• 콘크리트학회논문집
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• 제15권5호
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• pp.670-678
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• 2003

최근 폐기물 재활용에 대한 관심이 지대해 지기 시작하면서 많은 연구가 진행 중에 있다. 그 중 석탄회의 재활용 연구로는 시멘트 대체제로 및 고온소성법을 이용한 인공골재 개발등의 연구가 진행되었으나, 경제성에 있어서 부적합하였다. 본 연구에서는 비소성 고형화 기술을 사용하여 석탄회를 재활용한 건설재료의 토목, 건축 구조분야에 실용화하기 위한 기초자료를 제시하고자 한다. 재령에 따른 압축강도의 회귀분석을 하였고, 압축강도와 할선탄성계수를 구하였다. 그리고 Lineweaver와 Burk 방법을 적용하여 건조수축의 회귀분석을 실시하여 제안식을 도출하였다. 연구결과, 석탄회 경화체의 압축강도는 구조용 부재로 사용가능 한 수준이었으며 건조수축은 중용열 시멘트 모르터와 유사하였다. 또한, Bottom ash의 첨가가 석탄회 경화체 내부에서 골재의 역할을 수행하는 것으로 나타났다. 건조수축 양상을 중량감소율 측정결과와 종합하면 Bottom ash 치환율과 공시체 내부의 수분감소가 건조수축의 지배적인 요인임을 파악할 수 있었다. 또한 압축강도로부터 탄성계수를 추정하는 제안식은 본 연구에서의 압축강도 범위에서는 매우 높은 신뢰도를 보였다. 또한 Lineweaver와 Burk 방법으로 도출한 건조수축 추정 제안식도 매우 높은 신뢰도를 보였다.

• 대한소아치과학회지
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• 제35권1호
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• pp.18-29
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• 2008

본 연구는 복합레진 적층방법에 따른 복합레진의 수축양상을 스트레인 게이지를 이용하여 비교 평가하고자 하였다. 사용된 광중합기의 광원은 light-emitting diode(LED)와 plasma arc lamp(PAL)이었으며, 복합레진은 Filtek $Z350^{TM}$를 사용하였다. 교정 치료를 목적으로 발거된 60개의 소구치를 대상으로 하여, 교합면에 와동을 형성하고 일회충전법, 수평적층법, 사면적층법으로 나누어 복합레진을 충전하여 치면에 발생된 strain과 응력을 측정하였고, 법랑질 표면에 시편을 부착하여 동일한 적층방법으로 충전한 후 전단결합강도를 측정한 결과 다음과 같은 결론을 얻었다. 1. Strain의 변화를 살펴보면, LED와 PAL 조사군 모두 와동의 협설면에서는 주로 팽창이 일어났다가 시간이 지남에 따라 서서히 수축하는 양상을 보여주었다. 2. 와동의 근원심면에서는 팽창과 수축이 반복적으로 나타나면서 서서히 수축량이 증가하였다. 3. LED와 PAL 조사군 모두 적층방법 간의 응력 차이는 없었다(p>0.05). 4. LED 및 PAL 조사군 간의 응력 차이는 협면에서만 존재하였다(p<0.05). 5. 전단결합강도 측정 결과 LED 군에서는 사면적층법이 일회충전법, 수평적층법 보다 유의하게 낮게 나타났으나(p<0.05), PAL 광조사군에서는 유의차가 없었다(p>0.05). 6. 각 치면에 발생된 응력은 전단결합강도보다 낮았다(p<0.05).

• 비파괴검사학회지
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• 제36권2호
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• pp.121-129
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• 2016

As the lifespan of concrete structures increases, their load carrying capacity decreases owing to cyclic loads and long-term effects such as creep and shrinkage. For these reasons, there is a necessity for stress state monitoring of concrete members. Particularly, it is necessary to evaluate the concrete structures for behavioral changes by using a technique that can overcome the measuring limitations of usual ultrasonic nondestructive evaluation methods. This paper proposes the use of a nonlinear ultrasonic method, namely, nonlinear resonant ultrasonic spectroscopy (NRUS) for the measurement of nonlinearity parameters for stress monitoring. An experiment compared the use of NRUS method and a linear ultrasonic method, namely, ultrasonic pulse velocity (UPV) to study the effects of continuously increasing loads and cyclic loads on the nonlinearity parameter. Both NRUS and UPV methods found a similar direct relationship between load level and that parameter. The NRUS method showed a higher sensitivity to micro-structural changes of concrete than UPV method. Thus, the experiment confirms the possibility of using the nonlinear ultrasonic method for stress state monitoring of concrete members.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1993년도 봄 학술발표회 논문집
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• pp.142-147
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• 1993

In the reinforced concrete structure, as the height of building structure increases, the accurate estimation of differential column shortening is important factor in the structural design. In this study, the analysis of column shortening is applied to 36-story building structure to be built in time. As a result, it may found that, as the difference of compressive stress become larger, differential shortening effect due to creep and shrinkage are more signicant factor to structural designer.

• 한국세라믹학회지
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• 제29권11호
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• pp.843-850
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• 1992

The purpose of this study was to describe the heterogeneity effects on Intermediate/Final microstructure in isothermal liquid phase sintering. Several kinds of pore shapes were made by the different in the heterogeneity stress level during Intermediate/Final stage. Specimen with 48% green density especially showed that the local regions of a sintered compact were subject to more rapid shrinkage than the surroundings. This densification limiting factors generally inhibited sintering and made the large isolated crack-like pore in heterogeneous microstructures.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1989년도 가을 학술발표회 논문집
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• pp.73-76
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• 1989

A numerical procedure is developed to analyze the time-dependent behavior of prestressed concrete bridges constructed by the segmental cantilever method. The developed computer program accounts for the time-dependent properties of prestressed concrete materials due to the varing modulus of elasticity, creep and shrinkage of concrete and the stress relaxation of prestressing steel. It also accounts for the stiffness increase due to the presence of the steel reinforcements and the effects of the shear deformation of the prestressed concrete bridge girders. The program is applied to a multi-span continuous segmental prestressed concrete bridge to demonstrate its capabilities.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회 논문집(II)
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• pp.1001-1006
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• 2000

These should be constructed partially, because many prestressed concrete box girder bridges in situ have large cross section and long span. Therefore, accurate prediction of differences, both elapse time of each construction stage and exposure of atmosphere at each position of cross section, is very important. Though it is importance, engineers are apt to overlook it. This study predicted cracks due to shrinkage and stress concentration phenomenon by each construction stage and then, ascertained reduction of tensile stresses after applying retrofit scheme.

• 대한기계학회논문집A
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• 제26권2호
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• pp.340-348
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• 2002

Deformation analysis of injection molded articles whose geometry is considered as the assembly of thin flat plates has been conducted. For the in-mold analysis, thermo-viscoelastic stress calculation of thermo-rheologically simple amorphous polymer and in-mold deformation calculation considering the in-plane mold constraint have been done. Free volume theory has been used to represent the non-equilibrium density state during the fast cooling. At ejection, instantaneous deformation takes place due to the redistribution of in-mold residual stress. During out-of-mold cooling after ejection, thermoelastic model based on the effective temperature has been adopted for the calculation of out-of-mold deformation. In this study, emphasis is also made on the treatment with regard to lateral constraint types during molding process. Two typical mold geometries are used to test the numerical simulation modeling developed in this study.

• 한국해양공학회지
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• 제22권6호
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• pp.27-34
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• 2008

The temperature distribution in the weldment is not uniform because a weldment is locally heated. Thermal plastic deformation results from the local expansion and shrinkage by the heating and cooling of metal. Therefore, residual stresses and distortion occur in the weldment. In this study, we had conducted on the weld thermal cycle simulation that is supposed as the HAZ on SS400 steel and STS304 steel. The residual stresses that were obtained from the drawing and the weld thermal cycle simulation were estimated by X-ray diffraction. We also carried out ultrasonic test for the weld thermal cycle simulated specimens, and then conducted on nondestructive evaluation by the ultrasonic parameters obtained ultrasonic test. From the results, residual stresses of weld thermal cycle simulated specimens after the residual stress removal heat treatment are lower than that of the drawing.

• Computers and Concrete
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• 제33권3호
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• pp.309-324
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• 2024

Internal curing, a widely used method for mitigating early-age shrinkage in concrete, also offers notable advantages for concrete durability. This paper explores the potential of internal curing by partial replacement of sand with fine lightweight aggregate for enhancing the behavior of high-performance concrete at elevated temperatures. Such a technique may prove economical and safe for the construction of skyscrapers, where explosive spalling of high-performance concrete in fire is a potential hazard. To reach this aim, the physico-mechanical features of internally cured high-strength concrete specimens, including mass loss, compressive strength, strain at peak stress, modulus of elasticity, stress-strain curve, toughness, and flexural strength, were investigated under different temperature exposures; and to predict some of these mechanical properties, a number of equations were proposed. Based on the experimental results, an advanced stress-strain model was proposed for internally cured high-performance concrete at different temperature levels, the results of which agreed well with the test data. It was observed that the replacement of 10% of sand with pre-wetted fine lightweight expanded clay aggregate (LECA) not only did not reduce the compressive strength at ambient temperature, but also prevented explosive spalling and could retain 20% of its ambient compressive strength after heating up to 800℃. It was then concluded that internal curing is an excellent method to enhance the performance of high-strength concrete at elevated temperatures.