• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.609-614
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• 2001

This paper is to explain reasonable shear behavior that can apply usually to reinforced concrete beams on the basic concepts of existent analysis and experimental research information. This study is succession $paper^{2) 3) 4) 5)}$ of treatise announced in existing and main control variable of reinforced concrete beams with stirrups used internal force state factor($\alpha$). Shear failure of reinforced concrete beams with stirrups is Influenced greatly because of the actual geometrical shape(a/d) of the concrete and flexural reinforcement steel ratio, stirrup reinforcement ratio and concrete compression strength, size effect etc. Therefore, shear behavior of reinforced concrete beams with stirrups that flexural crack is happened can be explained easily through proper extent proposal of internal force state factor($\alpha$) that express internal force state flowing. Use existent variable truss model by analysis model to explain arch action. Also, wish to compose each failure factors and correlation with internal force state factor by function, and when diagonal cracks happens, internal force state factor($\alpha$) study whether shear stress and some effect are.

• Journal of Advanced Marine Engineering and Technology
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• 제35권8호
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• pp.1009-1015
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• 2011

본 연구에서는 고팽창사이클의 경우 가변밸브시스템을 구성하여 흡기밸브 닫힘시기를 늦추는 방식으로 실현하였고, 저압축에 따른 흡입공기의 감소는 과급압력으로 해결하였다. 이와 같이 디젤기관에 아트킨슨사이클을 실현하여 엔진의 열효율향상 가능성을 알아보았다. 그 결과 흡기밸브 닫힘시기 ABDC $40^{\circ}$ 부터 ABDC $80^{\circ}$ 까지 전 영역에 걸쳐 열효율 및 출력의 향상이 있었다. 다만, 흡기밸브 닫힘시기가 ABDC $70^{\circ}$이후로는 열효율 증가 폭이 둔화되는 경향을 보였다. 위와 같은 연구결과 저속 디젤-아트킨슨사이클화의 최적 연소조건은 흡기밸브 닫힘시기가 ABDC $70^{\circ}$전후로 보이며, 고부하영역이 저부하영역보다 더 효과적으로 나타났고, 중부하영역에서 기관운전은 안정적이었다. 이때 정미열효율은 통상의 디젤기관보다 평균 약 12.5% 높게 나타났다.

• 설비공학논문집
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• 제27권11호
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• pp.567-573
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• 2015

Commercial buildings account for significant portions of the total building energy in Korea, and thus, a variety of research on chiller operation has been carried out. However, most of the studies were carried out on the chiller itself, i.e., the part load ratio characteristics and the corresponding electricity energy consumption patterns were not analyzed in existing studies. In this study, the part load ratio and the operating characteristics of the vapor compression chiller were analyzed within an office building equipped with the conventional variable air volume system. As a result, significant portions of total operating hours, cooling load, and energy consumption turned out to be in the part load ratio range of 0 through 50%. Thus, energy consumption was significantly affected by the chiller COP at low part load conditions, indicating that chiller operation at the part load is an important factor in commercial buildings.

• 한국컴퓨터정보학회논문지
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• 제8권2호
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• pp.24-30
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• 2003

본 논문에서는 JPEG 영상의 오차(PSNR)의 개선을 위해 반올림 양자화와 내림 양자화의 장점을 조합하여 가변 임계값을 갖는 양자화 방법(VTQM: Variable Threshold quantization Method)을 제안하고, 실험에 의해 VTQM의 비트율 대비 PSNR을 표준 JPEG방법의 경우와 비교하였다. VTQM에서는 양자화 방법에 따라 영상의 압축률에 영향을 미치는 영역에서는 압축한 결과값의 길이가 줄어들 수 있도록 임계값을 조정하여 양자화하고, 그 외의 경우에는 원시 영상의 값을 유지하는 방향(반올림)으로 양자화 한다. 그 결과 최대한 화질을 유지하면서 비트율을 감소시킬 수 있다. 몇 개의 샘플 영상에 대한 실험 결과, VTQM은 기존의 반올림과 내림 양자화 방법보다 같은 비트율에서 PSNR이 각각 0.2∼0.3dB, 0.4∼0.5dB 향상되는 것을 보여주었다.

• 한국추진공학회지
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• 제19권3호
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• pp.65-72
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• 2015

본 연구에서는 이중램제트 엔진 및 로켓/터빈 기반 복합사이클 엔진에의 활용을 위해 Mach 3에서부터 Mach 8까지 넓은 마하수 영역에서 적용이 가능한 초음속흡입구의 형상설계를 수행하고 그 설계방법론에 대해 고찰하였다. 축대칭 가변흡입구를 기본 개념으로 중심콘 각도 및 경사충격파 각도를 이용한 기하학적 관계식으로부터 흡입구 형상을 설계하였으며, 100%에 준하는 포획면적비를 갖도록 하였다. 또한 전산해석결과로부터 Mach 3~8까지 조건에서 흡입구 중심콘에서 발생한 충격파가 올바르게 배치되는 것을 확인하였다.

• 전자공학회논문지CI
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• 제49권3호
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• pp.15-26
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• 2012

최근 공간정보표현을 위해 벡터데이터 기반 디지털 맵의 활용도의 증가와 측량기술의 발전에 기인하여 높은 수준의 해상도를 갖는 고용량의 GIS(geographic information service) 서비스가 활발히 이루어지고 있다. 본 논문은 방대한 범위에서 높은 해상도를 갖는 1cm(센티미터) 단위의 정밀 벡터맵의 효율적인 압축을 위해 공간 영역 상에서의 에너지 집중 기법(spatial energy compaction, SEC)을 이용한 벡터맵 압축 기법을 제안한다. 제안 기법은 벡터맵에서 공간정보를 표현하기 위해 주로 사용되는 폴리곤(polygon) 및 폴리라인(polyline) 오브젝트에 대해 압축을 수행한다. 제안 기법에서는 전체 벡터맵을 국부영역으로 나눈 후, 각 국부영역 내의 오브젝트 인접성 및 방향성을 이용하여 세 가지 종류의 빈으로 분류하여 에너지 집중을 수행하며, 미리 정의된 가변길이부호화를 이용해 부호화하여 압축한다. 실험결과 동일한 벡터맵에 대해 1m 정밀도의 벡터간소화 기법이 약 13%의 압축율을 갖는 데 반해, 제안 기법은 1cm 단위의 정밀도에서 원본 데이터의 80%이상 압축이 수행됨을 확인하였다. 또한 이것은 기존에 제안한 SEC 기반 압축 기법보다 높은 압축율을 가지면서 낮은 계산 복잡도를 유지하며, 기존의 벡터 근사화 기법보다 높은 정밀도에서 높은 압축률로 압축할 수 있음을 실험을 통해 확인하였다.

• 한국강구조학회 논문집
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• 제17권3호통권76호
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• pp.357-363
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• 2005

건축물이 고층이 될 수록 고강도 강재의 사용요구가 증대된다. 그러나 고강도 강재는 일반 강재와는 전혀 다른 기계적 특성을 갖고 있다. 고강도 강재를 건축구조물에 적용하기 위해서는 비탄성 영역에서의 거동이 일반 강재와 동등한가를 확인해야 한다. 본 연구에서는 SM570TMC 강재로 제작된 박스형 및 H형 단면을 갖는 기둥의 국부좌굴강도를 평가하기 위해서 중심압축실험을 세장비를 변수로 수행하였다. 단주압축 실험결과 판폭두께비의 제한치를 만족하는 기둥부재의 최대내력은 국부좌굴에 의해 결정되며, 판폭두께비를 만족시키지 못하는 경우에는 최대내력에 도달하기 전에 국부좌굴이 발생되었으나 급격한 내력저하는 발생되지 않았다. 장주압축 실험결과 SM570TMC 강재는 허용응력도 설계법과 한계상태 설계법에서 정하고 있는 설계기준을 만족하였다.

• Earthquakes and Structures
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• 제10권2호
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• pp.329-350
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• 2016

A parametric study was conducted to investigate the seismic deformation demands in terms of drift ratio, plastic base rotation and compression strain on rectangular wall members in frame-wall systems. The wall index defined as ratio of total wall area to the floor plan area was kept as variable in frame-wall models and its relation with the seismic demand at the base of the wall was investigated. The wall indexes of analyzed models are in the range of 0.2-2%. 4, 8 and 12-story frame-wall models were created. The seismic behavior of frame-wall models were calculated using nonlinear time-history analysis and design spectrum matched ground motion set. Analyses results revealed that the increased wall index led to significant reduction in the top and inter-story displacement demands especially for 4-story models. The calculated average inter-story drift decreased from 1.5% to 0.5% for 4-story models. The average drift ratio in 8- and 12-story models has changed from approximately 1.5% to 0.75%. As the wall index increases, the dispersion in the calculated drifts due to ground motion variability decreased considerably. This is mainly due to increase in the lateral stiffness of models that leads their fundamental period of vibration to fall into zone of the response spectra that has smaller dispersion for scaled ground motion data set. When walls were assessed according to plastic rotation limits defined in ASCE/SEI 41, it was seen that the walls in frame-wall systems with low wall index in the range of 0.2-0.6% could seldom survive the design earthquake without major damage. Concrete compressive strains calculated in all frame-wall structures were much higher than the limit allowed for design, ${\varepsilon}_c$=0.0035, so confinement is required at the boundaries. For rectangular walls above the wall index value of 1.0% nearly all walls assure at least life safety (LS) performance criteria. It is proposed that in the design of dual systems where frames and walls are connected by link and transverse beams, the minimum value of wall index should be greater than 0.6%, in order to prevent excessive damage to wall members.

• Geomechanics and Engineering
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• 제29권3호
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• pp.311-320
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• 2022

TBM concrete segment requires a higher level of material properties compared to general concrete structures due to difficulties in maintenance and uncertainty in ground conditions. In this regard, recently, as one of the methods to achieve enhancement effect on concrete strength, many researchers have been focusing on adding CNTs to concrete mixture. However, even CNTs do not compensate the weakness that concrete exhibits brittle behavior after cracking. Separately, over the past few decades, a number of studies have been conducted on fiber reinforced concrete which exhibits ductile behavior due to fibers bridging cracks. However, only limited studies have been conducted to employ the advantages of the both materials together. In this study, an experimental program has been conducted to investigate the effect of CNTs on the workability and the compressive behavior of PVA-ECC which exhibits ductile tensile behavior with well-distributed cracks even without a conventional rebar. In addition to the compression test, SEM analysis has been also conducted for detailed investigation in the microstructure. The variable was the CNTs mix ratio, which were set to 0.00, 0.25, and 0.50 wt.% to the binding materials. It was observed though the test results that as the CNTs mix ratio increased, the workability considerably decreased with the reduced slump and slump flow. From the compression test results, it was also investigated that the compressive behavior was improved since the compressive strength, the strain corresponding to the compressive strength, and the modulus of elasticity increased with an increase of CNTs mix ratio. The contents of this paper will be useful for relevant research areas such as fiber reinforced concrete with CNTs which might be applied for high performance TMB concrete segments.

• Steel and Composite Structures
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• 제35권1호
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• pp.13-27
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• 2020

To investigate the stress-strain relation of PVC-FRP Confined Concrete (PFCC) column with RC ring beam joint subjected to eccentric compression, the experiment of 13 joint specimens, which were designed with principle of "strong joint and weak column", were presented. Several variable parameters, such as reinforcement ratio, width and height of ring beam, FRP strips spacing and eccentricity, were considered. The specimens were eventually damaged by the crushing of concrete, the fracture of PVC tube and several FRP strips. With the FRP strips spacing or eccentricity increased, the ultimate carrying capacity of specimens declined. The strain of FRP strips and axial strain of PVC tube decreased as FRP strips spacing decreased. The decrease of eccentricity would slow down the development of strain of FRP strips and axial strain of PVC tube. The slope of stress-strain curve of PFCC column decreased as FRP strips spacing or eccentricity increased. The ultimate strain of PFCC column reduced as FRP strips spacing increased, while the effect of eccentricity on the ultimate strain of PFCC was not distinct. Considering the influence of eccentricity on the stress-strain relation, a modified stress-strain model for conveniently predicting the weak PFCC column and strong RC ring beam joint under eccentric compression was proposed and it was in good agreement with the experimental data.