• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.229-232
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• 2006

The HPFRCCs show that the multiple crack propagation, high tensile strength and ductility due to the interfacial bonding of the fibers to the cement matrix. Moreover, performance of cement composites varies according to type and weight contents of reinforcing fiber. and HPFRCCs with hybrid fiber have better performance than HPFRCCs with single fiber in damage tolerance. Total four cylindrical specimens were tested, and the main variables were the type and weight contents of fiber, which was polyvinylalchol (PVA), polyethylene (PE). In order to clarify effect of hybrid types on the characteristics of fracture and damage process in cement composites, AE method was performed to detect micro-cracking in HPFRCCs under cyclic compression. Loading conditions of the uniaxial compression test were monotonic and cyclic loading. And from AE parameter value, it is found that the second and third compressive load cycles resulted in successive decrease of the amplitude as compared with the first compressive load cvcle.

• 한국BIM학회 논문집
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• 제8권4호
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• pp.13-22
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• 2018

Future performance prediction of bridges is challenging task for structural engineers. Well-organized information from design, construction and operation stages is essential for the assessment of structures. Digital twin model is a new concept to realize more reliable data platform for management of infrastructures. Damage history including degradation of material, cracking, corrosion, etc. needs to be accumulated in the digital model. The digital model is linked to the analysis model for the assessment of structural performance considering changed mechanical properties of structural components. In this paper, initial definition digital twin model of a PSC-I girder bridge is proposed.

• 한국터널지하공간학회 논문집
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• 제3권3호
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• pp.31-43
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• 2001

본 연구에서는 안전진단에 관한 기본적 정보를 제공하고 유사한 변상의 발생을 최소화하기 위한 목적으로 터널의 변상사례들에 대한 조사와 분석을 수행하였다. 국내외 터널의 44개 변상사례에 대하여 4개 항목 즉, 내용수명, 변상유형 및 원인, 지질상태 등에 관한 빈도 수를 분석하였다. 이와 더불어 국내 터널분야의 전문가들로부터 안전진단 평가에 관련하여 총 28개 항목에 대한 설문조사를 수행하였다. 본 연구의 결과는 터널의 변상항목 중에는 균열에 의한 변상이 42~58% 정도로 가장 높은 비율을 나타났다. 변상 원인으로는 시공불량에 의한 영향이 높은 비율을 나타내고 있으므로 시공품질의 확보가 중요한 요인으로 사료된다. 설문조사 결과로부터 경직된 평가기준의 완화를 지적하였다. 그리고 각 항목별 중요도를 제시함으로써 인공지능기법 등을 안전진단분야에 적용하기 위한 기초자료로 활용될 수 있을 것이다.

• 보존과학회지
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• 제38권4호
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• pp.314-326
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• 2022

Investigation of conservation status, optical survey, infrared thermography, and ultrasonic examination were performed on Avalokitesvara Bodhisattva mural and Buddhist Monk Bodhidharma mural to determine the conservation status and physical properties. As a result of investigation of conservation status, the types of damage are largely divided into the wall and finishing layer damage, painting layer degradation, damage due to restoration materials, stains and contamination, and biological damage. As a result of the optical survey, drawing, stains, and repainted site were confirmed. Result of the infrared thermography, the delamination of the finishing layer was confirmed, and some locations and shapes of the wooden lath inside the wall were identified. The result of the 3D scanning, the deviation, and the separation of the wall was confirmed. As a result of ultrasonic examination, it was confirmed that the physical properties of the mural were identified and the ultrasonic speed was relatively low due to physical damage such as delamination and exfoliation of the finishing layer and cracking. Ultrasonic speed values were also high in some wall cracks or delamination, and it was confirmed by the infrared thermography results that the wooden lath inside the wall was located in those parts. It was possible to understand that the wooden lath inside the walls affects the ultrasonic speed during the ultrasonic examination. Therefore, management through periodic inspection of the relevant elements is necessary, and a countermeasure for damage that may occur in the future should be prepared along with intensive monitoring of the major damage identified in this diagnosis result.

• Composites Research
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• 제15권3호
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• pp.11-17
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• 2002

본 연구에서는 분산형 강화복합재료에 균열이 발생하면 하중부하능력이 감소와 더불어 재료의 손상을 초래할 수 있어 재료의 완전한 게재물과 균열이 존재한 게재물이 있는 경우를 상정하여 하중부하능력과 탄성 음력분포를 평가한다. 무한체가 전단음력을 받을 때 완전한 게재물과 균열이 내재한 경우에 대하여 3차원 유한요소해석이 수행되어 완전한 게재물의 경우는 게재물의 영역의 음력은 동일하고 게재물의 계면은 다소 불균일하게 나타났다. 그리고 균열이 내재한 경우에는 균열주변에는 음력이 집중되는 경우를 볼수 있을 뿐만아니라 아주 복잡한 분포를 볼수 있었다. 불균질물의 평균응력은 하중부하능력으로 표현이 가능하였고 완전만 게재물과 균열의 경우도 균열손상에 의해 하중부하능력의 차이를 볼 수 있었다. 특히, 균열이 내재한 경우에 에스펙터비(aspect ratio)가 증가할수록 하중부하능력이 증가함을 알 수 있었다.

• 한국안전학회지
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• 제29권6호
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• pp.9-14
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• 2014

Recently many efforts and researches have been done to cope with industrial facilities that require a low energy machines due to the gradual depletion of the natural resources. The fiber-reinforced composite materials in general have good properties and have the proper mechanical properties according to the change of the ply sequences and fiber distribution types. However, in the fiber-reinforced composite material, there are several problems, including fiber breaking, peeling, layer lamination, fiber cracking that can not be seen from the metallic material. Particularly, the fracture and delamination are likely to be affected by the thickness of the stacking laminates when the bi-material laminated structure is subjected to a load of the mixed mode. In this study, we investigated the effect of the thickness ratio of the difference in the CFRP/GFRP bi-material laminate composites by measuring the cracking behavior and the AE characteristics in a mixed mode loading, which may be generated in the actual structure. The results show that the thickness of the CFRP becomes more thick, the mode I energy release rate becomes a larger, and also the influence of mode I is greater than that of mode II. In addition, AE amplitude which shows the level of the damage in the structure was obtained the more damage in the CFRP with the thin thickness.

• 한국안전학회지
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• 제24권2호
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• pp.17-22
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• 2009

Thermal stress and elastic creeping stress analysis was conducted by finite element method to simulate start-up process of a boiler header of 500MW standard fossil power plant. Start-up temperature and operating pressure history were simplified from the real field data and they were used for the thermal stress analysis. Two kinds of thermal stress analysis were considered. In the first case only temperature increase was considered and in the second case both of temperature and operating pressure histories were considered. In the first analysis peak stress was occurred during the temperature increase from the room temperature. Hence cracking or fracture may occur at the temperature far below the operating maximum temperature. In the results of the second analysis von Mises stress appeared to be higher after the second temperature increase. This is due to internal pressure increase not due to the thermal stress. When the stress components of radial(r), hoop($\theta$) and longitudinal(z) stress were investigated, compression hoop stress was occurred at inner surface of the stub tube when the temperature increased from room temperature to elevated temperature. Then it was changed to tension hoop stress and increased because of the operating pressure. It was expected that frequent start-up and shut-down operations could cause thermal fatigue damage and cracking at the stub tube hole in the header. Elastic-creeping analysis was also carried out to investigate the stress relaxation due to creep and stabilized stress after considerable elapsed time. The results could be used for assessing the creep damage and the residual life of the boiler header during the long-tenn service.

• Smart Structures and Systems
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• 제26권3호
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• pp.319-329
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• 2020

Structural damage to an arch dam is often of major concern and must be evaluated for probable rehabilitation to ensure safe, regular, normal operation. This evaluation is crucial to prevent any catastrophic or failure consequences for the life time of the dam. If specific major damage such as a large crack occurs to the dam body, the assessments will be necessary to determine the current level of safety and predict the resistance of the structure to various future loading such as earthquakes, etc. This study investigates the behavior of an arch dam cracked due to water pressure. Safety factors (SFs), of shear and compressive tractions were calculated at the surfaces of the contraction joints and the cracks. The results indicated that for cracking with an extension depth of half the thickness of the dam body, for both cases of penetration and non-penetration of water load into the cracks, SFs only slightly reduces. However, in case of increasing the depth of crack extension into the entire thickness of the dam body, the friction angle of the cracked surface is crucial; however, if it reduces, the normal loading SFs of stresses and joints tractions reduce significantly.

• Smart Structures and Systems
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• 제17권1호
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• pp.91-105
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• 2016

One of the most commonly used techniques to strengthen steel reinforced concrete structures is the application of externally bonded patches in the form of carbon fiber reinforced polymers (CFRP) or recently, textile reinforced cements (TRC). These external patches undertake the tensile stress of bending constraining concrete cracking. Development of full-field inspection methodologies for fracture monitoring are important since the reinforcing layers are not transparent, hindering visual observation of the material condition underneath. In the present study acoustic emission (AE) and digital image correlation (DIC) are applied during four-point bending tests of large beams to follow the damage accumulation. AE helps to determine the onset of fracture as well as the different damage mechanisms through the registered shifts in AE rate, location of active sources and change in waveform parameters. The effect of wave propagation distance, which in large components and in-situ can well mask the original information as emitted by the fracture incidents is also discussed. Simultaneously, crucial information is supplied by DIC concerning the moments of stress release of the patches due to debonding, benchmarking the trends monitored by AE. From the point of view of mechanics, conclusions on the reinforcing contribution of the different repair methodologies are also drawn.

• Geomechanics and Engineering
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• 제32권4호
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• pp.427-443
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• 2023

Across the globe, rapid urbanization demands the construction of basements for car parking and sub way station within the vicinity of high-rise buildings supported on piled raft foundations. As a consequence, ground movements caused by such excavations could interfere with the serviceability of the building and the piled raft as well. Hence, the prediction of the building responses to the adjacent excavations is of utmost importance. This study used three-dimensional numerical modelling to capture the effects of twin excavations (final depth of each excavation, H_e=24 m) on a 20-storey building resting on (4×4) piled raft. Because the considered structure, pile foundation, and soil deposit are three-dimensional in nature, the adopted three-dimensional numerical modelling can provide a more realistic simulation to capture responses of the system. The hypoplastic constitutive model was used to capture soil behaviour. The concrete damaged plasticity (CDP) model was used to capture the cracking behaviour in the concrete beams, columns and piles. The computed results revealed that the first excavation- induced substantial differential settlement (i.e., tilting) in the adjacent high-rise building while second excavation caused the building tilt back with smaller rate. As a result, the building remains tilted towards the first excavation with final value of tilting of 0.28%. Consequently, the most severe tensile cracking damage at the bottom of two middle columns. At the end of twin excavations, the building load resisted by the raft reduced to half of that the load before the excavations. The reduced load transferred to the piles resulting in increment of the axial load along the entire length of piles.