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 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.     

锈蚀钢筋混凝土结构地震易损性分析

钢筋锈蚀是影响钢筋混凝土结构耐久性的一个重要因素,会引起结构的自振周期延长、地震需求变化及抗震能力衰减,使得锈蚀钢筋混凝土结构的地震易损性分析不同于未锈蚀钢筋混凝土结构。以一栋按我国规范设计的RC框架结构为研究对象,分别建立了未锈蚀和锈蚀结构的非线性有限元模型并进行了模型验证。分别采用云图法和条带法计算得到了钢筋混凝土结构在未锈蚀和锈蚀两种工况下的地震易损性曲线和函数参数,对锈蚀钢筋混凝土结构地震易损性分析的特殊性及其对地震易损性分析结果的影响进行了分析。分析结果表明：不考虑钢筋锈蚀引起的结构自振周期延长会错误估计锈蚀钢筋混凝土结构的地震易损性水平。采用云图法分析锈蚀钢筋混凝土结构的地震易损性会出现锈蚀结构的极限状态失效概率低于未锈蚀结构的情况。而条带法比云图法可以更好地反映钢筋锈蚀对钢筋混凝土结构地震易损性的影响。忽略钢筋锈蚀引起的结构抗震能力衰减会低估锈蚀钢筋混凝土结构地震易损性水平,建议在锈蚀钢筋混凝土结构地震易损性分析中采用基于Pushover的极限状态定义方法。     

Seismic fragility analysis of reinforced concrete structures considering reinforcement corrosion

钢筋锈蚀是影响钢筋混凝土结构耐久性的一个重要因素，会引起结构的自振周期延长、地震需求变化及抗震能力衰减，使得锈蚀钢筋混凝土结构的地震易损性分析不同于未锈蚀钢筋混凝土结构。以一栋按我国规范设计的RC框架结构为研究对象，分别建立了未锈蚀和锈蚀结构的非线性有限元模型并进行了模型验证。分别采用云图法和条带法计算得到了钢筋混凝土结构在未锈蚀和锈蚀两种工况下的地震易损性曲线和函数参数，对锈蚀钢筋混凝土结构地震易损性分析的特殊性及其对地震易损性分析结果的影响进行了分析。分析结果表明：不考虑钢筋锈蚀引起的结构自振周期延长会错误估计锈蚀钢筋混凝土结构的地震易损性水平。采用云图法分析锈蚀钢筋混凝土结构的地震易损性会出现锈蚀结构的极限状态失效概率低于未锈蚀结构的情况。而条带法比云图法可以更好地反映钢筋锈蚀对钢筋混凝土结构地震易损性的影响。忽略钢筋锈蚀引起的结构抗震能力衰减会低估锈蚀钢筋混凝土结构地震易损性水平，建议在锈蚀钢筋混凝土结构地震易损性分析中采用基于Pushover的极限状态定义方法。     

Seismic fragility assessment of highway bridges: a state-of-the-art review

Safety and serviceability of highway bridges, during and after an earthquake, is a prerequisite to ensure continuous transport facilities, emergency and evacuation routes. Recently, fragility curves have emerged as important decision support tools to identify the potential seismic risk and consequences during and after an earthquake. There has been a substantial increase in interest among researchers in the topic of seismic fragility assessment of highway bridges as evidenced by the growing number of published literature. Advanced computational techniques and available resources have led to the development of different methodologies for fragility assessment. This study presents a review of the different methodologies developed for seismic fragility assessment of highway bridges along with their features, limitations and applications. This study presents a review of available methodologies and identifies opportunities for future development. This study mainly focuses on the key features of different methods and applications rather than penetrating down to a critique of the associated analysis procedure or mathematical framework. It synthesises the existing information on fragility analysis, presents it in concise and useful tables, and explains different applications for different purposes, which would motivate decision-makers and stake holders to extend the application of fragility curves for more informed decision-making.     

Seismic risk assessment of reinforced concrete bridges in flood-prone regions

This article presents a conditional seismic risk evaluation framework of bridges located in seismically active flood-prone regions. Flood-induced bridge scour causes loss of lateral support at bridge foundations and thus the effect of seismic hazard on bridge performance gets amplified. Two example reinforced concrete bridges located in Sacramento County in California are considered. The regional multihazard scenario is characterised by combining scour resulted from regional flood events of different intensities with a suite of earthquake ground motions that represents regional seismicity. Uncertainties in the hazard models are discussed and their influences on bridge performance are investigated. A separate set of analysis is performed to evaluate the bridge performance only under earthquake ground motions. Seismic fragility curves and risk curves for the example bridges are generated. Result shows higher seismic risk of bridges when the impact of regional flood hazard on bridges is considered in the analysis framework. This suggests the use of a combined seismic and flood hazard model for reliable seismic risk evaluation of bridges located in flood-prone regions.     

Seismic fragility assessment of a tall reinforced concrete chimney

In China, a considerable proportion of reinforced concrete (RC) industrial chimneys in operation was designed and constructed in accordance with less rigorous outdated seismic criteria during the end of 19th and early 20th century. However, few research works have been reported till date on a realistic overall assessment of the seismic performance of these existing aging RC chimney structures. Therefore, in this study, fragilities of existing RC chimney were studied. For this purpose, an existing 240 m tall RC chimney was selected and structurally modeled with a lumped mass beam (stick) model by means of the OpenSees analysis program. In order to capture the uncertainties in ground motion realizations, a series of 21 ground motions are selected from the Next Generation Attenuation database as the input motions. To develop the analytical fragility curves, nonlinear incremental dynamic analysis of the studied RC chimney was then carried out using the selected input motions, which were normalized to different excitation levels. The section curvature ductility ratio was considered as the damage index. Based on material strain and sectional analysis, four limit states (LSs) were defined for five damage state. The seismic responses of the all sections were utilized to evaluate the likelihood of exceeding the LSs. Then the peak ground acceleration (PGA)‐based seismic fragility curves of the structure were constructed assuming a lognormal distribution. Finally, under the light of these fragility curves, the damage risks in existing RC chimney were discussed. The analytical results indicated that for design level earthquake of PGA = 0.1 g (g is the gravitational acceleration) and the maximum considered earthquake of PGA = 0.22 g, the probabilities of exceeding the light damage state were around 1.5% and 44%, respectively, while the exceedance probabilities corresponding to moderate, extensive and complete damage states were approximately zero in both cases. On the other hand, fragility analysis revealed that the RC chimney structure had considerable ductility capacity and was capable to withstand a strong earthquake with some structural damages. Copyright © 2014 John Wiley & Sons, Ltd.     

Seismic fragility curves for mid-rise reinforced concrete frames in Kingdom of Saudi Arabia

This article is concerned with the development of seismic fragility curves for typical mid-rise plane reinforced concrete moment-resisting frames in Kingdom of Saudi Arabia (KSA), which is considered as low-seismicity area. Two structural models; four- and eight-storey moment-resisting frames were considered. Three cities with different seismic intensities, Abha, Jazan and Al-Sharaf, were selected to cover various values of mapped spectral accelerations in KSA. The 0.2-s spectral accelerations range from 0.21 to 0.66 g, while the 1.0-s spectral accelerations range from 0.061 to 0.23 g. The structural models were designed under dead, live and seismic loads of these cities according to the Saudi Building Code. Incremental dynamic analysis was performed under 12 ground motions using SeismoStruct. Five performance levels, namely, operational, immediate occupancy, damage control, life safety and collapse prevention were considered and monitored in the analysis. Fragility curves were developed for the structural models of the three cities considering the five selected performance levels.     

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...     

Reinforced concrete and masonry arch bridges in seismic areas: typical deficiencies and retrofitting strategies

In recent years, appraisal of the condition and rehabilitation of existing bridges has become an ongoing problem for bridge owners and administrators in all developed countries. Reliable methodologies are therefore needed in the assessment and retrofit design phases, to identify the vulnerability of each bridge class. The specific problems of common arch bridge types are discussed herein, for both reinforced concrete and masonry structures, proper interventions for their static and seismic retrofitting are illustrated and several examples of applications are provided. Retrofitting is usually coupled with functional refurbishment, according to a methodological approach that takes into account bridge characteristics, state of maintenance and functional requirements, and environmental aspects connected with repair and strengthening systems.     

Capacity loss evaluation of reinforced concrete bridges located in extreme chloride-laden environments

This article provides a comprehensive procedure for the structural performance evaluation and life-cycle cost (LCC) analysis of reinforced concrete highway bridges located in extreme chloride-laden environments. An integrated computational methodology is developed to simulate the chloride intrusion and to estimate the corrosion initiation time. The effects of various influential parameters on the chloride diffusion process are examined and the changes in geometry and material properties of structural members are calculated over the entire life of the bridge. In order to evaluate the global structural degradation due to the corrosion mechanisms, an inventory of bridges with different structural attributes are investigated. The extent of capacity loss is calculated using the moment-curvature and nonlinear static (pushover) analysis. Results of this study are then utilised to find the LCC of bridges. Different inspection and maintenance strategies are considered to minimise the total LCC, which includes the initial construction cost, inspection and maintenance costs and service failure costs. The proposed approach indicates the inspection and maintenance intervals in a way that the inspection and maintenance costs are optimised while the safety of the bridge is ensured.     

近场地震作用下型钢-混凝土组合结构桥易损性分析

考虑近场速度脉冲型地震动特征,对型钢-混凝土组合结构桥梁的地震易损性进行分析。以一座工字型钢-混凝土组合梁桥为例,从PEER数据库挑选60条近场地震动记录作为输入,对桥梁结构整体性能和局部性能两个层次的易损性进行分析,给出了桥梁结构的整体和局部地震易损性曲线。通过与远场地震作用下的桥梁结构地震易损性分析结果的对比研究,发现：近场速度脉冲型地震引起的桥梁结构整体和局部地震需求均显著大于远场地震|在近场地震作用下,桥墩是型钢-混凝土组合桥梁的最易损构件,混凝土横梁与栓钉的易损性水平低于桥墩。     

既有钢筋混凝土桥梁评估中的可靠性研究

首先介绍了可靠度的计算方法,接着介绍了既有桥梁可靠性评估的特点和可靠性理论在桥梁评估中的应用方式,最后对既有桥梁应用可靠性进行评估的现有研究成果进行了概括,简单说明了研究中存在的不足。     

Seismic response and fragility analysis of fiber-reinforced concrete frame-shear wall structure

为研究在关键部位采用聚乙烯醇纤维增强混凝土材料的结构的地震反应,利用Perform-3D软件对一栋10层的框架 剪力墙结构进行单向罕遇地震（50年超越概率2%）作用下的非线性动力时程反应分析。结果表明,随着结构地震损伤程度的增加,纤维增强混凝土的优良性能发挥更加充分,对结构的抗震性能改善作用也更加明显;结构基本周期对应的加速度反应谱强度S_a(T₁)能较好地反映结构的损伤程度,适合作为地震动强度衡量指标。依据FEMA P695建议的增量动力分析方法,对22对地震动记录进行标准化处理和调幅,并通过结构地震易损性函数,给出结构在不同强度地震作用下达到“防止倒塌”极限状态的失效概率。对于框架-剪力墙结构,建议可采用墙肢塑性铰转角作为其“防止倒塌”极限状态地震易损性分析的结构反应参数。     

Simplified vulnerability assessment of reinforced concrete circular piers in multi-span simply supported bridges

This paper proposes a simplified procedure for the seismic vulnerability analysis of multi-span simply supported bridges, in the case of single piers with solid circular sections. The proposed method can be applied whenever the seismic response of the whole bridge depends on the most critical pier. For an assigned limit state, the procedure determines the capacity curve of the critical pier as a function of three parameters (elastic stiffness, displacement at yielding, displacement at collapse), starting from the behaviour under combined axial stress and bending, and then taking into account the different possible collapse modes (shear failure; lap splice failure of the longitudinal bars; buckling) and the geometric nonlinearity. A significant numerical example is presented in which the traditional FEM solution is compared with the proposed simplified procedure.     

非一致氯离子侵蚀下近海桥梁时变地震易损性研究

近海桥梁往往处于氯离子空间分布不均匀的复杂环境,在服役过程中往往会遭受非一致氯离子侵蚀,导致材料及结构性能不断退化,降低桥梁抵御地震的能力。为研究非一致氯离子侵蚀下桥梁地震损伤风险变化规律,文章以氯离子扩散规律及钢筋锈蚀机理为基础,基于Duracrete模型及以往试验结果,确定不同环境参数及锈蚀参数的概率分布类型及统计特征,建立钢筋及混凝土材料退化规律。结合地震易损性分析理论,建立非一致氯离子侵蚀环境下桥梁时变地震易损性评估流程。随后,以一座多跨连续梁桥为例,分析退化桥梁抗震能力变化特征,研究不同构件的地震损伤时变规律。研究结果表明,氯离子侵蚀下的桥墩截面抗弯承载力和曲率延性均表现出明显的退化,并且曲率延性退化程度高于抗弯承载力。非一致氯离子侵蚀会导致桥墩损伤分布发生演变,桥墩易损位置可能从墩顶、墩底转移至低水位处。随着服役时间增加,桥墩损伤概率明显增大,而支座、挡块及桥台的损伤概率略有降低。     

钢筋混凝土梁桥的常见病害与处理

针对钢筋混凝土梁桥经常出现的几种病害状况,提出相应的处理方案及具体措施,为此类桥梁的检测、维修加固、设计和施工提供参考及建议,以推广钢筋混凝土梁桥的应用。     

预应力混凝土梁桥病害分析研究

指出预应力混凝土梁桥是目前我国应用最为广泛的桥梁类型,但是由于服役时间的增长,结构性能下降,大量的公路桥梁产生了各种不同的病害,对预应力钢筋混凝土梁桥所常见的病害及其产生原因进行了研究总结,为研究预应力混凝土梁桥病害奠定了基础。     

Reliability-based capacity design for reinforced concrete bridge structures

In the seismic design of reinforced concrete (RC) bridge structures, there should be no brittle failures, such as shear failures, in the components, and a plastic hinge should be formed at the bottom of the bridge pier. These are important concepts in capacity design to guarantee the safety of bridges subjected to severe earthquakes. These concepts can maximise post-event operability and minimise the cost of repairing bridges after a severe earthquake. In this article, a reliability-based methodology to carry out capacity design with partial factors is proposed and applied to the seismic design of RC bridge structures. This ensures that (i) all of the components undergo the desired ductile failure mode, (ii) the damage due to an earthquake is induced only at the bottom of the bridge pier and (iii) the probability of failure is at most equal to a specified value.     

基于机器学习的钢筋混凝土柱失效模式两阶段判别方法增强出版（附加材料可在文章详情页“评审附件”下载）

钢筋混凝土柱在侧向地震力作用下具有弯曲、剪切和弯剪三种失效模式。不同的失效模式下钢筋混凝土柱具有不同的地震损伤特征。因此,准确地判别钢筋混凝土柱的失效模式对于准确评估钢筋混凝土结构的抗震性能具有重要意义。利用已有的钢筋混凝土柱滞回加载试验数据,采用机器学习方法,提出了一种钢筋混凝土柱失效模式两阶段判别方法。其中,第一阶段以钢筋混凝土柱的基本设计参数为输入变量,采用机器学习中的回归算法,建立钢筋混凝土柱的受弯承载力、受剪承载力、弯曲变形和剪切变形预测模型。第二阶段以钢筋混凝土柱的受弯承载力、受剪承载力、弯曲变形和剪切变形作为输入变量,采用机器学习中的分类算法,对钢筋混凝土柱的失效模式进行自动判别,实现了准确判别钢筋混凝土柱失效模式的目的。研究结果表明：极端随机树、AdaBoost、随机森林和梯度提升算法分别对受弯承载力、受剪承载力、弯曲变形和剪切变形的预测效果最佳;极端随机树、梯度提升算法和最近邻居法分别对弯曲失效、剪切失效和弯剪失效具有最佳的分类效果;相比已有的钢筋混凝土柱失效模式分类方法,提出的两阶段分类方法具有与真实失效模式最为接近的分类结果,分类精度可以达到96%。