• Earthquakes and Structures
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• 제18권3호
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• pp.297-312
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• 2020

The KiK-net by NIED is a vertical array measurement system. In the database of KiK-net, singular pulse waves were observed in the seismic record at the borehole of TTRH02 during the mainshock (the magnitude of Japan Meteorological Agency (M_J) 7.3, M_W 6.8) and aftershock (M_j 4.2) of Tottori-ken Seibu earthquake in 2000. Singular pulse waves were also detected in the seismic records at the borehole of IWTH25 during the Iwate-Miyagi Nairiku earthquake in 2008 (M_J 7.2, M_W 6.9). These pulse waves are investigated by using the wave shape analysis methods, e.g., the non-stationary Fourier spectra and the double integrated displacement profiles. Two types of vibration modes are discriminated as the occurrence mechanism of the singular pulse waves. One corresponds to the reversal points in the displacement profile with the amplitude from 10^-4 m to 10^-1 m, which is mainly related to the fault activity and the amplification pass including the mechanical amplification (collision) of the seismograph in the casing pipe. The other is the cyclic pulse waves in the interval of reversal points, which is estimated as the backlash of the seismograph itself with the amplitude from 10^-5 m to 10^-4 m.

• Journal of Electrical Engineering and Technology
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• 제10권3호
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• pp.983-989
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• 2015

Power transformer is one of the major and key apparatus in electric power system. Monitoring and diagnosis of transformer fault is necessary for improving the life period of transformer. The failures caused by short circuits are one of the causes of transformer outages. The short circuit currents induce excessive forces in the transformer windings which result in winding deformation affecting the mechanical and electrical characteristics of the winding. In the present work, a transformer producing only the radial flux under short circuit is considered. The corresponding axial displacement profile of the windings is computed using Finite Element Method based transient structural analysis and thus obtained displacements are compared with the experimental result. The change in inter disc capacitance and mutual inductance of the deformed windings due to different short circuit currents are computed using Finite Element Method based field analyses and the corresponding Sweep Frequency Responses are computed using the modified electrical equivalent circuit. From the change in the first resonant frequency, the winding movement can be quantified which will be useful for estimating the mechanical withstand capability of the winding for different short circuit currents in the design stage itself.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2014년도 추계학술대회 논문집
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• pp.411-414
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• 2014

Numerical modeling was conducted to estimate the amount of dislocation that may occur across a frictionless fracture during an earthquake using commercial code FLAC3D (Fast Lagrangian Analysis of Continua in 3 Dimensions). The applied motion was calculated to represent a Richter 6.0 magnitude earthquake at distances of 2 km from the fracture. The velocity-time history was generated from Svensk $K{\ddot{a}}arnbr{\ddot{a}}anslehantering$ AB report. In the report, The velocity field resulting from an earthquake on a fault located in the near-field (2 km distance) was modelled using a finite difference program, WAVE. The stress-time history was substituted for velocity-time history to perform dynamic analysis using FLAC3D. During the earthquake, the maximum dislocation and change of shear stress were about 1 cm and 2MPa, respectively. Because the fracture is frictionless in this study, all dislocations relax to zero after the earthquake motions have ceased.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 세계 도시지반공학 심포지엄
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• pp.1307-1316
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• 2009

In this case, powerfulness quorum of destruction side which we have expected are supposed general limit value for rock floor when retaining of earth on the section of rock floor in the urban area. For digging in the urban area, there are a lot of dislocations to be disadvantage for safety of digging ants. The displacement of the pondside didn't converged with the phase of the excavation. Also, the speed of displacement got higher than the percentages of risk in the construction. So, we put into operation Face mapping for checking special quality of dislocations which appear on the digging ants. This results were used to decide a destruction in the case of the final excavation by analyzing with other results. It was possible to know the unstable distribution of a fault line in Face Mapping and to get powerful lens of a surface of discontinuity by tests indoors and outdoors. The results were also used to make a solution. Therefore, It's a successful example using the Partial TopDown for stable digging. And it is important that Face Mapping have to be practiced for solving the uncertainty of ground organization when digging design in the urban city.

• 터널과지하공간
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• 제18권1호
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• pp.58-68
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• 2008

임하댐 비상여수로 터널 공사가 단층파쇄대가 포함된 화강암지역에 굴착되고 있는데 본 터널이 3련 터널임을 감안하여 터널이격거리, 터널막장간 이격거리를 검토하였으며 단층파쇄대가 여수로 터널의 안정성에 미치는 영향을 검토하였다. 이를 위해 여러 가지 지구물리학적 조사와 암반공학적 현장 실험을 실시하였다. 터널 막장간 이격거리는 최소 25 m 이상을 유지하면서 2터널의 선행 굴착이 적합하리라 판단되며 단층대의 영향을 받는 터널 만곡부의 3차원 수치해석결과 2터널의 천단변위 및 내공변위는 미미하며 숏크리트 최대 휨압 축응력, 숏크리트 최대전단응력, 록볼트 최대축력 등을 살펴보면 만곡부 굴착에 따른 응력집중은 미미하여 여수로 터널의 안정성에는 문제가 없는 것으로 판단되었다.

• Smart Structures and Systems
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• 제8권5호
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• pp.501-524
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• 2011

Recent studies have discovered that a conventional passive isolation system may suffer from an excessive isolator displacement when subjected to a near-fault earthquake that usually has a long-period velocity pulse waveform. Semi-active isolation using variable friction dampers (VFD), which requires a suitable control law, may provide a solution to this problem. To control the VFD in a semi-active isolation system more efficiently, this paper investigates experimentally the possible use of a control law whose control logic is similar to that of the anti-lock braking systems (ABS) widely used in the automobile industry. This ABS-type controller has the advantages of being simple and easily implemented, because it only requires the measurement of the isolation-layer velocity and does not require system modeling for gain design. Most importantly, it does not interfere with the isolation period, which usually decides the isolation efficiency. In order to verify its feasibility and effectiveness, the ABS-type controller was implemented on a variable-friction isolation system whose slip force is regulated by an embedded piezoelectric actuator, and a seismic simulation test was conducted for this isolation system. The experimental results demonstrate that, as compared to a passive isolation system with various levels of added damping, the semi-active isolation system using the ABS-type controller has the better overall performance when both the far-field and the near-fault earthquakes with different PGA levels are considered.

• Earthquakes and Structures
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• 제13권3호
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• pp.267-277
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• 2017

Base-isolation is now being adopted as a retrofitting strategy to improve seismic behaviour of reinforced concrete (r.c.) framed structures subjected to far-fault earthquakes. However, the increase in deformability of a base-isolated framed building may lead to amplification in the structural response under the long-duration horizontal pulses of high-magnitude near-fault earthquakes, which can become critical once the strength level of a fire-weakened r.c. superstructure is reduced. The aim of the present work is to investigate the nonlinear seismic response of fire-damaged r.c. framed structures retrofitted by base-isolation. For this purpose, a five-storey r.c. framed building primarily designed (as fixed-base) in compliance with a former Italian seismic code for a medium-risk zone, is to be retrofitted by the insertion of elastomeric bearings to meet the requirements of the current Italian code in a high-risk seismic zone. The nonlinear seismic response of the original (fixed-base) and retrofitted (base-isolated) test structures in a no fire situation are compared with those in the event of fire in the superstructure, where parametric temperature-time curves are defined at the first level, the first two and the upper levels. A lumped plasticity model describes the inelastic behaviour of the fire-damaged r.c. frame members, while a nonlinear force-displacement law is adopted for the elastomeric bearings. The average root-mean-square deviation of the observed spectrum from the target design spectrum together with a suitable intensity measure are chosen to select and scale near- and far-fault earthquakes on the basis of the design hypotheses adopted.

• Structural Engineering and Mechanics
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• 제75권1호
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• pp.33-47
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• 2020

In this paper the dynamic behavior of an isolated building subjected to idealized near-fault pulses is investigated. The building is represented with a simple 2-DOF model. Both linear and non-linear behavior of the isolation system is considered. Using dimensional analysis, in conjunction with closed form mathematical idealized pulses, appropriate dimensionless parameters are defined and self-similar curves are plotted on dimensionless graphs, based on which various conclusions are reached. In the linear case, the role of viscous damping is examined in detail and the existence of an optimum value of damping along with its significant variation with the number of half-cycles is shown. In the nonlinear case, where the behavior of the building depends on the amplitude of the excitation, the benefits of dimensional analysis are evident since the influence of the dimensionless 𝚷-terms is easily examined. Special consideration is given to the normalized strength of the non-linear isolation system that appears to play a complex role which greatly affects the response of the 2-DOF. In the last part of the paper, a comparison of the responses to idealized pulses between a linear fixed-base SDOF and the respective isolated 2-DOF with both linear and non-linear damping is conducted and it is shown that, under certain values of the superstructure and isolation system characteristics, the use of an isolation system can amplify both the normalized acceleration and displacement of the superstructure.

• 자원환경지질
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• 제43권6호
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• pp.637-648
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• 2010

옥천대의 북동변인 주천 지역에 분포하는 송봉층(소위 방림층군)은 선캠브리아 시대의 경기육괴 기반암위에 부정합 관계로 분포하며, 조선누층군의 하부 지층에 대비된다. 이것은 영남육괴와 조선누층군의 관계가 옥천대 남동변에서 역시 부정합이라는 사실과 함께 옥천대 양쪽 경계부의 기반암이 최소한 고생대 초에는 하나였을 것임을 의미한다. 주천 지역에서는 세 번의 변형작용이 인지된다. 첫 번째 변형작용에 의해서 선캠브리아 시대의 화강암이 연성전단대를 따라서 북북동 방향으로 옥천대의 고생대층 상위로 이동하였다. 두 번째 변형작용은 남동방향을 향한 충상단층운동과 이에 수반된 누루하지단층으로 특징 지워진다. 특히 누루하지단층을 경계로 하여 북동쪽 지괴와 남서쪽 지괴 사이에 변형작용 분리가 발생하였다. 세 번째 변형작용은 누루하지단층을 수 km의 변위를 갖는 우수향 주향이동단층으로 재활성시켰다.

• 한국안전학회지
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• 제26권3호
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• pp.52-58
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• 2011

지진별 특성이 사회간접시설에 미치는 영향을 평가하는 것은 내진성능의 향상을 위해 중요한 검토사항이다. 이 연구에서는 근거리 및 원거리 지진의 특성을 고려하여 장주기 골조구조물의 구조거동을 합리적으로 평가하는 방법을 비교분석하였다. 이를 위해서 입력지진동의 영향을 명확하게 반영할 수 있는 대상구조물을 선정하여 탄성 및 비탄성 시간이력해석을 수행하였다. 수치해석결과를 바탕으로 지진특성에 따른 전단력, 모멘트, 가속도 및 변위응답의 분포양상을 검토하고 차이점을 분석하였다. 또한 대상구조물의 비탄성 거동을 파악하기 위해서 소성힌지의 발생순서를 모사운용하여 붕괴발생모드를 해석하였다. 이 연구결과는 장주기 골조구조물의 내진안전성 평가를 위한 효율적인 방법을 제시하고 근거리 지진의 안전성에 미치는 영향을 분석하였다.