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.     

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.     

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。     

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.     

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。     

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.     

钢筋混凝土梁桥加固改造技术探讨

简单介绍了几种常见的钢筋混凝土梁桥加固改造技术,根据桥梁病害检测和评定结果,结合实际情况,选择了有效的加固方法,通过加固方法的实施,达到了加固补强的目的。     

Nonlinear analysis of multi-cell reinforced concrete box girder bridges

A numerical method of analysis is developed to determine the nonlinear response, collapse mechanisms and ultimate failure loads of multi-cell RC (reinforced concrete) box girder bridges under stepwise increasing static loads. Nonlinearities considered are material nonlinearities inherent in RC members such as cracking of the concrete, yielding of the reinforcement and formation of plastic hinges due to shear and flexure. The analytical model, based on a three-dimensional grillage, is developed for multicellular structures of arbitrary plan geometry and constant height. Realistic but simple assumptions for the interaction of internal forces due to flexure, shear and torsion in the cellular structure, as well as idealized trilinear force-deformation characteristics for the individual members comprising the grillage, result in a very economical nonlinear analytical model. The proposed analytical scheme, which is based on a mixed model formulation at the element level, is demonstrated and tested on a series of numerical examples and the analytical results indicate good agreement with experimental results obtained from large scale model tests on RC box girder bridges.     

混凝土中钢筋的电解液加速腐蚀方法

电解液腐蚀方法常用于诱导混凝土中钢筋的腐蚀以便加快腐蚀速度.为评价电解液腐蚀方法应用于混凝土中钢筋加速腐蚀的有效性和误差范围.在不同厚度混凝土中的光面钢筋的试验结果显示,实测腐蚀率与基于法拉第定律所计算的理论腐蚀率相符合.腐蚀过程中测量了电阻.结果显示实测电阻随累积腐蚀率变化.腐蚀初期电阻快速增大至其最大值,但随之又快速下降,再缓慢降低,直至在其最小值附近变化趋于停止.与前期研究结果的比较显示,光面钢筋与变形钢筋表现出相似的电阻-腐蚀率关系.     

基于碳化的既有钢筋混凝土桥梁耐久性的概率分析

分析讨论了混凝土碳化机理及其影响因素，并探讨了混凝土碳化深度的预测数学模型，基于既有钢筋混凝土桥梁的实测数据。对碳化系数和混凝土强度进行回归分析，建立了根据混凝土强度预测碳化深度的数学模型。将混凝土强度，保护层厚度。计算模式不确定性系数作为随机变量，以混凝土的碳化深度作为一个随时问变化的随机过程，建立了混凝土碳化到钢筋表面的时变概率随机模型．并以一座实际桥梁为例。给出了在不同使用年限时混凝土碳化到钢筋表面的预测值。结果表明，该模型可用于大气环境下基于碳化的钢筋混凝土桥梁结构耐久性评估。     

Fatigue-safety assessment of reinforced concrete (RC) bridges: application to the Brazilian highway network

During the assessment programme of Brazilian roadway bridges, it was noticed that two girder-slab reinforced concrete bridges, with cantilever girders on extremity spans, were a common structural solution adopted 40 years ago in Brazil. Particularities intrinsic to these systems like significant displacements expected on cantilevers associated with soil embankment settlement in bridge entrance can take to a sudden change in slope grades near its ends, provoking sometimes high impact factors. Besides that, traffic and axle load increase has been of concern because these bridges were designed with different scenarios 40 years ago. Therefore, these facts can affect the structural performance of these structures in face of 100 years life required on most current codes for new bridges. So, in this article, a safety assessment to this assembly of bridges is performed. For this study, a simulation model has been developed, which includes the most significant sources of uncertainty in the definition of traffic action and structural response of bridges. Database provided by dynamic tests of these bridges were used for this performance-based assessment. As a result, reliability indexes to fatigue and ultimate limit state of bending are calculated and compared with target values as specified by codes.     

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.     

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。     

预防碳化提高钢筋混凝土的耐久性

碳化是影响混凝土耐久性的一个重要因素,将加速混凝土中钢筋的腐蚀,从而缩短工程寿命。目前碳化破坏引起更加特别的重视,因全球关心的气候变化过程实质上就是空气中CO2浓度增加的过程。其次是因为使用高掺量混合材加剧了水泥的碳化破坏。加以高速发展新的基础设施,其中地下工程、地铁、火车站、城市中心等地的微气候中CO2的浓度显著增加。在施工过程中若养护不够,表面层空隙率增加,将更加加重CO2的腐蚀程度。本文将详细叙述这些因素,并提出解决碳化问题应采取的措施。     

模拟海洋环境下负载对锈蚀钢筋混凝土梁使用的影响

完成了对持续荷载作用下锈蚀梁、加载后卸载锈蚀梁、持续加载不锈蚀梁在使用阶段的对比试验。通过交替喷洒3.5%的盐水来模拟海洋潮汐环境,采用外加电流来加速钢筋锈蚀,整个试验过程中检测梁的锈蚀电流和跨中挠度。结果表明,荷载对钢筋锈蚀有明显影响,荷载作用使梁锈蚀加速,钢筋出现不均匀锈蚀。随着时间的增长,持续荷载作用下锈蚀梁的跨中挠度比没有锈蚀梁的挠度增长速度快。因此锈蚀钢筋混凝土结构在使用阶段的性能对耐久性能研究和使用寿命预测都非常重要。     

Three-dimensional modelling of structural effects of corroding steel reinforcement in concrete

The effect of corrosion products flowing through cracks becomes significant when large corrosion penetrations take place in reinforced concrete structures and wide cracks develop; this is favourable, as it decreases the splitting stress around the bar. The effect becomes more important when the corrosion rate is low, such as for natural corrosion. Acorrosion model describing the expansion due to voluminous corrosive products was previously developed. The model is here extended to include the flow of corrosion products through cracks. The volume flow of corrosion products through a crack is assumed to depend on the splitting stress and the crack width. The splitting stress is evaluated from the strain in the corrosion products, and the crack width is computed from the displacements across the crack. A one-dimensional flow model is used to formulate the flow phenomenon and to estimate the volume flow of corrosion products. The extended corrosion model, applied in detailed three-dimensional non-linear finite element analyses of highly corroded eccentric pull-out specimens, resulted in more corrosion cracks with smaller crack openings, which better corresponded to measurements of the tested specimens. Moreover, the results indicated the important effect of the flow phenomenon on the bond strength.     

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。     

钢筋混凝土框架的非线性分析

考虑结构的材料非线性、几何非线性、节点区锚固钢筋的滑移和节点刚域等因素的影响,采用5区段变刚度法,编制了钢筋混凝土框架分析程序。该程序可对多层多跨框架进行非线性分析,且通过与试验结果对比吻合较好,从而为研究钢筋混凝土框架的非线性设计提供了理论分析手段。     

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。     

锈蚀对钢筋混凝土梁的影响

采用六种不同类型的梁进行了试验研究,探讨了锈蚀对钢筋混凝土梁的影响,通过向混凝土梁环境中添加氯化钙加速锈蚀,分析了由于钢筋的锈蚀,对钢筋混凝土梁的极限承载力及跨中变形的影响规律。