• Structural Engineering and Mechanics
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• 제82권5호
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• pp.651-665
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• 2022

While the lateral confinement provided by an FRP jacket to a concrete column is passive in nature, confinement is activated when the concrete expands due to additional compression stresses or significant shear deformations. This characteristic of FRP jacketing theoretically leads to similar initial stiffness properties of FRP retrofitted buildings as the buildings without retrofit. In the current study, to validate this theoretical assumption, the initial stiffness characteristics, and thus, the potential seismic demands were investigated through forced vibration tests on two identical full-scale substandard reinforced concrete buildings with or without FRP retrofit. Power spectral density functions obtained using the acceleration response data captured through forced vibration tests were used to estimate the modal characteristics of these buildings. The test results clearly showed that the natural frequencies and the mode shapes of the buildings are quite similar. Since the seismic demand is controlled by the fundamental vibration modes, it is confirmed using vibration-based full-scale tests that the seismic demands of RC buildings remain unchanged after CFRP jacketing of columns. Furthermore, the damping characteristics were also found similar for both structures.

• Structural Engineering and Mechanics
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• 제67권3호
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• pp.233-244
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• 2018

This study aims at evaluating the performance of repairing technique with CFRPs in recovering cyclic performance of damaged columns in flexure in terms of structural response parameters such as strength, dissipated energy, stiffness degradation. A 2/3 scaled substandard reinforced concrete frame was constructed to represent the substandard RC buildings especially in developing countries. These substandard buildings have several structural deficiencies such as strong beam-weak column phenomenon, improper reinforcement detailing and poor material properties. Flexural plastic hinges occurred at the columns ends after testing the substandard specimen under both constant axial load and reversed cyclic lateral loading. Afterwards, the damaged columns were externally wrapped with CFRP sheets both in transverse and longitudinal directions and then retested under the same loading protocol. In addition, ambient vibration measurements were taken from the undamaged, damaged and the repaired specimens at each structural repair steps to identify the effectiveness of each repairing step by monitoring the change in the natural frequencies of the tested specimen. The ambient vibration test results showed that the applied repairing technique with external CFRP wrapping was proved to recover stiffness of the pre-damaged specimen. Moreover, the lateral load capacity of the pre-damaged substandard RC frame was restored with externally bonded CFRP sheets.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 추계학술대회논문집
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• pp.519-522
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• 2006

Accurate modeling of a dynamic system from experimental data is the bases for the model updating or heath monitoring of the system. Modal analysis or modal test is a routine process to get the modal parameters of a dynamic system. The modal parameters include the natural frequencies, damping ratios and mode shapes. This paper presents a new method that can derive the equations of motion for a dynamic system from the modal parameters obtained by the modal analysis or modal test. The present method based on the relation between the eigenvalues and eigenvectors of the state space equation derives the mass, damping and stiffness matrices of the system. The modeling of a cantilevered beam from modal parameters is an example to prove the efficiency and accuracy of the present method. Using the lateral displacements only, not the rotations, gives limited information for the system. The numerical verification up to now gives reasonable results and the verification with the test data is scheduled.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 춘계학술대회 논문집
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• pp.969-974
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• 2008

As the railway becomes higher, the reliable stability and riding comfort of higher railway are required. To improve the riding comfort of high-speed trains, it is very helpful to use active suspension system for railway. In Japan, the high-speed train, Shinkansen has adopted semi-active suspension system and now it is running in the main trunk. In this paper, the authors introduce several technical trends of vibration control methods of Japanese Shinkansen. And the installation of semi-active suspension to HSR 350x and the test result of test run on the Kyoung-Bu high speed ling are also explained. After development of HSR 350x, new R&D national project of high speed train is progressed by Ministry of Land, Transport, and Maritime Affairs. This project is the development of Electric Multiple Unit of high speed train with 400km/h of maximum test speed. These result would be helpful to progress next generation high speed project.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.273-276
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• 2004

Dynamic model of the Korea standardized rubber-tired AGT light rail vehicle, and boundary conditions between vehicle and infrastructures (running track, guidance rail) were defined to analyze vehicular vibration behaviors occurred at the worst condition for straight running track. Using the commercialized software RecurDyn, resultant forces and vibration accelerations of car body and bogies were analyzed. Based on the Korea performance test criteria for urban transit, vertical and lateral vibration of car body were calculated and evaluated as wearing condition of guide wheels. And resultant forces between bogie guidance frame and guide rail in straight running track were analyzed. As the results, the Korea standardized rubber-tired AGT light rail vehicle satisfied the performance criteria and design requirement .

• 한국철도학회논문집
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• 제4권3호
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• pp.116-122
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• 2001

As freight traffic becomes heavier, the high speed of existing freight cars is essential, instead of the construction of a new railway. The high speed can be achieved by the modifications of freight bogie design. In this paper, an analytical model of freight bogie is developed to decide the critical speed. The dynamic responses of the analytical model are compared with the experimental data from a running test of freight bogie and showed good agreements between them. The analytical model is used to find the design of freight bogie. The parameter studies show that the reduction of wheelset mass ratio and the increase of the axle distance of freight bogie can increase the critical speed, but the primary lateral stiffness has little effects on the critical speed. And this study also shows that smaller wheel conicity deteriorates the running safety of freight car, which means that the overhauling of the wheel of freight bogie should be done regularly.

• 한국지반신소재학회논문집
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• 제10권3호
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• pp.53-62
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• 2011

본 연구에서는 방수제 구조물 및 하부지반에 대하여 1/100 축소모형의 비율을 갖는 토조를 제작, 설계지진 가속도 0.154g의 진동하중 적용시 진동대 모형실험을 통하여 구조물의 거동특성과 내진 안정성을 평가하였다. 실제 시공순서를 재현하여 완성 후 진동대 모형토조 하부에 설정된 지진하중을 발생시켜 지진에 의한 하부지반과 방수제 구조물의 상호작용을 분석하였다. 즉, 구조물의 수평 및 수직 변위, 구조물 하부지반에 작용하는 간극수압 변화, 하부지반 및 방수제 구조물의 최대가속도 변화량 측정 등 계측결과를 비교 분석하여 내진 안정성을 판단하였다.

• Structural Engineering and Mechanics
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• 제64권4호
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• pp.461-472
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• 2017

The dynamic tests of recycled aggregate concrete (RAC) are carried out, the rate-dependent mechanical models of RAC are proposed. The dynamic mechanical behaviors of RAC frame structure are investigated by adopting the numerical simulation method of the finite element. It is indicated that the lateral stiffness and the hysteresis loops of RAC frame structure obtained from the numerical simulation agree well with the test results, more so for the numerical simulation which is considered the strain rate effect than for the numerical simulation with strain rate excluded. The natural vibration frequency and the lateral stiffness increase with the increase of the strain rate. The dynamic model of the lateral stiffness is proposed, which is reasonably applied to describe the effect of the strain rate on the lateral stiffness of RAC frame structure. The effect of the strain rate on the structural deformation and capacity of RAC is analyzed. The analyses show that the inter-story drift decreases with the increase of the strain rate. However, with the increasing strain rate, the structural capacity increases. The dynamic models of the base shear coefficient and the overturning moment of RAC frame structure are developed. The dynamic models are important and can be used to evaluate the strength deterioration of RAC structure under dynamic loading.

• Interaction and multiscale mechanics
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• 제3권4호
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• pp.365-372
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• 2010

Station is an important building in high-speed railway, and its vibration and noise may significantly affect the comfort of waiting passengers. A coupling vibration model for train-structure system is established to analyze and evaluate the vibration level of a typical waiting hall under dynamic train load. The motion of a four-axle vehicle with two suspension system is modeled in multi-body dynamics with linear springs and dampers employed. The station is modeled as a whole finite element structure which is 113 m in longitudinal and 163.5 m in lateral, and the stiffness of the station foundation is considered. According to the assumptions that both wheel and rail are rigid bodies and keep contact to each other in vertical direction, and the wheel/rail interaction and displacement coordination in horizontal direction is defined by the simplified Kalker creep theory, the vehicle spatial vibration model has 27 degrees-of-freedom. An overall analysis procedure is made of the train moving through the station, by which the dynamic responses of the train and the station are calculated. According to the comparison between analysis and test results, the actual connection status between different parts of the station is estimated and the vibration level of the waiting hall is evaluated.

• 소음진동
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• 제11권2호
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• pp.265-275
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• 2001

This research has been performed to reveal the hysteresis phenomena of the hunting motion in a railway passenger cars. It is found that there are some factors and its operation region to make the nonlinear critical speed reacts to them more sensitively than the linear critical speed. The simulation results show that a self steering bogie system can be a substitute proposal to improve curving Performance together with the reduction of hysteresis of critical speed. Full scale roller rig test is carried out for the validation of the numerical results. Finally, it is certified that wear of wheel profile and stiffness discontinuities of wheelset suspension caused by deterioration have to be considered in the analysis to predict the hysteresis of critical speed precisely.