• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.2
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• pp.54-61
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• 2013

Stay cable has a strong axial rigidity due to large initial tension and, on the other hand, it has a weak laterally flexural rigidity. Wind loads or traffic loads cause the cables to vibrate significantly and affect the mechanical properties and the performance of cables of cable-stayed bridge (CSB). Therefore, the development of vibration reduction design is an urgent task to control the vibration vulnerable long-span bridges. As Friction damper (FD) shows to reduce the amplitude and duration time of vibration of cable of CSB from measured date in field test, friction damper can be considered that it is effective device significantly to reduce the amplitude and duration time in vibration of cable of CSB under traffic load, wind load and so on. Vibration characteristics of cable can change according to manufacturing method and type of established form. Nevertheless, analysis method in this study can present the design of friction damper for vibration reduction of cable of cable-stayed bridge from now on.

• Composites Research
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• v.16 no.6
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• pp.48-55
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• 2003

This research makes comparisons of empirical fatigue-lives between AC8A A1 alloy and the metal matrix composites(A1/A12O3, A1/A12O3/A12O3p), and also includes comparisons of fatigue-lives between empirical fatigue-lives and estimated fatigue-lives from regular-periodic load testing, AE method to predict fatigue-crack initiation before visible in sight and SEM(scanning electron microscope) photographs of each material. According to the test results of the notched specimen. the fatigue life of the hybrid metal matrix composites and the metal matrix composites, which are more brittle than the base matrix was shorter than that of the base matrix under both types of loads. In addition, the fatigue-life estimated from the damage summation method and that from experiments at random loads were fairly identical.

• Journal of the Korea Concrete Institute
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• v.14 no.4
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• pp.467-473
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• 2002

The purpose of this study is to investigate the inelastic behavior and ductility capacity of reinforced concrete frame subjected to cyclic lateral load and to provide result for developing improved seismic design criteria. A computer program named RCAHEST(Reinforced Concrete Analysis in Higher Evaluation System Technology) for the analysis of reinforced concrete structures was used. Material nonlinearity is taken into account by comprising tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. The smeared crack approach is incorporated. The strength increase of concrete due to the lateral confining reinforcement has been taken into account to model the confined concrete. In boundary plane at which each member with different thickness is connected local discontinuous deformation due to the abrupt change in their stiffness can be taken into account by introducing interface element. The effect of number of load reversals with the same displacement amplitude has been also taken into account to model the reinforcing steel. The proposed numerical method for the inelastic behavior and ductility capacity of reinforced concrete frame subjected to cyclic lateral load is verified by comparison with reliable experimental results.

• Journal of Navigation and Port Research
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• v.27 no.1
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• pp.63-70
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• 2003

If semi-rigid connections are used for superstructures of very large floating structures (VLFS), the number of rigid connections can be reduced and more economical construction will be possible. In this study, considering service load and wave load in VLFS, the applicability of mixed use of rigid and semi-rigid connections have been studied using three types of connections for a four-bay eight-story frame. Three types of connections are used; top and seat-angle connections with double web-angle(TSD), extended end plate connections, steel tubular column with square external-diaphragm connections. ABAQUS(Finite element analysis program) is used for conducting second order elastic analysis.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.421-424
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• 2009

사장교 케이블의 감쇠비를 추정하기 위하여 실교량 계측을 수행하였다. 사장교 케이블은 감쇠비가 낮고, 고유 진동수가 케이블의 길이에 따라 넓은 범위에 걸쳐 분포하므로, 바람이나 지점 가진에 의하여 과도한 진동이 발생될 수 있다. 케이블 진동 현상의 원인과 발생되고 진행되는 구조는 다양하나, 진동 현상의 가장 중요한 요소는 감쇠비이며, 케이블 진동의 과도한 진동을 감소시키기 위하여, 케이블의 감쇠비를 증가시키는 방법이 널리 사용되고 있다. 사장교 케이블의 다양한 진동 현상에 대한 발생 여부를 판단하고, 케이블 댐퍼와 같은 여러 제진 대책을 설계하고, 설치된 케이블 제진 대책의 성능을 검증하기 위해서는, 케이블의 감쇠비를 추정하는 것이 매우 중요하다. 일반적으로 사용되어져 온 케이블의 감쇠비 추정 방법은 정해진 모드로 자유 진동을 발생시킨 후, 진폭의 감소 추세로부터 Logarithmic Decrement를 계산하여 감쇠비를 구하는 방법이다. 그러나 수백m에 이르는 긴 케이블에서 정해진 모드의 자유 진동을 발생시키는 것은 쉽지 않다. 최근에는 상시 진동으로부터 감쇠비를 추정하는 여러 기법들이 개발되어져 왔으며, Frequency Domain Decomposition Method나 Stochastic Subspace Identification Method 등이 많이 사용되고 있다. 이 논문에서는, 상시진동 기반의 기법들을 사용하여, 사장교 케이블의 감쇠비를 추정하였으며, 추정된 감쇠비의 신뢰도를 높이기 위해, 측정시간을 늘리고, 가진 풍하중의 영향을 반영하여 보정하였다. 또한 추정된 감쇠비를 Buffeting 진동과 와류 진동과 같이 진동 현상과 진폭별로 분석하였다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.1
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• pp.853-859
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• 2015

1-DOF shear building was designed, built and tested to investigate the interactions between the shear building and the shaking table excited harmonically by the electro-magnetic forces. In the experiments horizontal accelerations of the shaking table and the shear building were measured. To understand the experimental results experimental setting was modeled as an unconstrained 2-DOF system under the hormonic forces. The responses of the shear building and the shaking table of the unconstrained 2-DOF system were found with the equations of motions. The magnification factors of the table and the shear building with respect to the amplitude of the harmonic forces and the transmission of the shear building with respect to the table excitations were found and compared with the experimental results.

• Journal of Astronomy and Space Sciences
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• v.26 no.4
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• pp.511-520
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• 2009

In this study, the Ocean Tide Loading (OTL) constituents were detected by the Precise Point Positioning (PPP) technique using GPS. Then, the GPS estimates of OTL constituents were compared with the predictions of the ocean tide models. We picked three permanent GPS stations as test sites and they are ICNW, SEOS, and CJUN. To detect the OTL constituents using GPS, we created vertical coordinate time series at 10-minute intervals using the PPP approach implemented in the GIPSY software. Through the tidal harmonic analysis of this height time series, the four major constituents ($M_2$, $S_2$, $K_1$, $O_1$) were determined. The amplitude obtained from the GPS height time series of the OTL constituents showed best match with the model predictions at CJUN, while the phase showed closest match at ICNW. The amplitude accuracy of the $M_2$, which is the dominant factor out of the 11 major constituents, was 24.8% on average.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.2
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• pp.110-117
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• 1999

In order to ultrasonically evaluate creep cavities pure copper samples were subjected to creep test and their microstructures were examined. Ultrasonic velocities. frequency-dependent magnitude spectra and attenuations were measured on a series of copper samples obtained from the different stages of creep test. Velocities measured in three directions with respect to the loading axis decreased and their anisotropy increased as a function of the creep-induced porosity. The anisotropic behavior could be attributed to the progressive change of pore shape and preferred orientation as the creep advanced. The 2% porosity by volume decreased the longitudinal and shear wave velocities by 11% and 4%, respectively. Furthermore, both velocities decreased nonlinearly with the porosity. As the creep damage developed, the magnitude spectra lost high frequency components and their central frequencies shifted to lower values. The attenuation showed almost linear behavior in the frequency range used. Normalized velocity, central frequency shift and attenuation slope were selected as nondestructive evaluation parameters. These results were presented and showed good relations with the porosity content.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.12
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• pp.1027-1035
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• 2016

In this study, a strain-controlled fatigue test of widely-used 316L stainless steel with excellent corrosion resistance and mechanical properties was conducted, in order to assess its fatigue life. Low cycle fatigue behaviors were analyzed at room temperature, as a function of the strain amplitude and strain ratio. The material was hardened during the initial few cycles, and then was softened during the long post period, until failure occurred. The fatigue life decreased with increasing strain amplitude. Masing behavior in the hysteresis loop was shown under the low strain amplitude, whereas the high strain amplitude caused non-Masing behavior and reduced the mean stress. Low cycle fatigue life prediction based on the cyclic plastic energy dissipation theory, considering Masing and non-Masing effects, showed a good correlation with the experimental results.

• Composites Research
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• v.14 no.5
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• pp.46-53
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• 2001

In this research, damage behavior of singly oriented ply (SOP) fiber metal laminate (FML) subjected to concentrated load was studied. The static indentation tests were conducted to study fiber orientation effect on damage behavior of FML. During the static indentation tests, acoustic emission technique (AE) was adopted to study damage characteristics of FML. AE signals were obtained by using AE sensor with 150kHz resonance frequency and the signals were compared with indentation curves of FML. The damage process of SOP FML was divided by three parts, i.e., crack initiation, crack propagation, and penetration. The AE characteristics during crack initiation show that the micro crack is initiated at lower ply of the plate, then propagate along the thickness of the plate with creating tiber debonding. The crack grow along the fiber direction with occurring 60∼80dB AE signal. During the penetration, the fiber breakage was observed. As fiber orientation increases, talc fiber breakage occurs more frequently. The AE signal behaviors support these results. Cumulative AE counts could well predict crack initiation and crack propagation and AE amplitude were useful for the prediction of damage failure mode.