• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.2
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• pp.201-214
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• 1999

이 연구는 2경간 연속 PSC-Beam 교량의 경간 내측 지지점의 바닥판에서 발생할 수 있는 균열의 제어에 관한 내용을 다루고 있다. PSC-Beam 교량은 주형인 PSC-Beam을 거치시킨후 바닥판을 현장타설 콘크리트로 시공된다. 이로 인하여 주형 콘크리트와 바닥판 콘크리트의 시간의존적 거동차이, 주형의 연속화에 따른 거동 등에 의하여 부모멘트가 가장 크게 걸리는 지점부에서 균열이 쉽게 발생된다. 따라서 이 논문에서는 2경간 연속 PSC-Beam 교량의 연속화에 따른 거동을 수치적 방법으로 해석하여 지점부 바닥판의 균열거동이 예측되었다. 이를 위하여 해석모델에는 콘크리트의 시간의존적 현상인 크리프와 건조수축이 고려되었으며, 2경간 연속 PSC-Beam 교량의 거동에 영향을 나타내는 여러 가지 인자가 고려되어 해석되었다. 끝으로 콘크리트의 모델식을 이용하여 지점부 균열을 억제하기 위한 현장에서 관리가능한 방안이 수치적으로 제안되었다.

• Journal of the korean Society of Automotive Engineers
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• v.11 no.5
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• pp.34-45
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• 1989

성장하는 균열에 의한 변형 에너지해방에 기반을 둔 간단한 파괴역학적인 접근법이 고무의 여러가지 특성을 규명하는데 성공적으로 응용되는 예들을 논의하였다. 이 방법은 전통적인 강도, 즉 찢김, 균열성장, 피로, 인장파손 등 뿐만 아니라 오존내습(ozone attack), 예리한 공구들에 의한 마쇄, 절단현상을 규명하는데도 응용가능함을 밝혔다. 특히 에너지해방율은 여러가지의 다른 시험편에 대한 실험값들이 서로 연관성을 갖도록 허용하기 때문에 매우 유용한 특성이라 할 수 있다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.2
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• pp.119-128
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• 1999

본 연구는 등방탄성체에 고속충격하중이 작용하는 경우에 대한 유한요소해석에 관한 것으로 대상구조는 여러 가지 모양의 2차원 평면구조를 택하였다. Galerkin 방법을 이용하여 유한요소 정식화하였으며 직접시간적분법에 의해 수치해를 구하였다. 본 해석에서는 균열이 없는 평판으로 수치해와 이론해를 비교하여 수치해의 신뢰성을 확인하였으며, 0°, 30°, 45°경사 균열이 없는 평판에 적용한 3가지 예를 분석하였다. 수치해석 결과는 이론해의 결과와 상호 잘 일치하였다.

• Magazine of the Korea Concrete Institute
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• v.4 no.2
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• pp.103-110
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• 1992

본 연구는 인성지수에 의하여 섬유보강 콘크리트의 인성을 평가하는 기존의 여러 가지 방법을 검토하는, 하중-처짐곡선에서 초기균열시까지의 여러 가지 다른 곱으로 나타내어지는 방법의 불합리성을 지적하였다. 이를 위하여 본 연구에서는 유효인성이라고 부르는 새로운 방법을 강섬유 보강콘크리트의 인성을 평가하는데 제안하였다. 이는 초기균열을 가진 3점 휨강도 시험에 의한 하중-처짐곡선에서 지간의 1/150까지의 면적을 ligament면적으로 나눈값으로 나타낸다. 이 방법을 사용하여 강섬유 보강 고강도 콘크리트 인성특성을 검토한 결과 기존의 방법보다 더 효과적으로 인성을 평가할 수 있었다.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.229-238
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• 2006

암반터널굴착을 위한 발파시 이로 인한 암반의 최종 손상영역을 예측하는 것은 터널의 안전성을 위해 매우 중요하다. 그러나 복잡한 발파거동은 손상영역을 적절히 예측하는데 상당한 어려움이 있다. 이러한 어려움을 효과적으로 해결하기 위해 발파하중을 응력파와 가스압으로 분리한 많은 연구가 진행되었다. 응력파는 발파공 주위에 분쇄한(crushing annulus)과 파쇄균열대(fracture zone)를 형성시키며, 상당시간 지속되는 준정적인 가스는 파쇄균열대의 닫힌 균열내부에 침투하여 균열을 다시 진행시키는 역할을 하게 된다. 즉, 가스압은 최종적으로 암반에 손상을 가하는데 기여를 한다. 따라서 본 논문은 이러한 가스압에 의해 생성되는 균열의 최종 진행 길이를 예측함으로써 발파로 인한 최종 손상영역을 간단하게 예측할 수 있는 방법을 제시하고자 한다. 이를 위해 무한 탄성평면에서 발파공 주위에 대칭으로 형성되는 균열을 모델로 사용하였다. 이 모델에서 균열이 진행할 수 있는 조건과 가스의 질량이 일정하다는 두가지 조건을 사용하였다. 그 결과 응력집중계수는 균열이 진행할수록 감소하여 최종균열의 길이를 예측할 수 있었고, 그와 동시에 발파공에 작용하는 압력도 감소하는 것을 확인할 수 있었다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.6
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• pp.11-20
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• 2013

In this paper, the quantitative damage index for reinforced concrete (RC) columns with non-seismic details were presented. They are necessary to carry out the postearthquake safety evaluation of RC buildings under 5 stories without seismic details. The static cyclic test of the RC frame sub-assemblage that was an one span and actual-sized was first conducted. The specimen collapsed by the shear failure after flexural yielding of a column, lots of cracks on the surfaces of columns and beam-column joints and the cover concrete splitting at the bottom of columns occurred. The damage levels of these kinds of columns with non-seismic details were classified to five based on the load-displacement relationship by the test result. The residual story drift ratios and crack widths were then adapted as the quantitative index to evaluate the damage limit states because those values were comparatively easy to measure right after earthquakes. The highest one among the residual story drift ratios under the similar maximum story drift ratio decided on the residual story drift ratio of each damage limit state. On the other hand, the lowest and average ones among the respective residual shear and flexural widths under the similar maximum story drift ratio decided on the residual shear and flexural widths of each damage limit state, respectively. These values for each damage limit state resulted in being smaller than those by the international damage evaluation guidelines that are for seismically designed members under the same deformations.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.2
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• pp.173-182
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• 2007

Cracks in concrete structures should be measured to periodically assess potential problems in durability and serviceability. Conventional crack measurement systems depend on visual inspections and manual measurements of the crack features such as width, length, and direction using microscope and crack gage. However, conventional methods take long time as well as manpower, and lack quantitative objectivity resulted by inspectors. In this study, an evaluation technique for concrete surface cracks is developed using image processing and artificial neural network. Developed technique consists of three major parts: (1) crack detection (2) crack analysis and (3) pattern recognition. To examine validity of the technique developed in this study, crack analyzing tests were performed on the images obtained from various types of concrete surface cracks. The test results revealed that the system is highly effective in automatically analyzing concrete surface cracks in terms of features and patterns of cracks.

• Journal of the Korea Concrete Institute
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• v.19 no.2
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• pp.233-239
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• 2007

The main objective of this study was to evaluate the effect of recycled PET fiber made from waste PET bottle on the control of plastic shrinkage cracking of cement based composites. PET is blown as a plastic material and used in a variety products such as a beverage bottle. However, waste PET bottles are thrown after the usage, raising huge problems in terms of the environment. Thus, the research on the method to recycle the PET bottles indicates important aspects in environment and economy. The method to recycle waste PET bottles as a reinforcing fiber for cement based composites is one of effective methods in terms of the recycle of waste PET bottles. In this research, the effect of recycled PET fiber geometry and length on the control of plastic shrinkage was examined through thin slab tests. A test program was carried out to understand the influence of fiber geometry, length and fiber volume fraction. Three type of recycled PET fibers including straight, twist crimped and embossed type. Three volume fraction and two fiber length were investigated for each of the three fiber geometry. Test results indicated that recycled PET fibers are effective in controlling plastic shrinkage cracking in cement based composites. In respect to effect of length of fiber, longer fiber was observed to have efficient cracking controlling with low volume fraction in same fiber geometry while shorter fiber controled plastic shrinkage cracking efficiently as addition rate increase. Also, embossed type fibers were more effective in controlling plastic shrinkage cracking than other geometry fiber at low volume fraction. But, for high volume fraction, straight type fibers were most effective in plastic shrinkage cracking controlling in cement based composites.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.12
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• pp.1441-1446
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• 2014

In the present paper, the effects of the thickness and width of a curved wide-plate, the crack length, and the strain hardening exponent on the crack-tip constraint of the curved wide-plate were investigated. To accomplish this, detailed three-dimensional elastic-plastic finite element (FE) analyses were performed considering various geometric and material variables. The material was characterized by the Ramberg-Osgood relationship, and the Q-stress was employed as a crack-tip constraint parameter. Based on the present FE results, the variations in the Q-stress of the curved wide-plate with the geometric variables and material properties were evaluated. This revealed that the effect of out-of-plane constraint conditions on the crack-tip constraint was closely related to the in-plane constraint conditions, and out-of-plane constraint conditions affected the crack-tip constraint more than in-plane constraint conditions.

• Journal of the Korean Institute of Gas
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• v.19 no.5
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• pp.13-19
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• 2015

This paper presents a hydraulic fracture propagation model to describe propagation more realistically. In propagating the hydraulic fractures, we have used two criteria: maximum tangential stress to determine the fracture initiation angle and whether a hydraulic fracture intersects a natural fracture. The model was validated for the parameters relevant to fracture propagation, such as initiation angle and crossing ability through natural fracture. In order to check whether a hydraulic fracture crosses a natural fracture, the model results on crossing state excellently matched with the experimental data. In the sensitivity analysis for direction of maximum horizontal stress, frictional coefficient of fracture interface, and natural fracture orientation, the results show that hydraulic fracture intersects natural fracture, and then, propagated suitably with theoretical results according to fracture interaction criterion. In comparison of this model against vertical fracture approach, it was ascertained that there are discrepancies in fracture connectivity and stimulated reservoir volume.