• 대한기계학회논문집A
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• 제25권2호
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• pp.250-263
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• 2001

The up and down speed of heddle frames that produce woven cloth by insertion of weft yarns between warp yarns has been increased recently much for productivity improvement, which induces higher inertial stresses and vibrations in the heddle frame. the heddle frame is required to reduce its mass because the heddle frame contributes the major portion of the stresses in the heddle frames during accelerating and decelerating. Conventional aluminum heddle frames have fatigue life of around 5 months at 550rpm due to their low fatigue flexural strength as well as low bending stiffness. In this work, since carbon/epoxy composite materials have high specific fatigue strength(S/p), high specific modulus(E/p), high damping capacity and sandwich construction results in lower deflections and higher buckling resistance, the sandwich structure composed of carbon/epoxy composite skins and polyurethane foam were employed for the high-speed heddle frame. The design map for the sandwich beams was accomplished to determine the optimum thickness and the stacking sequences for the heddle frames. Also the effects of the number of ribs on the stress of the heddle frame were investigated by FEM analyses. Finally, the high-speed heddle frames were manufactured with sandwich structures and the static and dynamic properties of the aluminum and the composite heddle frames were tested and compared with each other.

• 한국건설순환자원학회논문집
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• 제9권3호
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• pp.338-347
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• 2021

본 논문은 층간 보강재를 보강한 3D 프린팅 콘크리트의 부착강도를 평가하기 위해 수행되었다. 겹침이음 길이에 따라 두 종류의 층간 보강 방법을 고려하였다. 첫 번째 방법은 층간 보강재의 겹침이음을 하지 않았으며, 두 번째 방법은 40mm의 겹침이음을 고려하였다. 또한, 기건양생 조건과 수중양생 조건의 서로 다른 양생 조건을 고려하였다. 실험 변수를 고려하여 3D 프린팅 콘크리트 시편의 압축강도, 쪼갬인장강도 및 휨인장강도를 세가지 하중 방향에서 측정하였다. 압축강도, 쪼갬인장강도 및 휨인장 강도는 하중방향에 영향을 받았다. 특히 3D 프린팅으로 제작한 콘크리트 시편의 층간 부착면에 인장력이 작용하면 쪼갬인장강도 및 휨인장강도가 크게 감소하였다. 그러나 층간 보강재가 보강된 층의 종방향으로 하중이 가해질 때, 프린팅된 시편의 휨인장강도 또는 부착강도는 크게 증가하였다. 또한 기건양생 조건의 휨인장강도 또는 부착강도는 감소하였으며, 기건 양생 조건에 의해 더 많은 공극의 형성을 유발하여 하중에 더 취약해지는 것으로 나타났다.

• 한국전산구조공학회논문집
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• 제13권3호
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• pp.351-360
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• 2000

복수의 내부튜브를 가진 골조 튜브 시스템의 전단지체 영향을 평가하기 위하여 수치적인 모델링 기법이 제안되었다. 이러한 튜브 구조물의 모든 튜브는 전단지체 영향 뿐만 아니라 휨과 전단변형의 영향을 설명할 수 있는 보로 각각 모델링된다. 수치적인 해석은 최소 포텐셜 에너지 원리에 근거한 변분 접근법에 기초한다. 복수의 내부튜브를 가진 튜브 구조물의 전단지체 현상이 부가적인 휨 응력에 의해서 조사되었다. 또한 튜브 구조물의 전단지체를 지배하는 구조변수를 연구하기 위하여 33개의 튜브구조물이 해석되었다.

• 콘크리트학회논문집
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• 제11권6호
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• pp.13-24
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• 1999

The external, unbonded prestressed concrete(PSC) members exhibit very different structural behavior from that of internal bonded PSC members because of eccentricity change and slip occurrence during loading process. The purpose of the present study is to propose the ultimate failure stresses of prestressing (PS) steels for those external unbonded PSC members. To this end, a comprehensive analysis has been made using the nonlinear finite element analysis program developed recently for external unbonded PSC members by authors. A series of major influencing variables have been included in the analysis. It was found that the span-depth ratio, neutral axis depth-effective depth ratio, load geometry, amount of ordinary steel, and prestressing steel ration have great influence for the ultimate failue stress of PS steel is preposed and is compared with experimental dat as well as existing formulas for internal unbonded members. The Comparison indicates that the proposed equation agrees relatively well with experimental data and that existing formulas including ACI and AASHTO equations show some discrepancies from experimental ones. The present study allows more realistic analysis and design of prestressed concrete structures with external unbonded tendons.

• 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.

• Structural Monitoring and Maintenance
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• 제7권3호
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• pp.233-259
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• 2020

Using bonded fiber-reinforced polymer laminates for strengthening wooden structural members has been shown to be an effective and economical method. In this research, properties of suitable composite materials (sika wrap), adhesives and two ways of strengthening beams exposed to bending moment are presented. Passive or slack reinforcement is one way of strengthening. The most effective way of such a strengthening was to place reinforcement laminates in the stretched part of the wooden beam (lower part in our case), in order to investigate the effectiveness of externally bonding FRP to their soffits. The model is based on equilibrium and deformations compatibility requirements in and all parts of the strengthened beam, i.e., the wooden beam, the sika wrap composite plate and the adhesive layer. The theoretical predictions are compared with other existing solutions. This research is helpful for the understanding on mechanical behaviour of the interface and design of the composite-wooden hybrid structures. The results showed that the use of the new strengthening system enhances the performance of the wooden beam when compared with the traditional strengthening system.

• Steel and Composite Structures
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• 제13권1호
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• pp.71-89
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• 2012

The paper investigates beam lateral buckling stability according to linear and non-linear models. Closed form solutions for single-symmetric cross sections are first derived according to a non-linear model considering flexural-torsional coupling and pre-buckling deformation effects. The closed form solutions are compared to a beam finite element developed in large torsion. Effects of pre-buckling deflection and gradient moment on beam stability are not well known in the literature. The strength of singly symmetric I-beams under gradient moments is particularly investigated. Beams with T and I cross-sections are considered in the study. It is concluded that pre-buckling deflections effects are important for I-section with large flanges and analytical solutions are possible. For beams with T-sections, lateral buckling resistance depends not only on pre-buckling deflection but also on cross section shape, load distribution and buckling modes. Effects of pre-buckling deflections are important only when the largest flange is under compressive stresses and positive gradient moments. For negative gradient moments, all available solutions fail and overestimate the beam strength. Numerical solutions are more powerful. Other load cases are investigated as the stability of continuous beams. Under arbitrary loads, all available solutions fail, and recourse to finite element simulation is more efficient.

• Computers and Concrete
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• 제1권3호
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• pp.303-324
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• 2004

The Component-Based Software Development (CBSD) has established itself as a sound paradigm in the software engineering discipline and has gained wide spread acceptance in the industry. The CBSD relies on the availability of standard software components for encapsulation of specific functionality. This paper presents the framework for the development of a software component for the design of general member cross-sections. The proposed component can be used in component-based structural engineering software or as a stand-alone program developed around the component. This paper describes the use-case scenarios for the component, its design patterns, object models, class hierarchy, the integrated and unified handling of cross-section behavior and implementation issue. It is expected that a component developed using the proposed patterns and model can be used in analysis, design and detailing packages to handle reinforced concrete, partially prestressed concrete, steel-concrete composite and steel sections. The component can provide the entire response parameters of the cross section including determination of geometric properties, elastic stresses, flexural capacity, moment-curvature, and ductility ratios. The component can also be used as the main computational engine for stand-alone section design software. The component can be further extended to handle the retrofitting and strengthening of cross-sections, shear and torsional response, determination of fire-damage parameters, etc.

• Smart Structures and Systems
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• 제26권2호
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• pp.253-262
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• 2020

In this paper, a new higher order shear deformation model is developed for static analysis of functionally graded beams with considering porosities that may possibly occur inside the functionally graded materials (FGMs) during their fabrication. The model account for higher-order variation of transverse shear strain through the depth of the beam and satisfies the zero traction boundary conditions on the surfaces of the beam without using shear correction factors. The present work aims to study the effect of the distribution forms of porosity on the bending of simply supported FG beam. Based on the present higher-order shear deformation model, the equations of motion are derived by the principle of virtual works. Navier type solution method was used to obtain displacement and stresses, and the numerical results are compared with those available in the literature. A comprehensive parametric study is carried out to assess the effects of volume fraction index, porosity fraction index, and geometry on the bending of imperfect FG beams. It can be concluded that the proposed model is simple and precise for the resolution of the behavior of flexural FGM beams while taking into account the shape of distribution of the porosity.

• 대한토목학회논문집
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• 제12권2호
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• pp.11-20
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• 1992

지진이나 바람과 같은 횡방향 하중이 가해졌을 때, 일반적으로 수직한 촉에 대해서만 대칭인 단면을 갖는 교량의 주형에는 횡방향 휨에 결합된 비틂이 유발되어 특히 사장교의 케이블등에는 예상치 못했던 추가응력이 유발될 수 있다. 이러한 거동은 일반적인 뼈대요소로는 해석할 수 없으므로, 임의의 단면 형상을 갖는 기하학적 비선형 3차원 뼈대요소를 사용하여야 한다. 본 연구에서 사용한 뼈대요소의 이론적인 배경과 검증은 이전에 발표된 논문에 수록되어 있다. 본 논문에서는 주형단면의 비대칭성을 고려한 지진해석을 수행하여 휨-비틂 결합작용에 의한 거동을 연구한다.