stable nonlinear ordinary differential equations, with deterministic coefficients and stochastic input, that are used in engineering applications: single-degree-of-freedom Duffing and Bouc-Wen systems, and a two-degree-of-freedom nonlinear energy sink system. The numerical results suggest that SROMs are able to estimate statistics of the stochastic responses for these systems efficiently and accurately, results validated by the benchmark MC results.
This paper proposes a novel fully probabilistic framework for the performance-based seismic desig... more This paper proposes a novel fully probabilistic framework for the performance-based seismic design of structures and uses tuned inerter dampers (TID) installed in civil engineering structures subjected to seismic loads to illustrate its applicability. The framework proposed is based on stochastic reduced-order models, which makes it computationally efficient and can be used for the design of TIDs installed in any complex nonlinear structures subjected to general nonstationary, non-Gaussian stochastic processes. In this study, the TID is installed in a multi-degree-of-freedom nonlinear structure that is subjected to synthetic seismic records. Numerical results show that the framework proposed is able to provide rigorous and robust values for the parameters of the TID. The design parameters obtained using the stochastic framework proposed are compared with benchmark deterministic approaches, tested also for a large data set of ground-motion real records. It is shown that the stochastic approach provides insightful designs of the TID that are consistent with the site seismicity and the frequency content of the stochastic excitation.
The seismic fragility of a system is the probability that the system enters a damage state under ... more The seismic fragility of a system is the probability that the system enters a damage state under seismic ground motions with specified characteristics. Plots of the seismic fragilities with respect to scalar ground motion intensity measures are called fragility curves. Recent studies show that fragility curves may not be satisfactory measures for structural seismic performance, since scalar intensity measures cannot comprehensively characterize site seismicity. The limitations of traditional seismic intensity measures, e.g., peak ground acceleration or pseudo-spectral acceleration, are shown and discussed in detail. A bivariate vector with coordinates moment magnitude m and source-to-site distance r is proposed as an alternative seismic intensity measure. Implicitly, fragility surfaces in the (m, r)-space could be used as graphical representations of seismic fragility. Unlike fragility curves, which are functions of scalar intensity measures, fragility surfaces are characterized by two earthquake-hazard parameters, (m, r). The calculation of fragility surfaces may be computationally expensive for complex systems. Thus, as solutions to this issue, a bi-variate log-normal parametric model and an efficient calculation method, based on stochastic-reduced-order models, for fragility surfaces are proposed. Keywords Seismic fragility Á Seismic intensity measures Á Monte Carlo simulations Á Stochastic reduced-order models Á Earthquake risk
This paper discusses several challenges to recording and reporting on loss data under the Sendai ... more This paper discusses several challenges to recording and reporting on loss data under the Sendai Framework. Additional insights to elaborate on discussion build upon commentary and examples raised during a workshop held on developing loss data that was hosted by the United Nations Office of Disaster Risk Reduction (UNISDR), the Integrated Research on Disaster Risk (IRDR) programme, and Public Health England (PHE) from February 1517 2017 at the Royal Society in London, United Kingdom
Catastrophe risk engineering (CRE) is the field of engineering that quantifies the risk of indivi... more Catastrophe risk engineering (CRE) is the field of engineering that quantifies the risk of individual assets exposed to natural catastrophes, such as earthquakes or hurricanes, for the purpose of finding risk management solutions. An accurate estimation of the risk is essential for decision makers, such as risk managers or insurance brokers, who seek to either reduce or transfer the risk of the high-valuable assets in their portfolios. Current practices in CRE use either oversimplifications of the structural systems and/or perform incremental dynamic analyses on limited number of ground motion records for the analyses selected by arbitrary heuristic methods. This paper proposes a novel framework for earthquake CRE. An accurate assessment of the earthquake risk requires a detailed analysis of the structural performance under site-specific seismic loading. Dynamic analyses of structures may be computationally expensive for complex structures, which are often overcome by simplifying assumptions at the expense of accuracy and rigor. The proposed framework uses a set of simulated ground-motion records consistent with the local-site seismicity. An efficient method based on stochastic reduced-order models is then used for running detailed dynamic analyses for the structural system. The methodology proposed is validated for linear and non-linear systems located in a highly-seismic zone. Comparisons between the newly proposed and the traditional CRE frameworks are conducted. c
Bulletin of the Seismological Society of America, Dec 1, 2014
Abstract Seismic site characterization requires large numbers of ground‐motion records, and such ... more Abstract Seismic site characterization requires large numbers of ground‐motion records, and such datasets are rarely available. Seismological models are generally used to enrich the existent sets of earthquake records with artificial ground acceleration time histories. The specific barrier model (SBM) is an earthquake source model that, as an integrating part of a seismological model, produces spectral densities of the ground‐motion process as a function of the moment magnitude m and source‐to‐site distance r . It is calibrated to regional records and, therefore, may only provide partial information on the site seismic characteristics. We propose a statistical update of the seismological model, constructed with the SBM such that it accounts for the site observations. A parametric probabilistic model is sought for the SBM spectral densities, and a Bayesian framework is used to statistically update it to local records. This new, enhanced version of the seismological model is used to simulate any number of ground‐motion samples and perform site‐specific probabilistic seismic‐hazard analyses (PSHAs). A numerical example of the PSHA calculations using the statistically updated seismological model is shown for a site in southern California. Online Material: MATLAB scripts to calculate basis functions, and parameter update.
Bayesian statistics are related to Bayes’ rule after Thomas Bayes, a Presbyterian minister, proba... more Bayesian statistics are related to Bayes’ rule after Thomas Bayes, a Presbyterian minister, probably born in 1701. Thomas Bayes’ fame rests in his paper “An Essay Towards Solving a Problem in the Doctrine of Chances” communicated to the Royal Society in 1763, after his death in 1761, by his friend Richard Price (1723–1791) (Bellhouse 2004). Bayes addresses the following question in his essay: “Given the number of times in which an unknown event has happened and failed: Required the chance that the probability of its happening in a single trial lies somewhere between any two degrees of probability that can be named (Bayes (1763), p. 376)” (Dale 1986; Edwards 1978). The question is answered in its famous Bayes’model table problem (Bellhouse 2004). Gillies (1987) calls this problem “Bayes’ billiard table example.” The problem assumes a unit-square table and two balls O and W. The ball W is thrown across the table once, and its rest point defines level p with respect to one of the sides of the table. The ball O is then thrown n times, and it is said that if ball O stops below level p, the event is a success. If we call the number of successes r, then the probability that ball O will stop between levels a and b is given by ðb
This study presents a calibration of CAT-in-a-Box and intensity-based index trigger mechanisms fo... more This study presents a calibration of CAT-in-a-Box and intensity-based index trigger mechanisms for parametric tsunami catastrophe bonds. Trigger conditions for the former are based on fundamental event characteristics, such as earthquake location and magnitude, whereas those for the latter utilize tsunami wave height measurements at a series of observation stations. These solutions are illustrated for a building portfolio in Iwanuma City in Miyagi Prefecture, Japan, by considering a new seafloor observation network S-net off the Tohoku-Hokkaido coast of Japan. Performances of the two types of parametric solutions are quantitatively evaluated and compared with each other to discuss their advantages and disadvantages.
Two aspects of seismic performance of structural systems are examined. The first relates to curre... more Two aspects of seismic performance of structural systems are examined. The first relates to current measures of seismic intensities. It is shown that fragilities corresponding to ground acceleration processes that have the same peak ground acceleration or ordinates of response spectra can differ significantly. The second aspect relates to life-cycle cost. A method is developed for calculating the probability distribution function of structural life-cycle cost rather than just its expectation. The expected life-cycle cost can be used during the design, construction and retrofit/rehabilitation decision making. Expected losses can also be used in insurance application to calculate appropriate premiums to cover cost of damage from probable earthquakes. On the other hand, the probability law of the cost is essential in risk transfer for the catastrophic events, which generally deals with tail of the distribution, i.e., the probability of cost exceeding a critical value. Developments in t...
Catastrophe (CAT) modelling is a field that combines science and engineering to assess natural an... more Catastrophe (CAT) modelling is a field that combines science and engineering to assess natural and man-made catastrophe risk to allow the risk-takers to better understand and manage their risks. CAT modelling has an essential role in the (re)insurance industry, in which probabilistic models are used to quantify the risk of perils, such as earthquakes. The purpose of this paper is to analyse whether the implementation of vibration-control systems can reduce the seismic risk. The CAT modelling framework described in this paper is for a hypothetical settlement, located in a seismic zone. Three main components are essential in CAT modelling: the hazard, the exposure, and the engineering parts, each modelled, in this paper, using simplified approaches. The seismic hazard is described by a probabilistic model for earthquakes characterized by two parameters, the moment magnitude and the epicentral distance. The exposure is represented by a deterministic distribution of buildings idealized ...
Extreme earthquakes may produce significant financial damage and affect a large number of people,... more Extreme earthquakes may produce significant financial damage and affect a large number of people, due to direct and indirect damage to structures and infrastructure. Transportation networks are essential parts of infrastructure, which can cause significant financial loss and downtime for large communities, as a result of extreme seismic events. An accurate risk assessment and high-performance risk reduction methods are essential tools for preparedness and resilience in case of catastrophic events. This study focuses on the assessment and reduction of the seismic risk of cable-structures, such as cable-stayed bridges, which could be indispensable but vulnerable components of critical transportation networks. Cables are slender structures with low inherent damping, exposed to a wide range of day-to-day and extreme excitation. The seismic risk assessment is achieved through estimating seismic fragility for cables, which is a widely-used measure for structural reliability. The seismic r...
The evaluation of the seismic risk relies on the vulnerability of structural systems as functions... more The evaluation of the seismic risk relies on the vulnerability of structural systems as functions of seismic intensity measures, such as the spectral acceleration. For these intensity measures to be sufficient, they need to fully define the response of the structural systems. This is possible only under the assumption that the response of complex structural system can be accurately approximated by the response of linear single-degree of freedom systems. Usually, these extreme events are often characterized by large magnitudes and relatively short epicentral distances. The response of structures subjected to such extreme excitation is highly non-linear, which exhibits a weak dependence between values of the spectral acceleration and the demand parameters. The correlation between ground-motion parameters and the structural demand must be analyzed using metrics of their statistical dependence. It is proposed to use directly parameters of the seismic process itself, such as the moment m...
Abstract This paper has a twofold aim: to assess the performance of tuned-inerter dampers (TIDs) ... more Abstract This paper has a twofold aim: to assess the performance of tuned-inerter dampers (TIDs) to reduce vibrations in cable structures subjected to seismic ground motions; and to extend an existing TID-design method for cables to a practical scenario of multiple cables in a cable-stayed bridge. In this study, TIDs are installed between the cables and the bridge’s deck, the cables being excited at both their ends by the response of the bridge’s deck and pylon to seismic ground motions. The seismic hazard is described in a general manner by rates of earthquakes and synthetic ground-motion time histories with respect to their moment magnitudes and epicentral distances. Two approaches that use an existing deterministic method to design TIDs to reduce vibrations in cables are discussed. The first one, perhaps more effective but impractical, assumes that each cable’s response is reduced by its own independently-designed TID. The second approach, more realistic and practical, proposes the design of one single TID for all cables to reduce their mid-span response in an optimal way. Numerical results are shown for cable models in the Evripos Bridge in Greece, for which a unique TID is designed for all cables in the bridge, subjected to a hypothetical seismic-hazard scenario. It is shown that the TID-controlled cables have generally a better response, that is a lower average maximum absolute mid-span displacement for most of the cables, and lower variability in the response.
Proceedings of the 6th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2015), 2017
Seismic fragility is the main tool used in the performance-based earthquake engineering, and repr... more Seismic fragility is the main tool used in the performance-based earthquake engineering, and represents the probability of a dynamic system to enter a damage state for a given intensity measure (IM). The most commonly-used seismic IMs are the peak ground acceleration (P GA), which is the absolute maximum of the ground acceleration, and the spectral acceleration (SA), which characterizes well the response of simple linear systems, but shows large uncertainties in the characterization of the seismic response of complex non-linear systems. The main assumption that underlies the basis of the selection of P GA or SA as IMs is that they correlate satisfactorily with the demand parameters (D) of realistic structures, i.e., nonlinear, complex dynamic systems. Statistics and tools of random vibrations are employed to quantify the dependence relations between seismic IMs and structural demand parameters, for non-linear systems subjected to seismic ground-motion records.
Abstract A large number of ground-motion time histories is required for a reliable probabilistic ... more Abstract A large number of ground-motion time histories is required for a reliable probabilistic seismic-hazard analysis. However, insufficient ground-motion records has been a major issue in earthquake engineering even in high-seismicity areas. Stochastic and seismological ground-motion models are used to simulate time histories in order to overcome this issue. Many times these models require a large number of records for calibration, are available only for regions with a wealth of data, or fail to characterize well specific sites. The current paper introduces a novel stochastic ground-motion model that allows simulation of realistic non-stationary, non-Gaussian time histories that are statistically consistent with data even at sites with very low numbers of records. This goal is achieved by combining the prior knowledge from a seismological model, calibrated to global data, with the site-specific data within a Bayesian framework. The proposed model uses the specific barrier model as the seismological model and numerical results consistent with records from a nuclear powerplant site in Romania are presented.
Civil and mechanical engineering systems are often subjected to vibrations which could alter thei... more Civil and mechanical engineering systems are often subjected to vibrations which could alter their behaviour or even lead to their damage or failure. Generated either by man-made processes, such as traffic or equipment, or by natural processes, such as seismic or ocean waves, vibrations may be represented by stochastic processes defined over certain ranges of frequencies. Vibration-control systems have been developed to reduce the undesired response of systems subjected to random vibrations. The aim of the current paper is to compare comprehensively the performance of three popular passive vibrationsuppression devices installed in linear single-degree-of-freedom (SDOF) systems subjected to Gaussian and non-Gaussian random vibrations with general frequency content, characterised by a power-spectral density function. The vibration-control systems analysed in this study are the viscous dampers (VD), the tuned-mass dampers (TMD) and the tuned-inerter dampers (TID), and their performance is assessed in terms of reliability metrics, such as the probability of failure and the first passage time. The twofold goal of this study is reached through (1) the development of explicit analytical relations of the controlledsystems' responses to the Gaussian input; and (2) Monte Carlo simulation estimates of the reliability metrics for the systems subjected to the non-Gaussian loads.
Two methods based on stochastic reducedorder models (SROM) are proposed to solve stochastic stabl... more Two methods based on stochastic reducedorder models (SROM) are proposed to solve stochastic stable nonlinear ordinary differential equations. One general method available for the probabilistic characterization of the response of nonlinear systems subjected to random excitation is Monte Carlo (MC), wherein the response of the nonlinear system must be calculated for a large number of samples of the input, which can be very computationally demanding. Random vibration theory is also inadequate for calculating response statistics for both linear systems under non-Gaussian inputs and nonlinear systems subjected to any kind of excitation. The two methods proposed are based on SROM, i.e., stochastic models with a finite number of optimally selected samples. The first method uses a SROM model for the random input. The second method is based on a surrogate model for the response of the nonlinear system defined on a Voronoi tessellation of the input samples. The newly proposed methods are applied for stable nonlinear ordinary differential equations, with deterministic coefficients and stochastic input, that are used in engineering applications: single-degree-of-freedom Duffing and Bouc-Wen systems, and a two-degree-of-freedom nonlinear energy sink system. The numerical results suggest that SROMs are able to estimate statistics of the stochastic responses for these systems efficiently and accurately, results validated by the benchmark MC results.
This paper proposes a novel fully probabilistic framework for the performance-based seismic desig... more This paper proposes a novel fully probabilistic framework for the performance-based seismic design of structures and uses tuned inerter dampers (TID) installed in civil engineering structures subjected to seismic loads to illustrate its applicability. The framework proposed is based on stochastic reduced-order models, which makes it computationally efficient and can be used for the design of TIDs installed in any complex nonlinear structures subjected to general nonstationary, non-Gaussian stochastic processes. In this study, the TID is installed in a multi-degree-of-freedom nonlinear structure that is subjected to synthetic seismic records. Numerical results show that the framework proposed is able to provide rigorous and robust values for the parameters of the TID. The design parameters obtained using the stochastic framework proposed are compared with benchmark deterministic approaches, tested also for a large data set of ground-motion real records. It is shown that the stochastic approach provides insightful designs of the TID that are consistent with the site seismicity and the frequency content of the stochastic excitation.
The seismic fragility of a system is the probability that the system enters a damage state under ... more The seismic fragility of a system is the probability that the system enters a damage state under seismic ground motions with specified characteristics. Plots of the seismic fragilities with respect to scalar ground motion intensity measures are called fragility curves. Recent studies show that fragility curves may not be satisfactory measures for structural seismic performance, since scalar intensity measures cannot comprehensively characterize site seismicity. The limitations of traditional seismic intensity measures, e.g., peak ground acceleration or pseudo-spectral acceleration, are shown and discussed in detail. A bivariate vector with coordinates moment magnitude m and source-to-site distance r is proposed as an alternative seismic intensity measure. Implicitly, fragility surfaces in the (m, r)-space could be used as graphical representations of seismic fragility. Unlike fragility curves, which are functions of scalar intensity measures, fragility surfaces are characterized by two earthquake-hazard parameters, (m, r). The calculation of fragility surfaces may be computationally expensive for complex systems. Thus, as solutions to this issue, a bi-variate log-normal parametric model and an efficient calculation method, based on stochastic-reduced-order models, for fragility surfaces are proposed. Keywords Seismic fragility Á Seismic intensity measures Á Monte Carlo simulations Á Stochastic reduced-order models Á Earthquake risk
This paper discusses several challenges to recording and reporting on loss data under the Sendai ... more This paper discusses several challenges to recording and reporting on loss data under the Sendai Framework. Additional insights to elaborate on discussion build upon commentary and examples raised during a workshop held on developing loss data that was hosted by the United Nations Office of Disaster Risk Reduction (UNISDR), the Integrated Research on Disaster Risk (IRDR) programme, and Public Health England (PHE) from February 1517 2017 at the Royal Society in London, United Kingdom
Catastrophe risk engineering (CRE) is the field of engineering that quantifies the risk of indivi... more Catastrophe risk engineering (CRE) is the field of engineering that quantifies the risk of individual assets exposed to natural catastrophes, such as earthquakes or hurricanes, for the purpose of finding risk management solutions. An accurate estimation of the risk is essential for decision makers, such as risk managers or insurance brokers, who seek to either reduce or transfer the risk of the high-valuable assets in their portfolios. Current practices in CRE use either oversimplifications of the structural systems and/or perform incremental dynamic analyses on limited number of ground motion records for the analyses selected by arbitrary heuristic methods. This paper proposes a novel framework for earthquake CRE. An accurate assessment of the earthquake risk requires a detailed analysis of the structural performance under site-specific seismic loading. Dynamic analyses of structures may be computationally expensive for complex structures, which are often overcome by simplifying assumptions at the expense of accuracy and rigor. The proposed framework uses a set of simulated ground-motion records consistent with the local-site seismicity. An efficient method based on stochastic reduced-order models is then used for running detailed dynamic analyses for the structural system. The methodology proposed is validated for linear and non-linear systems located in a highly-seismic zone. Comparisons between the newly proposed and the traditional CRE frameworks are conducted. c
Bulletin of the Seismological Society of America, Dec 1, 2014
Abstract Seismic site characterization requires large numbers of ground‐motion records, and such ... more Abstract Seismic site characterization requires large numbers of ground‐motion records, and such datasets are rarely available. Seismological models are generally used to enrich the existent sets of earthquake records with artificial ground acceleration time histories. The specific barrier model (SBM) is an earthquake source model that, as an integrating part of a seismological model, produces spectral densities of the ground‐motion process as a function of the moment magnitude m and source‐to‐site distance r . It is calibrated to regional records and, therefore, may only provide partial information on the site seismic characteristics. We propose a statistical update of the seismological model, constructed with the SBM such that it accounts for the site observations. A parametric probabilistic model is sought for the SBM spectral densities, and a Bayesian framework is used to statistically update it to local records. This new, enhanced version of the seismological model is used to simulate any number of ground‐motion samples and perform site‐specific probabilistic seismic‐hazard analyses (PSHAs). A numerical example of the PSHA calculations using the statistically updated seismological model is shown for a site in southern California. Online Material: MATLAB scripts to calculate basis functions, and parameter update.
Bayesian statistics are related to Bayes’ rule after Thomas Bayes, a Presbyterian minister, proba... more Bayesian statistics are related to Bayes’ rule after Thomas Bayes, a Presbyterian minister, probably born in 1701. Thomas Bayes’ fame rests in his paper “An Essay Towards Solving a Problem in the Doctrine of Chances” communicated to the Royal Society in 1763, after his death in 1761, by his friend Richard Price (1723–1791) (Bellhouse 2004). Bayes addresses the following question in his essay: “Given the number of times in which an unknown event has happened and failed: Required the chance that the probability of its happening in a single trial lies somewhere between any two degrees of probability that can be named (Bayes (1763), p. 376)” (Dale 1986; Edwards 1978). The question is answered in its famous Bayes’model table problem (Bellhouse 2004). Gillies (1987) calls this problem “Bayes’ billiard table example.” The problem assumes a unit-square table and two balls O and W. The ball W is thrown across the table once, and its rest point defines level p with respect to one of the sides of the table. The ball O is then thrown n times, and it is said that if ball O stops below level p, the event is a success. If we call the number of successes r, then the probability that ball O will stop between levels a and b is given by ðb
This study presents a calibration of CAT-in-a-Box and intensity-based index trigger mechanisms fo... more This study presents a calibration of CAT-in-a-Box and intensity-based index trigger mechanisms for parametric tsunami catastrophe bonds. Trigger conditions for the former are based on fundamental event characteristics, such as earthquake location and magnitude, whereas those for the latter utilize tsunami wave height measurements at a series of observation stations. These solutions are illustrated for a building portfolio in Iwanuma City in Miyagi Prefecture, Japan, by considering a new seafloor observation network S-net off the Tohoku-Hokkaido coast of Japan. Performances of the two types of parametric solutions are quantitatively evaluated and compared with each other to discuss their advantages and disadvantages.
Uploads
Papers by Alin Radu