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<正>《土木建筑与环境工程》06/2017高速铁路简支箱梁桥的概率地震需求模型及易损性分析基于已建成高速铁路桥结构类型统计数据,以典型预应力混凝土简支箱梁桥为对象进行易损性研究。考虑5个不确定性参数,基于拉丁超立方抽样的反复试验法建立桥梁样本。采用"装箱法"选择地震动记录,与桥梁样本配对后进行非线性时程分析得到结构响应。定义各构件的损伤状态,通过对构件需求能力比进行二次回归建立桥梁各构件的概率地震需求模型,并生成构件易损性曲线,运用二阶单一边界法生成全桥易损性曲线。结果表明:二次回归分析产生的概率需求模型比线性回归方法更可靠;在地震作用下,此类桥梁构件中的墩柱、活动支     

川藏线不同墩高铁路简支梁桥地震易损性分析

基于地震易损性分析的理论方法,建立了川藏线铁路简支梁桥的分析型地震易损性模型。根据桥梁结构自身不确定参数,采用拉丁超立方体方法进行抽样并建立桥梁分析样本库。利用实测的汶川地震动对各样本进行了非线性动力时程分析,获得结构各构件的最大动力响应数据,通过回归分析建立了地震动强度和桥梁构件地震需求之间的关系。在确定结构不同构件各损伤状态对应的极限状态后,基于对数正态分布假设,采用传统可靠度理论建立了桥梁各构件地震易损性曲线,获得的易损性曲线可以为川藏线抗震设计提供依据。     

地震作用下中等跨径RC连续梁桥系统易损性研究

中等跨径混凝土连续梁桥是一种广泛应用的桥梁结构形式,地震作用下该类桥梁的破坏主要体现在桥墩、桥台和支座位置。以一典型多跨连续梁桥为例,考虑材料强度和上部结构容重等不确定性因素的影响,运用拉丁超立方抽样方法建立了10个桥梁样本。根据场地类型从PEER强震数据库中选取100条地震波来模拟地震动的不确定性,并与10个桥梁样本随机组合。对结构进行非线性时程分析后得到结构的响应,并分别定义了各构件的四种极限破坏状态,采用传统可靠度概率方法形成了桥墩、桥台和支座的易损性曲线,并运用联合失效概率方法研究了结构的系统易损性。研究结果表明:该类型桥梁的支座比墩柱、桥台更容易遭受地震破坏,尤其是桥台处活动支座;采用一阶界限法和二阶界限法计算的结构系统失效概率均大于各构件破坏概率,显然用结构系统易损性来评估桥梁抗震性能更为合理。     

木-混凝土简支梁桥地震易损性分析方法

简述木-混凝土梁桥,总结在地震作用下木-混凝土组合梁桥主要构件的理论易损性曲线建立的基本步骤和方法。通过地震动参数、局部场地条件和桥梁结构及不确定性来确定概率需求模型,根据不同损伤状态进一步说明木-混凝土梁桥之间的螺栓连接件对整个桥梁体系易损性的影响。     

多维地震动作用下曲线连续桥梁地震易损性研究

基于OpenSees有限元平台建立三类曲线连续梁桥,对算例桥梁进行三向平动地震动作用下的增量动力分析,并采用概率性地震需求分析方法绘制三类曲线连续桥梁关键构件的地震易损性曲线。结果表明在地震作用下,曲率半径小的单弯曲线连续梁桥比曲率半径大的单弯曲线连续梁桥损伤概率稍大;S型曲线连续梁桥相对于单弯曲线连续梁桥在桥墩横桥向损伤概率更大,且在多遇地震地震动加速度峰值(PGA=0.2g)以内,支座损伤概率较大。     

基于长短时记忆神经网络易损性分析的适用性研究

桥梁的损坏或失效可能导致严重的人员伤亡和巨大的经济损失。因此,对桥梁的破坏损失和地震性能进行准确的定量评估至关重要。为了实现这一目标,通常会采用构建易损性曲线的方法。易损性曲线表征在给定地震动强度下,桥梁部件或结构达到或超过某一破坏程度的条件概率。采用桥墩位移延性比作为损伤指标,利用长短时记忆（long short-term memory,简称LSTM）神经网络成功地建立了桥梁地震易损性曲线。研究结果表明,该模型展现了高计算效率和精度,可快速而准确地预测地震作用下桥梁结构构件的损伤指标。     

非规则钢筋混凝土高墩连续刚构桥地震易损性分析

为了研究非规则钢筋混凝土高墩连续刚构桥的地震易损性,文章以某采用不等高钢筋混凝土高墩的大跨连续刚构桥为研究对象,基于Open Sees软件建立全桥有限元模型,并将地震波输入有限元模型进行增量动力非线性分析,确定易损性曲线。研究表明:碰撞效应降低了2#墩(矮墩)和3#墩(高墩)在各损伤阶段的损伤概率,并且2#墩的损伤概率对地震荷载敏感性更强。在采用不等高钢筋混凝土高墩的非规则钢筋混凝土高墩连续刚构桥抗震设计中,应重视矮墩的抗震性能设计,并综合考虑矮墩和高墩的墩高差对桥梁地震易损性的影响。     

考虑橡胶支座随机性下隔震与非隔震近海桥梁地震易损性对比

针对目前在隔震桥梁地震易损性分析中隔震支座性能参数随机性研究薄弱、从失效概率的角度开展隔震与非隔震桥梁对比研究缺乏的现状,详细统计分析了橡胶隔震支座力学性能参数的不确定性,建立了近海隔震与非隔震桥梁非线性动力分析模型。在考虑支座参数、地震动及桥梁结构不确定性的基础上,利用拉丁超立方抽样分别生成90个结构-地震动样本对。利用Sap2000有限元软件对每个样本对进行非线性动力时程分析,通过对大量数据的回归分析,得到桥墩、支座的易损性曲线,进而对隔震前后结构的地震易损性进行了对比分析。结果表明：在同一破坏等级相同地震作用下,非隔震桥墩的失效概率大于隔震桥墩,非隔震支座破坏的概率大于隔震橡胶支座|采用隔震技术后,桥墩发生严重破坏和倒塌的概率极低,震后可修复的概率很大|而非隔震桥墩发生严重破坏的概率最大,说明其震后可修复的概率很小而产生不可修复损伤的可能性极大。     

基于对数回归模型的结构易损性分析

综合考虑结构物理参数的随机性和响应的统计相关性,提出了基于对数回归模型的结构易损性分析方法。以蒙特卡罗模拟和随机时程分析法考虑物理参数的随机性,采用β-二项分布探讨响应统计相关性,并建立对数回归模型计算结构易损性。以某一钢筋混凝土两跨连续梁高速公路桥为算例,根据设计图获取其物理参数作为均值,选取合适的标准差做蒙特卡罗模拟,随机采样得到参数样本,通过随机时程分析获得最大响应样本,利用矩估计、最小二乘分别求得β-二项分布和对数回归模型未知参数,最终获得各等级破坏状态下的易损性曲线,并与提出的基于累积极限状态阈值的结构易损性相比较。结果表明:所提出的易损性分析方法,能够达到对结构易损性的保守估计,保证预测结果的合理性,为检测桥梁构件是否过度老化或意外损坏提供理论依据。     

基于响应面法的LRB基础隔震结构地震易损性分析

提出了一种基于响应面法的LRB基础隔震结构地震易损性分析方法,考虑了LRB基础隔震结构中各子结构之间(即上部结构和LRB隔震支座)地震需求的相关性。分析中考虑地震动与LRB基础隔震结构物理参数的不确定性,以均匀设计法建立地震动-LRB基础隔震结构样本,通过对有限元模型进行非线性时程分析,分别建立各子结构响应均值、方差及其相关系数与不确定参数之间的响应面模型。在此基础上,采用蒙特卡罗模拟得到LRB基础隔震结构在不同性能水准下的地震易损性曲线。分析结果表明,所建立的响应面模型精度高、结构可靠,减小了复杂有限元模型非线性时程分析计算的工作量,有效提高了LRB基础隔震结构地震易损性分析的时效性。为了准确建立LRB基础隔震结构的地震易损性曲线,应考虑各子结构地震响应需求之间的相关性。     

Seismic fragility estimates for corroding reinforced concrete bridges

Seismic fragility of reinforced concrete (RC) bridges is defined as the conditional probability that the seismic demand exceeds the corresponding capacity, specified for a certain performance level, for given seismic intensity measures. However, the structural properties of RC bridges change over time due to the onset of corrosion in the reinforcing steel. Therefore, seismic fragility of RC bridges changes during a bridge lifetime. This paper proposes a method to estimate the seismic fragility of corroding RC bridges. Structural capacities are defined using probabilistic models for deformation and shear capacities of RC columns. Probabilistic models are also used to estimate the corresponding demands for given seismic intensity measures. The capacity and demand models are then combined with probabilistic models for chloride-induced corrosion and time-dependent corrosion rate to model the dependency on time of the seismic fragility of RC bridges. In particular, the loss of reinforcing steel is modelled as a function of the thickness of the cover concrete for each reinforcing bar in the RC columns. The stiffness degradation in the cover concrete over time due to corrosion-induced cracking is also considered in the fragility estimates. Seismic fragility estimates are then formulated at the column, bent, and bridge levels. The fragility formulations properly incorporate the uncertainties in the capacity and demand models, and the inexactness (or model error) in modelling the material deterioration. The proposed method accounts for the variation of structural capacity and seismic demand over time due to the effects of corrosion in the reinforcing steel. As an application, seismic fragility estimates are developed for a corroding RC bridge with 11 two-column bents over a 100-year period.     

Seismic fragility increment functions for deteriorating reinforced concrete bridges

Fragility increment functions are developed to estimate the seismic fragility of reinforced concrete (RC) bridges subject to deterioration due to the onset and progression of corrosion of the reinforcement. For each mode of failure considered, the fragility at time t of a deteriorating bridge is obtained by multiplying the initial fragility of the undeteriorated bridge by a corresponding increment function expressed in terms of the environmental conditions, the original material properties, time, a measure of the seismic demand, and a set of unknown model parameters. The developed increment functions account for the effects on the fragility estimates of the loss of the reinforcement and of the increasing uncertainty over time. As an application, the developed increment functions are used to estimate the seismic fragility of an example RC bridge. The proposed fragility increment functions are useful to estimate the fragility of deteriorating bridges without any extra reliability analysis once the fragility of the undeteriorated bridge is known. In particular, the proposed fragility increment functions can be used to assess the time-variant fragility of bridges for applications such as reliability-based design, life-cycle cost analysis, and risk analysis.     

Effects of liquefiable soil and bridge modelling parameters on the seismic reliability of critical structural components

This study investigates the sensitivity of seismic fragility estimates for bridge components to variation in structural and liquefiable soil modelling parameters. A rigorous sensitivity analysis is conducted to evaluate the relative importance of 13 random variables that reflect uncertainty in the seismic performance assessment of bridges in regions with liquefiable soils. The results indicate that the fixed and expansion bearings and bent piles tend to be sensitive to the greatest number of modelling parameters for the case study system, while the abutments are less sensitive. The most significant modelling parameters affecting the seismic fragility include such parameters as undrained shear strength of soil, structural damping ratio, soil shear modulus, gap between deck and abutment, ultimate capacity of soil and fixed and expansion bearing coefficients of friction. The 5% and 95% confidence intervals reveal wide bounds on the seismic fragility curves, particularly for more vulnerable bridge components such as the piles or expansion bearings. The results offer insights to improve seismic reliability assessment in liquefaction susceptible regions and provide a basis for efficient bridge network reliability analyses. The findings guide future uncertainty treatment, management of computational resources and investment in refined modelling parameter estimates through field testing or other means.     

Fragility analysis of bridges due to overweight traffic load

In the U.S. overloading represents the third cause of bridge failures just after hydraulic events and collisions. Large data assembled by Weigh-In-Motion (WIM) systems can be used to obtain improved region-specific or network-specific characterization of vehicle loads on highway bridges for a more accurate evaluation of the safety of critical bridges and the failure consequences to the concerned communities. To achieve this goal it is important to develop tools that allow engineers to estimate the reliability of various types of bridges subjected to realistic ranges of heavy truck load intensities as encountered on highway networks. The objective of this paper is to describe an approach that combines field data and numerical simulations to perform the fragility analysis of bridges due to different percentages of overweight loads and truck traffic. Numerical examples are provided by analyzing typical bridges using field truck data collected at WIM sites in upstate New York. The results of the analysis show that the fragility curves for fatigue are function of the percentage of overweight trucks in New York as a second order polynomial, while the fragility curves of bridges for overstress can be modeled with a copula using both normal distributions for the overweight percentages and Average Daily Truck Traffic.     

Nonlinear Static Procedure for Seismic Vulnerability Assessment of Bridges

Abstract:   The impact of an earthquake event on the performance of a highway transportation network depends on the extent of damage sustained by its individual components, particularly bridges. Seismic damageability of bridges expressed in the form of fragility curves can easily be incorporated into the scheme of risk analysis of a highway network under the seismic hazard. In this context, this article focuses on a nonlinear static method of developing fragility curves for a typical type of concrete bridge in California. The method makes use of the capacity spectrum method (CSM) for identification of spectral displacement, which is converted to rotations at bridge column ends. To check the reliability of this current analytical procedure, developed fragility curves are compared with those obtained by nonlinear time history analysis. Results indicate that analytically developed fragility curves obtained from nonlinear static and time history analyses are consistent.     

地震作用下钢筋混凝土桥梁结构易损性分析

针对缺乏桥梁结构地震破坏数据的地区 ,考虑地震地面运动、局部工程场地条件和桥梁本身参数的不确定性 ,给出了一种地震作用下钢筋混凝土结构易损性曲线的系统性分析方法 ,对美国中东部受NewMadrid地震带影响的高速公路系统混凝土连续桥梁结构易损性进行分析 ,并给出了桥梁结构的易损性曲线 ,表明本文方法对该类地区桥梁结构的易损性分析具有适用性。     

Fragility analysis of track-on steel-plate-girder railway bridges in Korea

More than 40% of the bridges in conventional Korean railway lines are track-on steel-plate-girder (TOSPG) bridges. They are characterized by a superstructure consisting of railway tracks sitting directly on steel plate girders without any ballast system. Most of these bridges have been designed with little or no consideration given to seismic loading. In this paper, seismic fragility curves of TOSPG bridges in Korea are developed. Fragility curves are developed first for the components, by using the probabilistic seismic demand model. The developed component fragility curves show that the bearings are the most vulnerable components of the TOSPG bridges against seismic loading. On the other hand, the piers are much less vulnerable, although they contain no reinforcing bars. This is because the superstructure mass is very light, and therefore horizontal loading transferred from the superstructure to the piers is minimal. A generic damage measure is introduced for measuring the system-level damage of structures out of the component-level damages. The system fragility curves are then developed, using the generic damage measure. Finally, representation of seismic risk in terms of expected seismic losses is demonstrated. This demonstration shows how the fragility analysis is utilized for risk assessment and support in decision-making.     

Seismic fragility analysis of reinforced concrete continuous span bridges with irregular configuration

A set of fragility curves of a class of reinforced concrete bridges with different degrees of irregularity has been generated. Eighteen bridge configurations have been identified, from regular to so-called highly irregular models. The geometric irregularity in this class of bridges is assumed to vary with the height of the piers. Using non-linear analytical models and an appropriate suite of 60 ground motions, analytical fragility curves have been generated for the individual piers of each of these 18 bridge models. Discussions have been made about the imposition of the displacement ductility demand of the piers versus the earthquake intensity as well as the bridge regularity. Comparison of the fragility curves shows that the most vulnerable bridges are the irregular bridges and high damage probability is expected for the short piers of this class of bridges. It was found that the fragility curves may be used for categorisation of regular and irregular bridges.     

Vereinfachte Methoden zur Berechnung der dynamischen Antwort von Eisenbahnbrücken bei Zugüberfahrt

Simplified methods to calculate the dynamic response of railway‐bridges under crossing trains. In this paper, two different methods to calculate the dynamic response of single‐span bridges under moving forces are presented. The work is focused on beam bridges with constant cross‐section in underdamped condition. In the first method, referred to as “Impulse‐method”, the effective impulse resulting from the load is approximated by simple analytical functions. The bridge is modelled as a single degree of freedom system by means of modal analysis. For this simplified system describing bridge and load, closed analytical formulae to calculate the dynamic response can be set up. The “Impulse‐method” is exemplified by the HSLM‐A1 load train given in Eurocode 1 (EC1). In the second method the response spectrum analysis widely used in earthquake engineering is adopted for the present problem. The calculation of response spectra for beam bridges under the HSLM‐A load models is demonstrated. An example shows how this method is deployed.     

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.