| Summary: | 碩士 === 國立高雄應用科技大學 === 土木工程與防災科技研究所 === 91 === In civil engineering different structural bodies have their own natural frequencies. As the excitation frequency outside is close to the natural frequency of a structural body, resonance happens. And with the aging and damaging of the structural body, its natural frequency and acceleration, etc. will vary accordingly. Under the destruction model of various loads and earthquake forces, destruction of beam happens all the time. How to detect the current situation of structural use speedily and effectively and how to evaluate the safety are the issues we urgently need to develop and study.
The research paper primarily adopts traditional model analysis to engage in structural non-destruction inspection, and then investigates the variation characteristics of the natural frequency and mode shape of structure as there is a defect happened in the structure, and attempts to use the response values of the measured signals of various points to forecast the position where defect happens.
First of all, the researcher uses finite element to analyze the software, and thus finds out the approximate solutions of the natural frequencies and mode shapes of hollowed aluminum beam and RC beam, and then carries out mode experiment.
The research paper uses aluminum beam and RC beam to analyze and measure the responses before and after the defect, and tries to find out the position of defect. As for the part of analysis by finite element, when a defect is found on beam, and as the defect is deepening, the natural frequency tends to fall. And at the position the defect happens, its beam shape curve appears to be non-continuous.
When speaking of the beam shape, the greatest alteration of natural frequency of the mode shape before and after the defect is the model value. Compare the difference percentage between the response values of various measure points and measure values before the defect. Then compare the difference between the two adjacent points by using various difference percentages, then the place with the greatest variation between two adjacent points is the possible position of the defect. However, as shown from the difference percentages of the frequency response values of various measure points, if this method is adopted to find out the position of defect, it seems that there are doubts existed, and misjudgment might be caused.
When speaking of various mode shapes, the amplitude of each of the shapes can be magnified one by one. Then the possible position of the defect can be seen directly from the non-continuous mode shape.
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