• 콘크리트학회논문집
• /
• 제22권2호
• /
• pp.187-197
• /
• 2010

본 연구에서는 성능기반설계를 위한 기둥의 주철근비에 대하여 연구하였다. 일률적인 현행 설계기준과 달리, 다양한 기둥의 설계변수를 고려하여 기둥의 주철근을 정의하였다. 기둥의 최소철근비는 다음의 2 가지 사항을 고려하여 평가하였다; 1) 사용상태에서 콘크리트의 장기변형에 의한 철근의 조기항복 방지; 2) 내진설계시 기둥의 연성능력을 확보하기 위해 균열모멘트 이상의 극한휨강도 확보. 배근상태와 하중조건에 따른 기둥의 유효강성도 강도설계시 추가적으로 고려하였으며, 3 가지 사항을 고려한 주철근비 결정방법을 제안하였다. 제안된 방법은 설계예제에 적용되었다.

• 한국기계가공학회지
• /
• 제19권7호
• /
• pp.67-73
• /
• 2020

Shrinkage is inevitable in the curing of resins during the nanoimprint process. The degree of shrinkage that occurs as the resin transforms from a viscous liquid to solid differs depending on the type of resin. However, if the cured material is repeatedly cured using the same material, constant shrinkage can be confirmed. In this study, the pattern of change was observed by repeatedly performing the nanoimprint process using a resin with a constant shrinkage rate. The observed pattern for the change of shape was made using a triangular pyramid-shaped aluminum master mold and a flexible replica mold made from the master. Shrinkage that results from the nanoimprint process occurs linearly in the longitudinal direction of the pattern and can be predicted by simple calculations. The change of the pattern due to shrinkage occurred as expected. If the shrinkage rate remains constant, various patterns can be manufactured with high accuracy by correcting these changes before producing a specific shape. This study confirms that the pattern of the desired angle can be obtained by performing the repeated imprint without having to manufacture a master mold.

• International Journal of Korean Welding Society
• /
• 제5권1호
• /
• pp.44-52
• /
• 2005

The purpose of this study is to establish a design tool for the shrinkage margin of a deckhouse caused by welding and flame straightening. In order to do it, the effects of heat intensity and internal/external restraint condition on the shrinkage of the simple weldments were investigated, in order to identity the principal factors controlling shrinkage caused by welding process and flame straightening. Based on the results, predictive equations for longitudinal and transverse shrinkage at the welded structure were formulated as the function of heat intensity and in-plane rigidity. These equations were verified by comparing predicted results with the measured results at a panel structure of deckhouse.

• Advances in concrete construction
• /
• 제9권3호
• /
• pp.289-299
• /
• 2020

To investigate the long-term behavior of eccentrically loaded RC columns, which are more realistic in practice than concentrically loaded RC columns, long-term eccentric loading tests were conducted for 10 RC columns. Test parameters included concrete compressive strength, reinforcement ratio, bar yield strength, eccentricity ratio, slenderness ratio, and loading pattern. Test results showed that the strain and curvature of the columns increased with time, and concrete forces were gradually transferred to longitudinal bars due to the creep and shrinkage of concrete. The long-term behavior of the columns varied with the test parameters, and long-term effects were more pronounced in the case of using the lower strength concrete, lower strength steel, lower bar ratio, fewer loading-step, higher eccentricity ratio, and higher slenderness ratio. However, in all the columns, no longitudinal bars were yielded under service loads at the final measuring day. Meanwhile, the numerical analysis modeling using the ultimate creep coefficient and ultimate shrinkage strain measured from cylinder tests gave quite good predictions for the behavior of the columns.

• Structural Engineering and Mechanics
• /
• 제62권6호
• /
• pp.725-737
• /
• 2017

An analytical method considering axial equilibrium is proposed for the short- and long-term analyses of shear lag effect in reinforced concrete (RC) box girders. The axial equilibrium of box girders is taken into account by using an additional generalized displacement, referred to as the longitudinal displacement of the web. Three independent shear lag functions are introduced to describe different shear lag intensities of the top, bottom, and cantilever plates. The time-dependent material properties of the concrete are simulated by the age-adjusted effective modulus method (AEMM), while the reinforcement is assumed to behave in a linear-elastic fashion. The differential equations are derived based on the longitudinal displacement of the web, the vertical displacement of the cross section, and the shear lag functions of the flanges. The time-dependent expressions of the generalized displacements are then deduced for box girders subjected to uniformly distributed loads. The accuracy of the proposed method is validated against the finite element results regarding the short- and long-term responses of a simply-supported RC box girder. Furthermore, creep analyses considering and neglecting shrinkage are performed to quantify the time effects on the long-term behavior of a continuous RC box girder. The results show that the proposed method can well evaluate both the short- and long-term behavior of box girders, and that concrete shrinkage has a considerable impact on the concrete stresses and internal forces, while concrete creep can remarkably affect the long-term deflections.

• 한국해양공학회지
• /
• 제20권3호
• /
• pp.103-108
• /
• 2006

It has been well appreciated that reducing weld-induced deformation as law as possible is important during fabrication for a more efficient production of blocks. The weld-induced deformation is more serious in thin plates than in thick plates because heat affect zone of thin plates is wider than that of thick plates and in addition internal and external constraints much more influence upon weld-induced deformation of thin plates. This paper deals with the application of the mechanical tensioning method to butt weld of thin plates to reduce the weld-induced deformation. In order to investigate the quantitative effect of tensioning method upon the reduction of angular deformation and shrinkage in longitudinal and transverse direction of weld line, butt welding test have been carried out for several thin plate specimens with varying plate thickness and magnitude of tensile load. From the present experimental study, it has been found that the tensioning method is very effective on reduction of weld-induced residual stress as well as weld-induced deformation.

• 대한조선학회논문집
• /
• 제44권5호
• /
• pp.496-503
• /
• 2007

Although weld-induced deformation is inevitable in shipbuilding, it is important to reduce it as low as possible during fabrication for a more efficient production of ships' blocks. The weld-induced deformation is more serious in thin plates than in thick plates because heat affect zone of thin plates is wider than that of thick plates, and in addition internal and external constraints much more influence upon weld-induced deformation of thin plates. This paper deals with the application of the mechanical tensioning method to butt weld of thin plates to reduce the transverse and longitudinal deformation. in order to investigate the quantitative effect of tensioning method upon the reduction of angular deformation and shrinkage in longitudinal and transverse direction of weld line, butt welding test have been carried out for several thin plate specimens with varying plate thickness and magnitude of tensile load. Numerical simulation has been also carried out to compare the weld-induced deformation and residual stress. From the present study, it has been found that the tensioning method is very effective on reduction of weld-induced residual stress as well as weld-induced deformation.

• 한국구조물진단유지관리공학회 논문집
• /
• 제20권5호
• /
• pp.102-108
• /
• 2016

이 연구의 목적은 개착식 전력구 콘크리트에 발생하는 부등건조수축에 의한 균열특성을 파악하고, 수축저감제 혼입에 따른 건조수축균열특성을 분석하는데 있다. 따라서 이 연구에서는 전력구 박스형 콘크리트 구조물의 부등건조수축에 의한 균열특성을 파악하기 위하여 세 가지 주요영향인자를 고려한 수치해석과 수치해석을 한 결과와 실제 전력구 타설을 하여 측정한 차이를 확인해 보았다. 본 연구로부터 건조 수축 시험체에 대한 건조수축량을 산정에 대한 해석 기법을 개발하였으며, 실제 전력구 타설 실험을 통해 종방향 및 횡방향 균열발생 가능성을 입증 하였다. 전력구 실증시험체 건조수축량 수치해석 결과, 균열저감 콘크리트 배합의 경우 종방향 및 횡방향 응력에 있어 일반배합에 비해 40~50%정도의 현저한 감소를 보이며, 이에 따라 균열저감 콘크리트를 전력구에 적용하였을 경우 현저한 균열감소 효과를 보일 것으로 예측된다.

• Journal of Welding and Joining
• /
• 제25권1호
• /
• pp.42-48
• /
• 2007

For high performance and structural stability, application of high strength steel has continuously increased. However, the change of the base metal gives rise to problems with the accuracy management of the welded structure. It is attributed to the martensite phase transformation of the high strength low alloy steel weldment. The purpose of this study is to establish the predictive equation of transverse shrinkage and residual stress for the HY-100 weldment. In order to do it, high speed quenching dilatometer tests were performed to define a coefficient of thermal expansion(CTE) at the heating and cooling stage of HY-100 with various cooling rates. Uncoupled thermal-mechanical finite element(FE) models with CTE were proposed to evaluate the effect of the martensite phase transformation on transverse shrinkage and residual stresses at the weldment. FEA results were verified by comparing with experimental results. Based on the results of extensive FEA and experiments, the predictive equation of transverse shrinkage and longitudinal shrinkage force at the HY-100 weldment were formulated as the function of welding heat input/in-plane rigidity and welding heat input respectively.

• Journal of the Korean Wood Science and Technology
• /
• 제43권6호
• /
• pp.746-756
• /
• 2015

본 논문에서는 목재 수축률에 관한 1976-2015년도에 발표된 목재공학회지 논문을 정리하였다. 국내산 낙엽송(Larix kaempferi) 수축률을 측정한 연구자들간에 접선방향 수축률은 4.21%-9.79%, 방사방향 수축률은 2.09%-4.67%, 섬유방향 수축률은 0.17%-0.33%로 접선방향 2.3배, 방사방향 2.2배, 섬유방향 1.9배로 연구자들마다 측정 값에 차이가 나타났다. 소나무(Pinus densiflora) 시편 크기가 $20{\times}20{\times}20mm$에서 $100{\times}100{\times}100mm$로 증가함에 따라 접선방향, 방사방향, 부피수축률은 2.61%, 1.32%, 0.80% 감소하였다. 아피통(Dipterocarpus grandiflorus)을 밀폐건조, 오븐건조, 실온건조 하였을 때 부피수축률은 31.6%, 26.5%, 21.0%로 건조방법에 따라 5.5%-10.6% 차이가 나타났으며 건조온도가 $115^{\circ}C$, $120^{\circ}C$, $125^{\circ}C$로 증가함에 따라 낙엽송의 수축률은 일정한 증가, 감소 경향이 보이지 않았다. $20mm^3$ 크기의 삼나무(Cryptomeria japonica) 시편을 한국산업규격(KS F 2203, 2004)에서 제시하는 정밀도 0.01 mm의 길이측정도구로 수축률을 측정하였을 때, 방사, 섬유방향 수축률 측정오차는 1.97%, 35.7%로 크게 나타났다. 목재의 수축률은 시편 크기, 건조방법, 측정방법에 영향을 받는 것으로 나타났다.