• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.05a
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• pp.318-318
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• 2004

원통 연삭기(cylindrical grinding machine)는 원통형 공작물을 센터나 척으로 지지하면서 연삭 공정을 수행하기 때문에 연속적인 작업이 어렵지만, 무심 연삭기(centerless grinding machine)는 원통형 공작물을 받침판으로 지지하면서 연삭 숫돌(grinding wheel)과 조정 숫돌(regulating wheel)로 연삭 공정과 축방향 이송을 동시에 수행하기 때문에 연속적인 작업이 가능하다. 특히 고정밀 부품을 작업자의 숙련도와 무관하게 고능률적으로 가공할 수 있는 무심 연삭기는 구름 베어링, 축, 피스톤 핀 등과 같은 고정밀 기계류 부품들을 대량 연삭하기 위한 용도로 많이 사용되어 왔다.(중략)

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.12 s.105
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• pp.1340-1346
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• 2005

In this study, based on shaking table test results on a seismically isolated bridge model, an inelastic numerical model is refined by using Bouc-Wen model representing the hysteretic behavior of isolators. Seismic responses of isolated bridges are numerically investigated varying with relative stiffness ratio(RSR), which is a ratio of the effective stiffness of isolator to the lateral stiffness of bridge pier, From the results, it is found that an adequate range of relative stiffness ratio could be defined for seismic design of isolated bridges without considering the flexibility of piers.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.2
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• pp.15-21
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• 2010

Structural analysis used to evaluate the load carrying capacity of a bridge should implement behavioral characteristics similar to the actual behaviors of the structure through loading tests, but it is not feasible in many cases due to the behavioral characteristics of points, inadequate modeling method in structural analysis, errors in loading tests, changes in strength and rigidity resulting from cross-sectional damage, etc. This problem can be more serious if bridge bearings have been damaged or were not installed and, consequently, the bearings do not function properly. This study produced results similar to actual behaviors using a structural analysis model built with support moment derived from the difference $\Delta{\delta}$ between measured deflection obtained by confining the cantilever segment of a solid beam and calculated deflection under a unrestrained condition. When the load carrying capacity of a bridge in operation was evaluated in consideration of the confinement condition of supports, the result was 15~19% lower than load carrying capacity calculated by the existing method.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.18 no.3
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• pp.227-243
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• 2005

This paper presents a hybrid control system combining lead rubber bearings and hydraulic actuators for seismic response control of a cable stayed bridge. Because multiple control devices are operating, a hybrid control system could improve the control performances. However, the overall system robustness may be impacted negatively by additional active control devices. Therefore, a secondary on-off type controller according to the responses of lead rubber bearings is combined with LQG algorithm to improve the controller robustness. Numerical simulation results show that control performances of the hybrid system controlled by an on off type LQG algorithm are improved compared to those of the passive and active control systems and are similar to those of performance oriented hybrid system controlled by a LQG algorithm with the similar peak and normed control forces. Furthermore, it is verified that the hybrid system with an on-off type LQG controller is more robust for stiffness matrix perturbation than conventional hybrid control of system, and there are no signs of instability in the overall system. The proposed control system also maintains the control performance under not only the design earthquakes but also the other earthquakes. Therefore, the hybrid control system using on-off type LQG algorithm could be proposed as an improved control strategy for seismically excited cable-stayed bridges containing many uncertainties.

• Proceedings of the KSR Conference
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• 2009.05a
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• pp.599-605
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• 2009

The aim of the present study is the characteristics of bridge rubber pads and suggested how to determine the stiffness the pads. A disk bearing is operated as an elastic bearing in the vertical direction and is composed of a Polyether Urethane (polyurethane) disk for elastic support and Polytetrafluoroethylene (PTFE) to accommodate movement. Static tests are conducted in a laboratory to determine the static behavior of a Polyurethane disk. Finite Element (FE) analysis is also performed to verify the static performance. For dynamic behavior, four disk bearings having the identical Polyurethane disk used in the static tests are installed in a full size railway bridge and tested under a running locomotive. From the tests results, the static and dynamic stiffness of disk bearings are estimated and compared with each other. In the procedure to estimate the stiffness of a pad, the dead load(pre-load) of a bridge and live load of a vehicle are considered.

• Journal of the Korea Concrete Institute
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• v.27 no.4
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• pp.377-385
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• 2015

The span-lengthening of PSC I girder has increased the risk of lateral instability of the girder with the increases in the aspect ratio and self-weight of the girder. Recently, collapses of PSC I girder during construction raise the necessity of evaluating the lateral instability of the girder. Thus, the present study evaluated the lateral behavior and instability of PSC I girders under wind load, regarded as one of the main causes of the roll-over collapse during construction. Lateral instability of the girder is mainly dependent on the length of the girder and the stiffness of the support. The analysis results of this study showed the decrease in the critical wind load and the increase in the critical deformation and angle of the girder, leading to the lateral instability of the girder. Finally, this study proposed analytical equations that can predict the critical amount of wind load and lateral deformation of the girder, which would provide quantitative management values to maintain lateral stability of PSC I girder during construction.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.11
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• pp.230-236
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• 2018

Earthquakes over 5.0 on the Richter scale have recently occurred in Korea, which has led to interest in the seismic safety of structures. If a water storage facility is damaged by an earthquake, the water could leak, and the insufficient water would make fire suppression difficult. Therefore, a water storage facility should satisfy safety requirements for earthquakes. In this study, the seismic performance of a water tank was improved by installing a lead rubber bearing between the foundation and the tank. It designed the lead rubber bearing available to the existed concrete foundation. ANSYS was used for modeling to consider the interaction between the fluid and structure of the tank and the hydrostatic and hydrodynamic pressure using four seismic waves. In the case of hydrostatic pressure at 2.5 water level, full level, the same stress appeared irrespective of whether the seismic isolation was installed. When hydrostatic pressure and hydrodynamic pressures are applied at the same time, the seismic-isolated water tank showed less seismic force, and the damping ratio was lower than that of general seismic isolation. This occurred because the weight of the water tank is much smaller than the stiffness of the seismic isolation. The result is expected to be used for further research on seismic capacity evaluation for water tanks.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.123-128
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• 2018

Girder bridges and slab bridges are equipped with a system consisting of a flexible joint unit, support, inverted T shaped abutment, and a separate connecting slab structure. These systems have problems such as an increase in cost due to frequent breakage of the expansion joints and a decrease in durability due to a structure with low moment redistribution. To improve these problems, propose Inegral and Semi-Integral Hybrid Slab Bridge and examine the safety through structural analysis. As a result of the review, Inegral and Semi-Integral Hybrid Slab Bridge was the section stiffness is small. but it is confirmed that the structural safety, ductility and flexibility are higher than existing bridges because the moment redistribution and the force transmission are surely performed.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2003.04a
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• pp.487-495
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• 2003

Bearings at the obtuse corner are subjected to much larger vertical reactions than other bearings because of the geometric shape of skew bridges. The current relevant specifications require that additional bars should be disposed at the bottom of concrete deck slabs to deal with the large vertical reaction on bearings at the obtuse corner. In this study, new methods of reducing the magnitude of the vertical reaction on bearings at the obtuse corner by the stiffness adjustment of bearings were proposed. The basic concept of proposed methods was to redistribute support reactions by reducing the vertical stiffness of bearings at the obtuse corner showing a relatively large vertical reaction. For 45 simply supported skew bridges designed according to the current relevant specifications, the redistribution effect of vertical reactions by the stiffness adjustment of bearings was investigated. Parameters such as skew angle, girder spacing, and deck aspect ratio that affect the distribution of support reactions were considered. The results of the analyses show that the magnitude of the vertical reaction on bearings at the obtuse corner can be reduced to the levels of straight bridges by replacing the existing bearings at the obtuse corner with new ones having the value of 1/10 or 1/20 of the vertical stiffness of the existing bearings. The reduction effect of the vertical reaction on bearings at the obtuse corner increases as the girder spacing decreases and it is more pronounced when the deck aspect ratio is 2.0.

• Journal of the Earthquake Engineering Society of Korea
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• v.13 no.4
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• pp.25-35
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• 2009

This paper introduces the performance of a newly developed base isolation system made from the combination of a polyurethane disk - attached pot bearing and C-shape steel dampers. Ultimate compressive load tests, ultimate rotation tests, dynamic tests, and dynamic load repeat tests have been completed to determine dynamic characteristics and to verify performance characteristics. The experimental results are compared with the analytic results. It is determined that all requirements for bridge bearing in the specifications are satisfied, and that adequate energy dissipation has occurred. The EDC and effective stiffness estimated by tests are similar to the theoretical values.