混凝土桥梁基于残余应变监测的疲劳状况评估模式研究

发布时间：2018-06-04 17:49

本文选题：疲劳 + 残余应变　；参考：《重庆交通大学》2014年博士论文

【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。
[Abstract]:Some small structural defects are unavoidable in concrete bridges. Most of these defects appear in the form of micro cracks. During the long period of structural service, the fatigue damage caused by these tiny defects accumulates continuously because of the erosion of the environment, the aging and natural disasters of the materials, and the repeated fatigue of the traffic loads. As a whole, the bridge structure resists natural disasters, and even the ability of normal service load gradually decreases. Limited to the research means and test techniques, the previous fatigue analysis of bridge structures can only be limited to the visible fatigue cracks visible on the surface of the component or the detail surface, and the discovery and analysis of the early fatigue damage (crack initiation) is still very bad. In recent years, the long-term monitoring technology of bridge has made great progress. How to make full use of the means and technical advantages of bridge on-line operation monitoring, to find the fatigue damage and track the cumulative damage process of damage as soon as possible is a subject worth exploring in the bridge circle. At present, there are no more systematic research results in this field. Based on the theory and knowledge of fracture and damage mechanics, the characteristic factors that can characterize fatigue damage are obtained from the study of fatigue crack propagation of reinforced concrete bridges. At the same time, on the basis of a large number of real-time monitoring data, the fatigue characteristic parameters are excavated, so as to realize the safety assessment of fatigue damage of service concrete bridges. The main contents and conclusions of the paper are as follows:
(1) through the analysis of the crack propagation mechanism of reinforced concrete material, on the basis of the restoring force model, a modified Paris formula is put forward to integrate the influence factors of residual stress, and the numerical analysis is carried out. The results show that the effect of the residual stress is obviously different from that of the non considered. It is more effective and more practical.
Secondly, based on the analysis of the microscopic mechanism of the fatigue damage of concrete, combining the two fracture criteria of fatigue crack stability expansion and unstable expansion, the calculation model of residual strain is obtained on the basis of the corresponding hypothesis. At the same time, in order to make the application of the model more wide, especially for the reinforced concrete bridge serving in service, the model has been carried out in real time. The model of residual strain calculation is studied. It is proved that the model can meet the actual requirement and is not affected by the loading process. In addition, the fatigue damage status is divided by the amount of accumulated residual strain, and the real time fatigue safety assessment of concrete bridges is realized.
(3) through the nonlinear numerical simulation analysis of reinforced concrete beams, the development and change of the beam in different stages are obtained, especially the plastic deformation condition. At the same time, according to the fatigue test of the reinforced concrete beam under the single and multistage loads, it is found that the stress intensity factor which is integrated with the residual stress is more conventional. The stress intensity factor can better express the propagation rate of the crack. In addition, the residual strain calculated by the proposed residual strain calculation model is in good agreement with the measured residual strain at the beginning, and the later period is slightly higher than the measured value. It can be seen that the residual strain is used to evaluate the fatigue safety of the bridge structure under cyclic loading. It is feasible and partial to safety.
(4) in order to effectively eliminate the abnormal information in the monitoring data and reduce the amount of data, the method of wavelet analysis, according to the characteristics of the periodic changes of the monitoring data, provides a method for obtaining the standard circulation block (the day as a cycle). In addition, the cyclic characteristic parameters (peak IMAX and its corresponding cycle times) are evaluated by the fatigue safety assessment. On the basis of counting the counting principle and using the existing counting method, the improved cross mean peak counting method is put forward on the basis of counting the counting principle, and the application analysis of the actual monitoring data is carried out in the light of the counting principle.
5. Based on the typical concrete continuous rigid frame bridge, the long river bridge, which has been constructed, the current fatigue characteristic parameters (peak IMAX and its corresponding cycle times Ni) are extracted by using the actual monitoring data. At the same time, the residual strain is obtained by the residual strain calculation model, and the residual stress of the typical section of the typical section of the long river bridge is obtained. The value of the residual strain is very small, which indicates that the fatigue safety of the long river bridge is good, which is in line with the actual safety condition of the bridge. It is obvious that the evaluation model based on the residual strain has achieved the purpose of analyzing the fatigue safety of the bridge.
【学位授予单位】：重庆交通大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：U448.33

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