Documents disponibles écrits par cet auteur

Flexible videogrammetric technique for three-dimensional structural vibration measurement / C. C. Chang in Journal of engineering mechanics, Vol. 133 N°6 (Juin 2007) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 133 N°6 (Juin 2007) . - pp.656–664. Titre : Flexible videogrammetric technique for three-dimensional structural vibration measurement Type de document : texte imprimé Auteurs : C. C. Chang, Auteur ; Y. F. Ji, Auteur Année de publication : 2007 Article en page(s) : pp.656–664. Note générale : Applied mechanics Langues : Anglais (eng) Mots-clés : Photogrammetry  Vibration  Dynamic  response  Measurement  Imaging  techniques. Résumé : A videogrammetric technique is proposed for measuring three-dimensional structural vibration response in the laboratory. The technique is based on the principles of close-range digital photogrammetry and computer vision. Two commercial-grade digital video cameras are used for image acquisition. To calibrate these cameras and to overcome potential lens distortion problems, an innovative two-step calibration process including individual and stereo calibration is proposed. These calibrations are efficiently done using a planar pattern arbitrarily shown at a few different orientations. This special characteristic makes it possible to perform an on-site calibration that provides flexibility in terms of using different camera settings to suit various application conditions. To validate the proposed technique, three tests, including sinusoidal motion of a point, wind tunnel test of a cross-section bridge model, and a three-story building model under earthquake excitation, are performed. Results indicate that the proposed videogrammetric technique can provide fairly accurate displacement measurement for all three tests. The proposed technique is shown to be a good complement to the traditional sensors for measuring two- or three-dimensional vibration response in the low-frequency range. ISSN : 0733-9399 En ligne : http://ascelibrary.org/action/showAbstract?page=656&volume=133&issue=6&journalCo [...] [article] Flexible videogrammetric technique for three-dimensional structural vibration measurement [texte imprimé] / C. C. Chang, Auteur ; Y. F. Ji, Auteur . - 2007 . - pp.656–664. Applied mechanics Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 133 N°6 (Juin 2007) . - pp.656–664. Mots-clés : Photogrammetry  Vibration  Dynamic  response  Measurement  Imaging  techniques. Résumé : A videogrammetric technique is proposed for measuring three-dimensional structural vibration response in the laboratory. The technique is based on the principles of close-range digital photogrammetry and computer vision. Two commercial-grade digital video cameras are used for image acquisition. To calibrate these cameras and to overcome potential lens distortion problems, an innovative two-step calibration process including individual and stereo calibration is proposed. These calibrations are efficiently done using a planar pattern arbitrarily shown at a few different orientations. This special characteristic makes it possible to perform an on-site calibration that provides flexibility in terms of using different camera settings to suit various application conditions. To validate the proposed technique, three tests, including sinusoidal motion of a point, wind tunnel test of a cross-section bridge model, and a three-story building model under earthquake excitation, are performed. Results indicate that the proposed videogrammetric technique can provide fairly accurate displacement measurement for all three tests. The proposed technique is shown to be a good complement to the traditional sensors for measuring two- or three-dimensional vibration response in the low-frequency range. ISSN : 0733-9399 En ligne : http://ascelibrary.org/action/showAbstract?page=656&volume=133&issue=6&journalCo [...]

Nonlinear identification of lumped-Mass buildings using empirical mode decomposition and incomplete measurement / C. C. Chang in Journal of engineering mechanics, Vol. 136 N° 3 (Mars 2010) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 136 N° 3 (Mars 2010) . - pp. 273-281 Titre : Nonlinear identification of lumped-Mass buildings using empirical mode decomposition and incomplete measurement Type de document : texte imprimé Auteurs : C. C. Chang, Auteur ; Poon, C. W., Auteur Article en page(s) : pp. 273-281 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Nonlinear  response  Structural  behavior  Decomposition  Damage  Measurement. Résumé : Most structures exhibit some degrees of nonlinearity such as hysteretic behavior especially under damage. It is necessary to develop applicable methods that can be used to characterize these nonlinear behaviors in structures. In this paper, one such method based on the empirical mode decomposition (EMD) technique is proposed for identifying and quantifying nonlinearity in damaged structures using incomplete measurement. The method expresses nonlinear restoring forces in semireduced-order models in which a modal coordinate approach is used for the linear part while a physical coordinate representation is retained for the nonlinear part. The method allows the identification of parameters from nonlinear models through linear least-squares. It has been shown that the intrinsic mode functions (IMFs) obtained from the EMD of a response measured from a nonlinear structure are numerically close to its nonlinear modal responses. Hence, these IMFs can be used as modal coordinates as well as provide estimates for responses at unmeasured locations if the mode shapes of the structure are known. Two procedures are developed for identifying nonlinear damage in the form of nonhysteresis and hysteresis in a structure. A numerical study on a seven-story shear-beam building model with cubic stiffness and hysteretic nonlinearity and an experimental study on a three-story building model with frictional magnetoreological dampers are performed to illustrate the proposed method. Results show that the method can quite accurately identify the presence as well as the severity of different types of nonlinearity in the structure. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...] [article] Nonlinear identification of lumped-Mass buildings using empirical mode decomposition and incomplete measurement [texte imprimé] / C. C. Chang, Auteur ; Poon, C. W., Auteur . - pp. 273-281. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 136 N° 3 (Mars 2010) . - pp. 273-281 Mots-clés : Nonlinear  response  Structural  behavior  Decomposition  Damage  Measurement. Résumé : Most structures exhibit some degrees of nonlinearity such as hysteretic behavior especially under damage. It is necessary to develop applicable methods that can be used to characterize these nonlinear behaviors in structures. In this paper, one such method based on the empirical mode decomposition (EMD) technique is proposed for identifying and quantifying nonlinearity in damaged structures using incomplete measurement. The method expresses nonlinear restoring forces in semireduced-order models in which a modal coordinate approach is used for the linear part while a physical coordinate representation is retained for the nonlinear part. The method allows the identification of parameters from nonlinear models through linear least-squares. It has been shown that the intrinsic mode functions (IMFs) obtained from the EMD of a response measured from a nonlinear structure are numerically close to its nonlinear modal responses. Hence, these IMFs can be used as modal coordinates as well as provide estimates for responses at unmeasured locations if the mode shapes of the structure are known. Two procedures are developed for identifying nonlinear damage in the form of nonhysteresis and hysteresis in a structure. A numerical study on a seven-story shear-beam building model with cubic stiffness and hysteretic nonlinearity and an experimental study on a three-story building model with frictional magnetoreological dampers are performed to illustrate the proposed method. Results show that the method can quite accurately identify the presence as well as the severity of different types of nonlinearity in the structure. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...]

Nontarget stereo vision technique for spatiotemporal response measurement of line-like structures / Y. F. Ji in Journal of engineering mechanics, Vol. 134 n°6 (Juin 2008) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 134 n°6 (Juin 2008) . - pp.466–474. Titre : Nontarget stereo vision technique for spatiotemporal response measurement of line-like structures Type de document : texte imprimé Auteurs : Y. F. Ji, Auteur ; C. C. Chang, Auteur Année de publication : 2008 Article en page(s) : pp.466–474. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Measurement  Imaging  techniques  Displacement  Structural  response Résumé : With continuous advancement in optical, electronics, and computer technology, commercial digital cameras now are equipped with a high pixel resolution at a reasonable cost. Image sequences recorded by these cameras contain both spatial and temporal information of the target object; hence they can be used to extract the object’s dynamic responses and characteristics. This paper presents a nontarget stereo vision technique to measure response of a line-like structure simultaneously in both spatial and temporal domain. The technique uses two digital cameras to acquire image sequences of a line-like structure. It adopts a simple nondimensional length matching approach and the epipolar geometry to establish point correspondences within an image sequence and between two image sequences, respectively. After reconstructing a spatio-temporal displacement response from the two image sequences, wavelet transform is then used to extract the modal characteristics of the structure. The technique is illustrated using two free vibration tests: a steel cantilever beam and a bridge stay cable. Results show that the technique can measure the spatiotemporal responses, natural frequencies, and mode shapes of the two structures quite accurately. This image-based technique is a low-cost and simple-to-use approach that not only can complement current response measurement sensors but also offer special advantages which are hard to obtain using these traditional sensors. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A6%2846 [...] [article] Nontarget stereo vision technique for spatiotemporal response measurement of line-like structures [texte imprimé] / Y. F. Ji, Auteur ; C. C. Chang, Auteur . - 2008 . - pp.466–474. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 134 n°6 (Juin 2008) . - pp.466–474. Mots-clés : Measurement  Imaging  techniques  Displacement  Structural  response Résumé : With continuous advancement in optical, electronics, and computer technology, commercial digital cameras now are equipped with a high pixel resolution at a reasonable cost. Image sequences recorded by these cameras contain both spatial and temporal information of the target object; hence they can be used to extract the object’s dynamic responses and characteristics. This paper presents a nontarget stereo vision technique to measure response of a line-like structure simultaneously in both spatial and temporal domain. The technique uses two digital cameras to acquire image sequences of a line-like structure. It adopts a simple nondimensional length matching approach and the epipolar geometry to establish point correspondences within an image sequence and between two image sequences, respectively. After reconstructing a spatio-temporal displacement response from the two image sequences, wavelet transform is then used to extract the modal characteristics of the structure. The technique is illustrated using two free vibration tests: a steel cantilever beam and a bridge stay cable. Results show that the technique can measure the spatiotemporal responses, natural frequencies, and mode shapes of the two structures quite accurately. This image-based technique is a low-cost and simple-to-use approach that not only can complement current response measurement sensors but also offer special advantages which are hard to obtain using these traditional sensors. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A6%2846 [...]

Substructural time - varying parameter identification using wavelet multiresolution approximation / Yuanfeng Shi in Journal of engineering mechanics, Vol. 138 N° 1 (Janvier 2012) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 138 N° 1 (Janvier 2012) . - pp.50-59 Titre : Substructural time - varying parameter identification using wavelet multiresolution approximation Type de document : texte imprimé Auteurs : Yuanfeng Shi, Auteur ; C. C. Chang, Auteur Année de publication : 2012 Article en page(s) : pp.50-59 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Substructural  technique  Time-varying  system  identification  Wavelet  multiresolution  approximation Résumé : Identifying properties of civil engineering structures is an important task for their condition assessment, damage diagnosis, maintenance and repair, and life-cycle management. These structures usually contain a large number of degrees of freedom and exhibit some time-varying or nonlinear behavior, especially under extreme excitation or when damaged. In this study, an offline substructure method based on wavelet multiresolution approximation (WMRA) is proposed for the identification of arbitrary time-varying parameters in a shear-beam building. Assuming that the possible damage location of the building can be identified a priori, a substructural model containing both interface and internal restoring forces can be formulated. The WMRA can then be used to approximate the time-varying damping and stiffness parameters and convert a time-varying parametric identification problem into a time-invariant coefficient estimation problem. To obtain accurate estimation and minimize the computational effort, Akaike’s information criterion is used for the selection of a resolution level and the pruning of insignificant terms. Numerical and experimental results show that the proposed technique can locate and quantify the time-varying parameters in the substructure. The method inherits the wavelet’s excellent capability in the approximation of arbitrary functions and provides a flexible approach for identifying various types of time-varying parameters in shear-beam buildings. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29EM.1943-7889.0000307 [article] Substructural time - varying parameter identification using wavelet multiresolution approximation [texte imprimé] / Yuanfeng Shi, Auteur ; C. C. Chang, Auteur . - 2012 . - pp.50-59. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 138 N° 1 (Janvier 2012) . - pp.50-59 Mots-clés : Substructural  technique  Time-varying  system  identification  Wavelet  multiresolution  approximation Résumé : Identifying properties of civil engineering structures is an important task for their condition assessment, damage diagnosis, maintenance and repair, and life-cycle management. These structures usually contain a large number of degrees of freedom and exhibit some time-varying or nonlinear behavior, especially under extreme excitation or when damaged. In this study, an offline substructure method based on wavelet multiresolution approximation (WMRA) is proposed for the identification of arbitrary time-varying parameters in a shear-beam building. Assuming that the possible damage location of the building can be identified a priori, a substructural model containing both interface and internal restoring forces can be formulated. The WMRA can then be used to approximate the time-varying damping and stiffness parameters and convert a time-varying parametric identification problem into a time-invariant coefficient estimation problem. To obtain accurate estimation and minimize the computational effort, Akaike’s information criterion is used for the selection of a resolution level and the pruning of insignificant terms. Numerical and experimental results show that the proposed technique can locate and quantify the time-varying parameters in the substructure. The method inherits the wavelet’s excellent capability in the approximation of arbitrary functions and provides a flexible approach for identifying various types of time-varying parameters in shear-beam buildings. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29EM.1943-7889.0000307

Three-dimensional structural translation and rotation measurement using monocular videogrammetry / C. C. Chang in Journal of engineering mechanics, Vol. 136 N° 7 (Juillet 2010) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 136 N° 7 (Juillet 2010) . - pp. 840-848 Titre : Three-dimensional structural translation and rotation measurement using monocular videogrammetry Type de document : texte imprimé Auteurs : C. C. Chang, Auteur ; X. H. Xiao, Auteur Article en page(s) : pp. 840-848 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Photogrammetry  Measurement  Three-dimensional  analysis  Displacement  Rotation. Résumé : Measuring displacement for large-scale structures has always been an important yet challenging task. In most applications, it is not feasible to provide a stationary platform at the location where its displacements need to be measured. Recently, image-based technique for three-dimensional (3D) displacement measurement has been developed and proven to be applicable to civil engineering structures. Most of these developments, however, use two or more cameras and require sophisticated calibration using a total station. In this paper, we present a single-camera approach that can simultaneously measure both 3D translation and rotation of a planar target attached on a structure. The intrinsic parameters of the camera are first obtained using a planar calibration board arbitrarily positioned around the target location. The obtained intrinsic parameters establish the relationship between the 3D camera coordinates and the two-dimensional image coordinates. These parameters can then be used to extract the rotation and translation of the planar target using recorded image sequence. The proposed technique is illustrated using two laboratory tests and one field test. Results show that the proposed monocular videogrammetric technique is a simple and effective alternative method to measure 3D translation and rotation for civil engineering structures. It should be noted that the proposed technique cannot measure translation along the direction perpendicular to the image plane. Hence, proper caution should be taken when placing target and camera. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...] [article] Three-dimensional structural translation and rotation measurement using monocular videogrammetry [texte imprimé] / C. C. Chang, Auteur ; X. H. Xiao, Auteur . - pp. 840-848. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 136 N° 7 (Juillet 2010) . - pp. 840-848 Mots-clés : Photogrammetry  Measurement  Three-dimensional  analysis  Displacement  Rotation. Résumé : Measuring displacement for large-scale structures has always been an important yet challenging task. In most applications, it is not feasible to provide a stationary platform at the location where its displacements need to be measured. Recently, image-based technique for three-dimensional (3D) displacement measurement has been developed and proven to be applicable to civil engineering structures. Most of these developments, however, use two or more cameras and require sophisticated calibration using a total station. In this paper, we present a single-camera approach that can simultaneously measure both 3D translation and rotation of a planar target attached on a structure. The intrinsic parameters of the camera are first obtained using a planar calibration board arbitrarily positioned around the target location. The obtained intrinsic parameters establish the relationship between the 3D camera coordinates and the two-dimensional image coordinates. These parameters can then be used to extract the rotation and translation of the planar target using recorded image sequence. The proposed technique is illustrated using two laboratory tests and one field test. Results show that the proposed monocular videogrammetric technique is a simple and effective alternative method to measure 3D translation and rotation for civil engineering structures. It should be noted that the proposed technique cannot measure translation along the direction perpendicular to the image plane. Hence, proper caution should be taken when placing target and camera. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...]

Tracking of structural dynamic characteristics using recursive stochastic subspace identification and instrumental variable technique / Z. Li in Journal of engineering mechanics, Vol. 138 N° 6 (Juin 2012) 

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