• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 추계학술대회 논문집 Vol.17
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• pp.167-170
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• 2004

The stochiometric mix of evaporating materials for the $CuGaT_2$ single crystal thin films was prepared from horizontal furnance. Using extrapolation method of X-ray diffraction patterns for the $CuGaTe_2$ polycrystal, it was found tetragonal structure whose lattice constant $a_0$ and $c_0$ were 6.025 ${\AA}$ and 11.931 ${\AA}$, respectively. To obtain the single crystal thin films, $CuGaTe_2$ mixed crystal was deposited on throughly etched semi-insulator GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperature were $670^{\circ}C$ and $410^{\circ}C$ respectively, and the thickness of the single crystal thin films is $2.1{\mu}m$. The crystalline structure of single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). From the photocurrent spectrum by illumination of perpendicular light on the c - axis of the $CuGaTe_2$ single crystal thin film, we have found that the values of spin orbit coupling ${\Delta}s.o$ and the crystal field splitting ${\Delta}cr$ were $0.079\underline{1}eV$ and $0.246\underline{3}eV$ at 10 K, respectively. From the PL spectra at 10K, the peaks corresponding to free bound excitons and D-A pair and a broad emission band due to SA is identified. The binding energy of the free excitons are determined to be $0.047\underline{0}eV$ and the dissipation energy of the donor-bound exciton and acceptor-bound exciton to be $0.049\underline{0}eV$, $0.055\underline{8}eV$, respectively.

• Earthquakes and Structures
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• 제18권6호
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• pp.677-689
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• 2020

A building structural system of moment resisting frame (MRF) with concrete filled steel tubular (CFST) columns and wide flange H beams, is one of the most conveniently constructed structural systems. However, there were few studies on evaluating seismic performance of full-scale CFST columns under high axial compression. In addition, some existing famous design codes propose various limits of width-to-thickness ratio (B/t) for steel tubes of the ductile CFST composite members. This study was intended to investigate the seismic behavior of CFST columns under high axial load compression. Four full-scale square CFST column specimens with a B/t of 42 were carried out that were subjected to horizontal cyclic-reversal loads combined with constantly light, medium and high axial loads and with a linearly varied axial load, respectively. Test results revealed that shear strength and deformation capacity of the columns significantly decreased when the axial compression exceeded 0.35 times the nominal compression strength of a CFST column, P₀. It was obvious that the higher the axial compression, the lower both the shear strength and deformation capacities were, and the earlier and faster the shear strength degradation occurred. It was found as well that higher axial compressions resulted in larger initial lateral stiffness and faster degradation of post-yield lateral stiffness. Meanwhile, the lower axial compressions led to better energy dissipation capacities with larger cumulative energy. Moreover, the study implied that under axial compressions greater than 0.35P₀, the CFST column specimens with B/t limits recommended by AISC 360 (2016), ACI 318 (2014), AIJ (2008) and EC4 (2004) codes do not provide ultimate interstory drift ratio of more than 3% radian, and only the limit in ACI 318 (2014) code satisfies this requirement when axial compression does not exceed 0.35P₀.

• 한국건설순환자원학회논문집
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• 제8권4호
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• pp.571-580
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• 2020

본 연구에서는 열에너지 저장시스템의 중요한 요소인 저장 매체에 관한 연구를 수행하였다. 열에너지 저장 매체로써 콘크리트는 열적 및 역학적 특성이 우수하며 저렴한 비용으로 인해 다양한 이점을 갖는다. 또한, 강섬유가 혼입된 초고강도 콘크리트는 고인성 및 고강도 특성으로 인해 고온 노출에 우수한 내구성을 나타내며, 강섬유의 높은 열전도율은 축열 및 방열에 유리한 영향을 미친다. 초고강도 콘크리트의 온도분포 특성을 파악하기 위하여 콘크리트 블록을 제작하고 일정한 열사이클을 적용하여 가열실험을 수행하였다. 열유체 흐름에 의한 열전달을 위하여 열전달 파이프를 콘크리트 블록 중심부에 매립하였다. 또한, 열전달 파이프 형상에 따른 온도분포 특성을 비교하기 위하여 핀의 유무에 따라 원형 파이프 및 종방향 핀 부착 파이프를 설정하였다. 열사이클에 따른 온도분포 특성을 분석하고, 이를 토대로 시간에 따른 열에너지 및 누적 열에너지를 산정하여 비교 분석하였다. 열사이클이 반복될수록 강섬유 혼입 초고강도 콘크리트는 고온에 대하여 안정화를 나타내었다. 또한, 온도분포 및 열에너지 산정 결과를 통해 축열 성능을 보유한 것으로 판단되며, 열에너지 저장 매체 역할을 수행할 수 있는 재료로 기대된다.

• 한국지진공학회논문집
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• 제12권2호
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• pp.53-67
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• 2008

본 연구에서는 전단벽-모멘트골조 시스템으로서 전단벽이 주로 횡력을 부담하는 철근콘크리트 건물을 대상으로 다양한 설치형식과 마찰력의 총량 및 분포를 갖는 마찰형 감쇠기의 제진보강 효과를 수치해석을 통해 비교 분석하였다. 감쇠기의 설치형식으로서 전단벽에 인접한 대각가새형, 벽체가 없는 골조를 보강하는 대각가새형 및 벽체 단부를 보강하는 수직경계요소형을 고려하였다. 하중기준 강화로 설계용보다 크게 증가한 지진하중에 대해 건물의 재료비선형성을 고려한 비선형시간이력해석을 수행하여 에너지소산, 횡하중 및 부재손상도 측면에서 마찰형 감쇠기의 제진성능을 비교 분석하였다. 기준마찰력의 30% 수준의 총마찰력을 갖는 벽체보강 대각가새형 설치형식이 전반적으로 가장 우수한 제진성능을 보이며,이 경우에 마찰력 배분방식은 중요하지 않았다. 또한 일부층에 집중설치함으로써 전층설치에 약간 못미치는 제진성능을 얻을 수 있었다.

• 콘크리트학회논문집
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• 제17권6호
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• pp.1001-1009
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• 2005

고층 건물의 구조계획에서 벽체의 유용성은 오래전부터 인식되어 왔다. 구조물에서 적절한 위치에 벽체를 배치하며, 벽체는 구조물에 작용하는 횡하중에 매우 효과적으로 저항할 수 있다. 특히 병렬 전단벽 시스템의 구조물의 횡력저항 시스템으로서 가장 선호되는 구조이고 이러한 구조는 커플링보에 의해 벽체가 연결되게 된다. 커플링보는 강도, 강성, 연성 및 에너지 소산능력이 충분한 부재이어야 한다. 이러한 요구들을 만족시키기 위해 FBP를 적용한 철골 커플링보를 제안한다. FBP의 적용 여부를 변수로 하여 총 2개의 시험체를 계획하고 실험을 실시하였다. 이러한 실험 연구를 통하여 FBP를 적용한 철골 커플링보의 장점에 대해 서술하였고, 파괴모드를 제안하였다.

• Smart Structures and Systems
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• 제16권1호
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• pp.163-181
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• 2015

This research investigates the structural health monitoring of nonlinear structures after a major seismic event. It considers the identification of flag-shaped or pinched hysteresis behavior in response to structures as a more general case of a normal hysteresis curve without pinching. The method is based on the overall least squares methods and the log likelihood ratio test. In particular, the structural response is divided into different loading and unloading sub-half cycles. The overall least squares analysis is first implemented to obtain the minimum residual mean square estimates of structural parameters for each sub-half cycle with the number of segments assumed. The log likelihood ratio test is used to assess the likelihood of these nonlinear segments being true representations in the presence of noise and model error. The resulting regression coefficients for identified segmented regression models are finally used to obtain stiffness, yielding deformation and energy dissipation parameters. The performance of the method is illustrated using a single degree of freedom system and a suite of 20 earthquake records. RMS noise of 5%, 10%, 15% and 20% is added to the response data to assess the robustness of the identification routine. The proposed method is computationally efficient and accurate in identifying the damage parameters within 10% average of the known values even with 20% added noise. The method requires no user input and could thus be automated and performed in real-time for each sub-half cycle, with results available effectively immediately after an event as well as during an event, if required.

• 한국지진공학회논문집
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• 제26권2호
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• pp.71-82
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• 2022

This paper presents the effect on the inelastic behavior and structural performance of concrete and filled steel pipe through a numerical method for reliable judgment under various load conditions of the CJS composite structural system. Variable values optimized for the CJS synthetic structural system and the effects of multiple variables used for finite element analysis to present analytical modeling were compared and analyzed with experimental results. The Winfrith concrete model was used as a concrete material model that describes the confinement effect well, and the concrete structure was modeled with solid elements. Through geometric analysis of shell and solid elements, rectangular steel pipe columns and steel elements were modeled as shell elements. In addition, the slip behavior of the joint between the concrete column and the rectangular steel pipe was described using the Surface-to-Surface function. After finite element analysis modeling, simulation was performed for cyclic loading after assuming that the lower part of the foundation was a pin in the same way as in the experiment. The analysis model was verified by comparing the calculated analysis results with the experimental results, focusing on initial stiffness, maximum strength, and energy dissipation capability.

• Earthquakes and Structures
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• 제5권4호
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• pp.461-475
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• 2013

A new experimental system of base-isolated structures is proposed. There are two kinds of dampers usually used in the base-isolated buildings, one is a viscous-type damper and the other is an elastic-plastic hysteretic-type damper. The base-isolated structure with a viscous damper and that with an elastic-plastic hysteretic damper are compared in this paper. The viscous damper is modeled by a mini piston and the elastic-plastic hysteretic damper is modeled by a low yield-point steel. The capacity of both dampers is determined so that the dissipated energies are equivalent at a specified deformation. When the capacity of both dampers is determined according to this criterion, it is shown that the response of the base-isolated structure with the elastic-plastic hysteretic damper is larger than that with the viscous damper. This characteristic is demonstrated through the comparison of the bound of the aspect ratio. It is shown that the bound of aspect ratio for the base-isolated structure with the elastic-plastic hysteretic damper is generally smaller than that with the viscous damper. When the base-isolated structure is subjected to long-duration input, the mechanical property of the elastic-plastic hysteretic damper deteriorates and the response of the base-isolated structure including that damper becomes larger than that with the viscous damper. The effect of this change of material properties on the response of the base-isolated structure is also investigated.

• Structural Engineering and Mechanics
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• 제73권3호
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• pp.271-286
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• 2020

Passive control technologies are commonly used in several areas to suppress structural vibrations by the addition of supplementary damping, and some modal damping may be heavy beyond critical damping even for regular structures with energy dissipation devices. The design of passive control structures is typically based on (complex) mode superposition approaches. However, the conventional mode superposition approach is predominantly applied to cases of under-critical damping. Moreover, when any modal damping ratio is equal or close to 1.0, the system becomes defective, i.e., a complete set of eigenvectors cannot be obtained such that some well-known algorithms for the quadratic eigenvalue problem are invalid. In this paper, a generalized complex mode superposition method that is suitable for under-critical, critical and over-critical damping is proposed and expressed in a unified form for structural displacement, velocity and acceleration responses. In the new method, the conventional algorithm for the eigenvalue problem is still valid, even though the system becomes defective due to critical modal damping. Based on the modal truncation error analysis, modal corrected methods for displacement and acceleration responses are developed to approximately consider the contribution of the truncated higher modes. Finally, the implementation of the proposed methods is presented through two numerical examples, and the effectiveness is investigated. The results also show that over-critically damped modes have a significant impact on structural responses. This study is a development of the original complex mode superposition method and can be applied well to dynamic analyses of non-classically damped systems.

• Steel and Composite Structures
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• 제37권3호
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• pp.273-289
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• 2020

Due to the unique construction method of modular steel buildings (MSBs) with units prefabricated fully off the site and assembled quickly on the site, the inter-module connection for easy operation and overall performance of the system were key issues. However, it was a lack of relevant research on the system-level performance of MSBs. This study investigated the seismic performance of two-storey modular steel structure with a proposed vertical rotary inter-module connection. Three full-scale quasi-static tests, with and without corrugated steel plate and its combination, were carried out to evaluate and compare their seismic behaviour. The hysteretic performance, skeleton curves, ductile performance, stiffness degradation, energy dissipation capacity, and deformation pattern were clarified. The results showed that good ductility and plastic deformation ability of such modular steel structures. Two lateral-force resistance mechanisms with different layout combinations were also discussed in detail. The corrugated steel plate could significantly improve the lateral stiffness and bearing capacity of the modular steel structure. The cooperative working mechanism of modules and inter-module connections was further analyzed. When the lateral stiffness of upper and lower modular structures was close, limited bending moment transfer may be considered for the inter-module connection. While a large lateral stiffness difference existed initially between the upper and lower structures, an obvious gap occurred at the inter-module connection, and this gap may significantly influence the bending moments transferred by the inter-module connections. Meanwhile, several design recommendations of inter-module connections were also given for the application of MSBs.