【作者】 史波；

【导师】 赵国藩；

【作者基本信息】 大连理工大学 ， 结构工程， 2009， 博士

【摘要】 混凝土结构是各国基础设施的重要组成部分,暴露于海洋和公路除冰盐环境中的混凝土结构大多由于氯盐引发的钢筋锈蚀而发生性能退化甚至过早破坏。在某些情况下,这种退化在施工完成几年内就能出现。除了暴露环境过于严酷外,造成结构过早退化的因素还有:不良的施工工艺导致施工质量下降;由于缺乏对退化机理的认识而导致设计水平不高,等等。本文在国内外已有研究成果的基础上,针对氯盐环境下钢筋混凝土结构性能劣化的不同阶段,建立了相应的预测模型,并基于性能和可靠度的方法来确定混凝土结构的寿命周期。主要工作包括:1.针对混凝土中Cl^-扩散过程所涉及材料和环境变量存在的比较显著的不确定性,建立了Cl^-扩散的概率预测模型。该模型考虑了环境条件（温度和相对湿度）、养护时间、试验方法及荷载状态等因素对扩散系数的影响;通过引入对流区参数扣除了对流对Cl^-浓度分布的影响。在分析国内外大量试验数据和检测结果的基础上,初步确定了模型中各随机变量的统计参数。2.采用弹性力学中承受均匀内压力的厚壁圆筒模型,引入弥散裂缝的概念,考虑了钢筋周围连通孔隙体积以及混凝土的双线性软化曲线,并通过断裂力学方法确定开裂混凝土的软化模量,建立了混凝土保护层锈胀开裂过程中锈胀压力、混凝土径向位移、临界锈蚀量和胀裂宽度的计算模型。根据模型可以确定保护层完全胀裂的时间。3.针对锚固区保护层锈胀开裂的钢筋混凝土构件,通过定义“有效锚固系数”来反映锚固区混凝土锈胀开裂对构件有效锚固能力的影响。分析结果表明,锈胀裂缝的长度、宽度以及保护层厚度等因素对有效锚固系数有显著影响。提出了锚固区胀裂后构件锚固可靠度的分析方法,并采用一次二阶矩方法研究了锈胀裂缝长度及宽度、保护层厚度、初始锚固长度、混凝土抗拉强度和配箍率等参数对锚固可靠度的影响。分析结果表明,当保护层刚开裂时,锈胀裂缝长度对锚固可靠指标β₀的影响很小,此后,随着裂缝宽度的增加,β₀有了明显的降低;保护层厚度和锚固长度的变化对β₀有相当大的影响;改变箍筋的直径或间距对锚固抗力的影响很小,因此β₀变化的幅度也很小。4.根据氯盐环境下钢筋混凝土结构性能退化的阶段性特点,提出了基于时变可靠度和结构性能的寿命周期模型。性能指标可以定义为构件应满足的适用性（如挠度、开裂、振动等）或承载力。该模型包括四个阶段,即钢筋锈蚀诱导阶段、混凝土保护层锈胀开裂阶段、适用性达到允许限值的阶段以及构件承载力达到最小可接受程度所经历的阶段。采用可靠度分析方法确定混凝土结构寿命周期的每个时段,并以结构性能达到极限状态作为该时段终结的评判标准。更多还原

【Abstract】 Concrete structures generally make up an important part of the national infrastructures. A majority of concrete structures in marine environment and road condition with de-icing salt application shows signs of performance degradation even premature failure due to corrosion of reinforcement in the presence of chloride.In some cases,the degradation is visible within a few years of construction completion.Despite the fact that the exposure condition is particularly severe,other factors affect the premature deterioration caused by the steel corrosion,such as:poor construction quality as a result of poor workmanship;poor design as a result of insufficient information with regards to the parameters that influence the degradation process.The main objective of this research work is to develop the models for assessing the performance deterioration and predicting the life cycle of RC structures in chloride environment based on the performance criteria and reliability analysis.This dissertation presented here focus on the following aspects:1.A probability-based model for the chloride ingress into concrete,based on the Fick’s second law of diffusion,is developed that takes into account the uncertainties in the relevant material and environment factors influencing the diffusion process of chloride.From the previous laboratory and field data reported by other researchers,the quantitative effect of these factors,e.g.temperature,relative humidity,time of moist curing,test methods and loading condition,on the diffusion coefficient of chloride is estimated statistically. Furthermore,in order to avoid adverse effect on accuracy in predicting chloride profiles affected by the convection zone,which deviates from diffusion behavior,the two parameters regarding convection zone are introduced into the probabilistic model.2.By introducing the concept of smeared crack and considering the bilinear softening traction-separation curve for cracked concrete,an analytical model for concrete cracking caused by corrosion of reinforcement is developed.In the model,cover concrete with embedded reinforcing steel bar is modeled as a thick-wall cylinder subjected to the uniform internal pressure build-up of expansive corrosion products.By solving the corresponding differential equation,the analytical solutions for the variables with respect to cover cracking due to corrosion are derived.These variables include the corrosion-induced pressure,radial displacement of concrete cylinder,critical amount of rust products,and width of corrosion crack.Moreover,based on the critical amount of corrosion products and rate of rust production,the time-to-cracking for cover concrete can be estimated. 3.An effective anchorage coefficient is defined to express the influence of corrosion-induced cracking in anchorage zone on the effective anchorage capacity for RC members.Both length and width of corrosion crack and cover depth significantly affect the effective anchorage coefficient.In addition,an anchorage reliability analysis approach for simply supported RC members under corrosion attack in anchorage zone is developed.The effect of various parameters,including both length and width of cover cracking due to corrosion,cover thickness,tensile strength of concrete,anchorage length,and stirrup ratio,on the anchorage reliability was analyzed by the first-order second-moment method.The results show that the effect of corrosion-induced crack length on the reliability index?for anchorage,β₀,is negligible when the crack on the concrete surface was just appearing,but with the crack widening,theβ₀ value is reduced significantly;the considerable changes inβ₀ can result from a variation in cover depth and anchorage length;the effect of changes in diameter or space of stirrups on the anchorage resistance is very limited,and the variation inβ₀ is also very low.4.A reliability and performance based life cycle model for corrosion-affected reinforced concrete members located in the chloride environment is presented.The performance can be defined by serviceability requirements,which includes issues such as deflections,cracks and spalling,vibrations,or by load bearing capacity.In the model,the life cycle of structures consists of four phases of lifetime,e.g.,the time periods from the completion of a newly built structure to corrosion initiation in the structure,from the initiation of corrosion to corrosion induced concrete cracking,from the concrete cracking to acceptable serviceability limit states,and from loss in serviceability to acceptable minimum level of safety.Reliability analysis method is employed to determine the time periods for each phase of lifetime.The estimate criteria are established to identify the end of every phase in terms of serviceability and ultimate limit states.更多还原