Author: Zhang, Yi Jia
Title: Application of new technique on the condition assessment of a three-dimensional frame structure under environmental excitations
Degree: M.Sc.
Year: 2014
Subject: Hong Kong Polytechnic University -- Dissertations
Structural analysis (Engineering)
Department: Faculty of Construction and Environment
Pages: xi, 72 p. : ill. (some col.) ; 30 cm.
Language: English
Abstract: Evaluating the condition of structures is an area of professional practice in the field of structural engineering. Many of the structural condition assessment approaches have been proposed such as dynamic approach, static approach, time domain approach, and frequency domain approach. Structure analysis in the frequency domain is always requires a lot of measurements data. On the other hand, assessing the structural condition in the time domain is an alternative solution that requires not so much data during structural health monitoring work. While many works have been done in this field, there are still some gaps that restrict the application of this kind of method. Such as; it is usually very difficult to identify the parameter of the large-scale structural system due to the computational efficiency, accuracy and the convergence of the analysis. In most of the sensitivity process in time domain analysis, it needs the data of the excitation, and the initial response, which means initial of the acceleration, velocity and displacement, are usually considered to be zero, but the initial response is always unknown and it is non-zero value. So the time variant structural parameter identification is very difficult to be identified with the sensitivity method in the time domain. The covariance of responses obtained from ambient excitation has been used to estimate modal parameter and further assesses the structural health condition. Covariance of responses of a dynamic system under ambient excitation, which is an approach of time-domain analysis simulations has been proposed by X. Y. Li and S. S. Law (2008). Inspired by the white noise, the autocorrelation or the cross-correlation functions of responses can be expressed as explicit functions of physical parameters of the system and their sensitivity with respect to these parameters is subsequently derived by the theory of X. Y. Li (2008). In this report, a steel frame structure model is test in laboratory with hammer excitation and random ground motion excitation. Test data is processed to update the test model and identify the damage of the structure with frequency sensitivity method and acceleration response sensitivity method with hammer excitation. The first method, frequency sensitivity method, is applied for model updating with the hammer test data, damage detection in simulation study and damage detection in the damage stage of the test model with hammer excitation data. The second method, acceleration sensitivity method, is applied for model updating with the hammer test data and damage detection in simulation study. The third method, response covariance sensitivity method, is applied in simulation study only with random ground motion. In order to compare the accuracy of the three sensitivity method and verify the MATLAB program, all of the three mentioned methods are verified by simulation work first before they are applied to process test data.
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