• Journal of the Korean Society for Advanced Composite Structures
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• v.4 no.4
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• pp.30-36
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• 2013

Partially earth anchored (PEA) can improve the structural safety and economic feasibility of multiple span cable stayed bridge (CSB). The PEA-CSB can restrain axial compressive load acting on a tower and reduce the global buckling length of a stiffened girder. For these reasons, structural members subject to axial forces can be effectively utilized and material quantity required for a steel deck can be reduced to save construction cost. In this study, the PEA system was verified for its application on a multiple span CSB. The CSB is a four-tower multi-span bridge which has a main span length of 500 m. As high tensile stress was generated at the top of the bridge decks at the mid-span between two main columns, a hybrid deck system for enhancing the bridge deck sections was proposed. While the composite sections made of concrete and steel were used near to the main columns, steel sections were used at the mid-span between two main columns.

• Computers and Concrete
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• v.14 no.2
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• pp.109-125
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• 2014

The force transfer mechanism in positive moment continuity details for prestressed concrete girder bridges is investigated in this paper using a three-dimensional detailed finite element model. Positive moment reinforcement in the form of hairpin bars as recommended by the National Cooperative Highway Research Program Report No 519 is incorporated in the model. The cold construction joint that develops at the interface between girder ends and continuity diaphragms is also simulated via contact elements. The model is then subjected to the positive moment and corresponding shear forces that would develop over the service life of the bridge. The stress distribution in the continuity diaphragm and the axial force distribution in the hairpin bars are presented. It was found that due to the asymmetric configuration of the hairpin bars, asymmetric stress distribution develops at the continuity diaphragm, which can be exacerbated by other asymmetric factors such as skewed bridge configurations. It was also observed that when the joint is subjected to a positive moment, the tensile force is transferred from the girder end to the continuity diaphragm only through the hairpin bars due to the lack of contact between the both members at the construction joint. As a result, the stress distribution at girder ends was found to be concentrated around the hairpin bars influence area, rather than be resisted by the entire girder composite section. Finally, the results are used to develop an approach for estimating the cracking moment capacity at girder ends based on a proposed effective moment of inertia.

• Journal of the Earthquake Engineering Society of Korea
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• v.19 no.5
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• pp.239-246
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• 2015

Reinforced concrete shear walls are effective for resisting lateral loads imposed by wind or earthquakes. Observed damages of the shear wall in recent earthquakes in Chile(2010) and New Zealand(2011) exceeded expectations. Various analytical models have been proposed in order to incorporate such response features in predicting the inelastic response of RC shear walls. However, the model has not been implemented into widely available computer programs, and has not been sufficiently calibrated with and validated against extensive experimental data at both local and global response levels. In this study, reinforced concrete shear walls were modeled with fiber slices, where cross section and reinforcement details of shear walls can be arranged freely. Nonlinear analysis was performed by adding nonlinear shear spring elements that can represent shear deformation. This analysis result will be compared with the existing experiment results. To investigate the nonlinear behavior of reinforced concrete shear walls, reinforced concrete single shear walls with rectangular wall cross section were selected. The analysis results showed that the yield strength of the shear wall was approximately the same value as the experimental results. However, the yielding displacement of the shear wall was still higher in the experiment than the analysis. The analytical model used in this study is available for the analysis of shear wall subjected to high axial forces.

• Journal of Mechanical Science and Technology
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• v.19 no.2
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• pp.682-691
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• 2005

This paper describes the design, fabrication, and testing of a microturbine developed at Seoul National University. Here, the term 'microturbine' refers to a radial turbine with a diameter on the order of a centimeter. Such devices can be used to transmit power for various systems. The turbine is designed using a commercial CFD code, and it has a design flow coefficient of 0.238 and work coefficient of 0.542. It has 31 stator blades and 24 rotor blades. A hydrodynamic journal bearing and hydrostatic thrust bearings counteract radial and axial forces on the rotor. The test turbine consists of a stack of five wafers and is fabricated by MEMS technology, using photolithography, DRIE, and bonding processes. The first, second, fourth, and fifth layers contain plumbing, and hydrostatic axial thrust bearings for the turbine. The third wafer contains the turbine's stator, rotor, and hydrodynamic journal bearings. Furthermore, a turbine test facility containing a flow control system and instrumentation has been designed and constructed. In performance tests, a maximum rotation speed of 11,400 rpm and flow rate of 16,000 sccm have been achieved.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.2
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• pp.226-232
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• 2011

In this study, an optimized design of a triaxial load cell has been developed by the use of finite element analysis, design of experiment and response surface method. The developed optimal design was further validated by both stress-strain analysis and natural vibration analysis under an applied load of 30 kgf. When vertical, horizontal, and axial loads of 30 kgf were applied to the load cell with the optimal design, the calculated strains were satisfied with the required strain range of $500{\times}10^{-6}{\pm}10%$. The natural vibration analysis exhibited that the fundamental natural frequency of the optimally designed load cell was 5.56 kHz and higher enough than a maximum frequency of 0.17 kHz which can be applied to the load cell for wind-tunnel tests. The satisfactory sensitivity in all triaxial directions also suggests that the currently proposed design of the triaxial load cell enables accurate measurements of the multi-axial forces in wind-tunnel tests.

• Steel and Composite Structures
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• v.5 no.1
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• pp.35-47
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• 2005

This paper presents the results of a series of tests carried out on hollow and concrete-filled coldformed steel sections subjected to axial and bending forces. The effects of eccentricity ratio and strength of in-fill on the behaviour of these sections were studied. A total of forty-eight medium sized columns and six beams were tested to failure. Extensive measurements of material properties, strains, axial shortening and lateral deflection were carried out. Interaction of local and overall buckling was observed in the tests. Failure mode observations were local buckling coupled with overall buckling. A description of the specially fabricated end fixtures for applying eccentric loading to the columns and to simulate pinned end condition is also presented. The experimental results of hollow columns are compared with the existing Indian, British and American codes of practice and the results of concrete-filled columns are compared with EC4 recommendations. It is seen that in the case of hollow columns predictions based on British and American codes of practice and in the case of concrete-filled columns predictions based on EC4 recommendations agree reasonably well with the experimental results. From the experiments it is seen that the provision of in-fill substantially increases the ultimate load carrying capacity of the order of one and a half to two times and the increase in strength of the in-filled concrete from a low grade concrete of compressive strength 24.94 MPa to a high grade concrete of compressive strength 33.26 MPa increases the ultimate load carrying capacity by one and a half times irrespective of the eccentricity of loading.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.11
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• pp.1518-1526
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• 2001

In this paper, the mechanism of unsteady potential interaction and wake interaction in one stage axial turbine is numerically investigated at design point in two-dimensional viewpoint. The numerical technique used is the upwind scheme of Van-Leer's Flux Vector Splitting (FVS) and Cubic spline interpolation is applied on zonal interface between stator and rotor. The inviscid analysis is used to embody the influence of potential interaction only and viscous analysis is used to embody the influences of both potential interaction and wake interaction at the same time. The potential-flow disturbance from the stator into a rotor passage and the periodic blockage effect of rotor produce the unsteady pressure on the blade surface in inviscid analysis. After the wake is cut by rotor, two counterrotating votical patterns flanking the wake centerline in the passage are generated. So, these phenomena magnify the unsteady pressure in viscous analysis than that in inviscid analysis. The resulting unsteady forces on the rotor, generated by the combined interaction of the two effects by potential and wake interaction, are discussed.

• International Journal of Fluid Machinery and Systems
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• v.2 no.4
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• pp.375-382
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• 2009

Hydraulic instability associated with pressure fluctuations is a serious problem in hydraulic machinery. Pressure fluctuations are usually a result of a strong vortex created in the centre of a flow at the outlet of a runner. At every radial turbine and also at every single regulating axial turbine, the draft tube vortex appears at part-load operating regimes. The consequences of the vortex developed in the draft tube are very unpleasant pressure pulsation, axial and radial forces and torque fluctuation as well as turbine structure vibration. The consequences of the vortex are transferred upstream and downstream with amplitude and frequency modulation in respect of the turbine operating regime, cavitation conditions and air admitted content. Numerical prediction of the vortex appearance in the design stage is a very important task. The amplitude of the pressure pulsation is different for each operating regime therefore the main goal of this research was to numerically predict pressure pulsation amplitude versus different guide vane openings and to compare the results with experimental ones. For the numerical flow analysis of a complete Francis turbine (FT), the computer code ANSYS-CFX11 has been used.

• Tribology and Lubricants
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• v.30 no.2
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• pp.116-123
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• 2014

The objective of this study is to model and simulate the nonlinear lubrication performance of the sliding part between the piston and cylinder wall in a hydrostatic swash-plate-type axial piston pump. A numerical algorithm is developed that facilitates simultaneous calculation of the rotating body motion and fluid film pressure to observe the fluid film geometry and power loss. It is assumed that solid asperity contact, so-called mixed lubrication in this study, invariably occurs in the swash-plate-type axial piston pump, which produces a higher lateral moment on the pistons than other types of hydrostatic machines. Two comparative mixed lubrication models, rigid and elastic, are used to determine the reaction force and sliding friction. The rigid model does not allow any elastic deformation in the partial lubrication area. The patch shapes, reactive forces, and virtual local elastic deformation in the partial lubrication area are obtained in the elastic contact model using a simple Hertz contact theory. The calculation results show that a higher reaction force and friction loss are obtained in the rigid model, indicating that solid deformation is a significant factor on the lubrication characteristics of the reciprocating piston part.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.1066-1069
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• 2002

Dynamic postural control varies with the environmental context, specific task and intentions of the subject. In this paper, dynamic postural control against forward-backward perturbations of a platform was estimated using tri-axial accelerometers and a force plate. Ten young healthy volunteers stood upright in comfortable condition on the perturbation system which was controlled by an AC servo motor. With anterior-posterior perturbations, movements of ankle, knee and hip Joints were obtained by tri-axial accelerometers. and ground reaction forces with corresponding displacements of the center of pressure(CoP) by the force plate. The result showed that the ankle moved first and the trunk forward, which implies that the mechanism of the dynamic postural control in forward-backward perturbations, occurred in the procedure of the ankle, the knee and the hip. Knee flexion and hip extension in the period of acceleration, constant velocity and deceleration phase is very important fur the balance recovery. These responses depends on the magnitude and timing of the perturbation. From the present study the accelerometry-system appears to be a promising tool for understanding kinematic accelerative In response to a transient platform perturbation. A more through understanding of balance recovery mechanism may aid in designing methods for reducing falls and the resulting injuries.