【作者】 陈悦；

【导师】 周建庭；

【作者基本信息】 重庆交通大学 ， 桥梁与隧道工程， 2014， 博士

【摘要】 混凝土桥梁往往不可避免地存在某些细小结构缺陷，这些缺陷大多以微观裂纹形式出现，在长时间的结构服役期内，由于环境的侵蚀、材料的老化及自然灾害，加之交通荷载的反复疲劳作用，因这些细小缺陷引起的疲劳损伤不断累积，导致桥梁结构整体抵抗自然灾害，甚至正常服役荷载的能力逐渐下降。限于研究手段和测试技术，以往的桥梁结构疲劳分析只能局限于构件或细节表面已出现肉眼可见的疲劳裂纹，距离疲劳损伤早期（裂纹萌生）的发现和分析尚有很大差距。近年来，桥梁长期监测技术取得了较大进展，如何充分利用桥梁在线营运监测的手段和技术优势，尽早发现疲劳损伤和跟踪其损伤累积演化过程，是桥梁界值得探索的课题。目前，在该领域还没有较为系统的研究成果。鉴于此，本文利用断裂与损伤力学的相关理论与知识，从研究钢筋混凝土桥梁的疲劳裂纹扩展规律出发，获取能表征疲劳损伤的特征因子，同时，在大量实时监测数据的基础上，挖掘出疲劳特征参量，从而实现对服役混凝土桥梁疲劳损伤的安全状态评估。论文的主要研究内容和结论如下：①通过对钢筋混凝土材料的裂纹扩展机理分析，在恢复力模型的基础上，提出了融入残余应力影响因子的修正Paris公式，并进行了数值计算分析。分析结果表明：考虑残余应力影响之后的作用效果明显不同于未考虑的情况，其对裂纹扩展影响较大，更符合实际。②根据混凝土疲劳损伤微观机理分析，结合疲劳裂纹稳定扩展与不稳定扩展这两个断裂判据，在相应假设的基础上，获取了残余应变的计算模型；同时，为了使该模型的适用范围更广，尤其是对服役的钢筋混凝土桥梁，对其进行了实时残余应变计算模型的研究。经验证，该模型能满足实际情况需求，且不受加载历程的影响；此外，通过累积残余应变的多少来划分疲劳损伤状况等级，实现了混凝土桥梁的实时疲劳安全状况评估。③通过对钢筋混凝土梁的非线性数值模拟分析，获取了循环荷载作用下梁在不同阶段的发展变化状况，特别是塑性变形情况。同时，根据钢筋混凝土梁在单级和多级荷载作用下的疲劳试验，发现融入残余应力影响的应力强度因子较常规的应力强度因子能更好的表达出裂纹的扩展速率；此外，利用已提出的残余应变计算模型，计算出的残余应变与实测的残余应变初期吻合良好，后期略高于实测值，可见，利用残余应变评估循环荷载作用下服役桥梁结构的疲劳安全状况可行，且偏于安全。④为了有效剔除监测数据中的异常信息，压缩减小数据量，以小波分析为手段，根据监测数据呈周期性变化的特点，提供了标准循环块（以天为周期）的获取方法；此外，兼顾疲劳安全状况评估对循环特征参数（峰值imax及其对应的循环次数ni）的需求，在遵循计数原则的基础上，借鉴已有计数方法，提出了改进的跨均值峰值计数法，并针对实际的监测数据进行了应用分析。⑤选取已构建健康监测系统的典型混凝土连续刚构桥—龙河大桥为依托，利用其实时监测数据，提取出当前疲劳特征参数（峰值imax及其对应的循环次数ni），同时，借助残余应变计算模型，获取了龙河大桥典型截面相关位置目前的残余应变量值。该残余应变量值非常小，表明目前龙河大桥的疲劳安全状况良好，这与大桥实际安全状况相符。可见，基于残余应变的评估模式达到了进行服役桥梁疲劳安全状况分析的目的。更多还原

【Abstract】 Small structural defects inevitably tend to exist as microcosmic cracks in concretebridges. In long service period, because of erosion of the environment, materials aging,natural disasters and fatigue effect of repeated traffic loads, the fatigue damage causedby these tiny defects accumulates, resulting in the overall capacity of bridge structuresto resist natural disasters, even the normal service ability decreases. Limited by researchmethods and testing techniques, previous structural fatigue analysis can only limit tovisible fatigue cracks on bridge member or surface. In recent years, the long-term bridgemonitoring technology has made great progress. It is a topic worth exploring for bridgeresearchers that how to take full advantage of the bridge online operations monitoringmeasures and technical advantages, and how to detect the fatigue damage and track theevolution of damage accumulation. At present, there aren’t many systematic researchachievements in that field. Based on theories of Fracture and Damage Mechanics andfatigue crack propagation law of reinforced concrete bridges, this paper aims at gettingthe characteristic factors who can characterize the fatigue damage. Meanwhile based ona large number of real-time monitoring data, the paper strives to discover the fatiguecharacteristic parameters, accordingly realizing the security status assessment of fatiguedamage for concrete bridge in service. The main contents and conclusions are asfollows:①After analysis in crack propagation mechanism of reinforced concrete, andbased on restoring force model, this paper proposes the amendatory Paris Equation withintegration of residual stress factor. The numerical results of a reinforced concrete beamshow that the effect on crack propagation with residual stress considered differssignificantly to that of no consideration of residual stress, which has stronger influenceon crack propagation and more practical.②Based on microscopic mechanism of concrete fatigue damage, and combinedwith two fracture criterion of fatigue crack propagation, this paper establishes acomputational model of residual strain and studies the model with real-time residualstrain, which allows a wider scope for the model, particularly for the reinforced concretebridges in service. The model is proven to meet the actual situation. The paper alsodivides condition grades of fatigue damage by the amount of cumulative residual strain,which realizes real-time assessment of the security situation of bridge fatigue. ③Through nonlinear numerical simulation analysis for RC beam, the paper getsdifferent development and changes situation under recycle loads of the beam, especiallythe plastic deformation. According to the fatigue test of RC beam under single-stage andmulti-stage loads, stress intensity factor with residual stress considered expresses thecrack propagation rate better. The numerical model proposed residual stress shows thatthe residual stress is in good agreement with the initial, while the latter is slightly higher,which proves that the assessment based on residual stress is safer to assess structuralfatigue security situation under cycle loads.④In order to effectively eliminate abnormal information of monitoring data andreduce the amount of data, according to the characteristics of the cyclically changingmonitoring data, standard circle block method is provided by means of wavelet analysis.In addition, considering the fatigue safety situation assessment’s demand for circulationcharacteristic parameters (the peak value imaxand the corresponding cyclesni). Theimproved average peak counting method is put forward on the basis of following theprinciple of count. Moreover, the actual monitoring data is calculated and analyzed forApplication.⑤Choosing the typical concrete continuous rigid frame bridge with awell-performed health monitoring system-Bridge Longhe as modeling project, withreal-time monitoring data, the paper gets current fatigue characteristic parameters (thepeak value imaxand the corresponding cyclesni). And the computational model ofresidual strain gets the current magnitude of residual strain for the relative position of atypical cross section, which is very small, and proves that Bridge Longhe is in greatfatigue security situation, and also in line with the actual security situation of the bridge.Therefore, the assessment model based on residual strain meets the demand of fatigueanalysis of the security situation for in-service bridges.更多还原