• Proceedings of the Computational Structural Engineering Institute Conference
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• 1997.04a
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• pp.224-231
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• 1997

A study on the seismic responses for a base isolated structure subjected to earthquakes with different frequency characteristics is peformed with time history analyses. Two types of seismic inputs are considered in these analyses, one is short period earthquakes such as El Centro(1940, NS), the other is long period ones such as Mexico(1985). The seismic responses of the base isolated structure depend on seismic input types and isolation frequencies. In this study the 0.5 Hz of isolation frequency for short period earthquakes remarkably reduces the acceleration responses, increases the relative displacements of isolator that are still within the proposed limits of isolator. However higher isolation frequency for long period earthquakes is more adequate to reduce the seismic responses of the base isolated structures; in the study 0.75 Hz is effective to Mexico 1985 earthquake.

• Earthquakes and Structures
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• v.3 no.3_4
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• pp.315-340
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• 2012

There are many types of seismic isolation devices that are being used today for structural control of earthquake response in buildings. The most commonly used are sliding bearings and elastomeric bearings, the latter with or without lead core. An alternative solution is the use of steel springs combined with viscoelastic fluid dampers, which is the case discussed in this paper. An analytical study of a three-story building supported on helical steel springs and viscoelastic fluid dampers, GERB Control System (GCS), subjected to near-fault earthquakes is presented. Several earthquakes records have been obtained by the acceleration network installed in the isolated building and in its non-isolated twin since they were finished. These experimental results are analysed and discussed. The aim is to show that the spring-based system can be an alternative for base isolation of small building located near active faults.

• Structural Engineering and Mechanics
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• v.18 no.3
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• pp.343-362
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• 2004

Rocking response of rigid bodies with rectangular footprint, freely standing on horizontal rigid plane is studied analytically. Bodies are subjected to simulated single component of horizontal earthquakes. The effect of baseline correction, applied to simulated excitations, on the rocking response is first examined. The sensitiveness of rocking motion to the details of earthquakes and geometric properties of rigid bodies is investigated. Due to the demonstrated sensitivity of rocking response to these factors, prediction of rocking stability must be made in the framework of probability theory. Therefore, using a large number of simulated earthquakes, the effects of duration and shape of intensity function of simulated earthquakes on overturning probability of rigid bodies are studied. In the case when a rigid body is placed on any floor of a building, the corresponding probability is compared to that of a body placed on the ground. For this purpose, several shear frames are employed. Finally, the viability of the energy balance equation, which was introduced by Housner in 1963 and widely used by nuclear power industry to estimate the rocking stability of bodies, is evaluated. It is found that the equation is robust. Examples are also given to show how this equation can be used.

• Smart Structures and Systems
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• v.16 no.4
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• pp.725-742
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• 2015

Tuned mass dampers (TMD) are devices employed in vibration control since the beginning of the twentieth century. However, their implementation for controlling the seismic response in civil structures is more recent. While the efficiency of TMD on structures under far-field earthquakes has been demonstrated, the convenience of its employment against near-fault earthquakes is still under discussion. In this context, the study of this type of device is raised, not as an alternative to the seismic isolation, which is clearly a better choice for new buildings, but rather as an improvement in the structural safety of existing buildings. Seismic records with an impulsive character have been registered in the vicinity of faults that cause seismic events. In this paper, the ability of TMD to control the response of structures that experience inelastic deformations and eventually reach collapse subject to the action of such earthquakes is studied. The results of a series of nonlinear dynamic analyses are presented. These analyses are performed on a numerical model of a structure under the action of near-fault earthquakes. The structure analyzed in this study is a steel frame which behaves as a single degree of freedom (SDOF) system. TMD with different mass values are added on the numerical model of the structure, and the TMD performance is evaluated by comparing the response of the structure with and without the control device.

• Journal of Soil and Groundwater Environment
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• v.29 no.4
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• pp.32-43
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• 2024

Recently, numerous earthquakes have caused significant casualties and property damage worldwide, including major events in 2023 (Türkiye, M7.8; Morocco, M6.8) and 2024 (Noto Peninsula, Japan, M7.6; Taiwan, M7.4). In South Korea, the frequency of detectable and noticeable earthquakes has been gradually increasing since the M5.8 Gyeongju Earthquake. Notable recent events include those in Jeju (M4.9), Goesan (M4.1), the East Sea (M4.5), and Gyeongju (M4.0) since 2020. This study, for the first time in South Korea, monitored groundwater levels and temperatures at a 1Hz frequency to observe the responses in groundwater to moderate and small earthquakes primarily occurring within the country. Between April 23, 2023, and May 22, 2023, 17 earthquakes were reported in the East Sea region with magnitudes ranging from M2.0 to M4.5. Analysis of groundwater level responses at the Gangneung observation station revealed fluctuations associated with five of these events. The 1Hz observation data clearly showed groundwater level changes even for small earthquakes, indicating that groundwater is highly sensitive to the frequent small earthquakes recently occurring in South Korea. The analysis confirmed that the maximum amplitude of groundwater level changes due to earthquakes is proportional to the earthquake's magnitude and the distance from the epicenter. These findings highlight the importance of precise 1Hz-level observations in earthquake-groundwater research. This study provides foundational data for earthquake monitoring and prediction and emphasizes the need for ongoing research into monitoring the changes in groundwater parameters (such as aquifer characteristics, quantity/quality, and contaminant migration) induced by various magnitudes of earthquakes that may occur within the country in the future.

• Structural Engineering and Mechanics
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• v.76 no.6
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• pp.751-763
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• 2020

Available records of recent earthquakes show that near-field earthquakes have different characteristics than far-field earthquakes. In general, most of these unique characteristics of near-fault records can be attributed to their forward directivity. This phenomenon causes the records of ground motion normal to the fault to entail pulses with long periods in the velocity time history. The energy of the earthquake is almost accumulated in these pulses causing large displacements and, accordingly, severe damages in the building. Damage to structures caused by past earthquakes raises the need to assess the chance of future earthquake damage. There are a variety of methods to evaluate building seismic vulnerabilities with different computational cost and accuracy. In the meantime, fragility curves, which defines the possibility of structural damage as a function of ground motion characteristics and design parameters, are more common. These curves express the percentage of probability that the structural response will exceed the allowable performance limit at different seismic intensities. This study aims to obtain the fragility curve for low- and mid-rise structures of reinforced concrete moment frames by incremental dynamic analysis (IDA). These frames were exposed to an ensemble of 18 ground motions (nine records near-faults and nine records far-faults). Finally, after the analysis, their fragility curves are obtained using the limit states provided by HAZUS-MH 2.1. The result shows the near-fault earthquakes can drastically influence the fragility curves of the 6-story building while it has a minimal impact on those of the 3-story building.

• Journal of the Korean earth science society
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• v.40 no.3
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• pp.272-282
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• 2019

Although the knowledge of current seismicity is a critical information for making and implementing effective earthquake-related policy, the detailed seismicity information of the metropolitan areas with high-population density has been largely underestimated due to the high-level of cultural noise and small earthquake magnitude. This study presents 12 earthquakes including 2 earthquakes previously known and 10 additional earthquakes occurred from 2010 to 2017 in Busan, but they were unreported by the Korea Meteorological Administration. Matched filter technique is used to detect micro-earthquakes. Although the epicenters of micro-earthquakes though present a distinguished linearity, a correlation with faults in the area is unknown. A repeated micro-seismicity suggests that there are subsurface structures responsible for observed events. If large earthquakes occur along the fault in Busan, they may cause catastrophic natural disasters. Given the fact that the recent earthquakes did not accompany any surface signatures, it is highly recommended that the current micro-seismicity be investigated, and updated seismicity information be incorporated into establishing active fault maps in Korea.

• Journal of the Korean Geosynthetics Society
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• v.23 no.1
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• pp.49-60
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• 2024

Recently, the frequency and intensity of typhoon-induced wave loading are increasing due to changed marine environments such as climate change. In addition, frequent earthquakes are causing a lot of damage around the world, including in Japan, Chile, Haiti, China, and Indonesia. In Korea, damage from typhoons has also been increasing since the 2000s, and the frequency and intensity of earthquakes are also increasing. Korea is surrounded by sea on three sides, so typhoons can cause a lot of damage to coastal structures, and earthquakes also cause a lot of damage to coastal structures. As such, the frequency and intensity of typhoon-induced wave loading and earthquakes are increasing both domestically and internationally, but there is no research linking typhoons and earthquakes. Therefore, in this study, numerical analysis was performed for a total of four cases by linking typhoon waves and earthquakes to the caisson breakwater. Numerical analysis was performed by applying wave loads in Case 1 and seismic wave in Case 2, seismic wave after wave loads in Case 3, and wave loads after seismic wave in Case 4. As a result of the numerical analysis, it was confirmed that in Case 3 and Case 4, which linked a typhoon and earthquakes, the damage caused by each load increased compared to Case 1 and Case 2 because the load was applied while the existing ground strength was reduced. In addition, it was confirmed that the greatest damage occurred in Case 3, in which seismic wave were applied after the wave loads.

• Journal of the Earthquake Engineering Society of Korea
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• v.21 no.2
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• pp.95-103
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• 2017

In order to modeling seismic isolation system such as lead-rubber bearing (LRB), bilinear model is widely used by many researchers. In general, an actual force-displacement relationship for LRB has a smooth hysteretic shape. So, Bouc-Wen model with smooth hysteretic shape represents more accurately actual hysteretic shape than bilinear model. In this study, seismic responses for seismically isolated nuclear power plant (NPP) with LRB modelled by Bouc-Wen and bilinear models are compared with those of NPP without seismic isolation system. To evaluate effect of earthquake characteristics for seismic responses of NPP isolated by LRB, 5 different site class earthquakes distinguished by Geomatrix 3rd Letter Site Classification and artificially generated earthquakes corresponding to standard design spectrum by Reg. Guide 1.60 are used as input earthquakes. From the seismic response results of seismically isolated NPP, it can be observed that maximum displacements of seismic isolation modelled by Bouc-Wen model are larger than those by bilinear model. Seismic responses of NPP with LRB is significantly reduced than those without LRB. This reduction effect for seismic responses of NPP subjected to Site A (rock) earthquakes is larger than that to Site E (soft soil) earthquakes.

• The Journal of Engineering Geology
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• v.5 no.3
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• pp.309-329
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• 1995

Seismicity and stress state in the Korean peninsula are studied using the catalogue of historical earthquakes and that from the seismological observations before the 1960s, with the aid of instrumental catalogue up to 1995. It seems that the completeness of the historical catalogue has a significant enhancement during the first two hundred years of the Yi dynasty, i.e., from the 1400s to the 1600s. From then on the catalogue may be regarded as near to complete for strong earthquakes in an overall sense. From the distribution of strong earthquakes, three seismic zones may be identified. From the south to the north, those are the southern seismic zone (남부지진대), the Seoul-Pyongyang seismic zone (서울-평양지진대), and the northern seismic zone (북부지진대). The mechanisms of some earthquakes obtained using first motion read- ings are reevaluated with a grid testing method. The results indicate that the compressional axis is nearly horizontal along the EW direction.