• 한국소음진동공학회논문집
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• 제13권9호
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• pp.720-729
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• 2003

An iterative modal analysis approach is developed to determine the effect of transverse open cracks on the dynamic behavior of simply supported Euler-Bernoulli beam with the moving mass. The influences of the depth and the position of the crack in the beam have been studied on the dynamic behavior of the simply supported beam system by numerical method. The crack section is represented by a local flexibility matrix connecting two undamaged beam segments i.e. the crack is modelled as a rotational spring. This flexibility matrix defines the relationship between the displacements and forces across the crack section and is derived by applying fundamental fracture mechanics theory. As the depth of the crack is increased the frequency of the simply supported beam with the moving mass is increased.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.689-694
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• 2003

An iterative modal analysis approach is developed to determine the effect of transverse open cracks on the dynamic behavior of simply supported pipe conveying fluid subject to the moving mass. The equation of motion is derived by using Lagrange's equation. The influences of the velocity of moving mass and the velocity of fluid flow and a crack have been studied on the dynamic behavior of a simply supported pipe system by numerical method. The presence of crack results in higher deflections of pipe. The crack section is represented by a local flexibility matrix connecting two undamaged beam segments i.e. the crack is modelled as a rotational spring. Totally, as the velocity of fluid flow and the crack severity are increased, the mid-span deflection of simply supported pipe conveying fluid is increased. The time which produce the maximum dynamic deflection of the simply supported pipe is delayed according to the increment of the crack severity.

• Advanced Composite Materials
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• 제16권2호
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• pp.115-134
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• 2007

This study proposes two new approaches for identifying damage patterns in a holed CFRP cross-ply laminate using an embedded fiber Bragg grating (FBG) sensor. It was experimentally confirmed that the reflection spectrum from the embedded FBG sensor was significantly deformed as the damage near the hole (i.e. splits, transverse cracks and delamination) extended. The damage patterns were predicted using forward analysis (a damage analysis and an optical analysis) with strain estimation and the proposed damage-identification method as well as the forward analysis only. Forward analysis with strain estimation provided the most accurate damage-pattern estimation and the highest computational efficiency. Furthermore, the proposed damage identification significantly reduced computation time with the equivalent accuracy compared to the conventional identification procedure, by using damage analysis as the initial estimation.

• 전산구조공학
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• 제10권1호
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• pp.129-134
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• 1997

탄성 섬유와 점탄성 기지로 구성된 2차원의 단일방향 복합재료에서 발생하는 계면 응력 특이성을 시간영역 경계요소법을 사용하여 조사하였다. 먼저, 아무런 균열없이 섬유와 기지가 완전하게 결합되어 있는 단일방향 복합재료에 횡방향 인장변형이 작용할때 자유경계면 부근에 나타나는 계면 특이응력들을 조사하였다. 그러한 응력들은 섬유와 기지의 결합분리나 계면 모서리 균열을 야기 시킬수 있다. 다음에, 여러가지 크기의 모서리 균열들에 대한 응력확대계수가 계산되었다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 춘계학술발표대회 논문집
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• pp.111-114
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• 2004

Using the embedded optical fiber sensor of totally-reflected extrinsic Fabry-Perot interferometer(TR-EFPI), longitudinal strains(Ex) of the core and skin layers in glass fiber reinforced plastic(GFRP) cross-ply composite laminates have been measured. Transmission optical microscopy was employed to study the damage formation around the TR-EFPI sensor. It was observed that values of ex in the interior of the skin layer and the core layer measured by embedded TR-EFPI sensor was significantly higher than that of the specimen surface measured by strain gauges. The experimental results agreed well with those from finite element analysis on the basis of uniform stress model. Large strains in the core layer led to the occurrence of transverse cracks which drastically reduced the strain at failure of optical fiber sensor embedded in the core layer.

• Structural Engineering and Mechanics
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• 제36권4호
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• pp.447-461
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• 2010

Fiber reinforced polymer (FRP) bars have been widely used as reinforcement for concrete structures. However, under elevated temperatures, the difference between the transverse coefficients of thermal expansion of FRP rebars and concrete may cause the splitting cracks of the concrete cover. As a result, the bonding of FRP-reinforced concrete may not sustain its function to transfer load between the FRP rebar and the surrounding concrete. The current study investigates the cracking resistance of FRP reinforced concrete against the thermal expansion based on a mechanical model that accounts for the tensile softening behavior of concrete. To evaluate the efficacy of the proposed model, the critical temperature increments at which the splitting failure of the concrete cover occurs and the internal crack radii estimated are compared with the results obtained from the previous studies. Simplified equations for estimating the critical temperature increments and the minimum concrete cover required to prevent concrete splitting failure for a designated temperature increment are also derived for design purpose.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1996년도 춘계학술대회 논문집
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• pp.177-182
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• 1996

The objective of this thesis is to investigate the influence of welding residual stresses on the fatigue growth behavior of welding residual stresses on the fatigue growth behavior of cracks located transverse to the weld bead. For this purpose, G.T.A. (Gas Tungsten Arc) welding was performed on the Al. Alloy 1100-0 plate and the same initial crack is made on HAZ(Heat Affected Zone), weld metal and base metal respectively. C.T.(Compact Tension) specimens were used as experimental material. Initial welding residual stresses were measured by using strain gage sectioning method. All specimens were tested under constant amplitude load with stress ratio R=0.1

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1990년도 가을 학술발표회 논문집
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• pp.1-6
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• 1990

Joints are provided in cement concrete pavements to control transverse and longitudinal cracking that occur due to restrained deformations caused by moisture and temperature variations in the slab. But the construction of joints reduces the load-carrying capacity of the pavement at the joints, and pavements have beem deteriorated by cracks at the slab edges along the joints due to traffic loads. Therefore, it is important to analyze the behavior of joints accurately in the design of cement concrete pavements. In this study, the mechanical behavior of cement concrete pavement slabs is analyzed by the plate-finite element model, and Winkler foundation model is adopted to analyze the subgrades. The load transfer mechanism of joints are composed of dowel action, aggregate interlocking, and tied-key action, and the analytical program is developed using these joint models.

• 한국구조물진단유지관리공학회 논문집
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• 제20권5호
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• pp.109-115
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• 2016

최근 구조물의 대형화에 따른 큰 지지력의 말뚝에 대한 수요가 증가하는 추세이다. 이에 따라 기성 PHC말뚝의 경우에도 700~1,200 mm 범위의 대구경 말뚝에 대한 활용이 증가하고 있고 최근 국내 현장에 적용되고 있다. 이 연구에서는 대구경 PHC말뚝의 휨성능을 향상시키기 위해 철근과 콘크리트로 보강하여 합성 PHC말뚝을 제작하였다. 휨강도 평가는 4등분점 제하실험을 통해 변위제어 방법으로 수행되었다. 휨실험을 통해 LICPT 실험체 횡방향 철근의 변형률 분포를 분석한 결과 횡방향 철근의 배근은 전단균열의 진전과 균열폭 제어에 효과적인 것으로 나타났고, 복부전단균열 발생을 억제할 수 있었다. LICPT 실험체는 LICP 실험체 보다 휨강도가 약 1.08배, 중앙부 변위가 약 1.19배 증가하였고, 횡방향 철근의 배근은 말뚝의 연성적인 휨거동 확보에 유리한 것으로 나타났다. 말뚝 제작시 사용되는 각각의 재료가 휨강도에 기여하는 수준을 층상화 단면 해석으로 계산된 축강도-휨모멘트 상관도를 통해 평가하였다. 기성 PHC말뚝과 LICP 실험체의 실제 휨강도를 1.13배, 1.16배의 안전율로 예측할 수 있었다.

• 한국구조물진단유지관리공학회 논문집
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• 제26권5호
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• pp.135-142
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• 2022

본 연구에서는 초고강도 콘크리트에 적용된 겹침 이음의 안전성을 평가하기 위해 초고강도콘크리트 보의 휨성능을 평가하였다. 설계기준에서 정하고 있는 정착 길이 및 겹침이음 길이 산정식에서 겹침이음 길이에 영향을 미치는 횡보강근과 콘크리트 피복 성능의 검토가 수행되었다. 주요 변수는 콘크리트 피복의 구속 성능 증진을 위한 섬유의 혼입과 횡방향철근 배치로 설정하였다. 강섬유가 혼입되었으며 1% 및 2% 부피비로 섬유의 혼입량 증가에 따른 콘크리트 피복 성능의 변화를 검토하였으며, 이음 구간 내에 간격 100mm의 D10 스터럽이 배치되도록 하였다. 실험 결과, 스터럽으로 구속된 실험체는 주인장철근 방향으로의 수평균열 진전과 함께 급격한 하중저하 현상이 나타났으며, 강섬유로 보강된 실험체의 경우 주인장철근 방향의 균열 확대가 억제되고 급작스러운 하중지지능력의 상실을 경험하지 않는 것으로 나타났다. 특히, 2% 의 혼입률이 적용된 실험체의 주인장철근 위치의 변형률은 항복 변형률을 초과하는 것으로 나타났다. 콘크리트 표면에 대한 변형률 측정 결과 철근보다는 섬유가 더 콘크리트 표면의 손상을 방지하는 데에 효과적인 것으로 나타났다.