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UBC Theses and Dissertations

Dynamic analysis of civil engineering structures using joint time-frequency methods Black, Cameron John


The study of signals whose frequency content changes in time is prevalent in many academic fields. The objective of this thesis is to demonstrate that joint time-frequency analysis is suitable for the analysis of civil engineering vibration data. A discussion of different joint time-frequency analysis methods is presented with emphasis on the Wavelet Transform, the Wigner Distribution, Cohen's Class functions and the Short Time Fourier Transform. Most of Cohen's class functions are not directly applicable to the analysis of civil engineering vibration signals as they are not manifestly positive in the time-frequency plane. The Wavelet and the Short Time Fourier Transforms are manifestly positive and appear to be suitable for the analysis of civil engineering vibration data. This thesis explores the use of joint time-frequency analysis through 5 case studies. These include the analysis of ambient vibration data obtained from two bridges, data obtained from shake table testing and strong motion data collected from 2 instrumented buildings. The joint time-frequency analysis presented in the case studies makes use of the Short Time Fourier Transform. The dynamic behavior of 2 bridges is analyzed using ambient vibration data. It is shown that joint time-frequency analysis can be used to verify the stability of the dominant frequencies during the course of testing as well as explain anomalous results obtained from frequency domain analysis. During shake table testing of an unbonded concrete gravity dam model, upstream motion was observed at certain combinations of amplitude and frequency of base motion. Joint time-frequency analysis is used to improve the understanding of this phenomenon. The most promising application of joint time-frequency analysis is for the interpretation of strong motion data. The response of 2 instrumented buildings during the Northridge and San Fernando earthquakes is studied using frequency and joint time-frequency analysis techniques. A function called the Time Frequency Response Function is defined and used, to study many aspects of the dynamic behavior of structures not explained through typical frequency domain analysis of strong motion data. This includes the presence of coupling between modes of vibration and the temporal location of modal response. The case studies presented in this thesis demonstrate that joint time-frequency analysis is useful for the study of civil engineering vibration data and should be studied further.

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