• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.195-198
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• 2011

석유 및 천연가스 생산에 사용되는 고정식 해양플랜트에는 자켓 구조물이 가장 많이 사용되고 있다. 생산에 사용되는 자켓 구조물은 풍하중이나 파랑하중에 의해 인명의 피해 없이 변위 및 응력에 대해 안전해야 한다. 그러나 1940년대 후반부터 사용되어 온 자켓 구조물은 피로하중, 노후화로 인해 내구성에 문제가 생기고 있다. 본 논문에서는 자켓 구조물의 안전성을 검토하기 위해 모드형상을 이용하여 자켓 구조물의 손상 위치를 탐색하는 방법을 제시한다. 제시한 손상탐지기법의 효용성을 입증하기 위해 자켓 구조물의 유한요소모델에 임의의 손상을 모사하였다. 유한요소모델의 손상 전 모드형상과 손상 후 모드형상의 모달 변형에너지의 변화를 이용하여 손상 지수를 유도하고 유도한 손상지수를 사용하여 손상이 있는 부재와 손상이 없는 부재를 분류하였다. 연구 결과 손상지수가 '0'인 부재를 제외한 나머지 부재 모두 본 연구에서 제시한 손상탐지기법으로 손상 부재를 판별할 수 있었다.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2011.06a
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• pp.189-191
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• 2011

구조물의 동적특성인 모드형상을 통해 국부적인 손상을 탐지하는 손상평가 기법은 많은 연구자에 의해 발전되고 있다. 하지만 플로팅 구조물에 대한 손상탐지 기법은 그 사례를 찾아보기 힘들다. 본 논문에서는 플로팅 구조물의 함체 부분을 모델링 하고, 손상 전과 손상 후 구조물의 모드형상에서 얻을 수 있는 모달 변위로 나타낸 손상지수를 통해 플로팅 구조물에 발생할 수 있는 손상을 추정하여, 제안된 이론의 적용성을 검증 하였다.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.2
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• pp.119-128
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• 2016

In a performance-based design, the structural safety is estimated from pre-defined damage states and corresponding damage indices. Both damage states and damage indices are well defined for above-ground structures, but very limited studies have been performed on underground structures. In this study, we define the damage states and damage indices of a cut-and-cover box tunnel which is one of typical structures used in metro systems, under a seismic excitation from a series of inelastic frame analyses. Three damage states are defined in terms of the number of plastic hinges that develop within the structure. The damage index is defined as the ratio of the elastic moment to the yield moment. Through use of the proposed index, the inelastic behavior and failure mechanism of box tunnels can be simulated and predicted through elastic analysis. In addition, the damage indices are linked to free-field shear strains. Because the free-field shear strain can be easily calculated from a 1D site response analysis, the proposed method can be readily used in practice. Further studies are needed to determine the range of shear strains and associated uncertainties for various types of tunnels and site profiles. However, the inter-linked platform of damage state - damage index - shear wave velocity - shear strain provides a novel approach for estimating the inelastic response of tunnels, and can be widely used in practice for seismic designs.

• Journal of Korean Society of Steel Construction
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• v.10 no.2 s.35
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• pp.279-290
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• 1998

An existing Damage Index Method is verified to demonstrate its feasibility for detecting structural damage in truss bridges (1) for which modal parameters are available for a few modes of vibration and (2) for which baseline modal information is not available from its as-built state. The theory of approach to detect locations of damage and to identify baseline modal model is summarized on the basis of system identification theory and modal sensitivity theory. The feasibility of the Damage Index Method is demonstrated using a numerical example of a truss bridge with 11 subsystems of 211 members and for which only two modes of vibration were recorded for post-damaged state.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.3
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• pp.333-342
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• 2003

The objective of this paper is to present an algorithm to locate and size damage in a beam structure. The method uses the changes in the modal strain energy distribution. A damage index, utilized to identify possible location and corresponding severity of local damage, is formulated and expressed in terms of modal displacements that can be obtained from mode shapes of the undamaged and the damaged structures. The possible damage locations in the structure arc determined by the application of damage indicator according to previously developed decision rules. The robustness and effectiveness of the method arc demonstrated using numerical examples of beam structures with simulated damage.

• Journal of the Earthquake Engineering Society of Korea
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• v.15 no.1
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• pp.19-28
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• 2011

In this study, nonlinear finite element analysis procedures are presented for the structural performance assessment of damaged reinforced concrete structures. A computer program, named RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology), for the analysis of reinforced concrete structures was used. Material nonlinearity is taken into account by comprising tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. This paper defines a damage index based on the predicted inelastic behavior of reinforced concrete structures. The proposed numerical method for the structural performance of damaged reinforced concrete structures is verified by comparison with reliable experimental results.

• Magazine of the Korea Concrete Institute
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• v.9 no.5
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• pp.137-148
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• 1997

지진이 발생하는 환경에서 철근콘크리트구조의 신뢰성을 수명주기비용에 근거하여 체계적으로 평가하는 방법을 제시하였다. 구조물의 기능성과 경제적인 효용성을 나타내기 위하여 각각 손상확률과 평균수명 주기비용의 개념을 사용하였다. 생애주기 동안 발생할 수 있는 지진에 의하여 구조물이 입게 될 손상을 보상하기 위하여 소요되는 평균손상비용을 평균수명주기비용의 주요 항목으로 고려하여 분석하였다. 구조물의 다양한 손상상태에서 손상비용을 나타내기 위해 요구되는 비용함수는 Park-Ang 손상지수의 중앙값을 독립변수로 하는 함수로 가정하였다. 지진에 의한 구조물의 손상해석은 UCI에서 개발된 SMART-DRAIN의 시뮬레이션기법을 사용하여 그 불확실성을 고려하였다. 제시된 방법을 현행 규준에 의하여 설계된 7층 사무실 건물에 적용하여 그 가능성을 살펴보았다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.2 s.54
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• pp.115-121
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• 2009

The paper presents a signal-based damage detection algorithm of ARX model using dynamic acceleration data. An ARX model correlates acceleration data measured at two locations in a structure by considering those two sets of data as input and output signals. For detecting damage, the error between the measured data and the predicted response from the defined ARX model is computed in time and used for a statistical evaluation. A normal distribution function from the error in time is constructed and its statistical characteristic values are used for the evaluation of damage. By comparing the normal distribution functions before and after damage, three different types of damage indices are proposed. The efficiency and limitation of the proposed algorithm with the statistical evaluation of damage indices have been examined and discussed through laboratory experiments.

• Journal of Gastric Cancer
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• v.6 no.2
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• pp.91-96
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• 2006

Purpose: Cancer is a genetic disease caused by alterations in key regulators of cell growth and cell turnover, We investigated apoptotic cell death and cell proliferation in gastric adenomas and adenocarcinomas. Materials and Methods: The TdT-mediated dUTP-biotin nick end labelling (TUNEL) method and immunohistochemistry for Ki-67 were peformed, using paraffin-embedded tissues of 41 gastric adenomas and 100 gastric adenocarcinomas. These results were compared with histopathologic parameters. Results: The Ki-67 labelling index was higher in adenocarcinomas than in adenomas and the apoptotic index was higher in adenomas than in adenocarcinomas. There were no significant difference between the apoptotic index/Ki-67 labelling index and clinicopathological parameters. Conclusion: We propose that cell proliferation is more closely associated with gastric adenocarcinomas than apoptosis is, but that neither has any clinical significance as a prognostic factor in gastric adenocarcinomas. (J Korean Gastric Cancer Assoc 2006;6:91-96)

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.1
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• pp.165-174
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• 2010

In this paper, a two-phase structural health monitoring system using acceleration response signatures are presented to firstly alarm the change in structural condition and to secondly detect the changed location for full-scale concrete girder bridges. Firstly, Mihocheon Bridge which is a two-span continuous concrete girder bridge is selected as the target structure. The dynamic response features of Mihocheon Bridge are extracted by forced vibration test using bowling ball. Secondly, the damage alarming occurrence and the damage localization techniques are selected to design two-phase structural health monitoring system for Mihocheon Bridge. As the damage alarming techniques, auto-regressive model using time-domain signatures, correlation coefficient of frequency response function and frequency response ratio assurance criterion are selected. As the damage localization technique, modal strain energy-based damage index method is selected. Finally, the feasibility of two-phase structural health monitoring systems is evaluated from static loading tests using a dump truck.