• KSCE Journal of Civil and Environmental Engineering Research
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• v.10 no.4
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• pp.35-42
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• 1990

A method for the damage assessment of a structure by an inverse modal perturbation technique is studied. The first few natural frequencies and mode shapes of the damaged structure are assumed to be known. Then, the perturbation equation is formulated for the changes of the modal properties due to the stiffness changes. The stiffness changes due to damages are evaluated, using optimization techniques. Example analyses are carried out for several cases of stick models and a truss model. Results indicate that the present method yields very reasonable estimates for the element stiffness changes.

• Computational Structural Engineering
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• v.9 no.4
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• pp.209-217
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• 1996

An Inverse modal perturbation method was applied to estimate the assessments of the damages at the large-scaled marine structure, such as pier or dolphin, from the structural dynamic natural frequencies and mode shape. Vibrations of structural stiffness, natural frequencies and mode shapes from the eigenvalue analysis lead to the modal peturbation equations, which were considered with a second order term. This paper estimates the assessments of the damages for the structure with the decreased stiffness and shows the convergence of perturbation equation.

• Computational Structural Engineering
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• v.5 no.3
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• pp.119-126
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• 1992

Most civil engineering structures such as bridges, power plants, and offshore platforms are apt to suffer structural damages over their service lives caused by adverse loadings, such as earthquakes, wind and wave forces. Accumulation of structural damages over a long period of time might cause catastrophic structural failure. Therefore, a methodology for monitoring the structural integrity is essential for assuring the safety of the existing structures. A method for the damage assessment of structures by the second order inverse modal perturbation technique is presented in this paper. Perturbation equation consists of a matrix equation involving matrices of structural changes(stiffness and mass matrix changes) and matrices of modal property changes(natural frequency and mode shape changes). The damages of a structure are represented as changes in the stiffness matrix. In this study, a second order perturbation equation is formulated for the damage assessment of structures, and solved by an iterative procedure. The effectiveness of the proposed method has been investigated through a series of example analysis. The estimated results for the structural damage indicated that the present method yields resonable estimates for the structural changes.

• Computational Structural Engineering
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• v.11 no.3
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• pp.199-212
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• 1998

본 연구에서는 기설구조물에 대한 손상도 추정기법과 내진능력평가 방법에 대하여 연구하였다. 구조물의 손상도를 추정하는 방법으로는 소수의 계측 데이터를 이용한 모드섭동법(inverse modal perturbation)을 이용하였다. 구조물의 손상은 강성행렬의 감소로 표현하여, 각 요소행렬에 대한 손상을 손상지수를 사용하여 나타내었다. 구조적 손상과 이에 기인한 고유진동 특성의 변화량과의 관계를 섭동방정식으로부터 구한 후, 이로부터 손상지수와 고유진동 특성의 변화량과의 관계를 유동하였다. 따라서 손상 전과 후에서 구조물의 고유진동수와 모드형상을 측정하여 섭동식의 해를 구함으로써 구조물의 강성행렬의 감소로 나타나는 구조물의 손상도를 추정하게 된다. 손상도 추정에 의해 평가된 강성의 변화량에 기인한 손상 후의 기설구조물의 지진응답, 내진능력과 지진손상도의 평가를 손상전과 비교하였다. 내진능력은 구조부재에서 회전연성도 능력의 경험식을 이용하여 평가하였고, 지진손상도의 평가는 가장 많이 사용되는 방법인 Park & Ang 방법을 사용하였다. 예제해석은 다른 지진하중을 받는 2층과 8층의 예제구조물에 대해서 수행하였다.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1998.04a
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• pp.291-300
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• 1998

This paper demonstrates how ambient vibration measurements at a limited number of locations can be effectively utilized to estimate parameters of a finite element model of a large-scale structural system involving a large number of elements. System identification using ambient vibration measurements presents a challenge requiring the use of special identification techniques, which ran deal with very small magnitudes of ambient vibration contaminated by noise without the knowledge of input farces. In the present study, the modal parameters such as natural frequencies, damping ratios, and mode shapes of the structural system were estimated by means of appropriate system identification techniques including the random decrement method. Moreover, estimation of parameters such as the stiffness matrix of the finite element model from the system response measured by a limited number of sensors is another challenge. In this study, the system stiffness matrix was estimated by using the quadratic optimization involving the computed and measured modal strain energy of the system, with the aid of a sensitivity relationship between each element stiffness and the modal parameters established by the second order inverse modal perturbation theory. The finite element models thus identified represent the actual structural system very well, as their calculated dynamic characteristics satisfactorily matched the observed ones from the ambient vibration test performed on a large-scale structural system subjected primarily to ambient wind excitations. The dynamic models identified by this study will be used for design of an active mass damper system to be installed on this structure fer suppressing its wind vibration.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.1
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• pp.27-33
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• 2009

Human postural responses appeared to have stereotyped modality, such as ankle mode, knee mode and hip mode in response to various perturbations. We examined whether human postural control gain of full-state feedback could be decoupled along with the eigenvector. To verify the model, postural responses subjected to fast backward perturbation were used. Upright posture was modeled as 3-segment inverted pendulum incorporated with feedback control, and joint torques were calculated using inverse dynamics. Postural modalities such as ankle, knee and hip mode were obtained from eigenvectors of biomechanical model. As oppose to the full-state feedback control, independent eigenvector control assumes that modal control input is determined by the linear combination of corresponding modality. We used optimization method to obtain and compare the feedback gains for both independent eigenvector control and full-state feedback control. As a result, we found that simulation result of eigenvector feedback was not competitive in comparison with that of full-state feedback control. This implies that the CNS would make use of full-state body information to generate compensative joint torques.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1998.04a
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• pp.414-421
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• 1998

The content of this paper consists of two related subjects. One is the assessment of damages in the existing structure and the other is the evaluation of seismic capacity of the structure with damage. A method is presented for damage assessment of existing structures using the modal data measured at limited points by the inverse medal perturbation technique. For efficient damage assessment, the number of the unknown probable damaged members is reduced for each damage identification by grouping the members in the large structure. The aseismic capacity is evaluated for the structure using the results of damage assessment. An example analysis is carried out for a building structure subjected to different earthquake excitations.

• Journal of Korean Society of Steel Construction
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• v.16 no.5 s.72
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• pp.543-553
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• 2004

This paper covered two related subjects: the use of the inverse modal perturbation technique to assess structural damage in existing structures; and the use of a seismic capacity evaluation to assess damaged structures, with the aid of the identified structural damage. The substructural identification and the Tikhonov regularization algorithm were incorporated for efficient damage assessment of complex and large frame structures. The seismic capacity of a damaged structure was evaluated by comparing the structure's seismic responses and seismic damage indices. The effectiveness of the proposed method has been investigated through the numerical simulation study for a twenty-story frame structure with undamaged and damaged cases, and also different earthquake excitations.