The Dynamical Analysis Of The Cracked Structures And The Research On Crack Indentification

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.