• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.1
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• pp.175-181
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• 2010

The three truss models(equilibrium truss model, Mohr compatibility truss model, and the soften truss model) based on a rotating angle is called the rotating-angle model. The three rotating-angle models have a common weakness: they are incapable of predicting the so-called "contribution of concrete". To take into account this "contribution of concrete", the modern truss model(MCFT, STM) treats a cracked reinforced concrete element as a continuous material. By combining the equilibrium, compatibility, and the softened stress-strain relationship of concrete in biaxial state, MTM is capable of producing the nonlinear analysis of reinforced concrete structures composed of membrane element. In this paper, an efficient algorithm is proposed for the solution of proposed model incorporated with failure criteria. This algorithm is used to analyze the behavior of reinforced membrane element using the results of Hsu test.

• The Journal of the Petrological Society of Korea
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• v.28 no.3
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• pp.217-225
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• 2019

This study describes a large recumbent fold, which occurs at the north entrance slope of the Batjae tunnel, Pyeongchang-gun, Gangwon-do, and interprets its formation mechanism. The several-hundred-meter scale fold, developed in the Jeongseon Limestone of the Paleozoic Joseon Supergroup, has a nearly horizontal axial plane and its head is facing north. Stretching lineations ($L_1$) observed on the composite foliations of bedding and axial plane cleavage plunge southward at about $10^{\circ}$. Small A-type or eye-shaped sheath folds together with S-shaped asymmetrical folds are often observed in the fold limbs and their axes are nearly parallel to the lineations ($L_1$) within center and rear parts of the fold. It is thus interpreted that the recumbent fold is a large sheath fold produced by the top-to-the-north ductile shearing due to the Songrim orogeny during the late Paleozoic to Triassic.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.4A
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• pp.227-235
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• 2012

Recently, study of confining effect in column members is progressed. But these studies are limited to about RC column and external confining effect in hollow columns. Internal confining effect in hollow columns has not researched. Internal confining stress is assumed the same external confining stress in hollow columns. In this study, there are to investigate the internal direction confining effect in ICH CFT column by FEA analysis. FEA analysis methods have verified by experimental values. Parametric study has performed as thickness of internal tube, hollow ratio, diameter of column and bending stiffness between concrete and external tube. Modified equations have suggested to estimating economic and reasonable thickness of internal tube.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.37-37
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• 2011

최근 세계적인 지진의 발생과 함께 구조물의 내진성능 평가 및 증진 방법에 대하여 많은 연구가 진행 되고 있다. 특히 교량 구조물의 교각의 경우에는 상부구조의 고정하중 및 활하중을 지반에 전달하여 주는 역할을 하기 때문에, 역으로 지진이 발생하였을 경우 교각의 내진성능에 따라서 교량의 안전도에 많은 영향을 미칠 수 있다. 또한 산악지역이 국토의 70%이상을 차지하는 우리나라의 지형적인 특성상 고교각을 이용한 장대교량의 건설이 필요하며 도시지역의 교통량 증가로 인한 도시고속도로의 건설 등 고가교의 필요성이 점차 증가하고 있다. 그러나 CFT(Concrete Filled Tube)부재의 경우에는 콘크리트가 3축 구속 상태로 존재하지만 자중이 크며 내진 성능이 떨어지는 단점을 가지고 있다. 이러한 단점을 보완하기 위하여 CFT부재의 단면을 중공으로 만듦으로써 부재를 경량화하고 내부 튜브를 삽입하여 내부를 구속 시킨 내부 구속 중공 CFT 부재(Internally Confined Hollow CFT Member, ICH CFT)가 개발되었다. 이는 콘크리트가 내 외부 튜브에 의하여 구속되어 3축 구속 상태로 존재함으로써 콘크리트 중공부로의 취성파괴를 방지하여 연성도 및 강도를 향상시켜주며, 단면의 감소로 인해 재료비를 절감 할 뿐 아니라 자중 감소로 인해 내진 설계에도 유리하다. 현재 내부 구속 중공 CFT 부재에 대한 연구가 많이 진행되고 있지만, 튜브를 삽입함으로써 부재의 중공부로 발생하는 구속력의 특성을 해석적으로 정립한 연구는 미비한 실정이다. 본 연구에서는 압축을 받는 중공 CFT 부재에 내부 튜브를 삽입함으로써 발생하는 콘크리트의 구속력을 해석적 연구를 통하여 수행하였으며, 구속력을 파악하기 위한 평가 방법으로는 구속 콘크리트의 중공비와 직경, 외부튜브의 두께, 내부튜브의 두께 등으로 평가하였다. 해석적 연구 결과, 내부 튜브를 삽입함으로써 발생되는 외부 구속력은 이론적 수식에 의한 구속 응력값과 비슷한 값을 가지지만 내부로 발생하는 구속력은 이론적 수식에 의한 구속 응력값에 도달하지 못하는 것을 확인할 수 있었다.

• Journal of the Society of Disaster Information
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• v.20 no.2
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• pp.411-418
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• 2024

Purpose: This study aims to develop brand new bolt fastening type of seismic retrofit using high tensile alloy materials for existing reinforced concrete columns. Method: A T-type cross-sectional seismic retrofit made of SUS304 and SS275, and the high-tensile bolt of SCM435 was analyzed for the effect of material properties on seismic performance through bending test. Result: The experiment using SUS304 shows a 7% higher maximum strength and 22% higher yield strength and shows a higher compressive stress of 360MPa. In addition, the change in the neutral axis is also smaller. Conclusion: Seismic retrofit using SUS304 is considered to be better in terms of yield strength, tensile strength, neutral axis change, and ductility, and it is considered necessary to experiment with RC column real experiments in future studies.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.6
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• pp.1-9
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• 2017

Spiral reinforcement in a circular column plays an effective role in the ductile behavior of a column through position fixing and buckling restraining of the longitudinal reinforcement, and confining core-concrete. Each country has suggested the minimum volumetric ratio of spiral reinforcement in order to secure the ductility of concrete columns. The minimum volumetric ratio of spiral reinforcement suggested by ACI 318-14 and the national concrete structure design standard was developed based on the theory of Richard et al. (1928); furthermore it has been used until now. However, their theory cannot consider the effects of high strength concrete and high strength reinforcement, and arrangement condition of the spiral reinforcement. In this study, a modified minimum volumetric ratio equation is suggested, which is required to improve the ductility of reinforced concrete circular columns and to recover their stress. The modified minimum volumetric ratio equation suggested here considers the effect of the compressive strength of concrete, the yield strength of spiral reinforcement, the cross sectional area of columns, the pitch of spiral reinforcements and the diameter of spiral reinforcement. In this paper, the validity of the minimum volumetric ratios from ACI 318-14 and this study was investigated and compared based on the results of uniaxial compression experiment for specimens in which the material strength and the spiral reinforcements ratio were used as variables. In the end of the study, the modification method for the suggested equation was examined.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.221-226
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• 2005

In this paper, a dynamic model for the rotor shaft-coupling-blade system is developed. The blades are attached to a disk and driven by an electric motor shaft which is flexible in torsion. We assumed that the shaft torsional flexibility is lumped in the flexible coupling which is usually adopted in rotor systems. The Lagrangian approach with the small deformation theory for both blade-bending and shaft-torsional deformations is employed for developing the equation of the motion. The assumed modes method is used for estimating the blade transverse deflection. The numerical results highlight the effects of both structural damping of the system and the torsional stiffness of the flexible coupling to the dynamic response of the blade. The results showed strong coupling between the blade bending and shaft torsional vibrations in the form of inertial nonlinearif, stiffness hardening and softening.

• Tribology and Lubricants
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• v.16 no.1
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• pp.39-45
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• 2000

In this paper, the effects of shaft and bearing flexibilities are investigated for the accurate modeling of a shaft-bearing system supported by ball bearings. Generally, rolling bearings are modeled by simple rigid pin-joint in the mechanical design. However, they can no longer be modeled by ideal boundary conditions in the advanced applications because the rigid pin-joint model cannot satisfy the current trends of mechanical design decreasing mass and reducing volume. Consequently the flexible support model of ball bearing is investigated using the static analysis module developed by A .B. Jones and T. A. Harris. A simple two-bearing system, supported by two deep groove ball bearings and radially loaded on the shaft midway between the bearings, is utilized to validate the coupled model of shaft-bearing system. Numerical computations using the model indicate that the shaft span length, locating/floating bearing arrangements and applied bearing size are significant factors in determining the mechanical behaviors. The flexible support model of ball bearing can be escaped to over-estimate in the bearing fatigue life. The proposed simple design formulation obtained by numerical simulations can approximately predict a rate of bearing life reduction as a function of shaft span length/shaft diameter (L/d).

• Composites Research
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• v.14 no.5
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• pp.20-25
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• 2001

This paper deals with finite element analysis for free vibration and forced sinusoidal vibration of Ka- and Ku- band antenna structures using MSC/NASTRAN. The structures are designed to satisfy minimum resonance frequency requirement in order to decouple the dynamic interaction of the satellite antenna with the spacecraft bus structure. The large mass method was utilized to analyze output acceleration according to the forced sinusoidal vibration inputs in X-, Y- and Z- directions. The analysis results can also be used thor verification experimental planning of satellite antenna.

• Tribology and Lubricants
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• v.27 no.2
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• pp.57-64
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• 2011

Hybrid air-foil magnetic bearing integrates two oil free bearing technologies synergetically to adopt the strengths of two bearings with minimizing their weaknesses. This paper presents bending mode vibration control of a flexible shaft supported by the hybrid air-foil magnetic bearing. An experiment set-up of a flexible shaft supported by the hybrid air-foil magnetic bearing is built. In order to verify the effectiveness of the hybrid bearing, unbalance responses of the flexible shaft supported by three different bearings: air-foil, magnetic and hybrid bearings are compared. Effect of load sharing between air-foil and magnetic bearings are investigated through changing the control gain and the rotor center position of magnetic bearing. The experimental results shows that the hybrid bearing can control the bending mode vibration of the flexible shaft effectively and an optimal performance can be achieved with an appropriate load sharing between the air-foil and the magnetic bearings.