摘要
自从本世纪50年代以来，人们就意识到桥梁安全监测的重要性。现在很多桥梁都安装了监测系统。大型桥梁健康监测力求对结构整体行为的实时监控和对结构状态的智能化评估，本文总结了10多年来桥梁健康监测的研究状况，然后较系统地阐述桥梁结构健康监测的新概念。目前，健康监测系统尚不具备损伤识别的能力，如何设计一个高效的用于结构损伤识别的自动损伤识别系统是一个值得研究的问题。
自动损伤识别是桥梁健康监测系统的核心技术和热点研究问题。本文阐述了结构损伤识别的现状，并对有关损伤诊断的一些方法进行了评价，这些方法包括：固有频率、应变模态、模态置信度判据、柔度矩阵、小波分析、遗传算法等等。
考虑到曲率模态能较好的识别结构损伤，能够反映桥梁的局部状态变化，可以用来检测损伤位置和损伤程度，本文重点论述了曲率模态分析的理论依据及其特性，针对桥梁等承弯结构研究曲率模态与应变模态之间的关系，由于曲率模态是结构的中性面的变形模态，它对结构的局部变化较敏感，且其模态表达式将比应变模态简单，而应变与曲率之间有简单的关系，因此，曲率模态在损伤识别的应用上将更为方便。
本文(第4章)采用曲率模态法对一座预应力混凝土连续梁桥进行损伤仿真计算，文中分三种工况进行分析，研究和比较了位移模态、曲率模态方法对于单一损伤位置和多处损伤位置不同情况的诊断能力，以及不同损伤程度对于结构损伤识别的影响等。
第5章通过对一悬臂梁做实验，进一步检验曲率模态方法定位损伤和识别损伤程度的效果。文中重点突出了深度不同的裂纹对曲率模态的影响。我们得到以下结论：
(1)曲率模态是结构损伤识别的敏感标识量，曲率模态比频率和位移模态对损伤更敏感，可以用曲率模态检测梁式结构损伤的位置，且曲率模态对多处损伤部位敏感，各处损伤部位之间不相互影响，符合实际检测需要；
(2)曲率模态对结构的损伤程度也可以进行定性分析。实验表明，随着裂纹深度的增大(也即损伤程度的增大)，曲率模态值也随之增大，这与理论是完全相符的；
(3)在保证测量精度的前提下，该方法可用于工程实际的应用中。
Since the 50s of this century, people have realized the importance of health monitoring for bridges. Many bridges have been installed with monitoring system presently. A primary objective of long-span bridge health monitoring is to obtain the information on bridge condition through online monitoring of the structural performance. In this paper, after a brief overview of the development of bridge health monitoring, the connotation of bridge health monitoring is pointed out in an extended sense. The present bridge health monitoring systems have not the capacity to detect the damage in bridges. Further study is needed as to how to design an effective automatic damage detection systems for structural damage identification.
Automatic damage detection becomes a core technique of bridge health monitoring systems, which attracts the attention of many researchers. Actuality of damage identification for structures is expatiated and comments are made on the methods of them. These methods include natural frequency, strain modal shape, COM AC, flexibility matrix, wavelet analysis, genetic algorithms etc.
Considering that Curvature Mode can identificate the damage of structures and can show the change of local state of bridges, and it can be used to inspect the location and degree of damage. The theoretical basis was developed emphatically for the curvature modal analysis and the curvature mode properties in the paper. The relation between the curvature mode and the strain mode for structures such as bridges subjected to bending and vibration was discussed. The curvature mode is rather sensitive to the local change of structures. And the results show that the curvature mode will be more conveniently used than the strain mode.
In this paper(Chapter 4), curvature mode method is adopted to the calculation of damage imitation to one prestressed concrete continuous beam bridge. Three conditions is divided to carry out analysis and study and compare the diagnose ability about the displacement mode and curvature mode method to the different conditions of single damage location and a couples of ones, and the
effect of different damage degree to damage identification for structures.
In Chapter 5, a experiment about a slotted steel cantilever beam is given to inspect further the effect of curvature mode method to both location and degree of damage. The effect of different depth crackle to curvature mode was stood out as an emphasis. The conclusion is given as follows:
1. The curvature mode is rather sensitive to the damage of structure. It is more sensitive than frequency and displacement mode and can be used to locate the damage of structures like a beam, and it is also sensitive to several damage. Interact is not happened between damage positions. So it meets the need of actual detection.
2. Curvature mode can be used to carry out qualitative analysis to damage degree of structure. Experiment shows that curvature mode value will increase with the increase of the crack depth. It is conform completely with the theory.
3. Under the prerequisite of guaranteeing the measurement precision, the method can be used to the actual application on the project.
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