• International Journal of Concrete Structures and Materials
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• 제2권2호
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• pp.153-160
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• 2008

Fracture of prestressed concrete beams is studied with a novel and robust three-dimensional meshfree method. The meshfree method describes the crack as a set of cohesive crack segments and avoids the representation of the crack surface. It is ideally suited for a large number of cracks. The crack is modeled by splitting particles into two particles on opposite sides of the crack segment and the shape functions of neighboring particles are modified in a way the discontinuous displacement field is captured appropriately. A simple, robust and efficient way to determine, on which side adjacent particles of the corresponding crack segment lies, is proposed. We will show that the method does not show any "mesh" orientation bias and captures complicated failure patterns of experimental data well.

• Computers and Concrete
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• 제16권4호
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• pp.587-604
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• 2015

The hybrid-type penalty method (HPM) is suitable for representing failure phenomena occurring during the transition from continua to discontinua in materials such as concrete. Initiation and propagation of dominant cracks and branching of cracks can easily be modeled as a discrete crack. The HPM represents a discrete crack by eliminating the penalty that represents the separation of the elements at the intersection boundary. This treatment is easy because no change in the degrees of freedom for the discrete crack is necessary. In addition, it is important to evaluate the correct deformation of the continua before the crack formation is initiated. To achieve this, we implemented a constitutive model of concrete for the HPM. In this paper, we explain the implemented constitutive model and describe the simulation of an anchor bolt pullout test using the HPM demonstrating its capability for evaluating progressive failure.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1991년도 가을 학술발표회 논문집
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• pp.113-118
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• 1991

Fictitious Crack Model(FCM) is one of the Nonlinear Analysis Method which is presented strictly strain softening phenomena of concrete in the fracture zone. As no stress singularities occur, it is not necessary to use special crack tip elements for this analysis. A special feature of the used method is that it explains not only the growth of existing cracks, but aslo the formation of new crack, as it is assumed that cracks start forming when the tensile stress reaches ft, i.e., the same criterion is used for formation and propagation of cracks.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.215-220
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• 2001

The objective of this study is to examine the fracture characteristics of concrete at early ages such as critical stress intensity factor, critical crack-tip opening displacement, fracture energy based on the concepts of the effective-elastic crack model and the cohesive crack model. A wedge splitting test for Mode I was performed on cubic wedge specimens with a notch at the edge. By varying strength and age, load-crack mouth opening displacement curves were obtained and the results were analyzed by linear elastic fracture mechanics. The results from the test and analysis showed that critical stress intensity factor and fracture energy increased, and critical crack-tip opening displacement decreased with concrete age from 1 day to 28 days. The obtained fracture parameters at early ages may be used as a fracture criterion and an input data for finite element analysis of concrete at early ages.

• Advances in concrete construction
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• 제6권5호
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• pp.527-543
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• 2018

Crack control of precast members is crucial for durability. However, there is no clear provision to check the crack width of precast joints. This study presents an experimental investigation of loop joint details for use in a precast bridge deck system. High strength concrete of 130 MPa was chosen for durability and closer joint spacing. Static tests were conducted to investigate the cracking and ultimate behavior of test specimens. The experimental results indicate that current design codes provide reasonable estimation of the flexural strength and cracking load of precast elements with loop joint of high strength concrete. However, the crack width control of the loop joints with high strength concrete by the current design practices was not appropriate. Some recommendations to improve crack control of the loop joint were derived.

• International Journal of Railway
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• 제2권1호
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• pp.30-36
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• 2009

Crack and its damage of structure concrete in both FBS and TBS ballastless track are presented. The cause of concrete crack is analyzed. According to corresponding quantitative equation, effective technical measures to depression crack of concrete are put forward, at the same time the rationality of elastic ratio for HGT has been proved. At last, by the analysis of the characteristic of high-speed train, which are serving in the open air, bearing fatigue load, the short time for maintenance window and high speed of service, technical requirement for concrete repair material, repair technology and repair tools of ballastless track structure are presented.

• 콘크리트학회논문집
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• 제20권3호
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• pp.291-298
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• 2008

높은 수압에서 균열이 있는 콘크리트의 투수계수에 대한 연구를 수행하였으며, 이를 위해 기존의 균열이 있는 콘크리트 투수실험의 균열 유발 방법과 압력 조절 방법을 개선하였다. 실험체를 쪼갠 후 다시 붙이는 방법으로 확실한 관통 균열을 유발하였으며, 압력계와 감압계를 사용하여 압력조절을 간소화하였다. 균열폭을 측정할 때 균열폭 분류를 정하여 범위에 드는 실험체만 실험을 수행하였다. 실험 변수는 수압 (0.1$\sim$2 bar)과 균열폭 (30$\sim$100 ${\mu}m$)이다. 실험 결과, 균열폭과 수압이 증가함에 따라 투수계수가 증가하는 경향을 보였으며, 자기 치유의 영향으로 시간에 따라 투수계수가 점차로 감소하는 것으로 나타났다. 실험 초기의 투수계수는 균열폭에 많은 영향을 받지만, 최종 투수계수는 균열폭에 의한 영향이 상대적으로 작았다. 균열폭이 100 ${\mu}m$일 때는 균열폭이 30, 50 ${\mu}m$일 때에 비해 압력에 따른 투수계수의 변화가 컸는데, 수압이 0.1 bar에서 0.25 bar로 증가하면 투수계수가 약 190배로 크게 증가하는 것으로 나타났다.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2004년도 학술대회지
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• pp.33-38
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• 2004

This study was performed to know watertightness and reduction effect and crack occurred by hydration heat, restraint of multiplication of hydration heat, through mechanical test, strength test and crack control test using fluosilicate salt based inorganic compound made from by-product during phosphoric acid manufacturing process. Mix proportions for experiment were modulated at 0.45 of water to cement ratio and $0.5-2.0\%$ of adding ratio of fluosilicate salt based inorganic compound. Evaluation for watertightness of concrete was carried out permeability, absorption test and porosity analysis. Effect of crack reduction was evaluated by length, drying shrinkage as well as stress change of hardened concrete at unrestraint/restraint state and also elucidated crack pattern on the concrete surface. It is ascertained that characteristics of crack resistance and watertightness for concrete was improved by an adequate addition of fluosilicate salt based inorganic compound.

• 한국농공학회:학술대회논문집
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• 한국농공학회 1998년도 학술발표회 발표논문집
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• pp.124-129
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• 1998

The ultrasonic pulse measurements can be used to detect the development of cracks in concrete structures and to check deterioration due to frost or chemical action. An estimate of the depth of a visible crack at the surface can be obtained by measuring the transit times that across the crack for two different arrangements of the transducers placed on the surface. In this paper, the concrete cracks that artificially introduced crack of width 1, 2mm and depth 20, 40, 60, 80mm were measured by Tc-To, Direct and Indirect Method. The test results indicate that the Tc-To Method is the most useful in measuring crack of concrete structures. And the crack depth calculated by the Direct and Indirect Method is shown bigger than artificially introduced real crack depth.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2014년도 추계 학술논문 발표대회
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• pp.111-112
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• 2014

This research focuses on the study that micro-crack of concrete is repaired to use self-healing technology. Self-healing concrete is widely studied in domestic and international construction field recently. Micro-crack(less than 0.3mm)of concrete is repaired using a crack repair stick which containing self-healing agents. Therefore, the crack on construction structure will be easily repaired by using a crack repair stick. Also experiment was proceeded because of evaluating the long term durability.