• Structural Engineering and Mechanics
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• 제39권4호
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• pp.599-620
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• 2011

The investigation on possible causes of failures related to documented collapses is a complicated issue, primarily due to the scarcity and inadequacy of information available. Although several studies have tried to understand which are the inherent structural deficiencies or circumstances associated to failure of the main structural elements in a reinforced concrete frame, to the authors knowledge a uniform approach for the evaluation building static vulnerability, does not exist yet. This paper investigates, by means of a detailed case study, the potential failure mechanisms of an existing reinforced concrete building. The linear elastic analysis for the three-dimensional building model gives an insight on the working conditions of the structural elements, demonstrating the relevance of a number of structural faults that could sensibly lower the structure's safety margin. Next, the building's bearing capacity is studied by means of parametric nonlinear analysis performed at the element's level. It is seen that, depending on material properties, concrete strength and steel yield stress, the failure hierarchy could be dominated by either brittle or ductile mechanisms.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.433-433
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• 2013

Graphene, $sp^2$-hybridized 2-Dimension carbon material, has drawn enormous attention due to its desirable performance of excellent properties. Graphene can be applied for many electronic devices such as field-effect transistors (FETs), touch screen, solar cells. Furthermore, indium tin oxide (ITO) is commercially used and sets the standard for transparent electrode. However, ITO has certain limitations, such as increasing cost due to indium scarcity, instability in acid and basic environments, high surface roughness and brittle. Due to those reasons, graphene will be a perfect substitute as a transparent electrode. We report the graphene synthesized by inductive coupled plasma enhanced chemical vapor deposition (ICP-PECVD) process on Cu substrate. The growth was carried out using low temperature at $400^{\circ}C$ rather than typical chemical vapor deposition (CVD) process at $1,000^{\circ}C$ The low-temperature process has advantage of low cost and also low melting point materials will be available to synthesize graphene as substrate, but the drawback is low quality. To improve the quality, the factor affect the quality of graphene was be investigated by changing the plasma power, the flow rate of precursors, the scenario of precursors. Then, graphene film's quality was investigated with Raman spectroscopy and sheet resistance and optical emission spectroscopy.

• 한국방재학회 논문집
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• 제7권3호
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• pp.1-7
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• 2007

중공 RC 기둥은 중실 RC 기둥에 비해 자중의 감소 및 재료 절감에 대한 장점을 가진다. 그러나 중공 RC 기둥은 안쪽면의 취성파괴로 인하여 낮은 연성 거동을 할 가능성이 있다. 이러한 문제점을 해결하기 위해 중공 부재 내의 콘크리트 3축 구속 상태로 존재하게 하는 강관으로 보강된 중공 RC 기둥이 개발되었으며, 본 연구에서는 강관으로 보강된 중공 RC 기둥의 중공비를 $0.50{\sim}0.85$까지 변화 시켜 중공비에 따른 작용하중에 대한 안전율, 연성도, 재료비, 교각 총 중량에 대한 거동 특성을 파악하였다.

• 한국지진공학회논문집
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• 제22권1호
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• pp.23-32
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• 2018

In this study, we conducted a shake table test to verify the seismic performance of the paneling system with steel truss composed of bolt connections. The control group was set to the traditional paneling system with steel truss connected by spot welding method. Test results showed that the bolted connection type paneling system has excellent deformation capacity without cracking or brittle fracture of the steel truss connection parts compared to the welding type paneling system. Furthermore, in the bolted connection type, slight damage occurred at the time of occurrence of the same story drift angle as compared with the existing method, it is considered that it has excellent seismic performance. In compliance with the performance-based design recommended for the current code (ASCE 41-13) on non-structural components, it is judged that in the case of the bolted connection type paneling system, it can be applied to all risk category structures without restriction. However, in the case of traditional paneling system with spot welding method, it is considered that it can be applied limitedly.

• Earthquakes and Structures
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• 제7권5호
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• pp.691-704
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• 2014

Reinforced concrete (RC) shear walls are commonly used for building structures to resist seismic loading. While the RC shear walls can have a high load-carrying capacity, they tend to fail in a brittle mode under shear, accompanied by forming large diagonal cracks and bond splitting between concrete and steel reinforcement. Improving seismic performance of shear walls has remained a challenge for researchers all over the world. Engineered Cementitious Composite (ECC), featuring incredible ductility under tension, can be a promising material to replace concrete in shear walls with improved performance. Currently, the application of ECC to large structures is limited due to the lack of the proper constitutive models especially under shear. In this paper, a new Cyclic Softening Membrane Model for reinforced ECC is proposed. The model was built upon the Cyclic Softening Membrane Model for reinforced concrete by (Hsu and Mo 2010). The model was then implemented in the OpenSees program to perform analysis on several cases of shear walls under seismic loading. The seismic response of reinforced ECC compared with RC shear walls under monotonic and cyclic loading, their difference in pinching effect and energy dissipation capacity were studied. The modeling results revealed that reinforced ECC shear walls can have superior seismic performance to traditional RC shear walls.

• 한국터널지하공간학회 논문집
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• 제19권6호
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• pp.1013-1028
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• 2017

본 논문은 원형 자유면을 이용한 암반 파쇄에 대한 수치해석적 연구이다. 암반 파쇄시 균열 발생에 대한 메커니즘을 알아보기 위하여 수치해석을 통해 응력 및 변형율 경로를 분석하였다. 수치해석 결과로부터 균열선의 주응력 분석으로 최대 주응력을 산출하여 취성 재료의 파괴와 균열 진전에 대하여 분석 규명하였다. 또한 본 연구결과를 통하여 암반파쇄시 균열 진전 방향이 전환되는 거동 메커니즘을 제시하였다.

• 콘크리트학회논문집
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• 제14권1호
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• pp.110-117
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• 2002

공용하중의 증가 등에 따른 교량 바닥판의 성능향상 시 바닥판 두께, 콘크리트 강도, 철근강도 그리고 철근비와 더불어 보강재비에 의하여 바닥판의 파괴양상은 바뀌어 질 수 있다. 일반적으로 교량 바닥판의 파괴양상은 주철근 및 배력철근의 항복 이후에 펀칭전단파괴가 발생하는 것으로 나타나고 있으며, 외부부착공법을 적용함에 있어서 이러한 파괴양상을 유지해야 될 것으로 판단된다. 본 연구에서는 바닥판에 사용된 철근비 및 보강재비 등을 주요변수로 하여 항복선 이론 및 소성 펀칭모델 등을 적용한 항복강도 및 파괴강도를 해석하였으며, 철근비에 따른 임계보강재량을 제안하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.831-836
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• 2000

During machining, since more than 50% compliance of the cutting point in machine tool structures comes from headstocks, with the remainder coming from beds, slides and structural joints, the structural analysis of the headstock is very important to improve the static and dynamic performances. Especially, in case of machining hard and brittle materials such as glasses and ceramics with the grinding machine, the reinforced headstock with the high damping material is demanded. Since the fiber reinforced composite materials have excellent properties for structures, owing to its high specific modulus, high damping and low thermal expansion, it is expected that the dynamic and thermal characteristics of the headstock will be improved if they are employed as the materials fur headstock. In this paper, the design and the manufacturing methods as well as the static and dynamic characteristics of a steel-composite hybrid headstock were investigated analytically and experimentally to improve the performance of the grinding machine system.

• Earthquakes and Structures
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• 제13권1호
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• pp.29-38
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• 2017

Stone masonry is one of the oldest construction types due to the natural and free availability of stones and the relatively easy construction. Since stone masonry is brittle, it is also very vulnerable and in the case of earthquakes damage, collapses and causalities are very likely to occur, as it has been seen during the last Italian earthquake in Amatrice in 2016. In the recent years, some researchers have performed experimental tests to improve the knowledge of the behaviour of stone masonry. Concurrently, there is the need to reproduce the seismic behaviour of these structures by numerical approaches, also in consideration of the high cost of experimental tests. In this work, an alternative simplified procedure to numerically reproduce the diagonal compression and shear compression tests on a rubble stone masonry is proposed within the finite element method. The proposed procedure represents the stone units as rigid bodies and the mortar as a plastic material with compression and tension inelastic behaviour calibrated based on parametric studies. The validation of the proposed model was verified by comparison with experimental data. The advantage of this simplified methodology is the use of a limited number of degrees of freedom which allows the reduction of the computational time, which leaves the possibility to carry out parametric studies that consider different wall configurations.

• 한국자동차공학회논문집
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• 제2권6호
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• pp.87-93
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• 1994

This paper describes on the establishment of an optimal internal grinding conditions for the purpose of improving the grinding efficiency against to the high-speed grinding. Through the fundamental grinding tests for the brittle and hardened material, we are concluded that high-speed internal grinding is effective to improve the grinding accuracy as well as the grinding efficiency. The obtained results are as follows: (1) Under the speed ratio $(V_w/V_g)$ is constant, it is possible to increase the grinding efficiency with satifying the constraint conditions. (2) Increasing the wheel velocity, surface roughness and out-roundness are improved. (3) Under the wheel depth of cut is constant and increasing the speed ratio, workpiece residual stress is decreased. The described method, in this paper, is capable of determining the optimum internal grinding conditions taking into account some constraint conditions, and practical algorithm for optimum internal grinding conditions are presented.