• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.6
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• pp.67-74
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• 2010

Because of the difference between the actual and computed eccentricity of buildings, symmetrical buildings will be affected by torsion. In provisions, accidental eccentricity is intended to cover the effect of several factors, such as unfavorable distributions of dead- and live-load masses and the rotational component of ground motion about a vertical axis. The torsional amplification factor is introduced to reduce the vulnerability of torsionally imbalanced buildings. The effect of the torsional amplification factor is observed for a symmetric rectangular building with various aspect ratios, where the seismic-force-resisting elements are positioned at a variable distance from the geometrical center in each direction. For verifying the torsional amplification factor in provisions, nonlinear reinforced concrete models with various eccentricities and aspect ratios are used in rock. The difference between the maximum displacements of the flexible edge obtained between using nonlinear static and time-history analysis is very small but the difference between the maximum torsional angles is large.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.9
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• pp.637-643
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• 2015

In recent years, pattern recognition methods have been widely used by many researchers for fault diagnoses of mechanical systems. The soundness of a mechanical system can be checked by analyzing the variation of the system vibration characteristic along with a pattern recognition method. Recently, the hidden Markov model has been widely used as a pattern recognition method in various fields. In this paper, the hidden Markov model is employed for the fault diagnosis of the mass unbalance of a rotating system. Mass unbalance is one of the critical faults in the rotating system. A procedure to identity the location and size of the mass unbalance is proposed and the accuracy of the procedure is validated through experiment.

• Journal of the Earthquake Engineering Society of Korea
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• v.4 no.2
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• pp.83-98
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• 2000

자오방향 및 주변방향으로 피르스트레스트 하중이 작용된 축대칭 쉘 구조물을 기하학적으로 축대칭인 구조물의 특성을 최대한으로 이용할 수 있도록 회전 링요소로 모델화하였다 보강링 요소의 모델은 축대칭 쉘요소를 이용하였으며 본체 구조물과 절점에서 부착되있는 것으로 가정하여 이의 편심을 고려하였다 유체-구조물의 상호관계는 접촉면에서 구조물의 가속도에 비례한 부가질량으로 표현하였으며 부가질량은 유체를 비점성 비압축 및 비회전을 가정하여 유한요소법에 의해 구하였다 이에 대한 수치해석을 통하여 고유진동해석 및 지진하중을 주하중으로 한 동적해석을 실시하였다 프로그램을 통하여 해석한 결과를 프리스트레스 하중 하에서 고유진동수에 대한 정해와 비교한 결과 20개의 요소로 모델링한 경우에서도 정해와 근접한 해를 얻을 수 있었다 또한 내부유체가 있는 경우와 링보강을 한 경우에 대한 고유진동수를 문헌과 비교한 결과 근접한 해를 얻을 수 있었다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.7
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• pp.3577-3581
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• 2013

In order to analyze a pile constructed by vibro-hammer, vibrational characteristics of vibro-hammer should be investigated first. Analytical studies were conducted in order to investigate vibrational properties of vibro-hammer. It is thought that the concept of acting the spring force to the pile head should be replaced by the concept of considering the lumped mass of the exciter and the pile. For the situation of free vibration, spring force increase with increase of spring constant and the amplitude is little affected by the spring constant. Also for the situation of free vibration, amplitude is inversely proportional to the increase of mass of the exciter and it can be seen that spring force increase with amplitude by the same ratio. It can be seen that directions of the spring force and displacement are opposite to that of rotating mass.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.5
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• pp.107-115
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• 2014

In this study, we examined the seismic isolation effects due to the difference between the center of mass of the building and the center of stiffness of isolation layer. Because the base isolation technique is a technique that is highly dependent on the performance of seismic isolation devices installed on the seismic isolation layer, we have to examine the horizontal stiffness of seismic isolation devices after making them. If difference between the design stiffness and the actual stiffness of the seismic isolation device occurred, a big problem may be generated in the upper members on the seismic isolation layer. The analytical results show that the more eccentricity increases, the more maximum response acceleration, story shear and the member forces of the upper part of the structure increases, and the damage is expected to be in excess. Therefore, it is recommended that if possible, isolation devices have to be designed to coincide the center of mass of the building with the center of stiffness of isolation layer. If not after making isolation devices, they need to be relocated to prevent the eccentricity.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1660-1663
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• 2005

Unwanted vibrations are inevitably induced in other directions when pure unidirectional vibration motion is desired for the vertical scratching mechanism. Pure vertical vibration motion of the scratching machine can be obtained by driving identical two motors with symmetrically positioned eccentric unbalance masses. The desired optimal condition for driving pure vertical vibration for the scratching machine is assumed to be the resonance condition in that direction. Imposing the flexibility of the scratching machine in the horizontal direction, we can find out the amount of horizontal vibration component while maintaining the resonance in vertical direction. The desired stiffness in horizontal direction which produces the minimum vibration in horizontal direction are defined which can be used as a guide line to design the supporting structure of the scratching machine.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.10
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• pp.490-498
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• 2020

In this study, the seismic performance of low-rise piloti buildings with eccentric core (shear wall) positions was analyzed and reviewed. A prototype was selected among constructed low-rise piloti buildings with eccentric cores designed based on KBC2005. The seismic performance of the building showed plastic behavior in the X-direction and elastic behavior in the Y-direction. The inter-story drift is larger than that of a concentric core case and has the maximum allowed drift ratio. The displacement ratio of the first story is much larger than that of upper stories, and the frame structure in the first story is vulnerable to lateral force. Therefore, low-rise piloti buildings with eccentric cores need to have less lateral displacement, as well as reinforcement of the lateral resistance capacity in seismic design and seismic retrofit.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.04a
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• pp.218-223
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• 2011

Seated human subjects have been exposed to vertical vibration so as to investigate six-axis biodynamic response. Sixteen males were exposed to random vertical vibration in the frequency range(3~40Hz) at one vibration magnitude(0.224m/$s^2$ r.m.s.). Forces were measured in the vertical, fore-and-aft, lateral, roll, pitch and yaw direction on the seat. The median of cross-axis apparent mass magnitude in the fore-and-aft direction could reach up to 20% of the apparent mass magnitude at resonance frequency. And the median of apparent eccentric mass magnitude in the roll direction could reach up to 15% of the apparent eccentric mass magnitude in the pitch direction at resonance frequency. But cross-axis apparent mass in the lateral direction and apparent eccentric mass in the yaw direction showed very small.

• Journal of Korean Society of Steel Construction
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• v.29 no.5
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• pp.361-368
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• 2017

ASCE 7-10 defines the torsional irregular structure as the one that has large torsional responses caused by the eccentricity. The code requires that these structures should be designed abide by the torsional provisions. This study evaluates the influence of torsional provisions on the performance of the designed multiple steel moment frames with different eccentricity. In this study, 3D response history analyses are performed. The results show that the moment frame design according to the standard with torsional irregularity provisions showed larger performance as the eccentricity increased and the distribution of plastic hinges similarly to orthopedic structures.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.12
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• pp.1121-1127
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• 2010

Human characteristic responding to idle vibration on passenger vehicle was studied to find if affected by seating posture of passenger. When twelve male subjects are exposed to moderate vertical vibration of 0.224 $m/s^2$ r.m.s. at frequency range from 3 Hz to 40 Hz, it was found that seating posture significantly affects to biodynamical characteristics, apparent mass and apparent eccentric mass, at most range of idle vibration frequency(20~40 Hz). The supported thigh contact on rigid seat showed bigger values in the two biodynamical characteristics than the average thigh contact. The bigger apparent mass and apparent eccentric mass in the seating posture of the supported thigh contact can be assumed more strengthened muscle at the frequency range.