考虑氯离子侵蚀与混凝土碳化的公路桥梁时变可靠度分析

基于国内外对氯离子侵蚀和混凝土碳化环境下钢筋锈蚀速率的最新研究成果,建立了混凝土构件在氯离子侵蚀下考虑坑蚀和在混凝土碳化下考虑平均锈蚀的弯曲抗力退化模型,用Monte Carlo方法和统计回归法编制了退化钢筋混凝土构件及系统的时变可靠度计算程序。以北京地区一座公路桥为算例,结果表明:在氯离子侵蚀下考虑坑蚀的桥梁承载能力时变可靠度在30年左右即下降到设计目标可靠度,在混凝土碳化下考虑平均锈蚀的桥梁承载能力时变可靠度在50年左右即下降到设计目标可靠度,从而需要补强,这表明考虑主筋锈蚀后我国钢筋混凝土公路桥一般达不到100年设计使用期;对因主筋锈蚀导致混凝土保护层胀裂而言,构件达到抗裂正常使用极限状态远远早于达到承载能力极限状态,建议将混凝土保护层开裂时间作为桥梁检查/维修参考点。     

基于耐久性理论和限载政策的某城市桥梁可靠性评估

城市桥梁在户外各种不利环境因素的影响下，结构材料的耐久性能会发生退化，以致出现混凝土强度降低、钢筋锈蚀等耐久性病害，导致桥梁结构的安全性和可靠性逐渐下降。以某典型城市高架桥为例，基于混凝土结构耐久性理论和城市的限载政策，结合现场检测、实地交通调查结果，分析了桥梁结构的时变抗力和荷载效应的变化规律，最后，推算了桥梁控制截面抗弯承载能力可靠性功能函数的失效概率，并对其可靠度进行了评估。该研究方法为各地城市桥梁的可靠性评估、维修养护、交通荷载限载政策等提供借鉴和参考。     

预后验决策分析用于优化混凝土桥梁检修规划

桥梁检修规划是基于桥梁可靠度退化模型、检查修理的技术和费用模型之上的一种决策方法,其目的是确定在什么时间对桥梁进行检查、修理,采用什么样的检查和修理技术最为经济。桥梁修理保证在桥梁设计使用期间内桥梁的可靠度不低于规定的限值,修理决策依据桥梁承载力退化模型和荷载模型;桥梁检查是为了进一步获得桥梁承载力和荷载的信息,从而使得修理决策依据的信息越来越充分。将预后验决策方法应用于桥梁的检修规划,确立了一种桥梁检修的规划方法。     

基于贝叶斯更新和逆高斯过程的在役钢筋混凝土桥梁构件可靠度动态预测方法

在役钢筋混凝土桥梁在服役环境和车辆荷载的耦合作用下,其服役性能随时间不断退化,采用确定性的性能退化模型无法准确描述退化过程中的不确定性和时间变异性。该文采用逆高斯随机过程描述其抗力退化过程,同时采用复合泊松过程描述车辆荷载效应,建立了基于抗力-车辆荷载效应双随机过程的在役钢筋混凝土桥梁构件时变可靠度分析方法。结合检测数据,采用贝叶斯分析和期望最大化算法,对逆高斯过程抗力退化模型参数进行更新,提出了在役钢筋混凝土桥梁构件可靠度的动态预测方法。以一座钢筋混凝土T梁桥为例,采用其40年服役期的抗力退化数据,分别在四个服役时刻对逆高斯过程抗力退化模型参数进行了更新,演示了提出的可靠度动态预测方法。研究表明:逆高斯随机过程可更合理地描述钢筋混凝土桥梁构件抗力退化过程中的不确定性和时间变异性;融入桥梁服役期间检测的抗力退化信息,采用贝叶斯更新逆高斯过程抗力退化模型参数后,可更准确地预测桥梁未来的可靠度服役状况和估计桥梁的剩余使用寿命。     

公路桥梁限载标准的可靠性分析方法

基于结构可靠度理论,建立了公路桥梁不同可靠水平下的车辆荷载限载标准。根据公路桥梁抗力及荷载效应概率分布函数与统计参数,采用最基本荷载组合形式与不同的活恒载标准值效应比值,从设计可靠水平与最低容许可靠水平两个层次,分别计算了按新老规范设计桥梁的超载影响系数。在此基础上,以三轴载重汽车和五轴载重汽车为不同汽车运行状态下的标准限载车辆模式,提出了基于典型限载车辆模式的公路桥梁安全限载标准与最大容许限载标准。最后,考虑实际抗力水平的差异,给出了基于不同规范设计桥梁限载标准的分析方法。研究结果表明,该文提出的基于可靠性的公路桥梁限载标准,与现行规范衔接紧密,可作为公路桥梁限载与超重运输通行审核的依据。     

基于实时退化量的数控机床状态维修检测间隔期决策研究EI北大核心CSCD

针对传统状态检测易造成过度检测的问题,提出一种基于实时退化量的数控机床状态检测间隔期确定方法。基于Gamma过程描述数控机床的退化过程,并结合等故障风险,给出退化过程前期的状态检测间隔期;给出系统状态处于缺陷阈值时的期望剩余寿命,并利用其对退化过程后期的状态检测间隔期进行约束,建立两阶段非等周期状态检测间隔期决策模型。以数控机床主轴的加工精度退化过程为例对所提方法进行验证,并与等周期状态检测和基于可靠度的状态检测方法进行对比分析,结果表明,该方法能够大大减少检测次数,降低维修费用,避免了过度检测。该研究成果可为合理确定状态检测间隔期提供参考和借鉴。     

基于最大裂缝宽度的钢筋混凝土桥梁可靠度分析

依据可靠度理论、相关可靠度设计标准和桥梁设计规范,推导了基于最大裂缝宽度的钢筋混凝土桥梁正常使用极限状态功能函数。分析了功能函数中各随机变量的分布类型,选择验算点法进行可靠指标的计算。最后给出计算实例,采用Matlab编程实现可靠指标的计算,计算结果表明最大裂缝宽度可靠指标基本满足设计要求。在实例计算中,还对最大裂缝宽度可靠指标进行了敏感性分析,影响最大裂缝宽度可靠指标的因素众多,限于篇幅,该文仅分析了活载比对最大裂缝宽度可靠指标的影响。     

基于gamma过程的锈蚀钢筋混凝土柱维护策略优化

随着在役钢筋混凝土结构的不断退化，业主们迫切关心如何利用有限资金在恰当时候对量大面广的结构进行管理与维护。基于gamma随机过程，该文提出了一种适用于锈蚀钢筋混凝土柱的维护策略优化方法。通过分析锈蚀引起的混凝土柱退化情况，该文建立了适用于不同锈蚀程度与受力状态的混凝土柱残余承载力计算模型。同时，考虑到结构退化过程的不确定性，采用gamma过程对锈蚀柱的失效概率进行了预测，并通过平衡失效风险与维修成本的方法，确定了结构的最佳维护时间。通过一个数值算例验证了该文提出方法的可靠性和有效性。结果显示：损伤程度与受力状态对锈蚀柱残余承载力有较大影响；此外，锈蚀柱的允许退化极限越小，结构的最佳维护时间越早，对应的期望相对成本越高。     

基于动态可靠度和经济优化相结合的服役桥梁维修加固风险决策

服役桥梁的维修加固需要综合考虑安全和经济的问题,基于服役桥梁的动态可靠度,以后续服役期内收益期望值最大或损失期望值最小为目标函数,对服役桥梁的维修加固决策进行了探讨,利用实际检测数据修正抗力模型,对一座服役期为35年的钢筋混凝土梁桥动态可靠度进行了计算,同时,比较分析了汽车荷载等级的提高和采用不同维护加固措施对后续服役期内动态可靠度的影响。该方法结合工程实际,把失效损失与失效风险相结合,对桥梁结构的维修加固决策有一定的指导作用。     

基于应力释放原理的桥梁混凝土结构单轴原位应力识别方法

原位应力对桥梁的状态与可靠度评估具有重要意义。针对桥梁混凝土结构服役年限较长、实际受力状态复杂、构件尺寸较大以及单轴受力控制的特点,通过单轴应力释放影响函数建立了未知原位应力状态与表面释放应变之间的对应关系。以薄壁环作为释放区域,借助有限元标定了不同测量区域的影响函数。通过分步钻入试验,尝试识别处于单轴均匀应力场下的混凝土试块的原位应力。结果表明:影响函数能够有效反映原位应力与表层释放应变的对应关系,与试验结果吻合,识别方法具有可行性与适用性;多应变计综合识别能有效降低混凝土不均匀性与随机性引起的识别误差,对多步识别结果的优化求解可以进一步提高精度;识别结果的稳定性与应变计敏感栅尺寸有关。     

Reinforced concrete bridge deck reliability model incorporating temporal and spatial variations of probabilistic corrosion rate sensor data

The reliability of reinforced concrete (RC) bridge decks depends significantly on the rate of corrosion of the reinforcing steel. Structural health monitoring (SHM) techniques, including embedded corrosion rate sensors, can greatly improve the quantification of the steel corrosion rate, which can lead to improved estimates of structural safety and serviceability. Due to uncertainties in concrete properties, environmental conditions, and other factors, the rate of corrosion of reinforcing steel can be highly variable, both within a given structural component and over time. By placing multiple corrosion rate sensors throughout a structural component, such as a bridge deck, these spatial and temporal variabilities can be monitored and as such better predicted, for use in a reliability model. The objective of this investigation is to present a reliability model for a RC bridge deck incorporating both spatial and temporal variations of probabilistic corrosion rate sensor data. This objective is accomplished using a computational reliability model and Monte Carlo simulation. Corrosion rate sensor data is assumed for multiple critical sections throughout a RC bridge deck over time by applying empirical spatial and temporal relationships. This data is then used to improve an existing spatially invariant reliability model. The improved reliability model incorporates several sub-models to determine the changes in load effects on and resistance of a RC bridge deck slab over time, as well as spatial correlation of corrosion and a system approach to account for spatial variability. The improved reliability model incorporating both spatial and temporal variations in corrosion rate data provides a better estimate of the service life of a RC bridge deck slab.     

锈蚀RC桥梁弯曲抗力时变概率模型与试验研究

在退化RC结构的时变性能评估、剩余寿命预测以及维修加固决策分析中,其抗力模型的建立至关重要。钢筋锈蚀导致钢筋的屈服强度降低、改变钢筋力学行为和影响钢筋与混凝土之间的粘结行为。钢筋腐蚀损失量影响钢筋的失效模式,即从延性破坏到脆性破坏变化。该文发展了退化RC 桥梁的概率抗力时变模型,可以定量考虑腐蚀对钢筋力学行为、倒塌机理和粘结性能的影响。建立退化结构的抗力概率模型可以抓住退化结构的退化机理、点蚀分布、结构尺寸参数、粘结行为、腐蚀扩展、钢筋失效模式和计算模型的随机性和变异性。RC 梁的加速腐蚀试验和旧桥的破坏性试验验证了该文模型的正确性和可靠性。     

Inspection and monitoring planning for RC structures based on minimization of expected damage detection delay

The deterioration mechanism of reinforced concrete (RC) structures under corrosion is highly dependent on environment and material properties. Uncertainties in structural damage occurrence and propagation due to corrosion should be considered in a rational way using a probabilistic approach. In this study, such an approach is proposed to establish a life-cycle optimum inspection plan under uncertainty. This plan leads to cost-effective maintenance interventions, considering uncertainties associated with damage occurrence/propagation and inspection methods. Uncertainties associated with prediction of damage occurrence time are considered by using the Monte Carlo simulation. A damage detectability function is used to assess the quality of inspection method according to damage intensity. The inspection planning is formulated as an optimization problem with the objective of minimizing the expected damage detection delay. This formulation is further used for optimum monitoring planning. Effects of number of inspections and/or monitoring actions, quality of inspection, monitoring duration, and uncertainties associated with damage occurrence/propagation are investigated. The proposed approach is applied to an existing highway bridge. This approach can be used to develop cost-effective management strategies by considering effects of damage detection delay on life-cycle cost and performance of deteriorating structures.     

Probabilistic capacity models and seismic fragility estimates for RC columns subject to corrosion

In this paper, probabilistic drift and shear force capacity models are developed for corroding reinforced concrete (RC) columns. The developments represent a merger between a probabilistic model for chloride-induced corrosion, a time-dependent corrosion rate, and previously developed probabilistic models for drift and shear force capacity of pristine (undamaged) RC columns. Fragility estimates are obtained for an example corroding column by applying the developed models at given shear and drift demands. Model uncertainties in both the capacity and corrosion models are considered in the fragility estimation, in addition to uncertainties in environmental conditions, material properties, and structural geometry. Sensitivity analyses of the corroding RC column are carried out to identify the parameters to which the reliability of the example column is most sensitive. The developed models consider different combinations of chloride exposure condition, environmental oxygen availability, water-to-cement ratios, and curing conditions. They are applicable to both existing and new RC columns and may be employed for the prediction of service-life and life-cycle cost analysis of RC structures.     

基于氯盐最不利侵蚀下锈蚀RC框架结构时变地震易损性研究

基于一维Fick第二定律,采用DuraCrete规范中钢筋锈蚀初始时刻的概率预测模型,并基于概率统计的钢筋直径预测模型,计算不同龄期下RC结构中钢筋的锈蚀深度。基于修正斜压场理论并以锈蚀深度为单变量,对不同龄期下受压区锈胀开裂混凝土峰值应力进行计算;根据锈蚀深度对钢筋本构和Mander约束混凝土本构模型中相关参数进行了修正。于地震易损性模型中引入时间参数,建立含时间参数的RC结构地震易损性模型。最后,基于上述材料力学性能退化模型,采用基于力的纤维塑性铰模型,建立三层RC平面框架结构数值模型,并结合本文所提出的时变地震易损性模型,给出了三层平面RC框架0、5、10和15年龄期的易损性曲线和曲面。所提研究方法可用于既有RC框架结构生命周期内的抗震性能及损失预测分析。     

Probabilistic modeling of chloride-induced corrosion in concrete structures using first- and second-order reliability methods

Concrete structures are subjected to chloride-induced corrosion that can lead to shortened service life. Reliable predictions of life cycle performance of concrete structures are critical to the optimization of their life cycle design and maintenance to minimize their life cycle costs. This paper presents two simplified semi-analytical probabilistic models based on the first- and second-order reliability methods to model the uncertainty of the key parameters including surface chloride concentration, chloride threshold, cover depth and diffusion coefficient, which govern the chloride ingress into concrete and corrosion of reinforcing steel. A case study of a reinforced concrete highway bridge deck is used to illustrate the capability and efficiency of these simplified probabilistic models in modeling the uncertainty and predicting the time-dependent probability of corrosion. The models enable to quantify the impact of the different governing parameters on probability of corrosion and service life, which can be used to develop cost-effective management strategies.