• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.2
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• pp.59-68
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• 1987

Several series of fracture tests were conducted to explore the fracture characteristics and to determine the fracture energy of concrete. A stable three-point bend test was employed to generate the load-deflection curves. The fracture energy may then be calculated from the area under the complete load-deflection curve. The initial notch-to-beam depth ratio (${\alpha}_0$/H) was varied from zero to 0.6. The prediction formula for the fracture energy of concrete is also derived and is found to depend on the tensile strength and aggregate size. The proposed fracture energy formula can be used for the fracture analysis of concrete structures. The present study also devises an equivalent crack length concept to predict the maximum failure loads of concrete beams. A simple formula for the equivalent crack length is proposed.

• Journal of the Korean Society for Railway
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• v.12 no.1
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• pp.16-24
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• 2009

In this study, fatigue crack growth rate of a cracked railway bogie frame under variable amplitude loading is predicted by applying linear elastic fracture mechanics. For this purpose, we find the critical points by reference surveying on cracked railway bogie frames. And we make an effective load history by synthesizing the dynamic load measured from the critical points of railway bogie frame during commercial line operation and the static load calculated from structural analysis. Crack growth analyses are performed at the 3 critical points under the commercial operation loading condition by assuming an initial crack size as 40 mm. and the results are compared with the experimental results from Japanese railway bogie frame crack growth case. From the analysis results, we find that around 500,000 km operating distance is necessary to bring crack growth from the initial crack to unstable crack. And it takes around 3.8 normal operating years. We conclude that it is enough time to detect the crack between normal maintenance period.

• Magazine of the Korea Concrete Institute
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• v.10 no.1
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• pp.143-151
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• 1998

최근들어 반복하중에 의한 철근콘크리트 구조물의 손상이 자주 발견되고 있으며 교량 등의 구조물 등은 때때로 과적차량에 의한 초과하중을 받아 이러한 피로손상이 심화되고 있다. 본 연구에서는 이러한 반복 하중을 받는 철근 콘크리트보의 누적피로손상에 대한 실험적 연구룰 수행하여 피로하중에 의한 철근콘크리트보의 손상과정을 규명하였다. 실험 변수를 전단철근의 양과 반복되는 하중의 크기 및 반복횟수로 하여 실험부재를 제작하였으며, 하중제어에 의한 휨시험법에 의해 3Hz의 반복하중을 시편에 재하하였다. 사인장 균열하중과 사인장 균열 후 반복하중에서의 보의 손상누적거동 즉 처짐. 전단철근의 변형도, 에너지 손실 등의 변화를 실험적으로 평가하였으며, 이를 통하여 반복하중에 의한 누적손상에 의해 철근 콘크리트보의처짐 및 전단변형도가 초기하중상태에서는 급격히 증가하다가 이후 점진적으로 증가하는 것을 규명하였다. 본 연구의 결과는 사용하중상태에서 점진적으로 발생할 수 있는 피로손상의 누적과정을 기술하여 주고 있다.

• Journal of the Korea Concrete Institute
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• v.13 no.2
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• pp.153-160
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• 2001

In this study, the size effect on axial compressive strength for concrete members was experimentally investigated. Experiment of mode I failure, which is one of the two representative compressive failure modes, was carried out by using double cantilever beam specimens. By varying the eccentricity of applied loads with respect to the axis on each cantilever and the initial crack length, the size effect of axial compressive strength of concrete was investigated, and new parameters for the modified size effect law (MSEL) were suggested using least square method (LSM). The test results show that size effect appears for axial compressive strength of cracked specimens. For the eccentricity of loads, the influence of tensile and compressive stress at the crack tip are significant and so that the size effect is present. In other words, if the influence of tensile stress at the crack tip grows up, the size effect of concrete increases. And the effect of initial crack length on axial compressive strength is present, however, the differences with crack length are not apparent because the size of fracture process zone (FPZ) of all specimens in the high-strength concrete is similar regardless of differences of specimen slenderness.

• Tunnel and Underground Space
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• v.7 no.2
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• pp.143-149
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• 1997

암석의 파괴인성계수(fracture toughness)는 균열의 성장에 대한 암석의 저항을 나타낸다. 실험실에서 측정한 파괴인성계수는 일반적인 암석의 불균질성이나 이방성 외에도 시험편의 형상이나 하중조건에 의하여 크게 영향을 받는다. 따라서, 제한된 수의 시험편을 사용하여 측정된 파괴인성계수는 자료의 분산이 심하므로 실제 적용에 있어서 문제가 된다. 균열감응도란 파괴인성계수의 측정에 사용되는 시험편의 형상에 따라 결정되는 지수로서, 시험편의 파괴가 균열의 성장에 의한 것인지, 혹은 인장강도에 의한 것인지를 판별하는 기준이 된다. 이러한 균열감응도를 파악하여 암석의 파괴인성계수 측정에 유효한 시험편의 크기나 초기균열 길이의 범위를 설정할 수 있다. 이는 또한 실험실에서 측정된 차괴인성계수의 유효성 여부를 판별하는 기준으로 사용될 수 있다. 본 논문에서는 암석의 파괴인성계수의 측정에 흔히 사용되는 몇 가지 형태의 시험편들에 대하여 균열감응도를 계산하고 이에 따른 초기균열 길이의 범위를 제시하고자 한다.

• Journal of the Korean Society of Safety
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• v.12 no.4
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• pp.230-240
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• 1997

An experimental research investigation of the fracture properties of polypropylene fiber reinforced concrete is reported. Fibers used in this experiment were two types, monofilament and fibrillated polypropylene fibers. Fiber length was 19 mm, and volume fractions were 0, 1, 2, and 3%. Also, as initial notch depths influence the fracture properties of fiber reinforced concrete, the notch depth ratios by specimen height were 0.15, 0.30 and 0.45. The main objective of this experimental program is to obtain the load-deflection and the load-CMOD curves, to investigate the fracture properties of the polypropylene fiber reinforced concretes. Therefore, the flexural specimen testings on the four-point bending were conducted. Then, the load-load point displacement and the load-crack mouth opening displacement curves were measured. The effects of different volume fractions of the monofilament and the fibrillated polypropylene fiber reinforced concrete on the compressive strength, flexural strength and toughness, stress intensity factor, and fracture energy were investigated through the experimental results.

• Journal of the Korea Concrete Institute
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• v.14 no.2
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• pp.231-238
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• 2002

Dry shrinkage md temperature change cause to develope concrete bridge decks on main girders have initial unidirectional cracks in longitudinal or transverse direction. As they receive traffic loads, the crack gradually propagate in different directions depending on the concrete dimension and reinforcement ratio. Since existing equations that predict crack width are mostly based on the one directional bond-slip theory, it is difficult to determine the actual crack width of a bridge deck with varying the spacing of rebar or strengthening material and to estimate the improvement rate in serviceability of the strengthened bridge deck. In this study, crack propagation mechanism is identified based on the test results and a new crack prediction equation is proposed for evaluation of serviceability. Although more accurate results are derived using the proposed equation, the extent of error is increased as the strain of the rebar or the strengthening material increases after the yielding of rebar Therefore, further research is required to better predict the crack width after the rebar yields under fatigue loading condition.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05c
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• pp.359-364
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• 1996

'93.4월에 고리원자력 4호기 운전중(원자로 출력 100%, 발전기 출력 975MWe) 주증기 차단밸브 (MSIV)의 닫힘으로 인해 발전소가 정지되었다. 밸브분해 점검결과 밸브스템이 Back Seat Ring 조립부위 Notch 부위에서 Steam Flow와 평행한 방향으로 절단되어, 밸브스템의 손상원인을 규명하기 위한 본 연구에서는 피로해석절차도에 따라 S-N 곡선에 근거하여 피로해석을 수행하였다. 피로해석결과 밸브스템의 초기균열 생성원인은 Stem Notch 부위의 제작결함과 발전소 정지시 밸브를 급속히 닫을 때 작용하는 충격하중등에 의해 발생된 것으로 추정되며 인장평균응력과 관내 유체의 진동하중의 변동응력이 조합하여 피로균열을 가속시켜 파손을 일으킨 것으로 사교된다.

• Journal of Korean Society of Steel Construction
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• v.11 no.4 s.41
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• pp.409-416
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• 1999

The fatigue crack growth analysis based on the fracture mechanics is useful to the estimation of the fatigue life on welded structures under cyclic loading. The analysis procedure in fatigue crack growth under uniform axial loading is applicable to bending fatigue problem as well. The intent of the present study is to show the procedure for calculating the fatigue crack propagation lifetimes of deckplates under bending stress and to explain the crack growth rates for the two dimensional crack problems. It is shown that the fatigue crack grows at a decreasing rate and the fatigue life depends on the initial crack length and the crack shape. The numerically predicted crack growth agree with the experimental data.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.1
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• pp.101-110
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• 2014

Expansion agent is a very effective admixture for prevention of cracking due to autogenous/drying shrinkage and this can induce internal chemical prestress to embedded reinforcement. In this paper, tension-softening and hardening in cement mortar with steel and CSA expansion agent are experimentally evaluated. Cement mortar with steel reinforcement is prepared and tensile strength test is performed for evaluation of cracking and tensile behavior. In spite of slightly reduced strength and elasticity in CSA mortar, significantly increased tension-hardening behavior is evaluated in CSA mortar with induced chemical prestress. Furthermore previous tension softening models are compared with the test results and improvement are proposed.