• 한국생산제조학회지
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• 제21권6호
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• pp.892-896
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• 2012

CFRP composites with light weight, high strength, and high elasticity by comparing with metal are widely used rather than previous steel plates. However, CFRP composite material has the weakness at hydrothermal and collapsed impact environment. Especially, moisture absorption into composite material can change molecule arrangement and chemical properties under hydrothermal environment. And static collapse experiment is the research in the differences of absorbed energy and deformation mode between moisture and non-moisture absorbed specimens. This study is compared and analyzed on the progress change of moisture absorption ratio after setting up the temperatures of 60 and 80 degrees C in order to comprehend how the change in the temperature influences on moisture absorption status inside CFRP composite materials.

• 한국터널지하공간학회 논문집
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• 제20권2호
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• pp.235-253
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• 2018

지하관거 균열로 인한 지하수의 흐름은 주변 지반의 토사유실을 야기하여 관거 인접 지반에서의 공동발생, 나아가 지반함몰(싱크홀) 원인이 된다. 본 연구는 관거의 균열을 모사하는 모형시험을 통해 비점착성 지반에 위치한 지중 비압력 관거의 균열로부터 비롯되는 지반함몰 메커니즘과 이로 인한 파괴모드를 조사하였다. 토사유실 및 함몰 영향인자로서 균열크기, 관거유속, 지하수위, 토피고 그리고 지반구성재료 등을 채택하여 이들 인자들이 함몰거동에 미치는 영향을 조사하였다. 각 인자들에 따른 지반파괴의 형상(파괴모드)과 지반유실량을 분석한 결과, 토피고와 지하수위가 일치하는 경우 최종파괴모드는 침식각이 불연속적으로 변화하는 'Y'형으로 관찰되며, 지하수위가 더 높게 위치하는 경우 침식각이 일정한 파괴면 형상인 'V'형으로 나타난다. 토피고가 증가하는 경우의 파괴형상에서 토피고 영향에 무관한 길이와 토피고에 따라 점진적으로 증가하는 폭을 갖는 수직함몰구간이 형성되는 결과를 얻었다.

• Steel and Composite Structures
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• 제7권4호
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• pp.339-354
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• 2007

Arched Corrugated Steel Roof (ACSR) is a kind of thin-walled steel shell, composing of arched panels with transverse small corrugations. Four full-scale W666 ACSR samples with 18m and 30m span were tested under full and half span static vertical uniform loads. Displacement, bearing capacities and failure modes of the four samples were measured. The web and bottom flange in ACSR with transverse small corrugations are simplified to anisotropic curved plates, and the equivalent tensile modulus, shear modulus and Poisson's ratio of 18m span ACSR were measured. Two 18 m-span W666 ACSR samples were analyzed with the Finite Element Analysis program ABAQUS. Base on the tests, the limit bearing capacity of ACSR is low, and for half span loading, it is 74-75% compared with the full span loading. When the testing load approached to the limit value, the bottom flange at the sample's bulge place locally buckled first, and then the whole arched roof collapsed suddenly. If the vertical loads apply along the full span, the deformation shape is symmetric, but the overall failure mode is asymmetric. For half span vertical loading, the deformation shape and the overall failure mode of the structure are asymmetric. The ACSR displacement under the vertical loads is large and the structural stiffness is low. There is a little difference between the FEM analysis results and testing data, showing the simplify method of small corrugations in ACSR and the building techniques of FEM models are rational and useful.

• Steel and Composite Structures
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• 제49권4호
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• pp.381-392
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• 2023

This study experimentally investigates the flexural behavior of steel-UHPC composite slabs composed of an innovative negative Poisson's ratio (NPR) steel plate and Ultra High Performance Concrete (UHPC) slab connected via demountable high-strength bolt shear connectors. Eight demountable composite slab specimens were fabricated and tested under traditional four-point bending method. The effects of loading histories (positive and negative bending moment), types of steel plate (NPR steel plate and Q355 steel plate) and spacings of high-strength bolts (150 mm, 200 mm and 250 mm) on the flexural behavior of demountable composite slab, including failure mode, load-deflection curve, interface relative slip, crack width and sectional strain distribution, were evaluated. The results revealed that under positive bending moment, the failure mode of composite slabs employing NPR steel plate was distinct from that with Q355 steel plate, which exhibited that part of high-strength bolts was cut off, part of pre-embedded padded extension nuts was pulled out, and UHPC collapsed due to instantaneous instability and etc. Besides, under the same spacing of high-strength bolts, NPR steel plate availably delayed and restrained the relative slip between steel plate and UHPC plate, thus significantly enhanced the cooperative deformation capacity, flexural stiffness and load capacity for composite slabs further. While under negative bending moment, NPR steel plate effectively improved the flexural capacity and deformation characteristics of composite slabs, but it has no obvious effect on the initial flexural stiffness of composite slabs. Meanwhile, the excellent crack-width control ability for UHPC endowed composite members with better durability. Furthermore, according to the sectional strain distribution analysis, due to the negative Poisson's ratio effect and high yield strength of NPR steel plate, the tensile strain between NPR steel plate and UHPC layer held strain compatibility during the whole loading process, and the magnitude of upward movement for sectional plastic neutral axis could be ignored with the increase of positive bending moment.

• 콘크리트학회논문집
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• 제14권5호
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• pp.653-659
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• 2002

최근들어, 국내에서 공용중인 교량바닥판의 파손사례가 증가되고 있으며, 파손된 바닥판의 주요 파괴모드는 반복되는 중트럭 하중에 의한 국부적인 펀칭전단이 주원인이 되고 있다. 본 연구에서는 교축방향으로 프리스트레스가 도입된 프리캐스트 콘크리트 교량바닥판에 대해서 펀칭전단 파괴실험을 수행하여 펀칭전단 실험중에 얻어진 균열양상, 파괴모드, 처짐 및 응력 특성, 펀칭전단강도 등을 검토하였다. 정적 펀칭전단 실험결과 교량바닥판의 펀칭전단 파괴는 현행 시방서의 예측식에값 보다 더 큰 하중 수줄에서 발생되어 현행 시방서에서 규정하는 펀칭전단 강도는 안전측의 결과를 보이는 것으로 판단된다.

• 천문학회보
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• 제40권2호
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• pp.32.1-32.1
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• 2015

The gradual infall of small dark matter halos onto larger ones has become a relatively straightforward aspect of the standard hierarchical formation paradigm. What happens to the baryons they contain, however, is less well understood. Of special relevance are the processes that regulate and ultimately suppress star formation in galaxies in the early universe. The z=1.5-2.5 epoch is then particularly interesting as a transition period when global star-formation in the universe starts peaking but also where the first ostensibly collapsed and virialized galaxy clusters appear, along with segregated galaxy populations. From a theoretical point of view, the mode of gas accretion in massive halos is also expected to change around this time, switching from a cold to a hot phase and affecting the build-up and evolution of the galaxies they host. A lot of effort has thus been devoted to the search for high-redshift structures, in particular galaxy clusters, through a variety of methods. However, as the limited area for which deep datasets are available remains relatively limited, only few massive z>1.5 structures have been found so far. Here I will instead discuss the regulation of star-formation in lower-mass, X-ray detected halos at z~2 and its implication for galaxy quenching at high redshift. As these smaller, group-size halos are vastly more abundant and structurally simpler than massive clusters, they allow for true statistical studies and offer a novel way to probe environmental effects in this transitional epoch.

• 한국방재학회 논문집
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• 제5권2호
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• pp.29-35
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• 2005

우리나라에서는 홍수로 매년 90여개 이상의 교량이 붕괴되고 있으며, 이러한 교량의 붕괴는 대부분 기초의 세굴에 기인하고 있다. 그동안 교량의 설계 및 유지관리 분야에서 세굴에 대한 교량의 건전성을 정량적으로 평가하기 위한 평가기법 개발에 관한 연구는 체계적으로 수행되지 못한 실정이다. 본 연구에서는 홍수 발생 후 교각의 세굴 건전성을 평가하기 위한 긴급점검기법으로써 세굴로 인한 교각의 고유진동수 변화를 이용하기 위한 동적특성 평가실험을 수행하였다. 세굴을 모의한 확대기초 교각 모형의 동적특성 평가 실험결과 교각의 1차 모드 고유진동수를 이용하여 기초의 세굴을 평가할 수 있을 것으로 분석되었다.

• 공학논문집
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• 제3권1호
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• pp.131-138
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• 1998

본 논문은 기술적인 진보보다는 개념적 변화에 초점을 맞추어 근거리통신망의 진화 방향에 대하여 살펴본다. 현재까지 많이 사용되는 주요한 근거리통신망 기술을 토폴로지, 채널의 타이밍구조, 매체접근제어 항목으로 분류하고 최근 근거리통신망에서 나타난 진전된 기술 및 새로운 개념들을 살핀다. 근거리통신망의 진화에서 가장 영향을 미친 근본적인 요소는 집중형 백본 개념으로 보인다. 종래의 LAN의 개념과는 근본적으로는 다른 ATM 기술이 LAN에 적용되고 있으며, 전통적인 근거리통신망이 ATM과 경쟁하기 위해서는 QOS의 지원이 가능하도록 발전해야 될 것이다.

• Journal of Welding and Joining
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• 제20권6호
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• pp.78-78
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• 2002

Front-side members are structures with the greatest energy absorbing capability in a front-end collision of vehicles. This paper was performed to analyze initial collapse characteristics of spot welded hat and double hat-shaped section members, which are basic shape of side members, on the shift of flange weld pitches. The impact collapse tests were carried out by using home-made vertical air compression impact testing machine, and impact velocity of hat-shaped section members is 4.17m/sec and that of double hat-shaped section members is 6.54m/sec. In impact collapse tests, the collapsed length of hat-shaped section members was about 45mm and that of double hat-shaped section members was about 50mm. In consideration of these condition, axial static collapse tests(0.00017m/sec) of hat and double hat-shaped section members were carried out by using UTM which was limited displacement, about 50mm. As the experimental results, to obtain the best initial collapse characteristics, it is important that stiffness of vehicle members increases as section shapes change and the progressively folding mode induces by flange welding pitch.

• Journal of Welding and Joining
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• 제20권6호
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• pp.802-808
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• 2002

Front-side members are structures with the greatest energy absorbing capability in a front-end collision of vehicles. This paper was performed to analyze initial collapse characteristics of spot welded hat and double hat-shaped section members, which are basic shape of side members, on the shift of flange weld pitches. The impact collapse tests were carried out by using home-made vertical air compression impact testing machine, and impact velocity of hat-shaped section members is 4.17m/sec and that of double hat-shaped section members is 6.54m/sec. In impact collapse tests, the collapsed length of hat-shaped section members was about 45mm and that of double hat-shaped section members was about 50mm. In consideration of these condition, axial static collapse tests(0.00017m/sec) of hat and double hat-shaped section members were carried out by using UTM which was limited displacement, about 50mm. As the experimental results, to obtain the best initial collapse characteristics, it is important that stiffness of vehicle members increases as section shapes change and the progressively folding mode induces by flange welding pitch.