• Journal of the Earthquake Engineering Society of Korea
• /
• v.14 no.3
• /
• pp.23-30
• /
• 2010

Seismic qualification (SQ) is required prior to the installation of safety related electrical cabinets in nuclear power plants (NPPs). Modal identification of the electrical equipment is one of the most significant steps to perform SQ, and is an essential process to construct a realistic analytical model. In this study, shaking table tests were conducted to identify a variation of the dynamic characteristics of a seismic monitoring system cabinet installed in NPPs according to the excitation level. Modal identification of the cabinet has been performed by a frequency domain decomposition method. The results of this study show that the dynamic properties of the cabinet are nonlinearly varied according to the excitation level and the specimen behaves significantly in a nonlinear manner under safe shutdown earthquake motion in Korea. The main sources of the nonlinear behavior of the specimen have been judged by friction forces and geometrical nonlinearity rather than material nonlinearity. The nonlinear variation of the dynamic characteristics of the electrical cabinet might be accepted as an important fact that should be considered during the SQ of safety related equipment.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.12 no.9
• /
• pp.4239-4249
• /
• 2011

In the country with frequent earthquakes like Japan, resistance to earthquake is assessed on the basis that Dam body's Face slab is destroyed by concentrated stress. In our country this kind of modeling and analysis is not yet definitely established. This paper performed pseudo static analysis and dynamic analysis for CFRD and evaluated reliability with the results of Shaking Table Test. The Seismic coefficient method, modified seismic coefficient method, Newmark method of Pseudo-static analysis and frequency domain response analysis, time domain history analysis of dinamic analysis were used. The analysis results were differ between analysis method, but the trends of acceleration and displacement were good agreement with the results of shaking table test.

• 한국방재학회:학술대회논문집
• /
• 2011.02a
• /
• pp.74-74
• /
• 2011

본 연구에서는 중앙경간 54m, 교폭 4m의 사장교형식의 보도교로 측경간은 계단으로 이루어진 1경간 케이블교량을 대상으로 보행하중에 의한 수직진동을 제어하기 위해 제진장치(TMD)를 적용하기로 하고 실물 TMD의 설계 및 제작 그리고 설치 및 제어성능실험을 수행하였다. 우선 사장교형식의 교량. 그리고 1경간 교량이라는 점에서 상대적으로 감쇠율이 낮을 것으로 예측되었고 또한 54m의 경간장이 보행자가 가진 주파수에 근접한 고유진동수를 나타낼 것으로 사료되어 Eurocode 2 part 2(EC5-2)의 규준에 따라 1인 및 다수 보행하중에 의한 보도교의 발생가속도를 산출하였다. 이 경우 최대가속도는 다수의 보행자가 연속적으로 진행할 때 발생하였으며, 수직방향의 가속도가 사용성기준을 초과하는 것으로 나타났다. 또한 구조해석프로그램에 의한 고유치 해석결과, 보행하중의 주파수대역내에 진동모드가 존재하는 것으로 나타났다. 따라서 본 교량의 설계단계에 있어서 보행진동을 제어하기 위하여 유지관리가 용이한 수동형의 동조질량감쇠장치(Tuned Mass Damper)를 적용하기로 하였으며 TMD의 설계에서는 TMD의 제어목표를 만족시킬 수 있는 TMD의 가동질량(moving mass)을 우선적으로 결정하였고, 이로부터 Den Hartog의 제안식에 따라 TMD의 고유진동수비, 유효감쇠비를 산정하였다. 산정된 변수들을 이용하여 설계된 TMD는 현장설치 및 튜닝의 편의성을 고려하여 수평 외팔보형식으로 설계, 제작되었으며 제작된 TMD의 경우 회전축에 대해 질량, 스프링, 댐퍼의 중심거리를 조정함으로써 TMD의 진동수, 강성, 감쇠력을 상대적으로 매우 용이하게 조절할 수 있으며, 조정범위 또한 광범위하여 일반 TMD에 비해 현장설치시 대상구조물에 동조시키기가 용이하며, 작동시 마찰감쇠가 거의 없다는 장점이 있다. 현장설치전에 제작된 TMD를 대상으로 자유진동 시험을 통하여 질량의 중심거리, 스프링 크기 그리고 댐퍼의 설치유무를 각각 변화시키며 TMD의 자유진동 데이터를 취득하였다. 각각의 시험에서 얻어진 데이터로부터 스펙트럼해석을 통하여 고유진동수를 구하였고, 자유진동 파형으로 부터 감쇠비를 구하였다. TMD는 일반적으로 제어모드의 변형형상이 가장 큰 곳에 설치되었을 때 최대의 제진효과를 발휘할 수 있다. 그러나 현장여건상 설치가 불가능하거나 미관을 해치는 경우에는 가능한 범위 내에서 TMD 제어효율이 가장 크게 발휘할 수 있는 곳을 선택하여야 한다. 본 보도교의 경우, 중앙경간 중심부에서 가장 큰 모드변형형상을 나타내지만, 보도교의 상판 연결부 등에 따른 TMD 시공문제로 인하여 TMD 설치위치는 교량 중앙에서 양 방향으로 1.25m 떨어진 곳에 대칭으로 총 2기를 설치하기로 하였다. 일반적으로 TMD의 모든 설계변수는 구조물의 설계단계에서 수행된 구조해석결과에 근거하여 설정하므로 완공된 구조물, 즉 실제보도교의 동적특성을 계측하여 정확하게 진동수를 튜닝하여야 한다. 구조해석에 의한 보도교의 수직방향(TMD 작동방향) 고유진동수는 1.5225 Hz이며, 감쇠비는 규준에 의하여 0.6 %로 가정하였다. 그러나 이 값들은 구조해석모델 및 재료적 특성과 시공상의 오차에 의하여 실제와 다를 수 있으므로 현장계측에 의한 확인이 요구된다. 또한 TMD의 제진효율이 설계시의 목표대로 확보되었는지도 확인해야 하므로 현장튜닝 및 성능시험을 실시하였다. 보도교의 가진은 사전에 실시한 상시 미진동계측결과를 토대로 2Hz를 목표로 하여 인력가진실험을 수행하였고, 탁월진동 주파수는 1.9896Hz로 나타나 구조해석결과와 오차가 있음을 알 수 있다. 가진실험결과를 토대로 TMD의 진동수를 최적진동수비로 튜닝하고 인력가진 실험을 다시 실시하여 TMD의 진동제어성능을 검토하였다. TMD 튜닝 전, 후의 보도교 감쇠비를 비교한 결과, TMD를 설치함으로써 약 4.218%의 감쇠비 증가가 있음을 알 수 있다.

• Journal of the Korean Geotechnical Society
• /
• v.19 no.6
• /
• pp.363-369
• /
• 2003

The purpose of this study is to understand the dissipation pattern of excess pore pressure after liquefaction and to estimate the variation in permeability during shaking load, which should be known for settlement predictions of the ground undergoing liquefaction. In this study, 1-g shaking table tests were carried out for 5 different kinds of sands, all of which had high liquefaction potentials. During the tests excess pore pressure at various depths, and surface settlements were measured. The measured dissipation curve of the excess pore pressure after liquefaction was linearly simulated using the solidification theory, and from the analysis of the slopes of linearly simulated curves, the correlation between dissipation velocity and the gradation characteristics was obtained. By substituting this correlation and the measured settlement to the dissipation velocity equation recommended in solidification theory, the permeability during dissipation was calculated, which was used for estimating the permeability variation during shaking load. The dissipation velocity of excess pore pressure after liquefaction had a linear correlation with the effective grain size divided by the coefficient of uniformity. The permeability during dissipation and liquefaction increased by 1.1∼2.8 times and 1.4∼5 times compared to the initial permeability of the original ground, respectively. And the amount of increase became greater as the effective grain size of the test sand increased and the coefficient of uniformity decreased.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2001.05a
• /
• pp.342-349
• /
• 2001

Water tunnel에서 반향음의 영향을 효과적으로 배제하고 수중 소음원의 위치 및 소음 수준을 계측하기 위하여 하이드로폰 어레이 시스템을 개발하였다. 계측 시스템의 신호 대 잡음비를 개선하기위해 48채널의 하이드로폰 어레이를 사용하였고, 당사 고유의 하이드로폰 설치 방법을 개발하였다. 개발된 설치 방법은 터널 벽면의 난류 변동 압력의 영향을 감소시켜 200Hz-1KHz 영역에서 통상적이 설치 방법 대비 약 20㏈ 의 신호 대 잡음비 개선 효과를 얻었다. 또한 40KHz 이상의 주파수까지의 수중 방사 소음 계측을 위하여 100kS/s의 고속 동시 데이터 획득 장치를 개발하였다. 개발된 하이드로폰 어레이 시스템은 성능 시험을 통하여 20KHz 이내의 주파수 영역에서 단일 소음원의 위치를 비교적 정확하게 찾아낼 수 있었다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2011.10a
• /
• pp.446-451
• /
• 2011

External vibration occurred during vehicle's movement can affect performance of communication equipment and reliability of internal critical components of it. Therefore, through environmental testing, verification is performed prior to system test in order to prevent these problems. In this study, anti-vibration design is applied to compensate for the failure in certain frequencies during environmental test. Through the dynamic analysis according to the changes of mount configuration, optimization of the mount assemble structure was performed.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.16 no.5 s.110
• /
• pp.452-456
• /
• 2006

The critical speeds and mode shapes are most important to determine the behaviors of rotor in designing rotating machinery. As the capacity and span of turbine-generator increases, the turbine-generator system is composed of many components such as bearings, pedestal, turbine and hood and so on. Also, it is getting flexible and has many critical speeds. Especially, as the characteristics of bearing-pedestal are very complicated, they affect the entire vibration characteristics of turbine-generator system. In this paper, it is observed how to determine the equivalent dynamic stiffness of bearing-pedestal by analytical and experimental method.

• Journal of the Korean Geotechnical Society
• /
• v.17 no.6
• /
• pp.207-213
• /
• 2001

Shaking table tests to investigate the dynamic friction behavior of interfaces between dense dry granular soils and construction material(concrete) were performed and the results are reported. The results show the variation of dynamic interface friction coefficients between dense dry granular soils and construction material was small in the sliding velocity range employed in this study. It was also observed that dynamic interface friction coefficients decreased as mean grain sizes of granular soils increased. These coefficients were compared with the friction coefficients obtained from the peak internal friction angles of the same granular soils by plane strain compression tests.

• Journal of the Korea Concrete Institute
• /
• v.20 no.4
• /
• pp.451-458
• /
• 2008

The near-fault ground motion (NFGM) is characterized by a single long period velocity pulse of large magnitude. NFGM's have been observed in recent strong earthquakes, Izmit Turkey (1999), Kobe Japan (1995), Northridge USA (1994), etc. These strong earthquakes have caused considerable damage to infrastructures because the epicenter was close to the urban area, called as NFGM. Extensive research for the near-fault ground motion (NFGM) have been carried out in strong seismic region, but limited research have been done for NFGM in low or moderate seismic regions because of very few records. The purpose of this study is to investigate and analyze the effect of near-fault ground motions on reinforced concrete (RC) bridge piers with lap-spliced longitudinal reinforcing steels. The seismic performance of four RC bridge piers under near-fault ground motions was investigated on the shake table. In addition, a RC bridge pier is subjected to pseudo-dynamic loadings. Test results showed that large residual displacements were observed in RC bridge piers under NFGM. RC specimens on the shake table failed at relatively low displacement ductility, compared with the displacement ductility of RC bridge pier subjected to pseudo-dynamic loadings.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.22 no.4
• /
• pp.337-346
• /
• 2020

Traffic jam and congestion in urban areas has caused the need to improve the utility of underground space. In response, research on underground structures is increasingly being conducted. Notably, a double-deck tunnel is one of the most widely used of all those underground structures. This double-deck tunnel is separated by the middle slab into the upper and lower roadways. Both vehicle load and earthquake load cause the middle slab to exhibit dynamic behavior. Earthquake-related response characteristics, in particular, are highly complex and difficult to interpret in a theoretical context, and thus experimental research is required. The aim of the present study is to assess the stability of a double-deck tunnel's middle slab of the Collapse Prevention Level and Seismic Category 1 with regard to the presence of vibration-damping Rubber Bearings. In vibration table tests, the ratio of similitude was set to 1/4. Linings and vibrating platforms were fixed during scaled model tests to represent the integrated behavior of the ground and the applied models. In doing so, it was possible to minimize relative behavior. The standard TBM cross-section for the virtual double-deck tunnel was selected as a test subject. The level of ground motion exerted on the bedrock was set to 0.154 g (artificial seismic wave, Collapse Prevention Level and Seismic Category 1). A seismic wave with the maximum acceleration of 0.154 g was applied to the vibration table input (bedrock) to analyze resultant amplification in the models. As a result, the seismic stability of the middle slab was evaluated and analyzed with respect to the presence of vibration-damping rubber bearings. It was confirmed that the presence of vibration-damping rubber bearings improved its earthquake acceleration damping performance by up to 40%.