目标易损性概念和相关理论的探讨

目标易损性概念理论广泛应用于建筑、社会、金融、自然环境以及军事目标等领域。文章在对各个领域易损性的概念分析比较的基础上,总结了目标易损性研究的目的及概念的表达;介绍了不同领域易损性评估的方法,比较不同方法的优缺点,指出每种方法的适用对象,并对影响易损性的因素进行了初步讨论。     

具有中介状态结构地震易损性分析

在可靠性向量理论基础之上,提出了一种适合于单体结构和群体建筑快速易损性评估的方法,指出该方法可应用于单体结构和群体建筑的易损性评估,计算结果可以得到单体结构易损性矩阵和群体建筑易损性矩阵,从而为结构的抗震性能评估、抗震加固等提供决策数据。     

桥梁易损性研究的回顾与展望

介绍了桥梁易损性研究的概况,对桥梁易损性研究的由来、含义、分级方法和分析方法做了较为全面的论述,并对桥梁易损性研究提出了存在的问题和今后尚需开展的工作,以推动桥梁工程的发展。     

框架-剪力墙结构的地震易损性曲线建立方法

总结了地震作用下框架-剪力墙结构的理论易损性曲线的建立方法及其基本步骤,当然,还要考虑到地面运动、本地土壤条件等不确定性。框架-剪力墙结构体系则是目前高层结构所普遍采用的结构形式之一,因此展开该结构地震易损性分析研究对震害应急及防御都有重要的应用价值,并通过建立易损性曲线来直观了解框架-剪力墙结构地震易损性情况。     

高速公路钢筋混凝土桥梁地震易损性曲线建立方法

总结了地震作用下高速公路钢筋混凝土桥梁主要构件的理论易损性曲线的建立方法及其基本步骤,并且应该考虑到地面运动、本地土壤条件以及桥梁本身参数等不确定性.进一步说明如何考虑桥梁主要易损构件,如桥墩、支座和桥台等对整个桥梁体系易损性的影响,并且利用概率工具从单个构件的易损性直接预计桥梁体系的易损性,表明桥梁作为一个体系,比任何一个单独的构件更易损.     

城市交通系统易损性分析

本文采用经验统计法,模糊数学理论和Push-over等方法,对城市交通系统中的桥梁、道路进行易损性分析研究,结合三亚市交通系统实例分析计算,给出了不同烈度下桥梁、道路易损性分析结果,从中找出交通系统存在的薄弱环节,为编制城市抗震防灾规划和制定防灾决策提供重要的科学依据。     

结构地震易损性分析的研究

介绍了地震易损性分析在国内外的研究现状,基于结构易损性分析的必要性,从结构易损性分析的原理、分析方法、分析流程等方面,对结构易损性分析进行了研究,指出该研究对结构抗震安全性的评定、结构抗震设计等具有重要的意义。     

基于结构易损性理论的三角形钢屋架分析

基于拓扑构形的结构易损性理论,编制了相应的MATLAB结构易损性分析程序,并应用于三角形钢屋架的构形易损性分析,发现仅依靠增大构件截面提高结构构形度不一定能保证结构易损性的降低,而应合理优化构件截面,使结构整体性能达到最优。利用ANSYS软件分析了三角形钢屋架在实际荷载工况下的力学性能,与易损性分析结果相比较,表明结构的最易损失效模式所对应的结点位移达到最大值、同时杆件应力也相对较大,说明所采用的结构易损性分析方法能够有效地反映结构的易损部位,揭示结构的薄弱环节。     

优化藤Copula的桥梁结构系统地震易损性分析

为在桥梁结构系统易损性中更好地考虑不同构件个体之间的相关性,文章提出一种新的优化藤Copula分析桥梁结构系统易损性的方法。该方法与现有的考虑构件类别之间相关性的桥梁系统易损性分析不同,是将桥梁系统包含的各个构件的易损性作为藤Copula函数中的一个变量。通过不同构件个体的地震需求样本间的秩相关系数,基于最短哈密顿路径方法筛选优化的藤Copula函数。从而避免大量的联合概率密度函数的求解以及信息判定准则的试算。同时,提出优化藤Copula函数是基于构件易损性补集的联合概率密度函数(PDF),通过其分析桥梁系统易损性仅需构建一个联合PDF,可避免求解构件不同组合情况下较多的联合PDF。选用四跨有桥台混凝土桥梁结构模型,用桥梁剩余能力模型模拟桥梁的损伤,用提出的方法分析具有桥墩桥台和支座共10个构件个体相关性的桥梁系统易损性,并与目前通常采用的考虑构件类别之间相关性的桥梁系统易损性分析以及Monte Carlo(MC)方法的结果对比,验证提出方法的有效性。     

基于分步调幅法的钢筋混凝土结构主余震易损性曲面分析

传统主余震易损性分析多采用仅考虑主震强度或余震强度的标量式易损性函数，所获得的易损性曲线无法全面反映主、余震强度对结构抗震性能的综合影响。为解决这一问题，提出了一种同时包含主、余震强度的主余震易损性曲面分析方法。通过对主余震序列进行主、余震分步调幅，获得包含不同主、余震强度组合的主余震序列输入。通过分步拟合，构建同时包含主、余震强度的主余震需求模型，生成主余震易损性曲面，并进一步计算获得具有不同危险性水平的主、余震强度所对应的主余震易损性指数。以一栋按我国规范设计的钢筋混凝土框架结构为例，采用所提出方法进行了主余震易损性曲面分析。分析结果表明：所提出方法可以有效地生成结构的主余震易损性曲面，给定主震危险性水平而提升余震危险性水平或给定余震危险性水平而提升主震危险性水平，均可带来结构主余震易损性指数的提高，且后者引起的主余震易损性指数提高幅度更为显著，证明了主震作用在主余震易损性分析中的主导地位。     

Effect of the inelastic dynamic soil-structure interaction on the seismic vulnerability assessment

This paper presents a study of the influence of inelastic dynamic soil-structure interaction (DSSI) on the seismic vulnerability assessment of buildings. The seismic vulnerability is evaluated in terms of analytical fragility curves constructed on the basis of non-linear dynamic finite elements (FE) analysis. An analytical sensibility strategy is introduced in order to define a suitable size of the motion database to be used for computing fragility curves. The fragility curves developed in this study are compared with reference curves. Concerning the effect of the inelastic DSSI, a general reduction of seismic demand when DSSI phenomena are included is found. Derived fragility curve reflects this seismic demand reduction. The importance of the ground motion database is highlighted in terms of the variability of parameters describing derived fragility curves. Comparison with reference curves are satisfactory. Findings illustrate clearly the importance and the advantages of an adequate DSSI effects evaluation.     

Time-dependent seismic fragility curves for aging jacket-type offshore platforms subjected to earthquake ground motions

This paper assesses the seismic vulnerability of a recently designed jacket-type offshore platform through development of fragility curves and presents the formulation of time-dependent seismic fragility curves to capture the effects of ageing and deterioration on the seismic vulnerability of the representative platform. Among the various ageing processes, the corrosion deterioration of the structure is taken into account by applying a time-dependent model of corrosion deterioration of the tubular elements in the splash zone. Incremental dynamic analysis is performed on the initial uncorroded and corroded platforms considering soil–pile–structure interaction. A full probabilistic analysis is then performed to develop time-dependent seismic fragility curves for the immediate occupancy and collapse prevention limit states. Finally, a time variant cubic model is proposed to develop fragility curves at any point in time during platform’s service life, without need to perform a complete time-consuming fragility analyses. Results show substantial increase in probability of failure of the platform throughout its lifetime due to corrosion deterioration. The results also indicate that the time-dependent fragility curves can be used in offshore platforms to assess the seismic vulnerability of the structure and demonstrate the influence of various factors affecting the seismic vulnerability of the platform during its lifetime.     

Seismic vulnerability assessment of process towers using fragility curves

This study focuses on the seismic vulnerability assessment of process towers. A 96‐m process tower, located at the Shazand Refinery, is considered for a case study sample. The vulnerability of this structure is expressed with the development of fragility curves, which provide the probability of exceeding a prescribed level of damage for a wide range of ground motion intensities. The methodology of developing fragility curves for process towers is shown. The developed fragility curves can be very useful for emergency management agencies and insurance companies wishing to estimate the overall loss after an earthquake. The vulnerability of nonstructural equipments of tower is also assessed in subsequent step. To model the process tower with its base details, a nonlinear finite element model is generated. It was found that the fragility curves should be developed for external pressure condition because it is more critical state of loading. The results show that the damage to the process tower occurs in the shell; and the other types of damages, i.e. yielding of anchor bolts, structural damage to foundation and overturning of tower, do not occur. Copyright © 2013 John Wiley & Sons, Ltd.     

Seismic fragility analysis of low-rise unreinforced masonry structures

Unreinforced masonry (URM) is one of the most common structural types for low-rise buildings in the United States. Its dynamic behavior is highly nonlinear, and generally shows high vulnerability to seismic loading. Despite the need for seismic risk assessment of this class of structures, the fragility curves for URM buildings based on analytical models are scarce in the field of earthquake engineering. This study performs seismic fragility analysis of a URM low-rise building. Fragility curves are developed for a two-story URM building designed to represent a typical essential facility (i.e., a firehouse) in the central and southern US (CSUS) region. A structural modeling method is proposed such that it can be effectively used for fragility analysis without significant increase in computational time, and maintains an acceptable level of accuracy in representing the nonlinear behavior of the structures. A set of fragility curves are developed and include different configurations of the out-of-plane walls and their associated stiffness. The fragility analysis shows that the seismic performance of URM buildings is well below the desirable building seismic performance level recommended by current seismic codes, indicating high vulnerability of URM buildings within the CSUS region. It is also shown that the out-of-plane wall stiffness should not be ignored in the risk assessment of URM buildings because the overall seismic performance of URM buildings is rather sensitive to the out-of-plane wall stiffness. The analytical fragility curves developed are compared with those of HAZUS. The comparison shows that the analytical fragility curves developed have lower variation in the seismic response than those of HAZUS. Several reasons for the discrepancy are discussed. The model-based analytical fragility curves developed in this study can increase the accuracy and effectiveness of seismic risk assessment of essential facilities of the CSUS region. Moreover, the structural modeling method introduced in this study can be effectively used for development of the fragility curves of URM buildings.     

Drift-based and dual-parameter fragility curves for concentrically braced frames in seismic regions

This paper discusses the development of drift-based and dual-parameter fragility curves for steel braces as part of concentrically braced frames designed in seismic regions. The experimental results from 24 different research programs are compiled into a database for this effort. Drift-based fragility curves are developed for three damage states of steel braces subjected to cyclic loading associated with brace flexural buckling, local buckling and brace strength loss due to fracture. The effects of material variability, brace cross sectional shape and loading protocol on the drift-based fragility curves are investigated. The effect of global and local slenderness ratios on the fracture ductility of various shapes of steel braces is examined through dual-parameter fragility curves that relate these geometric ratios with the expected story drift ratios that each of the three pre-described damage states occur. The proposed fragility curves can be employed for rapid assessment of the seismic vulnerability of concentrically braced frames.     

钢筋混凝土框架结构的损伤状态相关余震易损性分析

一次主震过后通常伴有多次余震发生,由于主、余震间隔时间较短,主震损伤结构通常要遭受进一步的余震作用.为了评估震损结构的余震安全,提出了一种损伤状态相关的余震易损性分析方法.该方法采用有限次整体调幅的主余震序列作为输入,利用Park-Ang指数描述结构在主余震序列作用下的主震损伤和累积损伤,基于logistic回归方法生...     

Fragility of skewed bridges under orthogonal seismic ground motions

The paper evaluates seismic fragility characteristics of skewed bridges under simultaneous action of orthogonal ground motion components. The effect of skew angle on bridge seismic fragility characteristics is investigated through nonlinear time-history analyses of Painter Street Overpass, a 38.5° skewed bridge located in Rio Dell, CA, and six representative bridges with skew angles varying between 0° and 50°. Ground motion incident angle is varied from 0° to 180° to investigate the effect of the direction of ground motion incidence on bridge seismic performance. Bridge seismic response is used to generate fragility curves and contours plots that quantify the sensitivity of bridge fragility characteristics on skew angle and incident angle. For any value of incident angle, bridge seismic vulnerability increases with an increase in skew angle; however, no such general trend is found to describe the effect of incident angle on bridge fragility characteristics. Results show that the variation of maximum rotation of bridge columns for an earthquake does not follow any particular trend with the change in skew angle and incident angle. Analysis-based fragility curves are further compared with empirical fragility curves generated using real-life seismic damage data of skewed bridges and a reasonable agreement is observed between these two.     

Seismic vulnerability assessment of tilt-up concrete structures

This paper focuses on seismic vulnerability assessment for one-story tilt-up concrete structures. To capture the potential failure mechanisms, an analytical modelling approach using nonlinear properties is developed and verified with measured data from a shake table test documented in the literature. Nonlinear dynamic analyses using synthetic ground motions for Memphis, Tennessee, are performed to assess dynamic behaviour of the buildings. Then, probabilistic demand models for multiple limit states that represent potential failure mechanisms are developed with a Bayesian updating approach. These demand models are used in conjunction with appropriate capacity limits to develop fragility curves that provide a probabilistic measure of the seismic vulnerability of typical tilt-up concrete buildings. This study shows that the vulnerability of typical tilt-up structures in Mid-America is significant when seismic hazards are high. In addition, it is found that the aspect ratio of building geometry has a significant impact on the seismic performance and fragility estimates of tilt-up buildings.     

Drift-based fragility assessment of confined masonry walls in seismic zones

The paper presents drift-based fragility curves developed for confined masonry (CM) walls, which are the main structural components for the lateral load-resisting systems employed in housing dwellings in Latin-America. Drift-based fragility curves were developed for two key damage states associated with the structural performance and repairability of CM walls, from experimental results of 118 confined masonry specimens tested under lateral cyclic loading, during research programs carried out in Mexico, Chile, Peru, Venezuela and Colombia. In particular, four sources of uncertainty, due to specimen-to-specimen, finite-sample, measured diagonal compression strength of the masonry and wall height-to-length aspect ratio were included. These fragility curves are very useful for assessing the seismic vulnerability of CM structures, and for estimating the earthquake-induced economic losses employing recently proposed methodologies based on aggregating the estimated damage at the component level for a specific structure.     

An expert judgement approach to determining the physical vulnerability of roads to debris flow

The physical vulnerability of roads to debris flow may be expressed through fragility functions that relate flow volume to damage probabilities. Fragility relationships are essential components of quantitative risk assessments as they allow for the estimation of risk within a consequence-based framework. To the best of the authors’ knowledge, this is the first time that fragility curves have been produced in order to provide the conditional probability for a road to be in, or to exceed, a certain damage state for a given debris flow volume. Preliminary assessments were undertaken by means of a detailed questionnaire. A total of 47 returns were received from experts in 17 countries: 32 % academia, 51 % the commercial sector and 17 % governments. Fragility curves have been defined for three damage states (limited damage, serious damage and destroyed) for each of low-speed and high-speed roads in order to cover the typical characteristics of roads vulnerable to debris flow. The probability of any given damage state being reached or exceeded by a debris flow of a given volume (10–100,000 m³) was derived from the mean of the responses received. Inevitably there was a degree of scatter in the results, and the treatment of such variation, or ‘experimental errors’, was crucial to understanding the data and developing the fragility curves. Fragility curves are quantitative expressions of vulnerability. The method adopted is based upon qualitative, expert judgment of quantitative probabilities. In addition to an assessment of the probabilities of given damage states being exceeded, respondents to the questionnaire were polled as to their level of experience and confidence in their ability to provide a valid and coherent set of answers to the questions posed. The development of the fragility curves and their validation are described in the paper.