• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2009년도 춘계 학술대회 제21권1호
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• pp.103-104
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• 2009

본 연구는 지속하중을 받은 철근콘크리트보의 처짐 특성을 파악하고 하중이 제거된 후의 변형 회복특성을 파악하였다. 또한 잔존강도를 파악하기위해 정적 재하실험을 실시하였으며 지속하중을 받지 않은 RC보와 비교를 하였다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1997년도 봄 학술발표회 논문집
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• pp.308-314
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• 1997

Shrinkage and creep are the fundamental properties of concrete. These long term deformations can be seen as bothersome(increased deflection) or can be seen as reduction of compressive stress of prestressed concrete. Steel fibers advance the mechanical properties of concrete:tensile strength, ductility, flexural strength, fracture toughness, and post-cracking resistance, etc...Silica fume is pozzolanic material which combines with hydrated lime to generate silicate materials which increase the compressive strength and reduce somewhat the creep of concrete. This paper is the result of the long-term deformation by silica fume and steel fibers with varying percentages.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
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• pp.303-308
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• 2002

A governing differential equation (GDE) of PSC flexural member with constant eccentricity considering the long-term losses including concrete creep, shrinkage, and PS steel relaxation is derived based on the two approaches. The first approach utilizes the force and moment equilibrium equations derived based on the geometry of strains of the uniform and curvature strains while the second one utilizes the principle of minimum total potential energy formulation. The identity of the two GDE's is verified by comparing the coefficients consisting of the GDE's. The boundary conditions resulting from the functional analysis of the variational calculus are investigated. Rayleigh-Ritz method provides a way to get the explicit form of the continuous deflection function in which the total potential energy is minimized with respect to the unknown coefficients consisting of the trial functions. As a closure, the analytically calculated results are compared with the experiments and show good agreements.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.427-432
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• 2003

An analytical method to predict the flexural behavior of composite girder is presented in which the early-age properties of concrete are specified including maturing of elastic modulus, creep and shrinkage. The time dependent constitutive relation accounting for the early-age concrete properties is derived in an incremental format by expanding the total form of stress-strain relation by the first order Taylor series with respect to the reference time. The sectional analysis calculates the axial and curvature strains based on the force and moment equilibriums. The deflection curve of the box girder approximated by the quadratic polynomial function is calculated by applying to the proper boundary conditions in the consecutive segments. Numerical applications are made for the 3-span double composite steel box girders which is a composite bridge girder filled with concrete at the bottom of the steel box in the negative moment region. The one dimensional finite element analysis results are compared with those of the three dimensional finite element analysis and the analytical method based on the sectional analysis. Close agreement is observed among the three methods.

• 상하수도학회지
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• 제34권2호
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• pp.149-159
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• 2020

Cured-in-place-pipe(CIPP) is the most adopted trenchless application for sewer rehabilitation to extend the life of the existing sewer without compromising both direct construction and indirect social costs especially applied in the congested urban area. This technology is globally and domestically known to be the most suitable for partial and full deteriorated pipe structure rehabilitation in a sewer system. The typical design of CIPP requires a significant thickness of lining to support loading causing sewage flow interruption and increasing material cost. This paper presents development of a high strength glass fiber composite lining material for the CIPP application and structural test results. The test results exhibit that the new glass fiber composite lining material has 12 times of flexural strength, 6.2 times of flexural modulus, and 0.5 Creep Retention Factor. These test results can reduce lining design thickness 35% at minimum. Even though taking into consideration extra materials such as outer and inner films for actual field applications, the structural capacity of the composite material significantly increases and it reduces 20 percent or more line thickness as compared to the conventional CIPP. We expect that the newly developed CIPP lining material lowers material costs and minimizes flow capacity reduction, and fully replaceable to the conventional CIPP lining materials.

• 콘크리트학회논문집
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• 제16권2호
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• pp.155-162
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• 2004

초기재령 콘크리트의 탄성계수 변화와 크리프 및 건조수축 현상을 고려하는 강 합성 거더의 시간종속적 처짐해석을 수행하였다. 초기재령 콘크리트의 탄성계수 발현과정을 고려한 구성관계는 총 응력-변형률 관계를 Taylor의 선형급수 확장을 이용하여 기준시간에 관하여 확장함으로써 시간종속적 증분형태로 유도하였다. 강 박스거더의 단면형상 변화 위치와 지점부를 기준하여 거더를 분할하고 분할된 구간에서 단면해석을 통해 곡률을 구하여 2차 다항식으로 가정한 처짐곡선에 경계조건을 적용함으로써 처짐곡선의 증분관계식을 유도하였다. 부모멘트 구간의 강 박스 하단에 콘크리트를 타설한 이중합성 박스거더의 초기재령 거동해석을 수행하였으며, 강 박스 하단의 콘크리트 타설두께가 거더의 거동에 주는 영향을 수치해석 결과를 통해 분석하였다. 끝으로, 보 요소를 이용한 유한요소해석 결과와 개발된 단면해석법을 이용한 해석 결과를 비교함으로써 정확성을 검증하였다.

• 콘크리트학회지
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• 제4권1호
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• pp.107-118
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• 1992

본 연구는 고강도 고내구성이면서 신뢰성이 높은 폴리머 함침 탄소섬유보강 시멘트복합에의 개발 응용을 위한 여러 가지 특성을 검토하기 위하여, 복합체는 PAN계 및 Pitch계 탄소섬유, 조강포틀랜드 시멘트, Silica Powder 및 폴리머 함침재를 사용하여 제조하였고, 배합조건별, 재령별, 그리고 양생조건별로 역학적특성, 동결융해저항성 및 장기변형특성에 관한 실험연구를 행하였다. 연구결과, CFRC의 Flow값은 CF혼입율 증가에 따라 거의 직선적으로 저하하였고, 폴리머 함침 CFRC의 압축 인장 휨강도는 CF혼입율 증대에 따라 오토클래브 양생 및 기건양생의 경우에 비하여 현저히 증대하였으며, 또한 월등히 높은 강도를 나타내었다. 그리고, 인자응력-변형관계 및 휨응력-처짐관계는 기건양생 및 오토클래브 양생의 경우 연성적인 비선형을 나타낸 데 비하여 폴리머함침의 경우는 거의 직선적 으로 변화하였고, 동결융해저항성, 건조수촉변형특성 및 내크리프 특성도 다른 양생 방법의 경우에 비하여 크게 개선됨을 확인하였다.

• Structural Engineering and Mechanics
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• 제39권6호
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• pp.833-847
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• 2011

We have developed a lightweight aggregate (LWA) concrete made by expanding fine sediments dredged from the Shihmen Reservoir (Taiwan) with high heat. In this study, the performance of the concrete and of prestressed concrete beams made of the sedimentary LWA were tested and compared with those made of normal-weight concrete (NC). The test results show that the lightweight concrete (LWAC) exhibited comparable time-dependent properties (i.e., compressive strength, elastic modulus, drying shrinkage, and creep) as compared with the NC samples. In addition, the LWAC beams exhibited a smaller percentage of prestress loss compared with the NC beams. Moreover, on average, the LWAC beams could resist loading up to 96% of that of the NC beams, and the experimental strengths were greater than the nominal strengths calculated by the ACI Code method. This investigation thus established that sedimentary LWA can be recommended for structural concrete applications.

• 한국농공학회지
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• 제31권2호
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• pp.125-134
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• 1989

This study was conducted to investigate the flexural behaviour of sandwich constructions with cement concrete core and polymer concrete facings. Six different cross-sectional shapes using epoxy based polymer concrete facings were investigated. Some of the results from the static tests are given including the load-deflection responses, load-strain relationships, ultimate moment, and mode of failure. From the. results the following conclusions can be made. 1. The various strengths of polymer concrete were very high compared to the strengths for portland cement concrete, while modulus of elasticity assumed an aspect of contrast. 2. The thickness of core and facing exerted a great influence on the deflection and ultimate strenght of polymer concrete sandwich constructions. 3. The variation shape of deflection and strain depend on loading were a very close approximation to the straight line. The ultimate strain of polymer concrete at the end of tensile side were ranged from 625x10-6 to 766x10-6 and these values increased in proportion to the decrease of thickness of core and facings. 4. The ultimate moments of polymer sandwich constructions were 3 to 4 times that of cement concrete constructions which was transformed same section. It should he noted that polymer concrete have an effect on the reinforcement of weak constructions. 5. Further tests are neede to investigate the shear strain of constructions, and thermal expansion, shrinkage and creep of cement and polymer concrete which were composite materials of sandwich constructions.

• 한국구조물진단유지관리공학회 논문집
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• 제6권2호
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• pp.183-194
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• 2002

A general procedure to evaluate the sensitivity of design variables to stresses and strains in PSC flexural members is proposed. To accomplish the purpose of this study, long-term losses including creep, shrinkage, and PS steel relaxation are formulated based on the equilibrium states of the deformed sectional geometry. Thereby, the formulation follows the basic steps which consider the fundamental formulas adopted by CEB-FIP, ACI, and KCI rather than the age adjusted effective modulus concept. Twenty-one design variable including the material and geometrical properties of concrete, nonprestressing steel and prestressing steel, and the geometry of the cross section are considered in the sensitivity analysis. The gradients of the stresses and strains needed for the sensitivity assessment are calculated in a closed format. The derived formulation is applied to the T-type section PSC beam with prestressing and nonprestressing steels for the sensitivity analysis. The analytically calculated sensitivity results are compared with those numerically calculated to ensure the validity of the proposed procedure.