• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1995년도 봄 학술발표회 논문집
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• pp.245-250
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• 1995

Steel effects on creep deformation of prestressed concrete structues are investigated by a parametric study. Prestressed steel ratio, Prestressed steel distribution, initial flexural stress gradient, and modular ratio are selected as parameters. Sectional analysis for the beam section of parameter combination is performed to find curvatrue change due to creep. Based on the investigation, long-term curvature formulas from regression analysis are proposed. Application of the furmulas to simply supported prostressed concrete beam shows the effect of steel on deflection.

• 한국재료학회지
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• 제29권6호
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• pp.343-348
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• 2019

Structural and mechanical effects of the dynamical precipitation in two copper-base alloys have been investigated over a wide range of deformation temperatures. Basing upon the information gained during the experiment, also some general conclusion may be formulated. A one concerns the nature of dynamic precipitation(DP). Under this term it is commonly understood decomposition of a supersaturated solid solution during plastic straining. The process may, however, proceed in two different ways. It may be a homogeneous one from the point of view of distribution and morphological aspect of particles or it may lead to substantial difference in shape, size and particles distribution. The effect is controlled by the mode of deformation. Hence it seems to be reasonable to distinguish DP during homogeneous deformation from that which takes place in heterogeneously deformed alloy. In the first case the process can be analyzed solely in terms of particle-dislocation-particle interrelation. Much more complex problem we are facing in heterogeneously deforming alloy. Deformation bands and specific arrangement of dislocations in form of pile-ups at grain boundaries generate additional driving force and additional nucleation sites for precipitation. Along with heterogeneous precipitation, there is a homogeneous precipitation in areas between bands of coarse slip which also deform but at much smaller rate. This form of decomposition is responsible for a specially high hardening rate during high temperature straining and for thermally stable product of the decomposition of alloy.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.107-112
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• 2001

The IPC(Incremental Prestressed Concrete) which is gradually introducing the tensile force by tendons has been recently developed for reducing the effective depth of PSC bridges. As well known, concrete experiences long-term deformation such as creep and drying shrinkage, and the prediction of the long-term behavior of concrete bridges is essential for both safety and serviceability aspects. This paper was analysed the long-term behavior of a continuous 2-span IPC girder bridge taking into consideration of creep, drying shrinkage and the time of tensile force introduction. As results, the shrinkage of slab concrete increases the negative moment at interior support, and the The difference of concrete ages between slab and girder increases the camber. The effect of initial tensile force is larger than the effect of secondary tensile force in the tendons.

• 한국구조물진단유지관리공학회 논문집
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• 제2권3호
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• pp.194-204
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• 1998

This study was performed to suggest the proper maintenance method for the deteriorated gerber type PC box girder bridge by using the long term displacement monitoring data. For this study, the monitoring system which can measure the long term displacement and the concrete surface temperature was designed and operated. From the measurement and structural analysis results, the cause of the permanent deformation which the bridge has already was estimated, and based on this result, the allowable permanent displacement value at the hinge was suggested. From this study, it was known that the long term monitoring system can be applied to the active maintenance of the deteriorated bridge and the suggested allowable permanent displacement could be used for the maintenance of the bridge.

• 소성∙가공
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• 제14권5호
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• pp.466-472
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• 2005

Inelastic deformation behavior of metals and alloys is considered rate dependent. Uniaxial ratcheting experiments performed by Ruggles and Krempl, and Hassan and Kyriakides exhibited that higher mean stress for a fixed stress amplitude resulted in higher ratchet strain within a rate independent framework and higher stress rate resulted in lower ratchet strain, respectively. These phenomena are qualitatively investigated by numerical experiments through unified viscoplasticity theory. The theory does not separate rate-independent plasticity and rate-dependent creep, and thus uses only one inelastic strain to describe inelastic deformation processes with the concept of the yield surface. The growth law for the kinematic stress, which is a tensor valued state variable of the constitutive equations, is modified to predict the linear evolution of long-term ratchet strain.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1994년도 추계학술대회 논문집
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• pp.778-783
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• 1994

In operating automated manufacturing system, the long term stability and reliability of NC machine tools become most critical issues. Especially the machining accuracy is dominated by the thermal deformation of machine tools which remains still unsolved and causes troubles in manufacturing operations. Although researches have been carried out on the thermal behavior of a machine tools to minimize or control the thermal deformation of machine tools, the computer models for an analysis of the thermal behacior in machine tools has yet to appear in the open literature. The object of the paper is to present a method of modeling the thermal behavior of a machine tool. The method will make use of finite elements ad be capable of modeling whole machine structures as well as of heat generation processes in the kinematic system components. And temperature distributions and thermal deformations of a CNC lathe are analyzed using the finite element method and are compared with those measured in practice.

• 한국공간구조학회:학술대회논문집
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• 한국공간구조학회 2006년도 춘계 학술발표회 논문집 제3권1호(통권3호)
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• pp.214-223
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• 2006

Membrane structures, a kind of lightweight soft structural system, are used for spatial structures. The material property of the membrane has strong axial stiffness, but little bending stiffness. The design procedure of membrane structures are needed to do shape finding, stress-deformation analysis and cutting pattern generation. In shape finding, membrane structures are unstable structures initially. These soft structures need to be introduced initial stresses because of its initial unstable state, and happen large deformation phenomenon. Therefore, in this study, to find the structural shape after large deformation caused by initial stress, we need the shape analysis considering geometric nonlinear term. And we investigate the evaluation of shape analysis technique's convergence and efficiency according to the control method

• Advanced Composite Materials
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• 제17권3호
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• pp.247-258
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• 2008

This paper is concerned with the long-term performance of geo-textile (GT) composites in terms of creep deformation and frictional properties. Composites of PVA GT and HDPE GM were made to investigate the advanced properties of long-term performance related to waste landfill applications. The same experiments were also performed for typical polypropylene and polyester GT and compared to PVA GT/HDPE GM composites. We also develop high performance GT composites with GM by using PVA GT, which is capable of improving the frictional properties and thus enhances long-term performance of GT composites. Experimental study reveals that the friction coefficient of GT composites is relatively large compared with those of polyester and polypropylene non-woven GT as long as the friction media has similar size to the particles of domestic standard earth. In addition, the geo-composites bonded with geo-grid by a chemical process were investigated experimentally in terms of strain evaluation and creep response values. Geo-grid plays an important role as a reinforcing material. Three kinds of geo-grid were prepared as strong yarn polyester and they were woven type, non-woven type, and wrap knitted type. The sample geo-grids were then coated with PVC. The rib tensile strength tests were conducted to evaluate geo-grid products in terms of tensile strength with regard to single rib. The test was performed according to GRI-GGI. It was concluded again from the experiments that the tensile and creep strains of the geo-grid showed such stable values that the geo-grid prepared in this study could protect geo-textile partially in practical structures.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.697-700
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• 2008

본 논문은 유변학을 이용한 합리적인 크리프 예측 모델의 개발을 목표로 한다. 유변학은 응력에 의해 물질에 변형이 유발되었을 때, 변형과 응력 사이의 관계를 규명하는 학문으로 콘크리트와 같은 다공성의 점탄성 구조체의 변형 규명에 효과적이다. 본 논문에서 제안된 모델은 시간 의존성 여부와 발생 메커니즘에 따라 탄성거동, 장기크리프, 시간 의존적 단기크리프 그리고 시간 독립적 단기크리프로 나뉘며, 이와 같은 현상의 분류는 실제 실험값의 시간 경과에 따른 변형 양상을 근거로 한 것이다. 각 부분의 계수 추정 과정에서는 이론(미세프리스트레스 고체화 이론, Microprestress-solidification theory) 및 설계기준(CEB-FIP MC R99)을 최대한 활용하여 모델의 합리성의 높일 수 있도록 하였으며, 부득이하게 이론적 접근이 어려운 경우에는 제한적으로 수치적 접근을 시도하였다. 끝으로 수립된 모델을 실제 실험 데이터에 적용한 결과를 기존의 기준식 및 이론식의 적용 결과와 비교 평가 하였다.

• 한국섬유공학회:학술대회논문집
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• 한국섬유공학회 2007년도 학술발표회 논문집
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• pp.401-402
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• 2007

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