• Applied Science and Convergence Technology
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• 제26권4호
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• pp.79-85
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• 2017

The crack-free AlGaN template has been successfully grown by using selective area growth with triangular GaN facet. The triangular GaN stripe structure was obtained by vertical growth rate enhanced mode with low growth temperature of $950^{\circ}C$ and high growth pressure of 500 torr. The lateral growth rate enhanced mode of AlGaN for crack-free and flat surface was also investigated. Low pressure of 30 torr and high V/III ratio of 4400 were favorable for lateral growth of AlGaN. It was confirmed that the $4{\mu}m$ -thick $Al_{0.2}Ga_{0.8}N$ was crack-free over entire 2-inch wafer. The dislocation density of $Al_{0.2}Ga_{0.8}N$ was as low as ${\sim}7.6{\times}10^8/cm^2$ measured by cathodoluminescence. Based on the high quality AlGaN with low dislocation density, the ultraviolet laser diode epitaxy with cladding, waveguide and GaN/AlGaN multiple quantum well (MQW) was grown by metalorganic chemical vapor deposition. The stimulated emission at 349 nm with full width at half maximum of 1.8 nm from the MQW was observed through optical pumping experiment with 193 nm KrF laser. We also have fabricated the deep ridge type ultraviolet laser diode (UV-LD) with $5{\mu}m-wide$ and $700{\mu}m-long$ cavity for electrical properties. The turn on voltage was below 5 V and the resistance was ${\sim}55{\Omega}$ at applied voltage of 10 V. The amplified spontaneous emission spectrum of UV-LD was also observed from pulsed current injection.

• Structural Engineering and Mechanics
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• 제40권4호
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• pp.517-539
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• 2011

This paper presents the seismic responses of a 1:5-scale five-story reinforced concrete building model, which represents a residential apartment building that has a high irregularity of weak story, soft story, and torsion simultaneously at the ground story. The model was subjected to a series of uni- and bi-directional earthquake simulation tests. Analysis of the test results leads to the following conclusions: (1) The model survived the table excitations simulating the design earthquake with the PGA of 0.187 g without any significant damages, though it was not designed against earthquakes; (2) The fundamental mode was the torsion mode. The second and third orthogonal translational modes acted independently while the torsion mode showed a strong correlation with the predominant translational mode; (3) After a significant excursion into inelastic behavior, this correlation disappeared and the maximum torsion and torsion deformation remained almost constant regardless of the intensity of the two orthogonal excitations; And, (4) the lateral resistance and stiffness of the critical columns and wall increased or decreased significantly with the large variation of acting axial forces caused by the high bi-directional overturning moments and rocking phenomena under the bi-directional excitations.

• 산업기술연구
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• 제19권
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• pp.135-145
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• 1999

This thesis is to investigate the sliding behavior of cantilever retaining wall by using the commercially available program of FLAC to simulate its behavior numerically. Cantilever retaining walls with flat base, sloped base and base with shear key, uniform surcharges being applied on the surface of backfill, were investigated to figure out appropriate location of shear key beneath the base of wall and, thus, its applicability to field condition was assessed by comparing the analyzed results to each other. On the other hand, previously performed centrifuge model test results (Eum, 1996) were analyzed numerically with FLAC to compare test results with respect to characteristics of load-settlement of surcharges and load-lateral movement of wall. Based on the failure mechanism observed during centrifuge tests, limit equilibrium method of finding the ultimate load inducing the sliding failure of wall was used to compare with values of the ultimate load obtained from conventional method of limit equilibrium method. Therefore, appropriate location of shear key was determined to mobilize the maximum resistance against sliding failure of wall.

• 한국공간구조학회논문집
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• 제18권2호
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• pp.35-42
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• 2018

The outrigger damper system is a structural system with excellent lateral resistance when a wind load occurs. However, research on outrigger dampers is still in its infancy. In this study, dynamic response control performance of damper is analyzed according to change of stiffness value and damping value of damper. To do this, a real-scale 3D model of 50 stories has been developed and the artificial wind load has been entered for dynamic analysis. Generally, the larger the damping value, the smaller the stiffness value is, the more effective it is to reduce the maximum displacement and acceleration response. However, the larger the attenuation value as the cost of construction increases, it is necessary to select appropriate stiffness and damping value when applying an outrigger damper.

• Structural Engineering and Mechanics
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• 제31권5호
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• pp.605-619
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• 2009

A comparative experimental study of prestressed continuous steel-concrete composite beams was carried out. Two continuous composite beams were tested, one of which was plain continuous steel-concrete composite beam, while the other was a composite beam prestressed with external tendons. Cracking behavior and the load carrying capacity of the beams were investigated experimentally. Full plasticity was developed in the mid-span section each beam, the maximum moments attained at the internal support sections however were governed by local buckling which was related to the slenderness of composite section. It was found that in hogging moment regions, the ultimate resistance of an externally prestressed composite beam would be governed by either distortional lateral buckling or local buckling, or interactive mode of these two buckling patterns. The results show that exerting prestressing on a continuous composite beam with external tendons will increase the extent of internal force and moment redistribution in the beam. The influences of local and distortional buckling on the behaviors of the composite continuous beams are discussed. The Moment redistribution and the load carrying capacity of the prestressed continuous composite beams are evaluated, and it is found that at the ultimate state, the moment redistribution in the prestrssed continuous composite beams is greater than that in non-prestressed composite beams.

• 한국지반공학회지:지반
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• 제2권1호
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• pp.45-54
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• 1986

보강토잡벽에 대한 합리적인 설계 및 시공방법에 관한 경험적인 자료를 제홍하기 위하여 실내 모형실험이 실시되었다. 본 모형실험에서는 각 축조 단계에서의 보강재의 인장력 변화를 보강재상에 부착된 스트레인 게이지에 의하여 계측되었다. 또한 다이알게이지에 의하여 보강토파벽의 수평이동이 측정되었고, 도건의 붕괴형태가 조사되었다. 모형실험에서 측정된 값들은 보강토옹벽에 대한 기존 연구 결과와 비교.논의하였다. 본 모형실험의 중요한 결과는 보강재의 인장력이 벽면가까이에서 최대가 되어 비선형적으로 변화하며, 벽체에 연결된 보강재가 전류에 대한 안정성을 증가시킨다.

• Structural Engineering and Mechanics
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• 제83권6호
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• pp.799-810
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• 2022

This study investigated the effect of the strengthening efficiency of unbonded steel-bar truss system on the out-of-plane behavior of perforated masonry walls. Four full-scale unreinforced masonry (URM) walls with two different planes were prepared using the unbonded steel-bar truss system and a URM walls without strengthening. All masonry walls were tested under constant axial and cyclic lateral loads. The obtained test results indicated that the pinching effect in the out-plane behavior of masonry walls tends to decrease in the in- and out-of-plane strengthened URM walls using the unbonded steel-bar truss system with the higher prestressing force ratio (R_p) of vertical reinforcing bars in the unbonded steel-bar truss system, regardless of the perforated type of the masonry wall. Consequently, the highest maximum shear resistance and cumulative dissipated energy at peak load in the post-peak behavior were observed in the in- and out-plane strengthened URM walls with the highest R_p values, which are 2.7 and 6.0 times higher than those of URM. In particular, the strengthening efficiency of the unbonded steel-bar truss system was primarily attributed to the vertical prestressed steel-bars rather than the diagonal steel-bars, which indicates that the strains in the vertical prestressed steel-bars at the peak load were approximately 1.6 times higher than those in the diagonal steel-bars.

• 한국구조물진단유지관리공학회 논문집
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• 제18권3호
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• pp.1-9
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• 2014

본 연구에서는 기존 강재브레이스 내진보강법이 가지는 좌굴문제 등 단점을 극복할 수 있는 중 저층 철근콘크리트 건축물에 효과적으로 적용할 수 있는 새로운 내진보강법을 개발하였다. Carbon Fiber Composite Cable (CFCC)을 이용하여 건축물 골조 외부에 X자 형태로 내진보강을 실시하고, 상부 및 하부 보 양 단부에 CFCC X-브레이싱을 고정하기 위해서 평판 및 돌출형 나사식 접합으로 내진보강을 실시하는 내진보강법으로서, 반복하중 실험을 통하여 내진보강 효과를 규명하였다. 실험체는 비교용 비보강 골조, 평판형 및 돌출형 CFCC X-브레이싱 내진보강 골조 실험체 총 3개를 제작하였다. 실험결과, 본 연구에서 개발한 CFCC 내진보강법은 강도증진형 내진보강법으로 드러났으며, 기존 강재브레이스 보강법 대비 중량증가가 거의 없으며, 재료자체가 압축에 대한 좌굴이 없으며, 경량이므로 시공성이 매우 우수하고 중량 및 체적대비 우수한 강도가 발휘될 뿐만 아니라 특히, CFCC의 직경을 변경함으로서 내진보강 목적 (강도 보강량)에 대응하여 내진성능을 쉽게 변화시킬 수 있는 장점이 있다.

• Composites Research
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• 제22권4호
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• pp.33-40
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• 2009

유리섬유/에폭시 복합재료로 피막한 판유리의 표변파괴거동에 대한 섬유방향효과를 미소강구 충격실험을 통해 연구했다. 본 연구에서는 단순소다유리판(soda-lime glass plates), 일방향 유리섬유/에폭시박막 (glass/epoxy lamina ply)을 1층 및 2층 접착, 직교형 유리섬유/에폭시 박막 (2층)을 접착한 4종류의 시편을 사용하였다. 유리판 배면에 스트레인게이지를 부착하여 충격중의 최대 응력과 흡수파괴에너지를 측정하였다. 피막없는 판유리의 경우 충격속도 증가에 따라 링균열, 콘균열, 레이디얼 균열이 충격표면부에서 발생하였다. 복합재료 박막으로 피막한 결과, 소다유리판의 균열은 현저히 감소하였으며 섬유층과 판유리사이의 박리 및 소성변형영역의 방향은 섬유방향으로 진행했다. 최대응력과 흡수파괴에너지를 이용하여 구한 충격 표면파괴지수는 표면저항의 효과적인 평가지수로서 사용될 수 있었다.

• 콘크리트학회논문집
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• 제18권2호
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• pp.257-266
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• 2006

최근 공기단축, 낮은 층고, 자유로운 평면계획 등의 많은 장점을 가지는 플랫플레이트 구조형식이 고층주거건물의 구조형식으로 많이 사용되고 있다. 특히 국내에서 건설되고 있는 플랫플레이트 구조시스템은 횡력에 대한 저항성을 크게 하기 위하여 기둥의 단면이 매우 크며 직사각형 형태를 가지는 벽기둥(wall-column)을 사용하는 경우가 많으므로 접합부 강도산정모형에서는 이러한 기둥의 형태적 요소를 적절히 반영해야 한다. 기둥단면형상에 따른 플랫플레이트-기둥 접합부의 거동특성을 분석하기 위하여 기존의 강도모델을 검토하고 비선형 유한요소해석을 실시하였다. 기존 강도모델은 위험단면에서의 전단응력분포를 가정함에 있어서 기둥단면형상의 영향을 고려하지 못하여 플랫플레이트-기둥 접합부의 강도를 정확하게 예측하지 못하였다. 비선형 유한요소해석 결과, 하중가력방향과 평행한 기둥폭이 길어질수록 위험단면 측면에서 비틀림 전단을 받는 유효영역과 측면 최대전단강도가 줄어들어 접합부의 강도가 큰 폭으로 감소한다. 따라서 플랫플레이트-기둥 접합부의 강도를 정확히 산정하기 위해서는 하중가력방향과 평행한 기둥폭의 길이($c_1$)이 접합부 거동에 미치는 영향을 적절히 반영해야 할 것이다.