• Title/Summary/Keyword: 편심도

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Corneal Asphericity for Myopia in Korea (한국인 근시안의 각막 비구면성)

  • Kim, Hyo-Jin;Lee, Dong-Hee
    • Journal of Korean Ophthalmic Optics Society
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    • v.11 no.2
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    • pp.109-114
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    • 2006
  • We evaluated the contour using corneal asphericity of the myopic cornea in Korea and investigated the relationship between refractive error and other ocular dimensions in Korean myopia, including anterior chamber depth and asphericity. The monoocular asphericity value of 50 myopes with 4.83±2.38 D between early 20 age and early 30 age in adult was included. Cycloplegic refraction, corneal asphericity and anterior chamber depth using corneal topography were examined. The mean asphericity values were0.27±0.13 and the corneas of 96.0% were prolate ellipse. Refractive error was related to asphericity and anterior chamber depth among myopes. However, asphericity only were significant difference in high and low myopia group. Corneal configuration on the contact lens fits are discussed. We think that the longitudinal study for myopia and asphericity was required.

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Development of Mathematical Model to Predict Dynamic Muscle Force Based on EMG Signal (근전도로부터 동적 근력 산정을 위한 수학적 모델 개발)

  • 한정수;정구연;이태희;안재용
    • Journal of Biomedical Engineering Research
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    • v.20 no.3
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    • pp.315-321
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    • 1999
  • The purpose of this study is to develop a mathematical model for system identification in order to predIct muscle force based on eledromyographic signal. Therefore, a finding of the relalionship between characteristics of electromyographic signal and the corre spondng muscle force should be necessiiry through dynamic, joint model. To develop the dynamic joint model, the upper limb mcludmg the wrist and elbow joint has been considered. The kinematic and dynamic data, such as joint angular displacement, velocity, deceleration along with the moment of inertla, required to establish the dynamic model has been obtained by electrical flexible goniometer which has two degree-of-frcedoms. ln this model, muscle force can be predicted only electromyographs through the relationship between the integrated lorce and the mtegrated electromyographic signal over the duration of muscle contraclion in this study.

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Dynamic Bearing Pressure of Inverted T-type Retaining Walls Subjected to Seismic Motion (지진시 동토압을 받는 역 T형 옹벽의 접지압 산정에 관한 연구)

  • Lee, Jin-Sun
    • Journal of the Earthquake Engineering Society of Korea
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    • v.16 no.2
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    • pp.35-45
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    • 2012
  • Pseudo static analysis using the Mononobe-Okabe method and numerical analysis considering a small strain nonlinearity from the soil were performed to determine the bearing pressure changes of the inverted T-type retaining wall subjected to earthquake motions. In many cases, an inverted 'T' type retaining wall of more than 10 m shows bearing capacity failure under earthquake conditions, despite showing sufficient bearing capacity during normal conditions. The most important reason for this is the change of the effective base area during an earthquake. In this paper, the change of the effective base area of an inverted 'T' type wall is analyzed by using finite difference element code (FLAC). In addition, the effect of dynamic bearing capacity coefficients (which has been suggested by several researchers but not adopted in current design codes and procedures) was verified.

Ductility Confinement of RC Rectangular Shear Wall (장방형 철근 콘크리트 전단벽의 연성 보강)

  • 강수민;박홍근
    • Journal of the Korea Concrete Institute
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    • v.14 no.4
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    • pp.530-539
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    • 2002
  • In designing the boundary confinement of shear walls, the current design provisions and recommendations are empirical and prescriptive; they specify a certain confinement length and details, regardless of the actual requirement of ductility Therefore, they are inappropriate to the performance based-design. The purpose of the present study is to develop a ductility design method that Is applicable to the performance based-design of shear wall. For the purpose, experimental studies were performed to investigate variations in the ductility of shear walls with the length of the boundary confinement. Five specimens modeling the compressive zone of cross sections with different confinement area were tested against eccentric vertical load. Through the experimental studies, strength, ductility, and failure mode of the compression zone were investigated. In addition, nonlinear numerical analyses for the overall cross-sections of shear wall were performed to investigate variations of the stress and strain profiles with the length of compression zone. On the basis of the experimental and numerical studies, a ductility design method for shear wall was developed. By using the proposed design method, for a given ductility demand, the area of lateral confinement and corresponding reinforcement ratio can be precisely determined so that the ductile behavior and economical design are assured.

Bearing Strength of Concrete Column and Steel Beam Composite Joints (콘크리트 기둥과 철골 보 합성골조 접합부에서의 지압강도)

  • Kim, Byong-Kook;Lee, Won-Kyu;Choi, Oan-Chul
    • Journal of the Korea Concrete Institute
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    • v.15 no.3
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    • pp.417-424
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    • 2003
  • A bearing failure in RCS(Reinforced Concrete Column and Steel Beam) system is recognized as one of the distinct joint failure modes for the composite frames. Vertical and transverse reinforcement in addition to concrete are effective for better transfer of vortical forces through concrete bearing. To examine the effect of the vertical bars, tie bars, a U-type detail developed in this study and concrete confinement, local bearing tests were conducted using 22 small-scale concrete block specimens. Test results show that vertical reinforcement and tie bars mainly contribute to the bearing capacity. However larger amounts of tie reinforcement are required than those recommend from ASCE guidelines, to apply the nominal concrete strength as 2 fck over the bearing area. Cross ties are proved to be highly effective for resisting the vertical forces. Maximum bearing strength can be increased upto 2.5 fck . An accurate prediction model for bearing strength is proposed for better design of the composite Joint.

Deformability of Flat Plate Subjected to Unbalanced Moment (불균형 휨모멘트를 받는 플랫 플레이트의 변형능력)

  • Choi, Kyoung-Kyu;Park, Hong-Gun
    • Journal of the Korea Concrete Institute
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    • v.15 no.3
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    • pp.482-493
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    • 2003
  • Flat plate structures subjected to lateral load have less deformability than conventional moment frames, due to the brittle failure of plate-column connection. In the present study, parametric study using nonlinear finite element analysis was performed to investigate the deformability of flat plates. The numerical results show that as number of continuous spans increases, the deformability of flat plates considerably decreases. Therefore, existing experiments using sub-assemblages with 1 or 2 spans may overestimate the deformability of flat plates, and current design provisions based on the experiments may not be accurate in estimating the deformability. A design method estimating the deformability was developed on the basis of numerical results, and verified by comparison with existing experiment. In the proposed method, the effects of primary design parameters such as direct shear force, punching shear capacity, aspect ratio of connection, number of spans, and initial stiffness of plate can be considered.

Design Method of RC Flat Plate Slab Considering Unbalanced Moment (불균형모멘트를 고려한 RC 무량판 슬래브 설계방법)

  • Song, Jin-Kyu;Sing, Ho-Beom;Oh, Sang-Won;Han, Sun-Ae
    • Proceedings of the Korea Concrete Institute Conference
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    • 2008.04a
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    • pp.149-152
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    • 2008
  • In structural design provision, maximum punching shear stress of slabs is prescribed as combined stress of direct shear occurred by balanced gravity load and eccentric shear occurred by unbalanced moment. This means that the effect of unbalanced moment is considered to decide the punching shear stress. However, from the resistance capacity standpoint, the effect of unbalanced moment strength is not considered for deciding punching shear strength. For this problem, a model to show unbalanced moment-punching shear interrelation was proposed. In the model, the relation between load effect and resistance capacity in unbalanced moment-punching shear was two-dimensionally expressed. Using the interrelation model, a method how unbalanced moment strength should be considered to decide the punching shear strength was proposed. Additionally, a effective width enlargement factor for deciding the unbalanced moment strength of flat plates with shear reinforcements was proposed. The interrelation model proposed in this paper is very effective for the design because not only punching shear and unbalanced moment strengths but also failure modes of flat plates can be accurately predicted.

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Development of Optimum Design Program for PPC Structures using DCOC (이산성 연속형 최적성 규준을 이용한 PPC 구조의 최적설계프로그램 개발)

  • 한상훈;조홍동;이상근
    • Computational Structural Engineering
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    • v.10 no.4
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    • pp.315-325
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    • 1997
  • This paper describes the application of discretized continuum-type optimality criteria (DCOC) and the development of optimum design program for the multispan partially prestressed concrete beams. The cost of construction as objective function which includes the costs of concrete, prestressing steel, non-prestressing steel and formwork is minimized. The design constraints include limits on the maximum deflection, flexural and shear strengths, in addition to ductility requirements, and upper and lower bounds on design variables as stipulated by the design Code. Based on Kuhn-Tucker necessary conditions, the optimality criteria are explicitly derived in terms of the design variables-effective depth, eccentricity of prestressing steel and non-prestressing steel ratio. The prestressing profile is prescribed by parabolic functions. The self-weight of the structure is included in the equilibrium equation of the real system, as is the secondary effect resulting from the prestressing force. An iterative procedure and computer program for updating the design variables are developed. Two numerical examples of multispan PPC beams with rectangular cross-section are solved to show the applicability and efficiency of the DCOC-based technique.

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Nonlinear Finite Element Analysis on Global and Distortional Buckling of Cold-Formed Steel Members (냉간성형강재의 전체좌굴 및 뒤틀림좌굴에 대한 비선형유한요소해석)

  • Kang, Hyun Koo;Rha, Chang Soon
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.27 no.2
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    • pp.79-86
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    • 2014
  • This paper presents modelling approaches for the global and distortional buckling of cold-formed built-up steel sections using the finite element software packages, ANSYS and ABAQUS. Thin thickness of the cold-formed steel causes nonlinear behaviour due to local and distortional buckling, thus careful consideration is required in modelling for numerical analysis. Implicit static modelling using ANSYS provides unstable numerical results as the load approaches the limit point but explicit dyamic modelling with ABAQUS is able to display the behaviour even in post-buckling range. Meanwhile, axial load capacities obtained from the numerical analysis show higher values than the experimental axial capacities, due to eccentricity during the test. Axial capacities of the cold-formed steel obtained through numerical analysis requires reduction factor, and this paper suggests 0.88 for the factor.

Design of Crank Drive System Based on Gait Pattern for Stand-up Bicycle (보행패턴을 접목한 직립주행 자전거용 크랭크 구동장치의 거동분석)

  • Hyeong, Joonho;Roh, Jongryun;Kim, Sayup
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.41 no.10
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    • pp.991-996
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    • 2017
  • Gait stability is partly characterized by an extended stance phase that comprises 60 of the gait % cycle. In this study, a gait pattern was employed for a crank drive system that allows for stable lower limb kinematics during stand-up cycling. A quick return mechanism was applied to the crank system to allow for a slow rotation of the crank during the stance phase and for a quick return during the swing phase. Design parameters for the quick return crank mechanism were defined, and kinematic simulations were performed to understand the behavior of the mechanism. To evaluate the design, an experimental instrument was fabricated, and the cycling motion was analyzed. The results indicated that this new drive system can stabilize the center of mass of the user. This study can contribute to the development of a stand-up bicycle that allows for more comfortable leg kinematics.