• Structural Engineering and Mechanics
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• 제73권4호
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• pp.455-462
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• 2020

The hybrid method using the extended finite element method (XFEM) and the forward Euler approach is widely employed to predict the fatigue life of plate structures. Due to the accuracy of the forward Euler approach is determined by a small step size, the performance of fatigue life prediction of the hybrid method is not agreeable. Instead the forward Euler approach, a prediction method using midpoint method and support vector regression (SVR) is presented to evaluate the stress intensity factors (SIFs) and the fatigue life. Firstly, the XFEM is employed to calculate the SIFs with given crack sizes. Then use the history of SIFs as a function of either number of fatigue life cycles or crack sizes within the current cycle to build a prediction model. Finally, according to the prediction model predict the SIFs at different crack sizes or different cycles. Three numerical cases composed by a homogeneous plate with edge crack, a composite plate with edge crack and center crack are introduced to verify the performance of the proposed method. The results show that the proposed method enables large step sizes without sacrificing accuracy. The method is expected to predict the fatigue life of complex structures.

• 한국공간구조학회논문집
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• 제21권2호
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• pp.99-110
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• 2021

This study presents the estimation of crack depth by analyzing temperatures extracted from thermal images and environmental parameters such as air temperature, air humidity, illumination. The statistics of all acquired features and the correlation coefficient among thermal images and environmental parameters are presented. The concrete crack depths were predicted by four different machine learning models: Multi-Layer Perceptron (MLP), Random Forest (RF), Gradient Boosting (GB), and AdaBoost (AB). The machine learning algorithms are validated by the coefficient of determination, accuracy, and Mean Absolute Percentage Error (MAPE). The AB model had a great performance among the four models due to the non-linearity of features and weak learner aggregation with weights on misclassified data. The maximum depth 11 of the base estimator in the AB model is efficient with high performance with 97.6% of accuracy and 0.07% of MAPE. Feature importances, permutation importance, and partial dependence are analyzed in the AB model. The results show that the marginal effect of air humidity, crack depth, and crack temperature in order is higher than that of the others.

• 한국구조물진단유지관리공학회 논문집
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• 제27권6호
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• pp.138-143
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• 2023

이 연구에서는 탄산칼슘 형성 박테리아의 내생포자를 접종한 알지네이트 겔과 포자현탁액 형태의 균열치유제를 모르타르에 첨가하여 균열치유성능을 비교, 분석함으로써 균열치유제 제조방법별 균열치유성능을 분석하였다. 또한 박스형 암거 형태의 실 구조물에 적용하여 실험실 환경뿐만 아니라 개발된 균열치유제가 실제 현장에 적용될 수 있는 환경을 조성하여 실구조물 스케일에서 균열치유성능을 검증하고자 하였다. 건조 방식을 달리한 두 가지 형태의 알지네이트 겔로 구성된 균열치유제를 분석한 결과, 건열건조 방식의 균열치유제는 균열치유 성능을 나타내었으나, 동결건조 방식의 경우 얼음 결정에 의해 다수의 포자가 사멸되어 균열치유성능을 잃는 것으로 나타났다. 실스케일 구조물의 균열부에서 추출된 균열치유 추정물질의 SEM 사진과 XRD 패턴 분석 결과 균열치유제에 적용된 균열치유 미생물이 생성한 탄산칼슘 결정 중 하나인 calcite인 것으로 나타났으며, 미생물에 의한 균열치유메커니즘이 실구조물에서 구현될 수 있음을 확인하였다.

• 한국도로학회논문집
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• 제19권2호
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• pp.103-112
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• 2017

PURPOSES : In this study, field performance evaluation of crack treatment of pavement and the feasibility of surface treatment of pavement are presented. The performance and cost of preventive maintenance methods have been previously verified, and the methods are being used in many developed countries and cities. However, the performance and cost of the system have not been verified in domestic, field applications. Therefore, in order to improve performance, the field performance is evaluated, and a reasonable cost is proposed. METHODS : Visual Inspection was conducted to evaluate the field application and performance of the preventive maintenance method. In addition, the PCI index was calculated from the results of visual inspection of the application area of the surface treatment method, and the performance life of each method was predicted. For the economic evaluation, life cycle cost analysis was performed using the life cycle cost analysis program. RESULTS :In order to evaluate and quantify the field performance of crack repair material, the residue condition of the pavement surface after crack treatment, rather than the performance of the material, is evaluated. In addition, the crack resistance and performance life of surface treatment methods are evaluated. The cost of currently available treatment methods are compared to the common pavement cut and overlay method, and it is determined that the preventive method is not economical based on life cycle cost analysis. CONCLUSIONS :Because of the characteristics of cracking, it is necessary to conduct the evaluation of currently applied methods and the analysis of the cause of damage, by visual inspection. Moreover, in order to evaluate the performance and economic suitability of the currently applied surface treatment methods, it is necessary to acquire information on application sections by monitoring their long-term conditions and performance.

• 한국도로학회:학술대회논문집
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• 한국도로학회 2006년도 춘계학술대회 논문집
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• pp.97-104
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• 2006

• 한국건설순환자원학회논문집
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• 제9권3호
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• pp.383-388
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• 2021

본 연구에서는 정수위 투수시험을 통하여 무기계 치유소재를 사용한 자기치유 모르타르의 치유성능을 평가하였다. 자기치유 모르타르의 제조를 위해 무기계 소재로 고로슬래그 미분말, 황산나트륨, 무수석고를 사용하였으며, 시멘트 클링커 분말과 클링커 잔골재를 시멘트와 잔골재를 각각 대체하여 사용하였다. 정수위 투수시험을 수행하여 균열폭과 치유재령 경과에 따른 단위유출 수량을 측정하였다. 자기치유 모르타르의 치유성능평가 결과 Plain 모르타르와 비교하여 치유재령 28일에서 초기 균열폭이 0.3mm인 경우 치유율이 30%p 이상 증가하여 치유성능이 크게 증진된 것을 확인하였다. 또한, 투수시험결과로부터 얻은 상수(α)를 이용하여 치유재령 경과에 따른 등가균열폭을 산출하였으며, 등가균열폭과 치유율의 상관관계 분석을 통해 치유 목표균열폭을 만족하기 위한 초기 균열폭과 도달시기를 예측하였다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 봄 학술발표회 논문집(I)
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• pp.233-238
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• 1999

Localized failure analysis of concrete structures can be carried out effectively by modeling fracture process zone of concrete during crack initiation and propagation. But, the analysis techniques are still insufficient for crack modeling because of difficulties in numerical analysis procedure which describe progressive crack. In this paper, a finite element with embedded displacement discontinuity is introduced to remove the difficulties of remeshing for crack propagation in discrete crack model during progressive failure analysis of concrete structures. The performance of this so-called embedded crack approach for concrete failure analysis is verified by several analysis examples. The analysis results show that the embedded crack approach retains mesh size objectivity and can simulate localized failure under mixed mode loading. It can be concluded that the embedded crack approach cab be an effective alternate to the smeared and discrete crack approaches.

• 한국구조물진단유지관리공학회 논문집
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• 제22권3호
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• pp.84-89
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• 2018

최근 자기치유 재료에 대한 연구는 보수하기 힘들거나, 보수비용이 많이 소요되는 구조물에 대해 구조물 스스로 손상을 치유하여 사용수명을 증가시키기 위해 많이 수행되어오고 있다. 현재 널리 사용되고 있는 자기치유 평가 방법으로는 투수시험이 있다. 하지만, 자기치유 평가 방법에서 자기치유 성능은 콘크리트의 초기 균열 폭에 큰 영향을 받지만 일관된 기준을 가지고 있지 않은 실정이다. 따라서, 본 연구에서는 기존 연구에서 사용한 균열 폭과 투수량을 기반으로 균열 폭-투수량의 상관관계와 시간-투수량의 상관관계를 분석하였다. 또한, 광학현미경을 이용하여 측정한 초기 균열 폭은 신뢰성이 떨어지므로 Poiseuille flow에서 ${\alpha}$값을 도출하여 시간-균열 폭에 대한 상관관계를 분석하여 시간-투수량과 시간-균열 폭에 대한 경향을 분석하였다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 가을 학술발표회 논문집
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• pp.817-822
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• 2002

The problem of the crack which occures from the reinforced concrete structure could be caused by the complexed factors. When the crack happen, it caused fatal blemish to manage and maintain the structure such as structural problem, licking, spalling, viewing Even though they study and work hard to solve this kind of problem in the world, there are no countermeasure for perfect prevention of crack. After the crack checked out, a method of repair-reinforcement has been studied and operated actively, Generally, occurance of the crack in the concrete structure could be taken as granted, no need to mention the damage from the crack, domestic construction try to hide it rather than repair basically, In many cases the construction amount for repairing the crack has to be made in the construction area and the amount is very expensive. To save the repaing fee, companys repair it under the meeting of their desire. it can be expected for the effection of the construction. For this reason, we compare a new injection method to solve the demerits of the present method, to save and use the merit of the present method.

• 비파괴검사학회지
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• 제32권6호
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• pp.686-695
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• 2012

This paper proposes a noncontact thermography technique for fatigue crack evaluation under a cyclic tensile loading. The proposed technique identifies and localizes an invisible fatigue crack without scanning, thus making it possible to instantaneously evaluate an incipient fatigue crack. Based on a thermoelastic theory, a new fatigue crack evaluation algorithm is proposed for the fatigue crack-tip localization. The performance of the proposed algorithm is experimentally validated. To achieve this, the cyclic tensile loading is applied to a dog-bone shape aluminum specimen using a universal testing machine, and the corresponding thermal responses induced by thermoelastic effects are captured by an infrared camera. The test results confirm that the fatigue crack is well identified and localized by comparing with its microscopic images.