A thesis submitted in partial fulfillment of requirements for the degree of Master of Engineering, School of Civil Engineering

Thesis (M.Eng.) - Asian Institute of Technology, 2000

The main problem of using the displacement-measuring transducer or velocitymeasuring transducer to identify dynamic properties of structures is the distortion between the electrical output and the input structural vibration if structures vibrate at the frequency below the natural frequency of transducers. The signal obtained from these transducers cannot be used in some applications where the actual contribution of the vibration at each frequency must be known. This study uses the accelerometers, which have a linear proportion between the output signal and the input vibration in the frequency range from DC to 50 Hz, to identify dynamic properties of buildings and structures from microtremor vibration. Two accelerometers and a high-resolution data acquisition unit were used to identify dynamic properties of various types of structures such as a pedestrian bridge, floor structures and a tall building. It was found that accurate dynamic properties could be obtained with this small set of vibration-measuring instrument. Dynamic properties obtained from the Fast Fourier .Transform technique are in good agreement with those obtained from the random decrement technique. The modes of vibrations that contribute significant effect to total structural vibrations fall within the frequency bandwidth of the accelerometer. The acceleration signal obtained from this accelerometer is, therefore, very useful for the application that the contributions of vibrations at all frequencies must be known such as the application of vibration-control system.