• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.605-611
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• 2000

Presented in this paper is a new method of identifying the critical speed of rotor-bearing systems without actually reaching at the critical speed itself. Using the method, it is not only possible to calculate the critical speed by measuring a series of rotor responses at much lower rotating speeds away from and without reaching at the critical speeds but also the damping ratio and eccentricity of the system can be identified at the same time. Two types of test rotors were tested on the Rotor Dynamics Test Facility at the Rotordynamics Lab., KIMM, and the theory has been confirmed experimentally. The method can be adopted to monitor changes of the dynamic characteristics of critical rotating machinery before and after overhauls, repairs, exchanges of various parts, or to detect trends of direction of subtle changes in the dynamic characteristic parameters over a long periods of time.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2003.09a
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• pp.288-294
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• 2003

Increasing the volume of traffic on the roads causes social and economical problems such as increasing air-pollution and distribution cost. Prefabricated light weight bridge becomes a possible solution for these problems in the urban area where it is difficult to construct new one or expend the existing road. There are some merits in this kind of bridge. First, the design live and dead loads are minimized by allowing only passenger cars. Second employing prefabrication construction scheme reduces the construction time. Third, there is no need to buy land if the elevation road is placed on the top of existing one. In seismic design of bridges, base isolation has been an effective solution when the bridge has stiff piers and a heavy superstructure. The prefabricated light weight bridge has different dynamic characteristics from the ordinary bridges. In this paper, the applicability of base isolators such as lead rubber bearing and elastomeric bearing, to prefabricated light weight bridge is examined.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.65.5-65
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• 2001

In this study, we have designed and fabricated the slidacs type automatic voltage regulator(AVR) that is able to control the output voltage continuously according to road variation. Especially, the frictions between the surface of contact of the slidacs coils and the output wire moving rod are reduced by transforming the mechanical configuration of surface of contact of slidacs from the conventional sliding one into the proposed rotary one composed of cylindrical bearing. Thus, the slidacs type AVR using cylindrical bearing proposed in this study has less noise than conventional one owing to the reduction of frictions, and its breakdown ratio caused by the abrasion of contact materials is reduced. Furthermore, ...

• Structural Engineering and Mechanics
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• v.85 no.2
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• pp.265-274
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• 2023

The spherical steel bearings (SSBs) has been gradually replaced traditional rubber bearings and extensively applied to high-speed railway (HSR) bridges in China, due to their durability and serviceability. Nevertheless, SSB is generally simplified to the ordinary constraints in the finite element model, which cannot reflect its detailed mechanical characteristics, especially its seismic performance. To provide a more precisely simulation, an innovative and simplified finite element simulation method is proposed and the combined element group is developed in ANSYS. The primary parameters were determined by means of the performance test of SSB. The finite element model of SSB applied to a single-span HSR simply supported girder bridge was established through the proposed method. The seismic performance of the SSB was further investigated. A shake table test was conducted to evaluate the accuracy of the proposed simulation method. It is found that the numerical results could have a good agreement with the experiment, namely, the proposed method is feasible and efficient.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.4
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• pp.535-541
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• 2023

Friction material, an integral constituent of bearing supports, facilitates frictional interactions between two components. Polytetrafluoroethylene (PTFE), a commonly employed friction material in bearing supports, has assessed resultant friction equilibrium. Nonetheless, protracted utilization diminishes frictional performance as the lubricating agent is progressively depleted. Friction materials can affect the entire structural system. Hence, this study applied ceramic material as a friction material due to its high strength, low friction, and low deformation. The frictional behavior was investigated using a cyclic friction test, considering various friction materials as the primary design variables and examining their covariance in cyclic frictional movements. The results substantiated that the ceramic friction material yielded a low variance and friction coefficients in cyclic frictional movements.

• Journal of the Korean Geotechnical Society
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• v.31 no.7
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• pp.29-39
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• 2015

The vertical load imposed on the bucket foundation is transferred from the soil inside the bucket to the bottom of the foundation, and also to the outer surface of the skirt. For the design of a bucket foundation installed in sand, the vertical load transfer characteristics have to be clearly identified. However, the response of bucket foundations in sand subjected to a vertical load has not been investigated. In this study, we performed two-dimensional axisymmetric finite element analyses and investigated the vertical load transfer mechanism of bucket foundation installed in sand. The end bearing capacity of bucket foundation is shown to be larger than that of the shallow foundation, whereas the frictional resistance is smaller than that for a pile. The end bearing capacity of the bucket foundation is larger than the shallow foundation because the shear stress acting on the skirt pushes down and enlarges the failure surface. The skin friction is smaller than the pile because the settlement induces horizontal movement of the soil below the tip of the foundation and reduces the normal stress acting at the bottom part of the skirt. The calculated bearing capacity of the bucket foundation is larger than the sum of end bearing capacity of shallow foundation and skin friction of pile. This is because the increment of the end bearing capacity is larger than the reduction in the skin friction.

• Journal of the Korean Geotechnical Society
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• v.17 no.6
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• pp.181-191
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• 2001

Granular compaction piles increase the load bearing capacity of the soft ground and reduce the settlement of fecundation built on the reinforced soil. Also the granular compaction piles accelerate the consolidation of soft ground using the granular materials such as sand, gravel, stone etc. However, this method is one of unuseful methods in Korea. In the present study, the estimation procedure for the ultimate bearing capacity of randomly installed granular compaction pile group is proposed. Also, carbon rod tests have been peformed for verifying the group effect of granular compaction piles and the behavior characteristics such as bulging failure zone on granular compaction piles. From the test results, it is found that bulging failure shape of granular compaction piles was conical shape and the ultimate bearing capacity increased as the spacing of piles became gradually narrow. Also, from the proposed method in this study, the optimal locations of granular compaction piles with various installed cases are analyzed. The results were shown that the bearing capacity was increased in the case concentrated on the central part of pile group.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.2
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• pp.145-151
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• 2008

The research so far has primarily analyzed efficiency improvement but in this research, it analyzes the characteristics of earthquake behavior, with changed pier heights, through ordinary and seismic analysis. For this, the kind of bridge bearing has been changed against PSC I-shaped bridge, which is mostly used in practice, and at all times earthquake analysis has been performed with through height of pier. Especially considering sectional power resulting from earthquake analysis, displacement of PSC I-shaped bridge bearing, diameter of pier pillar by earthquake load, and upper spare gap have been analyzed. In case of high-pear, seismic isolated device is decided as proper for cars' driving and for management of bridge since it decreases movement of upper structure, than elastic bearing, reducing size of elastic connect device, and it's been analyzed it is effective for improvement of fine view and economic efficiency reducing section of lower bridge structure. Finally, when design PSC I-shaped bridge bearing, for the proper structure and high-pier side, applying seismic isolated device through precise inner analysis is proper than applying equal elastic bearing.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.6
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• pp.19-26
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• 2021

The seismic isolation system have been applied in order to protect the collapse of bridge by seismic load and the vertical load transmitted from the superstructure. However, the failure and damages of non-shrinkage mortar, isolator and wedge in total 12 bridge were reported by Pohang Earthquake. In this study, the damage mechanism and behavior characteristics of elastomeric bearing by an earthquake were evaluated to consider the seismic isolation system including non-shrinkage mortar and the seat concrete of pier. To discuss the effect of installed wedge and damage mode of elastomeric bearing, the compressive-shear tests were carried out. Also, the mechanical behaviors and damage mechanism for each component of elastomeric bearing were evaluated by using finite element analysis. From the test results, the cracks were created at boundary between non-shrinkage mortar and seismic isolator and the shear loads were rapidly increased after bump into wedge. The cause for damage mechanism of seismic isolation system was investigated by comparing stress distribution of anchor socket and non-shrinkage mortar depending on wedge during earthquake.

• Journal of the Korean Geotechnical Society
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• v.24 no.4
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• pp.5-13
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• 2008

Laboratory model test with soft silty ground (ML) and polluted silty ground with wastewater and factory waste oil ($ML_p$) was conducted and the applicability of changes of bearing capacity from the increase of pollutants was compared and analyzed with existing findings. As silty ground polluted with wastewater and factory waste oil had increased contents of pollutants, plasticization of ground was fostered compared to soft silt ground due to the influence of pollutants, and characteristics of ground strength decreased. Critical surcharge value of soft silty ground $q_{cr}=4.14c_u$, ultimate bearing capacity value $q_{ult}=9.53c_u$, critical surcharge value of silty ground polluted with wastewater and factory waste oil $q_{cr}=1.78c_u$ and ultimate bearing capacity value $q_{ult}=4.39c_u$. Critical surcharge and ultimate bearing capacity of silty ground polluted with wastewater and factory waste oil were less than those of soft silty ground. It meant that shearing resistance due to the increase of pollutants decreased and rather a smaller value was obtained.