钢筋混凝土结构基于耐久性劣化度的可靠性分析

结构耐久性的不足将引发其性能的劣化,并导致结构可靠度的降低。根据已建立的两种劣化度模型及极限状态法,以碳化深度和锈胀开裂两种不同的耐久性劣化度为指标,提出了混凝土结构使用寿命全过程可靠度的计算方法。结合工程实例,以荷载作用下的混凝土结构在碳化环境中的劣化问题为例,构建极限状态函数,基于两种劣化度模型,对其运用可靠度理论进行分析,得到了基于耐久性劣化度的结构可靠度求算方法。研究结果表明：可靠度与结构的混凝土保护层厚度及碳化速率的统计数值或钢筋锈蚀量密切相关。计算方法可为分析在役工程的耐久性提供参考。参14     

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.     

Redundancy-based service life assessment of corroded reinforced concrete elements considering parameter uncertainties

In order to assess the structural reliability and redundancy with respect to deterioration, appropriate models have to be selected which adequately describe the deterioration process. The parameters associated with these models have to be estimated based on statistical inference. In general, the uncertainties that arise from the estimation of parameters are not accounted for in reliability assessment and the obtained structural reliability indices are assumed to be constant values. When parameter uncertainties are considered, the structural reliability index can, however, be considered as a random variable which inevitably influences the full-probabilistic decision-making process. Furthermore, the structural reliability indices which are used in a reliability-based redundancy factor can be considered as random variables. Hence, this redundancy factor itself is a random variable as well. In this paper, a full-probabilistic framework is developed which allows for the service life assessment of reinforced concrete elements subjected to corrosion based on a probability-based redundancy factor and taking into account parameter uncertainties. It is proven that these parameter uncertainties have a significant influence on the lifetime estimates of concrete elements subjected to corrosion. Finally, a simplified method is proposed which allows to incorporate parameter uncertainties in the redundancy assessment.     

Robustness of corroded reinforced concrete structures – a structural performance approach

The aim of this work is to provide new contributions in order to define more accurately the structural robustness concept, particularly when applied to corroded reinforced concrete (RC) structures. To fulfil such a task, several robustness indicators are analysed and discussed with special emphasis on structural-performance-based measures. A new robustness definition and a framework are then proposed for its analysis, based on the structural performance lost after damage occurrence. The competence of the proposed methodology is then tested comparing the robustness of two RC foot bridges under corrosion. The damage considered is the longitudinal reinforcement corrosion level, and load carrying capacity is the structural performance evaluated. In order to analyse corrosion effects, a finite element (FE) based on a two-step analysis is adopted. In the first step, a cross-section analysis is performed to capture phenomenons such as expansion of the reinforcement due to the corrosion products accumulation; damage and cracking in the reinforcement surrounding concrete; steel–concrete bond strength degradation; effective reinforcement area reduction. The results obtained are then used to build a 2D structural model, in order to assess the maximum load carrying capacity of the corroded structure. For each foot bridge, robustness is assessed using the proposed methodology.     

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.     

Stochastic time–cost tradeoff analysis: A distribution-free approach with focus on correlation and stochastic dominance

The present study explores how correlated Monte Carlo simulation (MCS) coupled with a multiobjective particle swarm optimization algorithm can expand the time–cost tradeoff analysis in the presence of uncertainty. The goal of the proposed framework is to find the optimal set of activity options, whose objectives are evaluated as value-at-risk measures of project duration and total cost. The proposed framework incorporates the Gaussian copula into MCS to treat statistical dependence between uncertain variables, with no restriction on the estimation process and distribution type. This paper elucidates the definition of stochastic dominance relations, based on which a decision rule is established to prescreen dominated solutions so as to alleviate computational burden. A practical project has been used to validate the proposed framework by comparisons with enumeration and NSGA-II (non-dominated sorting genetic algorithm). In addition to nondominated solutions, the proposed framework provides insightful risk assessments.     

箍筋锈蚀钢筋混凝土柱受火后抗震性能试验研究及有限元分析

为研究箍筋锈蚀钢筋混凝土柱的火灾反应及其火灾后的抗震性能,设计并制作4根尺寸及配筋相同的钢筋混凝土柱,以锈胀裂缝为损伤指标,对混凝土柱的箍筋进行电化学加速锈蚀试验,得到箍筋不同锈蚀率的混凝土柱.对RC柱进行限时受火试验,研究箍筋不同锈蚀率的混凝土柱的高温反应.对历经高温的钢筋混凝土柱进行低周水平反复荷载试验,并利用AN...