• Steel and Composite Structures
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• 제15권4호
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• pp.357-377
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• 2013

In order to study the degradation and damage behaviors of steel frame welded connections, two series of tests in references with different connection constructions were carried out subjected to various cyclic loading patterns. Hysteretic curves, degradation and damage behaviours and fatigue properties of specimens were firstly studied. Typical failure modes and probable damage reasons were discussed. Then, various damage index models with variables of dissipative energy, cumulative displacement and combined energy and displacement were summarized and applied for all experimental specimens. The damage developing curves of ten damage index models for each connection were obtained. Finally, the predicted and evaluated capacities of damage index models were compared in order to describe the degraded performance and failure modes. The characteristics of each damage index model were discussed in depth, and then their distributive laws were summarized. The tests and analysis results showed that the loading histories significantly affected the distributive shapes of damage index models. Different models had their own ranges of application. The selected parameters of damage index models had great effect on the developing trends of damage curves. The model with only displacement variable was recommended because of a more simple form and no integral calculation, which was easier to be formulated and embedded in application programs.

• 터널과지하공간
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• 제14권4호
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• pp.248-260
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• 2004

응력 증가에 의한 취성 암석의 손상은 미세균열의 개시로부터 시작하여 각 개별 균열들의 전파 및 결합에 의해 거시적인 파괴면을 발생시킨다. 전통적으로 암반의 손상 및 파괴현상을 설명하기 위해 거시적인 파괴 기준이나 탄소성 모델과 같은 연속체적인 접근법이 주류를 이루어왔다. 하지만 개별적인 균열들의 개시와 전락 과정을 명시적으로 고려할 수 있다면 현상론적인 관점에서 보다 실제에 가까운 암석 손상 및 파괴 과정을 재현할 수 있을 것이다. 본 연구에서는 암석의 균열 진전 모델링을 위해 개발된 경계요소 코드인 FRACOD를 이용하여 암석의 손상 및 파괴 과정을 모사한 결과를 제시한다. 수치일축압축시험을 통해 개발된 모델의 적정성을 검증하고 암반의 치수효과를 고려한 현실적인 암석 파괴 과정을 재현하였다. 또한 이러한 접근법의 적용 사례로서, 실제 굴착이 진행중인 심부 수갱 암반 주변에서 심도와 암반 특성에 따라 균열 진전과 이에 따른 암반 손상의 범위를 예측한 결과를 제시하였다. 이 접근법은 취성도가 큰 암반에서 발생하는 안정성 문제에 대한 공학적인 해법을 찾는데 기여를 할 수 있을 것으로 기대된다.

• Geomechanics and Engineering
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• 제11권3호
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• pp.421-438
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• 2016

Explosions inside transportation tunnels might result in failure of tunnel structures. This study investigated the failure mechanisms of circular cast-iron tunnels in saturated soil subjected to medium internal blast loading. This issue is crucial to tunnel safety as many transportation tunnels run through saturated soils. At the same time blast loading on saturated soils may induce residual excess pore pressure, which may result in soil liquefaction. A series of numerical simulations were carried out using Finite Element program LS-DYNA. The effect of soil liquefaction was simulated by the Federal Highway soil model. It was found that the failure modes of tunnel lining were differed with different levels of blast loading. The damage and failure of the tunnel lining was progressive in nature and they occurred mainly during lining vibration when the main event of blast loading was over. Soil liquefaction may lead to more severe failure of tunnel lining. Soil deformation and soil liquefaction were determined by the coupling effects of lining damage, lining vibration, and blast loading. The damage of tunnel lining was a result of internal blast loading as well as dynamic interaction between tunnel lining and saturated soil, and stress concentration induced by a ventilation shaft connected to the tunnel might result in more severe lining damage.

• Wind and Structures
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• 제10권3호
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• pp.269-285
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• 2007

This paper assesses the damage to high-set rectangular-plan houses with low-pitch gable roofs (built in the 1960 and 70s in the northern parts of Australia) to wind speeds experienced in tropical cyclones. The study estimates the likely failure mode and percentage of failure for a representative proportion of houses with increasing wind speed. Structural reliability concepts are used to determine the levels of damage. The wind load and the component connection strengths are treated as random variables with log-normal distributions. These variables are derived from experiments, structural analysis, damage investigations and experience. This study also incorporates progressive failures and considers the inter-dependency between the structural components in the house, when estimating the types and percentages of the overall failures in the population of these houses. The progressively increasing percentage of houses being subjected to high internal pressures resulting from damage to the envelope is considered. Results from this study also compare favourably with levels of damage and related modes of failure for high-set houses observed in post-cyclone damage surveys.

• Geomechanics and Engineering
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• 제30권5호
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• pp.401-411
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• 2022

To obtain the dynamic mechanical properties, fracture modes, energy and brittleness characteristics of Furong Baijiao coal rock, the dynamic impact compression tests under 0, 4, 8 and 12 MPa confining pressure were carried out using the split Hopkinson pressure bar. The results show that failure mode of coal rock in uniaxial state is axial splitting failure, while it is mainly compression-shear failure with tensile failure in triaxial state. With strain rate and confining pressure increasing, compressive strength and peak strain increase, average fragmentation increases and fractal dimension decreases. Based on energy dissipation theory, the dissipated energy density of coal rock increases gradually with growing confining pressure, but it has little correlation with strain rate. Considering progressive destruction process of coal rock, damage variable was defined as the ratio of dissipated energy density to total absorbed energy density. The maximum damage rate was obtained by deriving damage variable to reflect its maximum failure severity, then a brittleness index BD was established based on the maximum damage rate. BD value declined gradually as confining pressure and strain rate increase, indicating the decrease of brittleness and destruction degree. When confining pressure rises to 12 MPa, brittleness index and average fragmentation gradually stabilize, which shows confining pressure growing cannot cause continuous damage. Finally, integrating dynamic deformation and destruction process of coal rock and according to its final failure characteristics under different confining pressures, BD value is used to classify the brittleness into four grades.

• Geomechanics and Engineering
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• 제20권2호
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• pp.113-120
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• 2020

Rock damage is the main cause of accidents in underground engineering. It is difficult to predict rock damage accurately by using only one parameter. In this study, a rock failure prediction model was established by using stress, energy, and damage. The prediction level was divided into three levels according to the ratio of the damage threshold stress to the peak stress. A classification predicting model was established, including the stress, energy, damage and AE impact rate using Bayesian method. Results show that the model is good practicability and effectiveness in predicting the degree of rock failure. On the basis of this, a multi-parameter classification predicting deterioration model of rock failure was established. The results provide a new idea for classifying and predicting rockburst.

• 산업경영시스템학회지
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• 제20권44호
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• pp.263-271
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• 1997

This paper presents a preventive maintenance model for determining the preventive replacement period of a system in which a failure rate is affected by the cumulative damage of fault and inspection. Especially, the failure rate function is considered to be a function of the cumulative damage of the fault and inspection time. Types of replacement considered are preventive replacement and failure replacement. Failure rate and expected cost function between replacement are derived. An optimal policy is obtained that minimizes the average cost per unit time for preventive replacement, failure replacement, inspection and repair.

• Composites Research
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• 제25권2호
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• pp.40-45
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• 2012

복합재료가 기계부품, 항공기 구조물에 폭 넓게 적용됨에 따라, 복합재료 구조물에서 가장 취약한 복합재료 체결부의 설계는 매우 중요한 연구 분야로 대두되고 있다. 본 논문에서는 기계적 체결방법의 문제점으로 발생하는 원공주위의 높은 응력집중현상을 감소시키기 위하여, 복합재료 키 조인트(composite key joint)를 제안하였고 파손강도를 평가하였다. 제안된 복합재료키 조인트 체결부의 파손 판정을 위해서 파손지수(failure index)와 파손영역법(damage area theory)이 각각 적용되었다. 실험 결과로부터 복합재료 키 조인트는 기계적 체결부의 파손강도보다 93% 높은 값을 가짐을 볼 수 있었고, 복합재료 키 홈 깊이(key slot depth)가 0.88 mm이고 끝단 길이(edge length)가 20 mm일 때 가장 높은 파손하중 나타내었다.

• 한국압력기기공학회 논문집
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• 제5권2호
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• pp.27-34
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• 2009

This paper proposes a simple numerical method to simulate ductile failure behaviors. The method is based on finite element analysis with a simple damage theory. To validate the proposed method, simulated results are compared with experimental data. Despite its simplicity, the proposed method well predicts experimental results systematic analyses are also performed to investigate the effect of the element size.

• 대한토목학회논문집
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• 제33권3호
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• pp.1007-1015
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• 2013

하중 발생과정에 따른 누적피해의 선형뿐만 아니라 비선형 거동을 해석할 수 있는 추계학적 확률모형이 수립되었다. 여러 종류의 피해강도함수를 도입하여 내용년수의 파괴확률과 비선형 누적피해의 거동이 자세히 해석되었다. 특히 본 연구에서는 저항한계를 임의의 분포함수를 갖는 확률변수로 취급하여 한계상태의 불확실성을 고려하였다. 또한 피복재에 대한 피해수준을 이용하여 처음으로 추계학적 확률모형을 경사제에 적용하였다. 실험 자료와의 비교를 통해 추정된 경사제 피복재에 대해 피해강도함수를 이용하여 내용년수에 따른 파괴확률과 비선형 누적피해의 거동을 해석하였다. 마지막으로 해석 결과를 이용하여 경사제 피복재의 보수 보강 시점과 최소한의 보수 보강규모를 정량적으로 산정할 수 있는 예방적 유지관리 방법을 제시하였다.