• 한국농공학회논문집
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• 제46권2호
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• pp.93-103
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• 2004

In trench excavation, essential factor of earth-retaining temporary work structure should be easy taking to pieces and movement, and dead weight must be less. This paper studies about the light weight material and application as earth-retaining structure to prevent the slope failure of sand soil ground caused by the variation of groundwater level in trench excavation. That is, light weight earth-retaining structural is proposed and a simulation with FEM on application of proposed structural in sandy soil is presented. The results are summarized as follows; (1) The study proposed FRP H-shaped pannel for the light weight member, and also presented estimation method about stability. (2) Mechanical property (bending moment, shear force, axial force, displacement) were changed according to groundwater level, but these values had been within enough safety rate and allowable stress. Therefore, proposed light weight pannel with FRP is available for bracing structure in trench excavation.

• Computers and Concrete
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• 제21권5호
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• pp.495-504
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• 2018

The possibility of earthquakes in vulnerable regions indicates that efficient technique is required for seismic protection of buildings. During the recent decades, the concept is moving towards the insertion of base isolation on seismic prone buildings. So, investigation of structural behavior is a burning topic for buildings to be isolated in base level by bearing device. This study deals with the incorporation of base isolation system and focuses the changes of structural responses for different types of Lead Rubber Bearing (LRB) isolators. A number of sixteen model buildings have been simulated selecting twelve types of bearing systems as well as conventional fixed-base (FB) scheme. The superstructures of the high-rise buildings are represented by finite element assemblage adopting multi-degree of freedoms. Static and dynamic analyses are carried out for FB and base isolated (BI) buildings. The dynamic analysis in finite element package has been performed by the nonlinear time history analysis (THA) based on the site-specific seismic excitation and compared employing eminent earthquakes. The influence of the model type and the alteration in superstructure behavior of the isolated buildings have been duly assessed. The results of the 3D multistory structures show that the lateral forces, displacement, inertia and story accelerations of the superstructure of the seismic prone buildings are significantly reduced due to bearing insertion. The nonlinear dynamic analysis shows 12 to 40% lessening in base shear when LRB is incorporated leading to substantial allowance of horizontal displacement. It is revealed that the LRB isolators might be potential options to diminish the respective floor accelerations, inertia, displacements and base shear whatever the condition coincides. The isolators with lower force intercept but higher isolation period is found to be better for decreasing base shear, floor acceleration and inertia force leading to reduction of structural and non-structural damage. However, LRB with lower isolator period seems to be more effective in dropping displacement at bearing interface aimed at reducing horizontal shift of building structure.

• 한국산학기술학회논문지
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• 제13권11호
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• pp.5566-5571
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• 2012

블록전단파괴는 인장부재의 한계상태에 해당하는 것으로 강구조물의 인장부재 또는 연결부 설계 시 주의를 요한다. 많은 연구 결과와 설계기준에서는 블록전단파괴에 대한 볼트 이음 방식의 영향을 고려하지 않고 있다. 본 연구에서는 볼트 이음 방식(지압이음과 마찰이음)이 블록전단파괴의 파괴모드와 파괴강도에 미치는 영향을 분석하고자 인장실험을 실시하였다. 실험결과의 분석으로부터 설계기준, 지압이음, 마찰이음에 따른 파괴모드의 차이를 제시하였으며 마찰이음에서 발생되는 마찰력으로 인한 블록전단파괴강도의 변화를 고찰하였다.

• 한국소음진동공학회논문집
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• 제26권4호
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• pp.443-448
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• 2016

A novel Permanent Magnet based Magneto Rheological (PM-MR) damper is proposed in this paper. The principle of proposed MR damper is achieved by designing a linearly varying magnetization area with-respect to the movable permanent magnetic based piston setup. Nowadays, commercially available MR damper uses electromagnetic coils for generating the variable magnetic fields corresponding to the variable damping force. The amount of magnetic field produced by the electromagnetic coils are depends on the biasing current of voltage source. The key enabling concept of the proposed MR damper is to replace the electromagnetic coils and the voltage sources by utilizing the variable area based permanent magnetic piston setup. The proposed unique design structure of PM-MR damper has an increasing shear mode damping force with the piston movement in both jounce and rebound motion. In this research, analytical model of the proposed structure is derived and the structural design of proposed concept is verified using numerical CAD tool. As a result, the damping force is increase when piston movement in both jounce and rebound motion.

• 한국정밀공학회지
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• 제32권5호
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• pp.423-429
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• 2015

Linear motion (LM) ball guides have good accuracy and high efficiency. They are widely applied for precision machinery such as machine tools, semiconductor fabrication machines and robots. However, friction force incurs heat between the balls and grooves. Thermal expansion due to the heat deteriorates stiffness and accuracy of the LM ball guides. For accurate estimation of stiffness and accuracy during the linear motion, friction models of LM ball guides are required. To formulate accurate frictional models of LM ball guides according to load and preload conditions, rolling and viscous frictional analyses have been performed in this paper. Contact loads between balls and grooves are derived from Hertzian contact analysis. Contact angle variation is incorporated for the precision modeling. Viscous friction model is formulated from the shear stress of lubricant and the contact area between balls and grooves. Experiments confirm validity of the developed friction model for various external load and feedrate conditions.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1999년도 춘계학술대회 논문집
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• pp.128-133
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• 1999

In recent years, LSI devices have become more powerful and lower-priced, caused by a development of various wafer materials and an increase in the diameter of wafers. On the other hand, these have created some serious problems in manufacturing of wafers because materials used as semiconductor substrate are very brittle. In view of this fact, there are some trials to apply shear-mode(or ductile-mode) grinding for efficient manufacturing of semiconductor wafers instead of conventional lapping process. In fact grinding process that has not only more excellent degree of accuracy but also more adaptable to fully automated manufacturing than lapping, is already used in Si machining field. This paper described the elementary studies to establish the grinding technology of wafers. First, we investigated the variation of grinding force and the transition of grinding mode as various grinding conditions. Then, it was inspected that the change of grinding force affected the integrity such as the topography and the roughness of ground surfaces, and led to the chemical defects generation and distribution in damaged layer. The degree of defects was estimated by FT-IR(Fourier Transformed Infrared) Spectroscopy and Auger Electron Spectroscopy

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.181-184
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• 2008

단순지지된 콘크리트 보 부재의 경우 전단 경간에서 내부 모멘트 팔길이가 변화하는 아치 현상이 발생하게 된다. 최근 이러한 점을 고려한 전단해석모델이 개발되었으나 집중 하중에 대해서만 적용할 수 있어 등분포 하중과 같은 보다 일반적인 하중에 대해서는 적용할 수 없는 실정이다. 따라서 본 연구에서는 일반적인 분포하중에 대해 내부 모멘트 팔길이의 변화에 대한 기본 식을 유도하고, 특히 등분포하중이 작용할 경우 아치 작용에 의한 전단력의 비율을 산정하는데 있어 이용되는 전단변형적합 조건을 도출하였다. 제안된 해석 모델을 이용하여 기존 연구자가 수행했던 RC보를 해석하여 그 경향을 분석한 결과, 등분포하중을 받는 RC보의 경간에 따른 전단변형률의 변화를 어느 정도 잘 묘사하는 것으로 나타났다. 하지만, 전단변형률이 작게 예측되는 것으로 보아 아치 작용에 의한 전단력의 영향을 추가적으로 고려해야 할 것으로 사료된다.

• 한국전산구조공학회논문집
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• 제33권5호
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• pp.339-349
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• 2020

외피 구조로서의 강박스와 내부의 철근콘크리트 슬래브로 구성되는 양개형 방폭문은 방호 및 대피 구조물의 출입구에 설치되는 구조체이다. 방폭문과 그 후면의 벽체 사이에는 일정의 설치 간격이 존재하게 되는데, 이로 인한 지지조건 및 구조거동의 변화는 방폭 해석 및 설계에 적절히 고려되지 않고 있다. 본 연구에서는 설치 간격에 의한 지지조건 및 폭압의 변화에 따른 방폭문의 구조응답 및 파괴거동을 유한요소 해석방법으로 비교·분석하였다. 해석 결과에 따르면, 설치 간격 및 폭압의 변화는 방폭문의 최대 처짐 및 영구 처짐과 같은 처짐 거동에 영향을 미치며, 설치 간격이 크고 작음에 따라 방폭문과 벽체의 충돌 접촉 정도 및 이에 의한 충격력이 크게 변화하는 것으로 나타났다. 또한, 방폭문에 작용하는 이와 같은 충격력의 변화는 슬래브의 전단파괴와 같은 파괴거동에 영향을 미치는 주요 요인으로 분석되었다. 설치간격 10mm 미만의 방폭문은 전단파괴에 취약해지고, 15mm 내외 수준인 경우가 휨성능 발현에 비교적 더 적합한 것으로 나타났다. 본 연구에서는 설치 간격 및 폭압과 같이 기본적인 조건의 변화에 한해서 비교 해석을 하였다. 향후, 부재 재원 및 강도변화, 전단설계 여부 등 다양한 변수에 따른 구조거동 변화에 대해 실험적 및 해석적 연구가 필요하다.

• 한국구조물진단유지관리공학회 논문집
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• 제21권6호
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• pp.106-112
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• 2017

본 연구에서는 콘크리트 시공줄눈 면의 전단마찰 내력을 합리적으로 평가하기 위하여 콘크리트 소성론의 상계치 이론에 기반한 수학적 모델을 제시하였다. 전단면에서 횡보강근의 전단전달에 대한 과대평가를 피하기 위하여 시공줄눈 면에서의 하중전달에 대한 스트럿-타이 모델에서 콘크리트 할렬 및 압괴의 한계상태로부터 전단마찰 내력의 상한값을 유도하였다. 제시된 모델은 시공줄눈 면에서 콘크리트 점착력과 마찰계수를 거친 면의 경우 각각 $0.27(f_{ck})^{0.65}$와 0.95를, 부드러운 면의 경우 각각 $0.11(f_{ck})^{0.65}$와 0.64로 결정하였는데, 여기서 $f_{ck}$는 콘크리트 압축강도이다. 직접전단에 대한 기존 문헌으로부터 수집한 146 실험데이터와의 비교로부터, 제시된 모델은 AASHTO 및 fib 2010 식에 비해 예측 값과 실험 값들의 비의 표준편차 및 변동계수에 대해 더 낮은 값을 보였다. 특히 전단마찰 내력 평가에서 기준식들의 상당한 과소평가 경향과 달리 제시된 모델은 실험결과와 잘 예측하였다.

• 드라이브 ㆍ 컨트롤
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• 제20권4호
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• pp.115-122
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• 2023

This study utilized a discrete element method (DEM) simulation, as one of the virtual field trials, to predict the impact of tillage depth on the rotary blade shaft during rotavator tilling. The virtual field for the simulation was generated according to soil properties observed in an actual field. Following the generation of particles for the virtual field, a sequence of calibration steps followed to align the mechanical properties more closely with those of real soil. Calibration was conducted with a focus on bulk density and shear torque, resulting in calibration errors of just 0.02% for bulk density and 0.52% for shear torque. The prediction of the load on a rotary tiller's blade shaft involved a three-pronged approach, considering shaft torque, draft force, and vertical force. In terms of shaft torque, the values exhibited significant increases of 42.34% and 36.91% for every 5-centimeter increment in tillage depth. Similarly, the vertical force saw substantial growth by 40.41% and 36.08% for every 5-centimeter increment. In contrast, the variation in draft force based on tillage depth was comparatively lower at 18.49% and 0.96%, indicating that the effect of tillage depth on draft force was less pronounced than its impact on shaft torque and vertical force. From a perspective of agricultural machinery research, this study provides valuable insights into the DEM soil modeling process, accounting for changes in soil properties with varying tillage depths. These findings are expected to be instrumental in future agricultural machinery design studies.