Browsing by Author "Su, Wei-Chih"

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A study on Gabor frame for estimating instantaneous dynamic characteristics of structures
(2017-02-01)
Su, Wei-Chih
;
Huang, Chiung-Shiann
;
土木工程學系
;
Department of Civil Engineering
A structure under damage normally exhibits nonlinear dynamic behaviors and time-dependent stiffness and damping. By estimating instantaneous dynamic characteristics of a structures is generally very useful when assessing structural damage in real application. This study presents a novel and effective approach that accurately estimating instantaneous dynamic characteristic of a structure using time-varying autoregressive exogenous (TVARX) model on Gabor frame. To evaluate the time-varying coefficient matrices of a time-series model, the proposed procedure applies Gaussian-based weighted function and Fourier transform on time series model, then the Gabor-transform-based time series formula could be obtained. The dynamic characteristics of a structure are determined from the coefficient matrices. Numerical analyses demonstrate that the proposed approach is superior to traditional time-frequency analysis in accurately estimating instantaneous dynamic characteristics of a structure. Finally, the proposed approach is applied to process measured data for a steel frame specimen subjected to a series of base excitations in shaking table tests.
Estimating the Stiffness Parameters of a Building by Using Time Series Model and Gram-Schmidt Process in Morlet Wavelet Domain
(2016)
Su, Wei-Chih
;
Huang, Chiung-Shiann
;
Lien, Ho-Cheng
;
土木工程學系
;
Department of Civil Engineering
Identifying the structural modal parameters based on the measured responses of structure is a major application for structural health monitoring. This study presents a procedure based on Gram-Schmidt process to improve the accuracy of the calculated stiffness matrix of a structure. The continuous wavelet transfoun is applied to the measured responses of a structure and the time series model could be reconstructed to denoise for the measured noisy responses. The identified modal parameters would be obtained from the coefficient in time series model. Next, correcting the identified mode shapes via Gram-Schmidt process. Finally, the structural stiffness matrix can be created via the identified natural frequencies and the corrected mode shapes. The accuracy of this procedure is numerically confirmed; the effects of the wavelet parameters and noise on the ability to accurately estimate the stiffness matrix are also investigated.
Identification of Instantaneous Modal Parameters of a Nonlinear Building via a Gabor-frame-based Approach
(2016)
Su, Wei-Chih
;
Huang, Chiung-Shiann
;
Lien, Ho-Cheng
;
土木工程學系
;
Department of Civil Engineering
This work presents the use of a Gabor transform to deteunine the instantaneous modal parameters (natural frequencies, damping ratios and mode shapes) of a structure from its dynamical responses, such as free vibration or earthquake response. The Gabor transform is applied to the measured acceleration responses of a structural system for reconstructing the time-varying time series model in time-frequency domain. The instantaneous modal parameters of a time-varying system can be directly estimated from the time-varying model coefficients. The proposed procedure is further applied to process the dynamic responses of three-storey steel frames with or without nonlinear elements from the simulated earthquake events via SAP2000 to identify the differences among the frames. The linear or nonlinear behaviors of these steel frames under earthquake input are accurately reflected in the instantaneous natural frequencies that are obtained by the proposed approach.
Identification of Structural Stiffness Parameters via Wavelet Packet from Seismic Response
(2017-01-01)
Su, Wei-Chih
;
Huang, Chiung-Shiann
;
土木工程學系
;
Department of Civil Engineering
Vibration-based damage assessment approaches are conventionally and widely adopted to monitor the structural health of a building during the bases excitation process. This study explores the possibility of using structural stiffness parameters to locate the storeys of building that are damaged in an earthquake event. A damaged storeys usually exhibits stiffness parameters variations during a strong enough earthquake, and the corresponding stiffness of storey often change in the earthquake. The wavelet packet transform is applied to the measured acceleration responses of a structure to reconstruct the autoregressive with exogenous input (ARX) model in wavelet packet domain. The modal parameters of the structure are estimated directly through the identified coefficient matrixes of the ARX model. Next, the stiffness parameters of the structure that could be reconstructed form the identified natural frequencies and mode shapes would be used to detect the damage locating of a building. The accuracy of this procedure is numerically confirmed, the effects of the wavelet parameters and noise on the ability to accurately estimate the dynamic properties are also investigated. (C) 2017 The Authors. Published by Elsevier Ltd.
Identifying the stiffness parameters of a structure using a subspace approach and the Gram-Schmidt process in a wavelet domain
(2017-07-13)
Su, Wei-Chih
;
Huang, Chiung-Shiann
;
Lien, Ho-Cheng
;
Le, Quang-Tuyen
;
土木工程學系
This article presents a procedure to improve the accuracy of calculated stiffness matrix of a structure based on the identified modal parameters from its measured responses. First, a continuous wavelet transform is applied to the measured responses of a structure, and the state-space model can be reconstructed by the wavelet coefficients of acceleration that can be obtained from the measured noisy responses. The modal parameters are identified using the subspace approach. Second, the identified mode shapes are corrected via Gram-Schmidt process. Finally, the identified natural frequencies and the corrected mode shapes in previous steps are utilized to build the stiffness matrix of structure. The accuracy of the proposed approach is numerically confirmed, and the noise effects on the ability to precisely identify the stiffness matrix are also investigated. The measured data of two eight-story steel frames in a shaking table test are analyzed to demonstrate the applicability of the procedure to real structures.