• 한국농공학회논문집
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• 제61권3호
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• pp.55-65
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• 2019

Although crack on concrete exists from its early formation, crack requires attention as it affects stiffness of structure and can lead demolition of structure as it grows. Detecting cracks on concrete is needed to take action prior to performance degradation of structure, and deep learning can be utilized for it. In this study, transfer learning, one of the deep learning techniques, was used to detect the crack, as the amount of crack's image data was limited. Pre-trained Inception-v3 was applied as a base model for the transfer learning. Web scrapping was utilized to fetch images of concrete wall with or without crack from web. In the recognition of crack, image post-process including changing size or removing color were applied. In the visualization of crack, source images divided into 30px, 50px or 100px size were used as input data, and different numbers of input data per category were applied for each case. With the results of visualized crack image, false positive and false negative errors were examined. Highest accuracy for the recognizing crack was achieved when the source images were adjusted into 224px size under gray-scale. In visualization, the result using 50 data per category under 100px interval size showed the smallest error. With regard to the false positive error, the best result was obtained using 400 data per category, and regarding to the false negative error, the case using 50 data per category showed the best result.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.214-219
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• 2004

Crack tip behavior of single mode loading condition(mode I)depend on tensile loading component but one of mixed mode loading condition(mode I+II) have influenced on shear loading component like the practical structure. Because crack closure is caused by shear loading component under mixed-mode loading a research on the behavior in the stage of crack initiation and propagation require to be evaluate about crack closure effect by fatigue crack surface friction. For that reasion we examined the behavior at the crack tip by direct measuring method. Measured behavior at the crack tip was analyzed through vector crack tip displacement. As a result, crack propafation equation was corrected by considering with crack closure effect. In addition we compared fatigue fracture crack surface and crack closure level.

• International Journal of Precision Engineering and Manufacturing
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• 제3권3호
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• pp.76-81
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• 2002

In order to study the fatigue crack and retardation mechanism in variable loading, the effects of crack tip branching in crack growth retardation were examined. The characteristics of crack tip branching behavior were considered with respect to microstructure and crack tip branching angle was examined. Crack tip branching was observed along the grain boundary of finite and pearlite structure. It was found that the branching angle ranges from 25 to 53 degrees. Using the finite element method, the variable of crack driving farce to branching angle was examined. The effective crack driving farce (K$\_$eff/) decreased as the branching angle increased. The rate of decrease was 33% for kinked type and 29% for forked one. It was confirmed that the effect of crack tip branching is a very important factor in crack growth retardation. Therefore, crack branching effect should be considered in building the hypothetical model to predict crack growth retardation.

• 대한기계학회논문집A
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• 제34권1호
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• pp.103-110
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• 2010

본 연구에서는 프랑스의 RCC-MR A16 절차에 기초하여 Mod.9Cr-1Mo 강(ASME Grade 91) 구조의 크리프-피로 균열 개시 및 성장 평가법을 확장 개발하였다. 현재의 A16 지침은 오스테나이트 스테인리스강에 대해서만 크리프-피로 균열 개시 및 성장 평가법을 제시하고 있지만, 현재 초초임계(USC) 화력발전소는 물론 미래형 원자로 시스템의 구조재료로서 폭넓게 채택되고 있는 Mod.9Cr-1Mo 강에 대한 지침은 제시하지 않고 있다. 본 연구에서는 FMS(페리틱-마르텐사이트강)에 대한 크리프-피로 균열 개시 및 성장 평가법을 제시하고 있고, 구조물에 대한 크리프-피로 균열 거동 평가를 수행하였다. 평가결과는 구조시험을 수행한 결과 얻은 관찰 이미지와 비교하였다.

• 한국건설관리학회논문집
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• 제16권3호
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• pp.143-151
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• 2015

콘크리트 구조물에 발생하는 균열은 구조물의 내력, 내구성, 방수성 등 모든 기능을 저하시키는 주요한 원인으로, 그 대책의 필요성은 구조물이 존재하는 한 계속될 것이다. 하지만 콘크리트 구조물에서의 균열은 재료와 시공 및 사용환경, 구조적 요인 등 다양한 변수가 복합적으로 작용하고 있어 이에 대한 대책 마련과 사전 예방이 쉽지 않은 것이 현실이다. 이에 본 연구에서는 공동주택 외벽에서 균열이 발생한 사례를 분석하여 이에 대한 데이터베이스를 구축하고, 발생한 균열과 부재의 속성간의 관계를 상관관계를 도출하고자 한다. 이는 각 부재가 가지는 기본적 속성이 유사함을 고려하여 균열과 부재의 관계를 분석하고 부재의 속성을 검토하여 균열에 대한 대책 마련에 일조하고자 함이다.

• 한국건축시공학회지
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• 제7권1호
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• pp.107-113
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• 2007

This study investigates the filed application in Daebul Free Trade Zone applying both a flowing method using drying shrinkage-reducing superplasticizer(SRS) and an insulating curing method using double layer bubble sheet. Test results showed that fresh concrete satisfied target slump and air content. A structure adding SRS significantly decreased the total bleeding capacity and accelerated the setting time. As for the crack occurrence, the structure applying the flowing method and double bubble sheets simultaneously exhibited the most favorable crack endurance, while conventional concrete showed more than 1mm size of crack in overall. In addition, a structure applying the flowing concrete method partially presented the micro crack. For the area proportion of crack occurrence, the structure using the double bubble sheets indicated 9.8%, while others applying flowing concrete method was 28%, compared with that of conventional one. For the compressive strength of specimens, standard curing specimens indicated $3{\sim}33%$ higher value than that of specimens cured besides the field construction. The specimens containing SRS improved the strength of $2{\sim}6MPa$, which is $10{\sim}22%$ higher than that of conventional concrete.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2006년도 추계 학술논문 발표대회 논문집
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• pp.13-16
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• 2006

This study investigates filed application in Daebul Free Trade Zone of a flowing method using drying shrinkage-reducing superplasticizer(SRS) and an insulating curing method using double bubble sheets. Test showed that fresh concrete satisfied target slump and air content. A structure adding SRS significantly decreased the total bleeding capacity and accelerated the setting time. As for the crack occurrence, the structure applying the flowing method and double bubble sheets simultaneously exhibited the most favorable crack endurance, while conventional concrete showed more than 1mm size of crack in overall, and a structure applying only the flowing method partially presented micro crack. For the area proportion of crack occurrence, the structure using the double bubble sheets indicated 9.8%, while others applying flowing method was 28%, compared with 100% of conventional one. Standard curing specimens had about $3{\sim}6%$ higher compressive strength than that of specimens cured at adjacent field construction. In addition, using SRS improved about $5{\sim}7MPa$, than that of conventional concrete at 91 days elapse.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.521-526
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• 2001

Box-culvert is very important structure used almost every road construction. However this is treated very simple structure in design and construction. So many crack such as nonstructural crack has been occurred. This crack is very harmful on durability of concrete. In this study, thermal crack, one of the nonstructural crack, of box-culvert controled by using rapid-strength belite cement concrete. In this process, not only heat of hydration and thermal stress but also material mechanics properties and characteristics of durability were tested. and same model box-culvert using OPC concrete is constructed in same condition for comparison.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2003년도 학술.기술논문 발표회
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• pp.1-4
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• 2003

Recently, a structure has been larger and higher under the improvement of construction technique. So, a concrete constructions that a mat foundation thickness of structure is over 80cm have been many. Also, because of the reason high strength concrete, the matter of thermal crack have become an important task to be solved absolutely. In a cause a thermal crack occurrence, there used, mixture of concrete, construction and so forth. In this study, we executed temperature and stress analysis of mat foundation to know the effect the construction condition a thermal crack of mat foundation. And we evaluated quantitatively about the occurrence possibility of thermal crack using the hydration heat analysis program. By using of this analysis technique, will can control skilfully the quality of a mat foundation in advance.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2003년도 학술.기술논문발표회
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• pp.1-4
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• 2003

Recently, a structure has been larger and higher under the improvement of construction technique. So, a mass concrete constructions that a mat foundation thickness of structure is over 80cm have been many. Also, because of the reason of high strength of concrete, the matter of thermal crack have become an important task to be solved absolutely. tn a cause of a thermal crack occurrence, there are material used, mixture of concrete, construction condition and so forth. In this study, we executed temperature and stress analysis of mat foundation to know the effect of the construction condition on a thermal crack of mat foundation. And we evaluated quantitatively about the occurrence possibility of thermal crack using the hydration heat analysis program. By using of this analysis technique, we will can control skilfully the quality of a mat foundation in advance.