The main target of this research is utilizing the structure ambient random vibration response to detect the damage level and location. The advantage of using ambient vibration is that the excitation is caused by service conditions such as normal vehicle traffic on a highway bridge, train passage on a railroad bridge, or wind loads on a tall building. This eliminates the need to apply a special impact or dynamic load, or interrupt traffic on a bridge in regular service. An approach is developed in which the free vibration of the structure is extracted from a random vibration response in the time domain (acceleration versus time) by averaging out the random component of the response. The result is the free vibration that includes all modes based on the sampling rate on time, and then transfers this free vibration to the frequency domain using a Fast Fourier Transform (FFT). Variations in the frequency response are function of the structural stiffness and member end-conditions. Such variations are used as a measure to identify the change is the structural dynamic properties, and ultimately detect damage. The approach seems to achieve good results for a structure with a limited number of degrees of freedom.

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