Seismic life-cycle cost analysis of ageing highway bridges under chloride exposure conditions: modelling and recommendations

Chloride-induced corrosion of highway bridges constitutes a critical form of environmental deterioration and may result in significant escalation of seismic life-cycle costs due to increased fragility during earthquake events. Most of existing literature tends to adopt simplistic uniform area loss assumptions in lieu of potentially complex, yet realistic and more detrimental, pitting corrosion models for seismic vulnerability analysis. Since the degree of deterioration depends on the severity and duration of exposure, there exists a need to investigate the influence of uniform vs. pitting corrosion assumption on seismic life-cycle costs for varied chloride exposure conditions. A case-study example of a highway bridge in Central and Southeastern US reveals consideration of pitting corrosion as critical for extreme exposures compared to relatively minor settings. Subsequently this study provides recommendations to aid bridge engineers and stakeholders to balance between computational cost and accuracy of results to aid prompt decisions on rehabilitation of ageing bridges in different exposure conditions. A framework is also included to compute seismic life-cycle costs from generic measures of corrosion, independent of assumed exposure scenario. This framework is particularly helpful for seismic loss assessment of highway bridges in chloride exposure zones with periodic field measurements to estimate the extent of structural deterioration.     

基于〖WTHZ〗Copula函数的渡槽结构地震动易损性分析

在结构易损性分析中，由于构件之间的地震需求存在相关性，直接建立渡槽系统中基本构件的联合概率分布函数较为困难，为此引入二维Copula函数对构件地震需求之间的相关结构进行描述，简化联合分布函数的建模过程。首先，对某输水渡槽中的一跨进行时程分析，以地面峰值加速度为自变量，以排架的位移延性比和橡胶支座的变形大小为损伤指标，考虑地震动和结构参数的不确定性，建立排架、橡胶支座的易损性曲线；其次，通过Copula函数建立渡槽系统的易损性曲线；最后，通过1阶界限法得到渡槽系统易损性的上、下界。计算结果表明，基于Copula函数计算得到的失效概率均位于1阶界限法的上、下界之间。研究结果有助于简化渡槽系统易损性曲线的建模过程，为研究渡槽构件地震需求之间的相关性提供新思路和方法。     

基于MSA的土石坝群体地震易损性研究

针对地震发生后亟需对土石坝群体震害进行快速评估的问题,基于统计数据和MSA方法,提出了土石坝群体震害易损性分析方法。通过分析土石坝群体震害数据,对震损大坝进行等级划分,结合地震破坏损失比和破坏比建立土石坝地震易损性矩阵。并引入MSA方法,建立土石坝群体震害易损性评估模型,计算出四种烈度下易损性参数及易损性曲线和概率,为土石坝群体震害快速评估提供了依据。     

多维性能极限状态随机性及相关性研究

同时考虑性能极限状态随机性及相关性,提出结构系统多维易损性评估方法。开展增量动力分析获取极限状态阈值样本,构造多维性能极限状态方程,创新地提出二维性能极限状态带确定结构失效域,借助区间估计确定某一置信水平下极限状态带上、下界,利用相关系数定量描述极限状态相关程度。开展非线性动力时程分析获取需求参数,建立结构多维概率地震需求模型,以桥梁系统为例计算多维易损性置信区间,开展易损性敏感性分析。结果表明性能极限状态带可较好解决极限状态随机性问题,多维易损性区间长度随极限状态带置信度的下降而变窄;随着极限状态相关系数的增加,极限状态相关性变弱,易损性评估结果偏小,产生非保守估计,不利于结构风险控制。     

Performance-based seismic fragility analysis of retaining walls based on the probability density evolution method

Seismic fragility analysis is an efficient way to study the seismic behaviour and performance of structures under the excitation of earthquakes of varying intensity, and an essential part of the seismic risk assessment of structures. A recently developed dynamic reliability methodology, the probability density evolution method (PDEM), is proposed for the dynamic reliability and seismic fragility analysis of a retaining wall. The PDEM can obtain an instantaneous probability density function of the seismic responses and easily acquire the seismic reliability of the structural system. An important advantage of the PDEM is its high efficiency relative to that of the Monte Carlo simulation method, which is often used in the reliability and fragility analysis of structures. The present study uses a typical gravity retaining wall to illustrate stochastic seismic responses and fragility curves that can be obtained by the PDEM. The combined uncertainties of the seismic force and soil properties are explicitly and systematically modelled by stochastic ground motions and random variables respectively. The performance of the retaining wall is analysed for different acceptable levels of backfill settlement. Additionally, seismic fragility curves are constructed without assuming the distribution of the seismic response.     

桥梁地震易损性分析的研究现状

介绍了国内外桥梁抗震易损性分析理论的近期发展，简要评述了经验和理论易损性曲线的形成，指出了目前研究中存在的问题与发展前景。     

Fragility analysis for ballistic design

Effective structural design to resist ballistic effects such as small arms or fragmenting weapons has been a goal since weapons were developed. Approaches currently in use for ballistic design are predominantly deterministic and allow designers to decide what wall thickness should be used to stop a prescribed projectile impacting at a predefined velocity. The research presented in this paper provides a framework for conducting reliability analysis of structures subjected to bullet and fragment demands. Thus, pseudo-fragility curves are developed for the limit states related to spall and perforation of wall panels, residual velocities of bullets and fragments, and injury to personnel. The pseudo-fragility analysis provides engineers and owners with a tool to quickly assess the reliability of a wall system subjected to high velocity, low mass projectiles. In particular, the proposed analysis method allows designers and owners to determine the probability of spall and perforation, residual velocity, and injury as a function of wall thickness or threat standoff distance.

Abbreviations: Cumulative distribution function (CDF): Gives the probability that a stochastic variable ‘X’, with a proper probability density function, is equal to or less than a value (x). Coefficient of variation (COV): The quotient of the standard deviation and the mean     

基于复杂网络理论的宝鸡公交网络构建与分析

选取陕西省宝鸡市的43条公交线路和344个公交站点,以公交站点作为节点,相邻站点之间存在公交线路作为连边,基于复杂网络理论构建了宝鸡公交网络模型。对网络的统计性质与拓扑特征分析表明,公交网络是稀疏的,具有无标度特性以及部分小世界性质,网络度分布服从幂律分布,少数枢纽节点在网络中起重要的作用,对应于城市的关键站点或主要换乘站点。公交网络同时存在鲁棒性与脆弱性,网络稳定性的研究可为城市公交网络的优化及交通规划提供一定的理论依据。     

蒸汽发生器非线性支承系统的抗震能力分析

计算核电厂设备的高置信度低失效概率(HCLPF)抗震能力是地震概率安全评价、地震裕度评价的一个重要步骤。以蒸汽发生器支承为研究对象,建立其详细的非线性有限单元模型,通过逐步增大地面运动水平,反复计算系统的响应,最后得到蒸汽发生器支承的抗震能力,并与通过确定性失效裕度法得到的HCLPF进行比较。结果表明,两者的计算结果差别较大。本文建议对于非线性较强的设备需采用非线性时程分析方法计算设备的HCLPF。     

考虑多重不确定性的我国多层#br# 冷成型钢结构地震风险评估

准确评估建筑结构的地震风险是实现其性能化抗震设计的重要组成部分。冷成型钢结构体系作为绿色和工业化建筑的典型代表,却鲜有针对于我国的地震风险评估研究。文章旨在分析和评估多层冷成型钢结构抗震分析所涉及的多重不确定性因素,进而定量评估该类结构在我国的地震风险。文章设计1栋八度抗震设防的6层冷成型钢结构,基于经过振动台验证的简化数值分析方法建立结构的简化数值模型,定量求解结构的多重不确定性因素和在使用周期内(50年)的地震风险。研究结果表明：由于我国一些地区的地震危险性形状系数较大,在考虑多重不确定性后,结构的破坏概率显著提高,50年使用周期内倒塌概率的增幅达到10倍以上;算例结构在50年使用周期内基本满足“小震不坏、中震可修、大震不倒”的抗震设防要求,对于个别特殊区域应适当控制结构发生轻微破坏的概率。此外,文章建议应全面考虑多重不确定对冷成型钢结构地震风险的影响,对不确定性参数的取值和地震风险的计算方法可提供借鉴。