• Structural Engineering and Mechanics
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• 제23권1호
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• pp.75-95
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• 2006

Two-step identification approaches for effective bridge health monitoring are proposed to alleviate the issues associated with many unknown parameters faced in real structures and to improve the accuracy in the estimate results. It is suitable for on-line monitoring scheme, since the damage assessment is not always needed to be carried out whereas the alarming for damages is to be continuously monitored. In the first step for screening potentially damaged members, a damage indicator method based on modal strain energy, probabilistic neural networks and the conventional neural networks using grouping technique are utilized and then the conventional neural networks technique is utilized for damage assessment on the screened members in the second step. The effectiveness of the proposed methods is investigated through a field test on the northern-most span of the old Hannam Grand Bridge over the Han River in Seoul, Korea.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 추계학술대회 논문집
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• pp.1397-1402
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• 2008

In this paper, damage detection method by using the time reversal is developed to detect damage on composit structures. The time reversal was investigated for direct root between PZT and PZT, but in case of a circular PZT, lamb wave moves not only along the direct root but also another roots. The center frequency of lamb wave is kept when the lamb waves are reflected from damage. This paper presents experimental and theoretical results for the new structural health monitoring method by above features of lamb wave, and we can increase accuracy of the new structural health monitoring method by using STFT(Short Time Fourier Transform).

• 한국전산구조공학회논문집
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• 제21권6호
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• pp.615-632
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• 2008

교량 건전성 모니터링은 응답 데이터를 활용한 구조모델링기술, 신호분석, 정보처리 기술의 발전에 따라 손상추정 및 안전성평가와 함께 중요한 연구주제로 부각되었다. 교량 모니터링 시스템은 일반적으로 센서, 데이터 취득장비, 전송시스템 등과 같은 하드웨어와 신호처리, 손상추정, 전시 및 데이터 관리 등과 같은 소프트웨어로 구성된다. 본 논문에서는 교량의 건전도 모니터링을 위한 정보처리기술에 대한 연구 개발 활동을 정리하였다. 교량 건전성 모니터링의 과정에 대한 간단한 소개와 함께, 다양한 신호처리 및 손상추정 알고리즘을 포함한 정보처리기법에 대해서 소개하였다. 현 교량 건전성 모니터링 시스템에서의 주요 문제점과 향후 연구개발활동을 논의하였다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2004년도 가을 학술발표회 논문집
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• pp.550-557
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• 2004

In this paper, structural damage in PSC bridges is monitored by using model-based damage detection methods. First numerical experiments on the test structure are described. Dynamic responses of the test structures are obtained fur several damage scenarios. The change in natural frequency and the change in nude shape curvature are selected as features to represent the states of the structure. Next a damage localization algorithm from monitoring the changes in natural frequency is outlined. Also, the damage localization algorithm from monitoring the changes in nude shapes is outlined. Finally, the damage localization algorithms are used to predict damage in the test structure. The results of the analysis indicate that the model-based damage detection methods correctly predicted damage in the test structure.

• Structural Engineering and Mechanics
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• 제26권3호
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• pp.315-341
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• 2007

A sudden change of stiffness in a structure, associated with the events such as weld fracture and brace breakage, will cause a discontinuity in acceleration response time histories recorded in the vicinity of damage location at damage time instant. A new damage index is proposed and implemented in this paper to detect the damage time instant, location, and severity of a structure due to a sudden change of structural stiffness. The proposed damage index is suitable for online structural health monitoring applications. It can also be used in conjunction with the empirical mode decomposition (EMD) for damage detection without using the intermittency check. Numerical simulation using a five-story shear building under different types of excitation is executed to assess the effectiveness and reliability of the proposed damage index and damage detection approach for the building at different damage levels. The sensitivity of the damage index to the intensity and frequency range of measurement noise is also examined. The results from this study demonstrate that the damage index and damage detection approach proposed can accurately identify the damage time instant and location in the building due to a sudden loss of stiffness if measurement noise is below a certain level. The relation between the damage severity and the proposed damage index is linear. The wavelet-transform (WT) and the EMD with intermittency check are also applied to the same building for the comparison of detection efficiency between the proposed approach, the WT and the EMD.

• Structural Engineering and Mechanics
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• 제32권6호
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• pp.787-809
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• 2009

Recent interest in the use of wireless sensor networks for structural health monitoring (SHM) is mainly due to their low implementation costs and potential to measure the responses of a structure at unprecedented spatial resolution. Approaches capable of detecting damage using distributed processing must be developed in parallel with this technology to significantly reduce the power consumption and communication bandwidth requirements of the sensor platforms. In this investigation, a damage detection system based on a distributed processing approach is proposed and experimentally validated using a wireless sensor network deployed on two laboratory structures. In this distributed approach, on-board processing capabilities of the wireless sensor are exploited to significantly reduce the communication load and power consumption. The Damage Location Assurance Criterion (DLAC) is used for localizing damage. Processing of the raw data is conducted at the sensor level, and a reduced data set is transmitted to the base station for decision-making. The results indicate that this distributed implementation can be used to successfully detect and localize regions of damage in a structure. To further support the experimental results obtained, the capabilities of the proposed system were tested through a series of numerical simulations with an expanded set of damage scenarios.

• 한국방재학회 논문집
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• 제9권5호
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• pp.9-13
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• 2009

현재까지 구조건전성 모니터링과 관련하여 제안된 대부분의 손상인식기법은 모달영역응답을 이용하고 있으나, 모달영역응답은 별도의 후처리가 필요하며 추출과정에서 오차를 포함하게 되므로 손상인식의 정확성을 저하시키는 요인이 되어왔다. 본 논문에서는 이동하중응답을 직접 이용하는 손상인식기법의 적용성을 실내 실험을 통하여 검증하였다. 실험은 강재로 만든 보에 이동하중을 재하시켜 수행하였으며, 보의 응답은 변위계를 이용하여 측정하였다. 이동하중은 쇠구슬과 활강장치를 이용하여 모사하였으며, 주기성과 비주기성 이동하중으로 구분하여 재하하였다. 계측된 응답을 이용한 손상인식 결과, 이동하중을 이용한 손상인식기법은 구조물의 손상을 성공적으로 탐지하는 것으로 나타났다.

• Smart Structures and Systems
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• 제33권3호
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• pp.227-241
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• 2024

Safety and structural integrity of civil structures, like bridges and buildings, can be substantially enhanced by employing appropriate structural health monitoring (SHM) techniques for timely diagnosis of incipient damages. The information gathered from health monitoring of important infrastructure helps in making informed decisions on their maintenance. This ensures smooth, uninterrupted operation of the civil infrastructure and also cuts down the overall maintenance cost. With an early warning system, SHM can protect human life during major structural failures. A real-time online damage localization technique is proposed using only the vibration measurements in this paper. The concept of the 'Degree of Scatter' (DoS) of the vibration measurements is used to generate a spatial profile, and fractal dimension theory is used for damage detection and localization in the proposed two-phase algorithm. Further, it ensures robustness against environmental and operational variability (EoV). The proposed method works only with output-only responses and does not require correlated finite element models. Investigations are carried out to test the presented algorithm, using the synthetic data generated from a simply supported beam, a 25-storey shear building model, and also experimental data obtained from the lab-level experiments on a steel I-beam and a ten-storey framed structure. The investigations suggest that the proposed damage localization algorithm is capable of isolating the influence of the confounding factors associated with EoV while detecting and localizing damage even with noisy measurements.

• 대한의생명과학회지
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• 제17권3호
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• pp.239-243
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• 2011

Radiation exposure may cause tissue damage by ionized or excited atoms. The molecules are transformed from water or they directly interact with cells. Antioxidants such as vitamin E, vitamin C are used to reduce the interference of radiation. Especially, vitamin E inhibits the formation and accumulation of lipid and oxidation and the activity of drug-metabolizing enzymes. After irradiation of 3 Gy to the testis, the entire shape of testis was partly depressed and an irregular vacuole was observed to the edge. The 3 Gy group after treatment with vitamin E showed the low destruction of spermatogonia and partial tissue damage as compared to the 3 Gy group. Vitamin E inhibited the production of vacuoles from the cell death and generated the block to prevent the condensation of the seminiferous tubules.

• Smart Structures and Systems
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• 제6권1호
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• pp.17-27
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• 2010

The approach to damage detection and localization adopted in this paper is based on a statistical comparison of models built from the response time histories collected at different stages during the structure lifetime. Some of these time histories are known to have been recorded when the structural system was undamaged. The consistency of the models associated to two different stages, both undamaged, is first recognized. By contrast, the method detects the discrepancies between the models from measurements collected for a damaged situation and for the undamaged reference situation. The damage detection and localization is pursued by a comparison of the SSE (sum of the squared errors) histograms. The validity of the proposed approach is tested by applying it to the analytical benchmark problem developed by the ASCE Task Group on Structural Health Monitoring (SHM). In the paper, the results of the benchmark studies are presented and the performance of the method is discussed.