Seismic Failure Risk Assessment of Post Electrical Equipment on Supporting Structures

지진취약도 분석을 통하여 교량의 지진 위험도를 평가하였다. 지진취약도 분석에서는 교각 하부의 소성힌지의 거동을 주요 손상인자로 분석하였으며, 또한 한반도 지진재해지도를 근거로 하여 지진발생확률을 산정한 후 이들을 이용하여 교량의 성능단계에 따른 손상발생확률을 분석하였다. 이 연구에서는 교각에 직접 전달되는 지진이 아닌 암반노두에서의 지진의 최대지반가속도에 대하여 지진취약도를 분석하였으며, 비선형 지진해석을 위해서는 층상지반의 영향으로 증폭된 지진하중을 고려하였다. 제안된 방법으로 예제교량의 지진위험도를 분석하였으며, 면진받침이 설치된 교량에 대한 지진 위험도의 저감 효과를 정량적으로 분석하였고, 지진재해지도에서의 조건이 다른 지역에 시공되는 경우의 지진위험도를 분석함으로써 현 시방서의 타당성을 간접적으로 검토하였다. Seismic risk assessment of bridge is presented using fragility curves which represent the probability of damage of a structure virsus the peak ground acceleration. In theseismic fragility analysis, the structural damage is defined using the rotational ductility at the base of the bridge pier, which is obtained through nonlinear dynamic analysis for various input earthquakes. For the assessment of seismic risk of bridge, peak ground accelerations are obatined for various return periods from the seismic hazard map of Korea, which enables to calculate the probability density function of peak ground acceleration. Combining the probability density function of peak ground acceleration and the seismic fragility analysis, seismic risk assessment is performed. In this study, seismic fragility analysis is developed as a function of not the surface motion which the bridge actually suffers, but the rock outcrop motion which the aseismic design code is defined on, so that further analysis for the seismic hazard assessment may become available. Besides, the effects of the friction pot bearings and the friction pendulum bearings on the seismic fragility and risk analysis are examined. Lastly, three regions in Korea are considered and compared in the seismic risk assessment.

Seismic risk in the form of impending disaster has been seen from past records that moderate-to-large earthquakes have caused the loss of life and property in all parts of Nepal. Despite the availability of new data, and methodological improvements, the available seismic hazard map of Nepal is about two decades old. So an updated seismic hazard model at the country level is imperative and logical. The seismic hazard and risk model constitute important tools for framing public policies toward land-use planning, building regulations, insurance, and emergency preparedness. In fact, the reliable estimation of seismic hazard and risk eventually minimizes social and economic disruption caused by earthquakes. In this frame of reference, the seismic risk assessment at a country level is elementary in reducing potential losses stemming from future earthquakes. Thus, this study investigates structural vulnerability, seismic risk, and the resulting possible economic losses owing to future earthquakes in Nepal. To this end, seismic risk assessment in Nepal is done using an existing probabilistic seismic hazard, a newly developed structural vulnerability, and recently released exposure data. The OpenQuake-engine, the open-source platform for seismic hazard and risk assessment from the Global Earthquake Model initiative, was used to calculate the seismic hazard and risk in Nepal. The seismic hazard and mean economic loss map were formulated for the 1, 2, 5, and 10 % probability of exceedance in 50 years. Finally, the distribution of building damage and corresponding economic losses due to the recurrence of the historical 1934 earthquake was presented in this study.

In recent years, the nuclear industry and the Nuclear Regulatory Commission (NRC) have made a tremendous effort to assess the safety of nuclear power plants as advances in seismology have led to the perception that the potential earthquake hazard in the United States may be higher than originally assumed. The Seismic Probabilistic Risk Assessment (S-PRA) is a systematic approach used in the nuclear power plants in the U.S. to realistically quantify the seismic risk as by performing an S-PRA, the dominant contributors to seismic risk and core damage can be identified. The assessment of component fragility is a crucial task in the S-PRA and because of the conservatism in the design process imposed by stringent codes and regulations for safety related structures, structures and safety related items are capable of withstanding earthquakes larger than the Safe Shutdown Earthquake (SSE). One major aspect of conservatism in the design is neglecting the effect of Soil-Structure-Interaction (SSI), from which conservative estimates of In-Structure Response Spectra (ISRS) are calculated resulting in conservative seismic demands for plant equipment. In this paper, a typical Reactor Building is chosen for a case study by discretizing the building into a lumped mass stick model (LMSM) taking into account model eccentricities and concrete cracking for higher demand. The model is first analyzed for a fixed base condition using the free field ground motion imposed at the foundation level from which ISRS are calculated at different elevations. Computations taking into account the SSI effects are then performed using the subtraction method accounting for inertial interactions by using frequency dependent foundation impedance functions depicting the flexibility of the foundation as well as the damping associated with foundation-soil interaction. Kinematic interactions are also taken into account in the SSI analysis by using frequency dependent transfer functions relating the free-field motion to the motion that would occur at the foundation level as the presence of foundation elements in soil causes foundation motions to deviate from free-field motions as a result of ground motion incoherence and foundation embedment. Comparing the results of the seismic response analyses, the effects of the SSI is quantified on the overall seismic risk and the SSI margin is calculated. A family of realistic seismic fragility curves of the structure are then developed using common industry safety factors (capacity, ductility, response, and strength factors), and also variability estimates for randomness and uncertainty. Realistic fragility estimates for structures directly enhances the component fragilities from which enhanced values of Core Damage Frequency (CDF) and Large Energy Release Frequency (LERF) are quantified as a final S-PRA deliverable.

Risk assessment and management is an important step towards resilient and sustainable cities. Among many other perils, both natural and manmade, seismic risk is a major threat for resilience and sustainability. In recent decades, several methods for seismic risk assessment have been proposed, including the well-known Vulnerability Index Method (VIM). In this study, a probabilistic version of the VIM, which we call the Vulnerability Index Method-Probabilistic (VIM_P), is proposed. The VIM_P requires essential information on the seismic hazard and on the vulnerability of the building stock. Seismic hazard is determined using the exceedance rates of macroseismic intensities, as defined in the European Macroseismic Scale (EMS). Seismic vulnerability is defined by means of vulnerability probability density functions (pdf) that describe the probability distribution of the corresponding vulnerability index. Beta-like functions are used for these pdfs. VIM_P quantifies seismic vulnerability by means of three vulnerability curves, Lower, Best and Upper, according to the quantity and quality of available information, thus allowing three estimates of seismic vulnerability and risk. Then, seismic risk is computed via the convolution of seismic hazard and seismic vulnerability, considering semi-empirical damage functions. Seismic risk is given through the exceedance frequencies of the damage grades. To highlight the capabilities of the VIM_P, the seismic risk of about 70,000 residential buildings in Barcelona was assessed. According to the results, the exceedance frequency of the collapse damage state for more than the 50% of the buildings in the Eixample district would be greater than 1 × 10−5. This confirms the relatively high seismic risk in the city, mainly due to the high vulnerability of the built environment. Specific software, USERISK20015, has been developed for routine applications of VIM_P. It is hoped that VIM_P and this new tool for seismic risk assessment will be useful to stakeholders and civil protection authorities for risk management and prioritizing actions that can help to create more resilient, sustainable cities.

This study evaluates the impact, on estimates of seismic risk and its uncertainty, of alternative methods in treatment and characterization of earthquake ground motions. The objective of this study is to delineate specific procedures and characterizations that may lead to less biased and more precise seismic risk results. This report focuses on sources of conservatism and variability in risk that may be introduced through the analytical processes and ground-motion descriptions which are commonly implemented at the interface of seismic hazard and fragility assessments. In particular, implication of the common practice of using a single, composite spectral shape to characterize motions of different magnitudes is investigated. Also, the impact of parameterization of ground motion on fragility and hazard assessments is shown. Examination of these results demonstrates the following. (1) There exists significant conservatism in the review spectra (usually, spectra characteristic of western U.S. earthquakes) that have been used in conducting past seismic risk assessments and seismic margin assessments for eastern U.S. nuclear power plants. (2) There is a strong dependence of seismic fragility on earthquake magnitude when PGA is used as the ground-motion characterization. When, however, magnitude-dependent spectra are anchored to a common measure of elastic spectral acceleration averaged over the appropriate frequency range, seismic fragility shows no important nor consistent dependence on either magnitude or strong-motion duration. Use of inelastic spectral acceleration (at the proper frequency) as the ground spectrum anchor demonstrates a very similar result. This study concludes that a single, composite-magnitude spectrum can generally be used to characterize ground motion for fragility assessment without introducing significant bias or uncertainty in seismic risk estimates.

Use of fragility curves to assess the seismic vulnerability in the risk analysis of mountain tunnels

This work investigates the effect of the level of detailing of site conditions as well as the selection of the fragility and vulnerability models on large scale seismic risk assessment. For this we consider the application of selected components of the recent European Seismic Hazard (ESHM20) and Risk (ESRM20) Models and we focus on Thessaloniki, Greece, a city which is very well documented in terms of local site conditions and exposure. Seismic risk results are compared in terms of expected damages and economic losses for a seismic hazard with a 475-year return period. The results indicate that the level of site conditions modelling does not significantly affect the estimated aggregate damages and economic losses at city scale, however significant discrepancies may occur at local scale. On the other hand, the selection of the vulnerability model for the building stock may considerably affect the intensity and the spatial distribution of damages, resulting in a considerable differentiation in the economic losses estimate.KeywordsESHM20ESRM20Site modellingSite amplificationFragility and vulnerability modelsSeismic risk model

Soil types and depth of bedrock are not available for the majority of bridge embankments to allow detailed seismic analysis and risk assessment. The accompanying paper provides a quick methodology for preliminary seismic risk assessment, ranking, and prioritization of bridge embankments along priority routes. The objective of this paper is to apply the methodology to identify the seismic risk of 127 bridge embankments along I-24 in western Kentucky. The variables of each embankment including the geometry, type and properties of underlying soil, elevation of the natural ground line, and level of bedrock are estimated. The seismic slope stability capacity/demand ratio, displacement, and liquefaction potential of each bridge embankment are calculated. Three categories are presented to identify the failure risk of the embankments. A priority list of the embankments with the highest seismic risk of failure is generated for I-24 bridge embankments in western Kentucky during designated seismic events. The priority list will enable decision makers to decide on either carrying out further detailed evaluation or considering other appropriate actions for the embankments with the highest failure risk.

Following U.S. Department of Energy Order 420.1 C for the mitigation of natural phenomena hazards, such as earthquakes, to nuclear facilities through periodic reassessments, Idaho National Laboratory (INL) has developed the Seismic Hazard Periodic Re-Evaluation Methodology (SHPRM). The SHPRM involves seven criteria that evaluate changes to the seismic hazard at a site due to changes in the input models/data over time. Should these changes to the seismic hazard result in an increase in the design or licensing-basis ground motion of the facility from that which the facility was designed for, the SHPRM includes a criterion for reevaluating the facility risk objectives. While the criteria corresponding to the reevaluation of the seismic hazard and the design basis have been previously demonstrated and published, there is currently no guidance on reevaluating seismic risk for the purpose of SHPRM. This paper complements the published reports and papers on the application of SHPRM by demonstrating the risk objectives criterion for a generic nuclear facility (GNF), thereby closing the loop on the application of the SHPRM. The GNF is assumed to be located at the INL site and designated as a Seismic Design Category-3 facility as per American Society of Civil Engineers (ASCE)/Structural Engineering Institute (SEI) 43-05. The demonstration includes a risk assessment for a baseline seismic hazard calculated in 2006 and an updated seismic hazard calculated in 2015. After presenting the baseline and the updated seismic hazard curves at this site, the state-of-practice methodology for calculating fragility functions for the facility is presented, along with the fragilities calculated for the GNF. Employing a fault tree analysis using the INL in-house seismic analysis and risk assessment software MASTODON, the seismic risks of collapse of the GNF for the baseline and updated seismic hazards are computed to be 5.27E−05 and 5.2E−06, respectively. The results show that not only the reevaluated seismic risk is smaller, but more importantly, that it meets the risk objectives set by ASCE/SEI 43-05.

Rapid seismic risk assessment

While earthquakes can have a devastating impact on the economic growth and social welfare of earthquake prone regions, probabilistic seismic risk assessment can be employed to assess and mitigate such risks from future destructive events. In a previous study (Sianko et al. in Bull Earthq Eng 18:2523–2555, 2020), a probabilistic seismic hazard analysis (PSHA) tool based on the Monte-Carlo approach, was developed to predict the seismic hazard for high seismicity areas. In this study, a seismic risk assessment framework is developed incorporating the previously developed PSHA tool, with vulnerability functions based on various damage criteria, exposures and casualty models. Epistemic uncertainty is addressed using logic trees and distribution functions. The developed seismic risk assessment framework can estimate human and economic losses for particular return periods using an event-based stochastic procedure. The framework is applied to a case study area, the city of Adapazari in Turkey. Seismic risk assessment is carried out for different return periods to identify the most vulnerable areas of the city. The verification of the developed seismic risk framework is performed by comparing the predicted seismic losses to those observed during the 1999 Kocaeli earthquake that severely affected the city of Adapazari. The results of the study indicate that while overall predictions for extensive and complete damage states demonstrate strong correlation with the observed data, accurate risk predictions at the district level are not achievable without microzonation studies.

A better seismic design for building and other structures is the most effective way to reduce seismic risk and avoid earthquake disaster. Adoption and implementation of new seismic safety regulations and design standards have caused serious problems in many communities in the New Madrid region, including western Kentucky, however. The main reasons for these problems are (1) misunderstanding of the national seismic hazard maps and (2) confusion between seismic hazard and seismic risk. Both are caused by probabilistic seismic hazard analysis (PSHA). PSHA is a mathematical formulation derived from a probability analysis on the distribution of earthquake magnitudes, locations, and ground-motion attenuation. Some assumptions and distributions associated with PSHA have been found to be invalid in earth science, however. In addition, PSHA contains a mathematical error: equating a dimensionless quantity (the annual probability of exceedance – exceedance probability in one year) to a dimensional quantity (the annual frequency of exceedance with the unit of per year [1/yr]). Thus, PSHA is scientifically flawed and the resulting seismic hazard and seismic risk estimates are artifacts. The national seismic hazard curves and maps are artifacts because they were produced from PSHA, even though the inputs are scientifically sound. Although seismic hazard and seismic risk have often been used interchangeably, they are two fundamentally different concepts. Seismic hazard describes the natural phenomenon or property of an earthquake, whereas seismic risk describes the probability of loss or damage that could be caused by a seismic hazard. Seismic hazard and seismic risk play different roles in engineering design and other policy considerations. Furthermore, measures for seismic hazard mitigation are different from those for seismic risk reduction. The difficulties in the development of design ground motion for NEHRP provisions are caused by the use of the national seismic hazard maps which are neither seismic hazard nor seismic risk. The resulting design ground motions for building codes and other policy considerations are therefore problematic. California’s experience proves that deterministic/scenario seismic hazard analysis is an appropriate approach for seismic hazard assessment, seismic risk assessment, as well as *Kentucky Geological Survey, University of Kentucky, 504 Rose Street, Lexington, KY 40506; phone (859) 323-0564; fax (859)257-1147; e-mail: zmwang@uky.edu. 112 Seismic Hazard Design Issues in the Central United States engineering design and other policy considerations. Deterministic/scenario seismic hazard analysis is also appropriate for engineering design and other policy considerations in the New Madrid region, as well as other regions.

Seismic hazard and risk are two very important concepts in engineering design and other policy considerations. Although seismic hazard and risk have often been used interchangeably, they are fundamentally different. Furthermore, seismic risk is more important in engineering design and other policy considerations. Seismic hazard assessment is an effort by earth scientists to quantify seismic hazard and its associated uncertainty in time and space and to provide seismic hazard estimates for seismic risk assessment and other applications. Although seismic hazard assessment is more a scientific issue, it deserves special attention because of its significant implication to society. Two approaches, probabilistic seismic hazard analysis (PSHA) and deterministic seismic hazard analysis (DSHA), are commonly used for seismic hazard assessment. Although PSHA has been proclaimed as the best approach for seismic hazard assessment, it is scientifically flawed (i.e., the physics and mathematics that PSHA is based on are not valid). Use of PSHA could lead to either unsafe or overly conservative engineering design or public policy, each of which has dire consequences to society. On the other hand, DSHA is a viable approach for seismic hazard assessment even though it has been labeled as unreliable. The biggest drawback of DSHA is that the temporal characteristics (i.e., earthquake frequency of occurrence and the associated uncertainty) are often neglected. An alternative, seismic hazard analysis (SHA), utilizes earthquake science and statistics directly and provides a seismic hazard estimate that can be readily used for seismic risk assessment and other applications.

Probabilistic seismic performance assessment of aqueduct structures considering different sources of uncertainty

Probabilistic seismic risk assessment for spatially distributed lifelines is less straightforward than for individual structures. While procedures such as the ‘PEER framework’ have been developed for risk assessment of individual structures, these are not easily applicable to distributed lifeline systems, due to difficulties in describing ground‐motion intensity (e.g. spectral acceleration) over a region (in contrast to ground‐motion intensity at a single site, which is easily quantified using Probabilistic Seismic Hazard Analysis), and since the link between the ground‐motion intensities and lifeline performance is usually not available in closed form. As a result, Monte Carlo simulation (MCS) and its variants are well suited for characterizing ground motions and computing resulting losses to lifelines. This paper proposes a simulation‐based framework for developing a small but stochastically representative catalog of earthquake ground‐motion intensity maps that can be used for lifeline risk assessment. In this framework, Importance Sampling is used to preferentially sample ‘important’ ground‐motion intensity maps, and K‐Means Clustering is used to identify and combine redundant maps in order to obtain a small catalog. The effects of sampling and clustering are accounted for through a weighting on each remaining map, so that the resulting catalog is still a probabilistically correct representation. The feasibility of the proposed simulation framework is illustrated by using it to assess the seismic risk of a simplified model of the San Francisco Bay Area transportation network. A catalog of just 150 intensity maps is generated to represent hazard at 1038 sites from 10 regional fault segments causing earthquakes with magnitudes between five and eight. The risk estimates obtained using these maps are consistent with those obtained using conventional MCS utilizing many orders of magnitudes more ground‐motion intensity maps. Therefore, the proposed technique can be used to drastically reduce the computational expense of a simulation‐based risk assessment, without compromising the accuracy of the risk estimates. This will facilitate computationally intensive risk analysis of systems such as transportation networks. Finally, the study shows that the uncertainties in the ground‐motion intensities and the spatial correlations between ground‐motion intensities at various sites must be modeled in order to obtain unbiased estimates of lifeline risk. Copyright © 2010 John Wiley & Sons, Ltd.