【作者】 李学平；

【导师】 余志武；

【作者基本信息】 中南大学 ， 桥梁与隧道工程， 2009， 博士

【摘要】 基于结构振动特性的损伤识别方法是近年来国内外研究的热点,它利用结构的反应或动力特性的变化来对结构的整体性能进行损伤监测。其核心是将结构系统的实测模态特性与健康结构的模态特性进行比较,判断结构是否发生损伤及损伤程度。本文对损伤结构的动力特性进行了分析,并提出了两种基于频率测试结果识别结构裂缝的方法,最后通过对混凝土简支梁在高温前后的模态分析,对由于高温引起的梁内裂缝进行了评估。(1)将裂缝模拟为一无质量又具有一定刚度的转弹簧,应用传递矩阵方法得到了多处裂缝结构的动力特征方程,进而求解特征值。通过数值模拟,讨论了裂缝对梁的动力特性的影响,并与试验结构进行了比较,为结构损伤识别建立了理论基础。(2)另外提出了一种计算多处裂缝梁结构固有基频的近似方法。考虑Euler-Bernouilli梁的弯曲振动,获得了梁固有基频的闭式表达形式。(3)建立了基于梁能量变化的识别裂缝的算法,推导了含裂缝简支梁、悬臂梁和固支梁能量变化的表达式,介绍了裂缝识别的详细过程。并编制了计算程序。(4)运用摄动方法和线弹性断裂力学理论,由振动系统的动力方程推导出结构损伤和模态参数间的联系,获得了基于有限元方法识别结构裂缝位置以及裂缝深度的算式。(5)混凝土简支梁高温后的模态分析及其裂缝识别。对梁在高温前后进行了模态试验,得到损伤识别时所需的参数。本文在分离弹性模量对频率影响的基础上,应用前述损伤识别算法,对梁内由于高温产生的裂缝进行了识别。验证了本文提出的裂缝识别方法的有效性。更多还原

【Abstract】 Damage identification based on vibration features of the structure is under heated discussion both at home and abroad. This specific method takes advantage of the structure response or its dynamic features to monitor the structure totality. The core of it is to compare the obtained matrix with the ideal supposition, and hence to make sure whether there exists damage and its corresponding degree. Base upon analysis of the dynamic features of the damage structure, the present dissertation proposes two effective ways to distinguish crack by frequency testing, and the essay moves onwards to study the mode of the concrete simple supporting beams before and after being applied under high temperature. Hence, the author can conclude with assessing the inner-beam cracks caused by high temperature. The creativities of the present study are as follows:(1) This paper simulates the crack to a weightless rotational spring with certain stiffness, therefore, it will be easy to obtain the feature formula of 2×2 matrix, and it is also easy to get the dynamism feature formula of the cracks with the application of transfer matrix. Through numerical simulation, the author illustrates the influence upon the beam’s dynamic features from the cracks including the alternation of the natural frequency due to the cracks position change as well as the alternation of the shape and the revolving angles. Thereby, the author establishes a solid theoretical foundation for damage discrimination.(2) This paper puts forward an approximate method to calculate the beam structure with multi-damage. In consideration of the bending vibration of the Euler-Bernouilli beam, The closed formula of the beam’s natural frequency can be worked out.(3) This paper establishes a ways of cracks discrimination based on the change of the energy. The formula of change of the energy about simple supporting beams, cantilever beam and beam with two fixed end is educed. And the computing program is completed.(4) The other way makes use of perturbation method and linear elastic fracture mechanics. Formulas of discriminating the structures crack location and the crack depth are obtained based on finite element method.(5) This paper illustrates the mode analysis and crack discrimination of concrete simple supporting beams after being applied under high temperature. The modes of the beams are experimented before and after the high temperature so to get the necessary parameters in time of damage discrimination. The present dissertation focuses on discriminating the inner-beam cracks caused by high temperature with the above-mentioned discrimination calculation formulas, and the calculation results show that the theory and program in the paper are correct and reasonable.更多还原