Multivariate Probabilistic Seismic Demand Model for the Bridge Multidimensional Fragility Analysis

Qi’ang Wang,Ziyan Wu,Shukui Liu 대한토목학회 2018 KSCE Journal of Civil Engineering Vol.22 No.9

Seismic fragility analysis for bridges is an essential issue for risk assessment of transportation networks exposed to seismic hazards. Considering multiple Performance Limit States (PLSs) and seismic demand parameters, the study proposes a multidimensional fragility evaluation methodology for engineering structures, and the objective of the paper is to show that the uncertainty and dependence between seismic demand parameters should be considered for fragility analysis. Thus, a new Probabilistic Seismic Demand Model (PSDM) following multivariate logarithmic normal distribution is addressed. Taking PLS correlation into consideration, multidimensional PLS formula is constructed to identify the structural failure domain. A RC bridge is studied to show the proposed theory. To consider bridge column plastic deformation and bearing nonlinear characteristic, nonlinear dynamic analyses are carried out. The bridge multidimensional fragility curves are derived and compared with fragility curves for an individual component. Results indicate that uncertainty and dependence of demand parameters can be properly dealt with by the multivariate PSDM. The multidimensional fragility is higher than fragility of any individual component, and the bridge as a system is more fragile. The ignorance of multiple components contribution to the system will generate an overestimation for the whole structural performance, which is adverse to engineering structural safety.

지진격리된 원자력발전소 연결배관의 실제 손상 기반 지진취약도 분석

전법규 ( Jeon Bubgyu ),김성완 ( Kim Sungwan ),윤다운 ( Yun Dawoon ),임승현 ( Eem Seunghyun ),함대기 ( Hahm Daegi ) 한국복합신소재구조학회 2021 복합신소재구조학회논문집 Vol.12 No.3

원자력 발전소에 지진격리장치를 설치하여 내진성능을 향상시킬 수 있다. 그러나 지진격리장치의 적용으로 지반과 구조물 사이에서 큰 상대 변위가 발생하게 된다. 따라서 지진격리된 구조물과 일반 구조물을 연결하는 연결배관시스템의 경우 지진리스크가 증가할 수 있다. 따라서 이러한 배관시스템의 지진취약도를 분석할 필요가 있다. 본 연구에서는 지진취약도 분석을 위해 지진격리된 APR1400 원자력발전소와 주증기관을 대상으로 지진취약도를 분석하였다. 주증기관은 지진격리된 nuclear island의 보조 건물과 터빈 건물을 연결하는 인터페이스 배관이다. 지진취약도 분석을 위한 파괴모드는 누출관통균열로 정의하였다. 누출은 실험결과와 수치해석을 통해 손상지수로 정량화하여 취약도 분석을 위한 파괴기준으로 사용하였다. 파괴기준의 변동에 의한 취약도 곡선의 변동성을 확인하기 위하여 손상지수의 최솟값, 최댓값, 평균값 및 중앙값을 파괴기준으로 하여 지진취약도 곡선을 작성하였다. A seismic isolation system installed in a nuclear power plant (NPP) can withstand a load caused by an earthquake. However, a larger relative displacement may occur in the system compared with its absence. Therefore, the seismic risk in an interface piping system that connects base-isolated and general structures can increase. Hence, seismic-fragility analysis of these piping systems is necessary. In this study, a seismic-fragility analysis was performed on base-isolated APR1400 NPPs and their main steam line. The main steam line is an interface pipe that connects the base-isolated auxiliary and turbine buildings. The failure mode of the seismic-fragility analysis was defined as a leak-through crack. The leakage point was quantified as a damage index through the experimental and numerical analysis results and was employed as a failure criterion in the seismic-fragility analysis. The seismic-fragility curves were assigned representative values as damage indexes, namely, average, median, maximum, and minimum, at the leak point by considering the uncertainty of the failure criterion.

Earthquake risk assessment of seismically isolated extradosed bridges with lead rubber bearings

김두기,이진학,Hyeong-Yeol Seo,장준호 국제구조공학회 2008 Structural Engineering and Mechanics, An Int'l Jou Vol.29 No.6

This study presents a method to evaluate the seismic risk of an extradosed bridge with seismic isolators of lead rubber bearings (LRBs), and also to show the effectiveness of the LRB isolators on the extradosed bridge, which is one of the relatively flexible and lightly damped structures in terms of seismic risk. Initially, the seismic vulnerability of a structure is evaluated, and then the seismic hazard of a specific site is rated using an earthquake data set and seismic hazard maps in Korea. Then, the seismic risk of the structure is assessed. The nonlinear seismic analyses are carried out to consider plastic deformation of bridge columns and the nonlinear characteristics of soil foundation. To describe the nonlinear behaviour of a column, the ductility demand is adopted, and the moment-curvature relation of a column is assumed to be bilinear hysteretic. The fragility curves are represented as a log-normal distribution function for column damage, movement of superstructure, and cable yielding. And the seismic hazard at a specific site is estimated using the available seismic hazard maps. The results show that in seismically-isolated extradosed bridges under earthquakes, the effectiveness of the isolators is much more noticeable in the columns than the cables and girders.

Earthquake risk assessment of seismically isolated extradosed bridges with lead rubber bearings

Kim, Dookie,Yi, Jin-Hak,Seo, Hyeong-Yeol,Chang, Chunho Techno-Press 2008 Structural Engineering and Mechanics, An Int'l Jou Vol.29 No.6

This study presents a method to evaluate the seismic risk of an extradosed bridge with seismic isolators of lead rubber bearings (LRBs), and also to show the effectiveness of the LRB isolators on the extradosed bridge, which is one of the relatively flexible and lightly damped structures in terms of seismic risk. Initially, the seismic vulnerability of a structure is evaluated, and then the seismic hazard of a specific site is rated using an earthquake data set and seismic hazard maps in Korea. Then, the seismic risk of the structure is assessed. The nonlinear seismic analyses are carried out to consider plastic deformation of bridge columns and the nonlinear characteristics of soil foundation. To describe the nonlinear behaviour of a column, the ductility demand is adopted, and the moment-curvature relation of a column is assumed to be bilinear hysteretic. The fragility curves are represented as a log-normal distribution function for column damage, movement of superstructure, and cable yielding. And the seismic hazard at a specific site is estimated using the available seismic hazard maps. The results show that in seismically-isolated extradosed bridges under earthquakes, the effectiveness of the isolators is much more noticeable in the columns than the cables and girders.

노후도를 고려한 교량의 시스템-수준 지진취약도 평가

꽁시나,문지호,송종걸 한국전산구조공학회 2022 한국전산구조공학회논문집 Vol.35 No.3

As a bridge ages, its mechanical properties and structural performance deteriorate, degrading its seismic performance during a strongearthquake. In this study, the aging of piers and bridge bearings was quantified in several stages and reflected in the analysis model, enablingthe evaluation of the member-level seismic fragility of these bearings. Moreover, by assuming that the failure mechanism of a bridge system isa series system, a method for evaluating the system-level seismic fragility based on the member-level seismic fragility analysis result isformulated and proposed. For piers with rubber and lead–rubber bearings (members vulnerable to aging effects), five quantitative degrees ofaging (0, 5, 10, 25, and 40%) are assumed to evaluate the member-level seismic fragility. Then, based on the result, the system-level seismicfragility evaluation was implemented. The pier rather than the bridge bearing is observed to have a dominant effect on the system-level seismicfragility. This means that the seismic fragility of more vulnerable structural members has a dominant influence on the seismic fragility of theentire bridge system. 교량은 사용년한이 증가함에 따라 노후화로 인해 역학적인 성질과 구조적인 성능이 저하되고 이로 인해서 강진 시에 내진성능이저하된다. 교각과 교량받침에 대한 노후화를 몇 가지 단계로 정량화하여 해석모델에 반영하였고, 노후화된 교각과 교량받침에 대하여 부재-수준의 지진취약도를 평가하였다. 교량 시스템의 파괴 메카니즘을 직렬시스템으로 가정하여, 부재-수준의 지진취약도 해석결과로부터 시스템-수준의 지진취약도를 평가하는 방법을 제안하였다. 노후도에 취약한 부재인 교각과 교량받침에 대하여, 5가지 정량적인 노후도(0, 5, 10, 25, 40%)를 가정하여 부재-수준의 지진취약도를 평가하였고, 이 결과로부터 시스템-수준의 지진취약도 평가를 수행하였다. 시스템-수준의 지진취약도는 교량받침 보다는 교각이 지배적인 영향을 줌을 알 수 있었다. 이는 보다 취약한 구조부재의 지진취약도가 전체 교량시스템의 지진취약도에 지배적인 영향을 주는 것을 의미한다.

Seismic Reliability Assessment of Mid- and High-rise Post-tensioned CLT Shear Wall Structures

Sun, Xiaofeng,Li, Zheng,He, Minjuan Council on Tall Building and Urban Habitat Korea 2020 International journal of high-rise buildings Vol.9 No.2

Currently, few studies have been conducted to comprehend the seismic reliability of post-tensioned (PT) CLT shear wall structures, due to the complexity of this kind of structural system as well as due to lack of a reliable structural model. In this paper, a set of 4-, 8-, 12-, and 16-storey benchmark PT CLT shear wall structures (PT-CLTstrs) were designed using the direct displacement-based design method, and their calibrated structural models were developed. The seismic reliability of each PT-CLTstr was assessed based on the fragility analysis and based on the response surface method (RSM), respectively. The fragility-based reliability index and the RSM-based reliability index were then compared, for each PT-CLTstr and for each seismic hazard level. Results show that the RSM-based reliabilities are slightly less than the fragility-based reliabilities. Overall, both the RSM and the fragility-based reliability method can be used as efficient approaches for assessing the seismic reliabilities of the PT-CLTstrs. For these studied mid- and high-rise benchmark PT-CLTstrs, following their fragility-based reliabilities, the 8-storey PT-CLTstr is subjected to the least seismic vulnerability; while, following their RSM-based reliabilities, the 4-storey PT-CLTstr is subjected to the least seismic vulnerability

Seismic Fragility Analysis of V-Shaped Continuous Girder Bridges

Leping Ren,Gang Zhang,Yongfei Zhang,Shuanhai He 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.3

This paper presents an improved approach for evaluating seismic performance of V-shaped continuous girder bridges with different V-angles. A 3-D finite element model is established using the OpenSees for tracing the response of a typical three-span V-shaped continuous girder bridge. The analysis is performed in three steps: component fragility analysis, validated system fragility analysis and V-angle analysis. A series of nonlinear time history analysis(NLTHA), considering the uncertainty in bridge structural parameters and ground motions characteristics, is carried out to investigate the potential fragile position of a V-shapedcontinuous girder bridge. Subsequently, a new improved product of conditional marginal(PCM) method is validated successfully and utilized to form the system fragility curves. The application of the validated method is used to analyse the influence of V-angle on the bridge structural system fragility. The analysis result shows that variation of V-angle has significantinfluence on seismic fragility of V-shaped continuous girder bridges. The V-shaped continuous girder bridges with 80° V-angle has good seismic performance when PGA ≤ 0.8 g. Smaller V-angle can result in higher seismic fragility of V-shaped continuous girder bridges.

Fragility assessment of RC-MRFs under concurrent vertical-horizontal seismic action effects

Ehsan Noroozinejad Farsangi,Abbas Ali Tasnimi,Babak Mansouri 사단법인 한국계산역학회 2015 Computers and Concrete, An International Journal Vol.16 No.1

In this study, structural vulnerability of reinforced concrete moment resisting frames (RC-MRFs) by considering the Iran–specific characteristics is investigated to manage the earthquake risk in terms of multicomponent seismic excitations. Low and medium rise RC-MRFs, which constitute approximately 80-90% of the total buildings stock in Iran, are focused in this fragility–based assessment. The seismic design of 3-12 story RC-MRFs are carried out according to the Iranian Code of Practice for Seismic Resistant Design of Buildings (Standard No. 2800), and the analytical models are formed accordingly in open source nonlinear platforms. Frame structures are categorized in three subclasses according to the specific characteristics of construction practice and the observed seismic performance after major earthquakes in Iran. Both far and near fields’ ground motions have been considered in the fragility estimation. An optimal intensity measure (IM) called Sa, avg and beta probability distribution were used to obtain reliable fragility–based database for earthquake damage and loss estimation of RC buildings stock in urban areas of Iran. Nonlinear incremental dynamic analyses by means of lumped-parameter based structural models have been simulated and performed to extract the fragility curves. Approximate confidence bounds are developed to represent the epistemic uncertainties inherent in the fragility estimations. Consequently, it’s shown that including vertical ground motion in the analysis is highly recommended for reliable seismic assessment of RC buildings.

전기 캐비닛-앵커 시스템의 지진 취약도 분석

손호영,정우영,전법규,주부석 한국복합신소재구조학회 2019 복합신소재구조학회논문집 Vol.10 No.6

The recent earthquakes in Gyeongju and Pohang have caused a lot of damage to structural elements as well as structural elements due to seismic waves that contain a lot of high frequency areas. Among the non-structural elements, the electrical cabinet keeps the power generation system controller of the plant, so that the damage in the electrical cabinet can be extended to secondary damage, such as the interruption of stable energy supply and the fire accident. In this study, the finite element model of electrical cabinet-anchor system is constructed and verified to apply input earthquake considering high frequency earthquake to perform seismic fragility analysis. For the finite element model of the electrical cabinet, the resonance frequency search result had a error of approximately 1% with the target frequency, and the finite element model of the post installed anchor showed a good match of the initial stiffness and maximum load point when compared with the experimental results. The time history analysis was performed by varying the scales to 0.2g, 0.5g, 0.8g, and 1.2g. Based on the analysis results, the seismic fragility assessment was performed, which is a probabilistic safety assessment. The analysis of time history of 0.2g scale showed that the stress generated by the anchors was the greatest at 280.15MPa and that they reacted sensitively to high frequency earthquakes. The slope changed rapidly between 0.2g and 0.5g when analyzing the seismic fragility with the stress of the anchors limited, and the displacement at the top of the cabinet was shown to be more sensitive to the displacement of the X-axis than the displacement of the Z-axis when analyzing the seismic fragility. 최근 발생한 경주 및 포항 지진은 고주파 영역의 성분이 많이 포함된 지진파로 구조적 요소 뿐만아니라 비구조적 요소에 피해가 많이 발생하였다. 비구조적 요소 중 전기 캐비닛은 발전소의 발전 시스템 컨트롤러를 보관하는 함으로써 전기 캐비닛의 피해는 안정적인 에너지 공급의 중단과 화재 등의 2차적인 피해로 확장될 수 있다. 따라서 본 연구에서는 전기 캐비닛- 앵커 시스템의 유한요소 모델을 구축하고 검증하여 세계 각지에서 발생한 지진파 적용을 통한 지진 취약도 평가를 수행하고자한다. 전기 캐비닛의 유한요소 모델의 경우 공진탐색 결과의 타겟 주파수와 약 1%의 오차가 발생하였으며 선설치 앵커의 유한요소 모델은 실험결과와 비교하였을 때 초기 강성 및 최대 하중점이 잘 일치하는 것으로 나타났다. 0.2g, 0.5g, 0.8g, 1.2g로 스케일을 변화시켜 시간이력해석을 수행하였으며 해석결과를 바탕으로 확률론적 안전성 평가인 지진 취약도 평가를 수행하였다. 0.2g 스케일의 시간이력 해석결과 경주 지진을 적용하였을 때 앵커에서 발생한 응력은 280.15MPa로 가장 크게 발생하였으며 고주파 지진에 민감하게 반응하는 것으로 나타났다. 앵커의 응력을 한계상태로 지진취약도 분석 시 0.2g와 0.5g 사이에서 기울기가 급격히 변하였으며 캐비닛 최상단의 변위를 한계상태로 지진 취약도 분석 시 Z축 변위 보다 X축 변위에 대해 민감하게 반응하는 것으로 나타났다.

개착식 철도 터널 구조물의 기존 지진취약도 모델 적합성 평가

양승훈,곽동엽 사단법인 한국터널지하공간학회 2022 한국터널지하공간학회논문집 Vol.24 No.1

A weighted linear combination of seismic fragility models previously developed for cut-and-cover railway tunnels was presented and the appropriateness of the combined model was evaluated. The seismic fragility function is expressed in the form of a cumulative probability function of the lognormal distribution based on the peak ground acceleration. The model uncertainty can be reduced by combining models independently developed. Equal weight is applied to four models. The new seismic fragility function was developed for each damage level by determining the median and standard deviation, which are model metrics. Comparing fragility curves developed for other bored tunnels, cut-and-cover tunnels for high-speed railway system have a similar level of fragility. We postulated that this is due to the high seismic design standard for high-speed railway tunnel. 본 연구에서는 기존에 개발된 개착식 철도 터널의 지진취약도 모델들을 가중 조합하여 새로운 모델을 제시하고 제시한 모델의 적정성을 평가하였다. 지진취약도 함수의 형태는 최대지반가속도의 대수정규분포형태로, 누적확률분포로 표현된다. 독립적으로 개발된 각 모델을 선형 가중 조합하는 것으로 모델의 불확실성을 줄일 수 있기에 4개의 모델에 대하여 25%씩 동등하게 선형가중을 부여하였다. 조합된 지진취약도 곡선에 최대 지반가속도에 대한 피해발생확률을 이용하여 지진취약도 곡선의 중앙값과 표준편차를 결정하여 새로운 지진취약도 함수를 개발하였다. 개발된 지진취약도 함수의 적합성을 평가하기 위하여 다양한 터널의 지진취약도 곡선과 비교 분석을 진행하였다. 개발된 곡선은 상대적으로 지진피해에 안전한 굴착식 터널의 지진취약도 함수와 비슷한 취약도를 갖는 것으로 나타나는데, 대상 터널은 국내 고속철도 개착식 터널로 높은 내진설계 기준에 의해 기인하는 것으로 판단된다.