• Wind and Structures
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• 제21권6호
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• pp.657-675
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• 2015

In this study, the feasibility of vibration-based damage detection methods for the wind turbine tower (WTT) structure is evaluated. First, a frequency-based damage detection (FBDD) is outlined. A damage-localization algorithm is visited to locate damage from changes in natural frequencies. Second, a mode-shape-based damage detection (MBDD) method is outlined. A damage index algorithm is utilized to localize damage from estimating changes in modal strain energies. Third, a finite element (FE) model based on a real WTT is established by using commercial software, Midas FEA. Several damage scenarios are numerically simulated in the FE model of the WTT. Finally, both FBDD and MBDD methods are employed to identify the damage scenarios simulated in the WTT. Damage regions are chosen close to the bolt connection of WTT segments; from there, the stiffness of damage elements are reduced.

• Earthquakes and Structures
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• 제16권2호
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• pp.197-208
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• 2019

The objective of this study is to propose new seismic intensity parameters based on the Hilbert spectrum and to associate them with the seismic damage potential. In recent years the assessment of even more seismic features derived from the seismic acceleration time-histories was associated with the structural damage. For a better insight into the complex seismic acceleration time-history, Hilbert-Huang Transform (HHT) analysis is utilized for its processing, and the Hilbert spectrum is obtained. New proposed seismic intensity parameters based on the Hilbert spectrum are derived. The aim is to achieve a significant estimation of the seismic damage potential on structures from the proposed new intensity parameters confirmed by statistical methods. Park-Ang overall structural damage index is used to describe the postseismic damage status of structures. Thus, a set of recorded seismic accelerograms from all over the word is applied on a reinforced concrete frame structure, and the Park-Ang indices through nonlinear dynamic analysis are provided and considered subsequently as reference numerical values. Conventional seismic parameters, with well-known seismic structural damage interrelation, are evaluated for the same set of excitations. Statistical procedures, namely correlation study and multilinear regression analysis, are applied on the set of the conventional parameters and the set of proposed new parameters separately, to confirm their interrelation with the seismic structural damage. The regression models are used for the evaluation of the structural damage indices for every set of parameters, respectively. The predicted numerical values of the structural damage indices evaluated from the two sets of seismic intensity parameters are inter-compared with the reference values. The numerical results confirm the ability of the proposed Hilbert spectrum based new seismic intensity parameters to approximate the postseismic structural damage with a smaller Standard Error of Estimation than this accomplished of the conventional ones.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 춘계학술발표대회 논문집
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• pp.89-92
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• 2001

Drop weight impact tests were performed to investigate the impact behavior of carbon fiber/epoxy composite laminates reinforced by short fibers and other interleaving materials. Characterization techniques, such as cross-sectional fractography and scanning acoustic microscopy, were employed quantitatively to assess the internal damage of some composite laminates. Scanning electron microscopy was used to observe impact damage and fracture modes on specimen fracture surfaces. The results show that composite laminates experience various types of fracture; delamination, intra-ply cracking, matrix cracking and fiber breakage depending on the interlayer materials. Among the composite laminates tested in this study, the composites reinforced by Zylon fibers showed very good impact damage resistance with medium level of damage, while the composites interleaved by poly(ethylene-co-acrylic acid) (PEEA) film is expected to deteriorate the bulk strength due to the reduction of fiber volume fraction, even though the damaged area is significantly reduced.

• 대한한의학원전학회지
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• 제33권4호
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• pp.33-56
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• 2020

Objectives : The objective of this paper is to develop a standardized patient program with a focus on diagnosis and treatment of internal damage fever in Korean Medical education. Methods : First, cases of diagnosis and treatment of internal damage fever were collected from various classical texts, then a module was developed according to pre-existing standardized patient program's protocols based on selected cases. Careful consideration was given to developing evaluation criteria on history taking and physical examination that are necessary to accurately differentiating the 9 types. Results : Nine types of differentiation models on internal damage fever were selected, which are qi deficiency from overexertion/fatigue and famish; blood deficiency from overexertion/fatigue, famish and fullness; fire stagnation from excessive eating and cold foods; food damage; yang deficiency; yin deficiency; phlegm; stagnated blood; liver qi stagnation. For each type, evaluation criteria in regards to history taking, physical examination, communication with patient, and patient education were developed. Conclusions : When developing a standardized patient program using internal damage fever cases, it would better reflect the characteristics of Korean Medicine in clinical education of Korean Medicine if the program is based on classical texts. It would also be useful in evaluating students' graduation competence in exams such as CPX.

• Advanced Composite Materials
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• 제16권1호
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• pp.45-61
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• 2007

This paper describes a damage accumulation mechanism in cross-ply CFRP laminates $[0_2/90_2]_{2S}$ subjected to out-of-plane loading. Drop-weight impact and static indentation tests were carried out, and induced damage was observed by ultrasonic C-scan and an optical microscope. Both tests gave essentially the same results for damage modes, sizes, and load-deformation history. First, a crack occurred in the bottom $0^{\circ}$ layer accompanying some delamination along the crack caused by bending stress. Then, transverse cracks occurred in the middle $90^{\circ}$ layer with decreasing contact force between the specimen and the indenter. Measured local strains near the impact point showed that the stress state changed from a bending dominant state to an in-plane tensile dominant state. A cohesive interface element was used to simulate the propagation of multiple delaminations and transverse cracks under static indentation. Two types of analytical models are considered, one with multiple delaminations and the other with both multiple delaminations and transverse cracks. The damage obtained for the model with only multiple delaminations was quite different from that obtained from the experiment. However, the results obtained from the model with both delaminations and transverse cracks well explain the characteristics of the damage obtained in the experiment. The existence of the transverse cracks is essential to form the characteristic impact damage.

• 한국강구조학회 논문집
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• 제16권5호통권72호
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• pp.543-553
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• 2004

이 연구는 구조물의 내진성능평가와 관련하여, 기설구조물의 현재 상태에서의 구조손상을 추정하고, 이를 반영하여 내진성능을 평가하도록 하는 절차를 제안하였다. 구조손상 추정을 위해서는 역섭동법을 사용하였고, 역섭동법의 단점을 극복하기 위하여 부분구조법과 Tikhonov의 정규화 방법을 도입하였다. 손상된 구조물의 내진성능 평가를 위하여 구조물의 지진응답과 해당 구조물의 지진손상지수를 이용하였고, 제안 방법을 20층 예제구조물에 적용하여 손상추정 결과를 반영하는 것의 영향을 분석하였다.

• 한국환경과학회지
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• 제29권5호
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• pp.551-558
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• 2020

This study aims to increase the ability to adapt to the ecosystem and promote a sustainable use of the natural environment, by classifying the types of damaged lands according to various factors, such as the characteristics of the target area and form, cause, and impact of damage. Moreover, the study suggests the development of evaluation categories and criteria by each type. The results obtained are as follows: first, for the assessment of damaged lands, the changed areas were identified utilizing land cover maps. Video analysis was performed to increase the accuracy, and 88 sites were obtained. Second, the types of damage were classified into ecological infrastructure and ecological environment, and the sub-factors of the cause of damage were classified into 12 factors. Third, each evaluation system for the types of damage was composed of four steps, considering each type of damage and the level of evaluators being higher than paraprofessionals. To supplement this study, it will be necessary to utilize the database of damaged lands other than the Seoul Metropolitan Area and conduct an on-site survey for verification in the future.

• Structural Engineering and Mechanics
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• 제60권5호
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• pp.875-890
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• 2016

A new structural damage index for seismic fragility analysis of reinforced concrete columns is developed based on a local tensile damage variable of the Lee and Fenves plastic-damage model. The proposed damage index is formulated from the nonlinear regression of experimental column test data. In contrast to the response-based damage index, the proposed damage index is well-defined in the form of a single monotonically-increasing function of the volume weighted average of local damage distribution, and provides the necessary computability and objectivity. It is shown that the present damage index can be appropriately zoned to be used in seismic fragility analysis. An application example in the computational seismic fragility evaluation of reinforced concrete columns validates the effectiveness of the proposed damage index.

• 한국지반환경공학회 논문집
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• 제22권11호
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• pp.15-21
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• 2021

도심지 지하에 매설된 열수송관 등 지하매설관이 점차 노후화함에 따라 파손에 의한 인적, 경제적 피해가 증가하고 있다. 외부로 노출되지 않아 파손 등 문제점을 즉시 확인하기 어려운 열수송관의 특징을 고려할 때, 시설물 유지관리를 통해 주기적으로 수집하는 이력정보를 기반으로 시설물의 상태를 간접적으로 확인하는 방법이 현실적이다. 본 논문에서는 열수송관 이력정보를 검토하여 파손확률과 연관성을 가지는 평가인자를 도출하고, 이를 통해 파손확률을 추정하는 방법론을 제시하고자 한다. 파손확률 추정을 위한 영향인자는 유럽의 사례, 국내 열수송관 관리기준 등을 분석해 도출하였으며, 데이터의 확보 가능성도 함께 고려하여 선정하였다. 열수송관 설치기준이 변경된 1999년을 기준으로 매설시기에 따라 2가지 파손확률 추정 함수를 달리 제시하고 관경, 용도, 관리주체 등 평가인자별 정보에 따른 가중치를 부여하여 파손확률을 보정하여 파손확률추정의 신뢰성을 확보하였다.

• 한국산학기술학회논문지
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• 제19권1호
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• pp.127-135
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• 2018

최근 국내에서의 잦은 지진 발생으로 지진에 대한 관심이 증가함에 따라 이에 대한 해석법 및 손상도를 평가하는 여러 가지 방법이 제시되고 있다. 그러나 해석 및 손상도를 평가함에 있어 각각의 부재에 대한 변위와 부재력 뿐 아니라 실제 발생하는 지지에 대하여 구조물의 손상고를 정량적으로 평가하기에는 기준 및 방법이 미비한 실정이다. 따라서 본 논문에서는 케이블지지 교량인 사장교를 대상으로 실제지진하중 및 여러 가지 형태의 지진파에 대하여 지진해석을 수행하고 그 결과를 바탕으로 손상도 평가방법을 제시하였다. 손상지수는 사장교의 주탑 기울기를 기반으로 산정하였으며 물리적 내진손상 특성은 각각 A, B, C, D 레벨의 4단계로 제안하였다. 또한 지진해석방법에 따라 내진 손상지수가 항상 크거나 또는 작게 나온다고 단순하게 판단 할 수는 없었으며 본 연구는 사장교를 대상으로 하여 내진 손상지수의 제안 및 손상도 평가를 수행한 것이나 지진하중 하에서 비슷한 최대 변위응답 특성을 보이는 구조물에도 확장하여 적용할 수 있으리라 생각된다.