Search Results (21)

This study investigates how structural dynamic characteristics affect the response to high-frequency dominant seismic excitations, using a 3D numerical analysis considering soil–structure interaction (SSI). For this purpose, an SSI analysis was conducted using the finite element analysis software LS-DYNA, incorporating four representative Korean geotechnical characteristics and the 2016 Gyeongju earthquake, characterized by dominant high-frequency components. A comparison was conducted between a fixed-end model without considering SSI and an embedded model with SSI for a high-rise structure (40 stories) with low natural frequencies, and a low-rise structure (5 stories) with high natural frequencies. The analysis focused on key dynamic responses, including the natural frequency, frequency of maximum response, and maximum relative displacement of the structures, to identify differences in the SSI effect based on the structures’ dynamic characteristics and the soil types. The analysis generally revealed that the SSI effect lowers the natural frequencies of structures and increases the damping effect. It was also found that depending on the match between the dominant frequency range of the seismic excitations and the range of the structure’s natural frequencies, larger dynamic responses were calculated when SSI was considered, suggesting that it may be necessary to consider SSI for conservative design results. Full article

This study examines the hydrogeological response to the 12 September 2016 Gyeong-Ju earthquake (ML 5.8) in the southeastern region of the Korean Peninsula. Using 2D hydro-mechanical coupled bonded particle modeling, we simulated the dynamic fault rupture process to analyze stress redistribution and its impact on pore pressure and groundwater levels (GWLs). The results indicated that compressional areas correlated strongly with pore pressure increases and GWL rises, while extensional areas showed decreases in both. Observations from the groundwater monitoring Well 5 at Gyeong-Ju San-Nae and Well 8 at Gyeong-Ju Cheon-Buk, located approximately 15 km from the earthquake’s epicenter, aligned well with the model’s predictions and interpretation, providing validation for the simulation. These findings highlight the capability of hydro-mechanical models to capture fault-induced hydrological responses and offer valuable insights into the interplay between seismic activity and groundwater systems. Full article

In Korea, the underground silo structure for low- and intermediate-level radioactive waste disposal facilities has been constructed and operated since 2014. Large-scale earthquakes occurred in 2016 and 2017, respectively, in Gyeongju and Pohang areas near the underground silo structures, and interest in the stability of the underground silo increased significantly. In this paper, one-dimensional free-field analyses have been carried out before the three-dimensional silo dynamic analyses subjected to earthquake loadings. As an additional study, a new form of the finite element equilibrium equation is derived in terms of relative motions, which is essentially the same equation expressed in terms of total motions where the base shear force is applied to the earthquake load. The accuracy of conventional finite element solutions is evaluated by directly comparing them with closed-form solutions by frequency domain analysis such as SHAKE91. Full article

Due to a heightened interest in the field of earthquakes after two moderately sized earthquakes occurred in Gyeongju and Pohang, this study explores which ground motion prediction equations are compatible for the South Korea region. Due to data availability, ground motions from five earthquakes of moderate magnitude were used for comparing against selected ground motion models. Median rotated response spectral ordinates at a period of 0.2 s were extracted from these ground motions, which served as a basis for comparison. Twelve ground motion models were considered from the Next Generation Attenuation West, West2, and East programs due to their extensive databases and robust analytical techniques. A comparison of relative residuals, z-score, and each event found that the subset of Next Generation Attenuation—East ground motion prediction equations did not perform as well as the suite of Next Generation Attenuation—West2 ground motion prediction equations, most likely due to the regional simulations involved in developing the database. Interestingly, the ground motion models that performed relatively well were from the set designed for rock conditions. Full article

After the Gyeongju earthquake in 2016 and the subsequent one in Pohang the following year, there is an imminent necessity to evaluate the risk of earthquakes accurately as well as respond to the risks on the Korean peninsula. For this purpose, the existence and movement of a fault should be investigated in the area. In this study, we calculated the displacement of the crust around the mass production fault using GNSS (Global Navigation Satellite System) data and analyzed the deformation characteristics by applying the method of stress calculation. The Yangsan Fault Zone has been analyzed with a total of 24 GNSS stations between 2018 and 2021. Data processing was conducted with Bernese GNSS Software, which requires high-precision orbit, satellite clock, ionosphere information for high-precision position estimation. By accumulating daily solutions over the three years to produce the final solution with the velocity of the stations, the Yangsan Fault Zone moved about 32 mm per year southeast on average. Based on the results, the movements of the stations on either side of the Faults are almost the same. Stress analysis of the Yangsan Fault Zone showed a large east–west expansion during 2018–2019 but decreased in stress afterwards, thus it is evaluated to be relatively stable compared to the past. However, due to the nature of crustal variation continuous monitoring research with long-term data processing should be followed, which will be discussed in further research. Full article

Groundwater levels at a power plant site were analyzed using statistical techniques to ascertain if there was any influence from an earthquake that occurred approximately 27 km away. This earthquake was the Mw 5.5 Gyeongju earthquake that occurred on 12 September 2016 at 11:32 UTC in South Korea. Groundwater levels at five groundwater monitoring wells were examined against the 2016 Gyeongju earthquake, local precipitation, and local tide levels. A visual examination of the groundwater monitoring well data suggested no real effect or influence from the earthquake. However, precipitation data implied a rise in groundwater levels. Cross-correlation analyses also showed no significant relationship between groundwater levels and the earthquake in question. Interestingly, three of the five groundwater monitoring wells suggested a low-to-moderate correlation between groundwater and tide levels while the remaining two groundwater monitoring wells showed a low-to-moderate correlation between groundwater levels and precipitation. Granger causality tests suggested a closer relationship between tide and groundwater levels for two of the wells, questionable results describing precipitation for another two wells, and no relationship with the earthquake for four of the wells. Data resolution plays an important role in the analyses. Full article

Earthquake damage to electrical systems degrades their performances and disrupts their normal functioning. Furthermore, it disrupts nuclear power plant (NPP) operations. NPPs in South Korea have been designed based on the Regulatory Guide 1.60 (RG 1.60) design spectra; however, the Gyeongju earthquakes in South Korea were of high frequency, with magnitudes of 5.1 and 5.8. Therefore, the seismic performances of electrical systems (high-frequency sensitive) must be evaluated to consider low- and high-frequency motions. In this study, to ensure the operation of NPPs in South Korea, the seismic performance and dynamic characteristics of the battery charger (BC) in the electrical subsystem were evaluated experimentally. Seismic tests of the BC were performed to consider low frequencies, high frequencies and a combination of both. The dynamic characteristics of the inside and outside of the cabinet, depending on the input motions, were evaluated and compared based on the tests. Moreover, the acceptance criteria for relay contact chatter were evaluated using the measured output signal during the seismic tests. From seismic test results, the peak acceleration of CRS at the top location (A6) was 1.31 times larger than that of UHS and 1.51 times than that of RG 1.60 and it increased rapidly with increasing PGA levels. Contact chatter was not observed under a peak acceleration of 3.4 g on the installed relay of the panel; however, the relay chatter for more than 2 ms dropped below the reference voltage 46 times. The major components of the electric cabinet were significantly affected by high-frequency motion. Full article

Earthquakes with magnitudes over 5.0 occurred near Gyeongju and Pohang in southern Korea in 2016 and 2017, respectively. These earthquakes had both low- and high-frequency components. Due to earthquakes with high-frequency motions, damage to nonstructural systems has been observed to be relatively more than that in structural systems. Consequently, the seismic design or performance evaluation of nonstructural components in critical facilities has emerged as a key research area in Korea. This study presents the results of experimental and numerical analyses using a high-fidelity finite element (FE) simulation in the ABAQUS platform for a press-to-connect piping system as a nonstructural component. Press-to-connect piping systems based on NFPA-13 with two elbows, a flexible coupling, and a T-joint were used. In addition, a cyclic loading protocol was applied using the KBC 2016 and IBC 2015. Based on the component-level experimental test, an FE model of the press-to-connect elbow was developed, and the high-fidelity large-scale piping system with an elbow was validated in this study. In both the experimental and analytical results, no leakage or plastic deformation of the piping system was observed under cyclic loading conditions. The results of the high-fidelity simulation model of the large-scale piping system were identical to those of the experimental test. More specifically, the error of the von-Mises stress at the upper and lower elbows was less than 9%, and the angle between the elbows was less than 2%, corresponding to the limit state of the drift ratio of the building system. Therefore, the high-fidelity simulation model of a large-scale piping system can have high application value. In addition, the design requirements and engineering demands of the piping system, such as the condition of ASME B and PV section III for service level D, were satisfied. Full article

In this study, we evaluated the response spectra of 24 earthquake series, which includes 15 from the Kumamoto earthquake series and 9 from the Pohang earthquake series, and explored the effects of earthquake magnitude on the resonance frequencies of structures and buildings. Furthermore, the observations of this study were compared with the design response spectra, Regulatory Guide 1.60 (The United States Nuclear Regulatory Commission, 1973) for Korean nuclear power plants, and with the Korean Building Code (MOLIT, 2016, hereinafter referred to as KBC 2016) for general structures and buildings. The response spectra, after normalization with reference to the peak ground acceleration (PGA), were derived using a total of 423 horizontal and vertical accelerations. It was observed that the shapes of the horizontal and vertical response spectra were strongly dependent on the magnitude of the earthquake and the resonance frequency. Given the strong dependence of the response on the magnitude, it is suggested to consider magnitude > ML ~ 6.0 when establishing design response spectra. Compared to inland areas, a fairly higher amplitude of response at significantly lower frequency ranges could be attributed to the local geological environment of Jeju Island, which was formed by a surface volcano eruption and the distribution of unconsolidated Pleistocene marine sediments in the Jeju area. It is necessary to study the characteristic influence of layers with low shear wave velocity distributed in the Jeju region on seismic responses more rigorously while considering the frequency band and amplitudes at the surface of Jeju. The resonance frequencies of general low-rise and mid-rise buildings by the brief formula and those by design response spectra both suggested by KBC 2016 were overlapped, and these indicated that the seismic hazard could be much higher on general buildings in the Jeju region than in inland areas. Lastly, it is necessary to make the design standard criteria for Reg. Guide 1.60 and KBC 2016 more conservative in the lower frequency range of higher than 0.6 Hz and 2.0–6.0 Hz, respectively, which is significantly lower than those of the inland area, and to establish improved design response spectra with site-specific seismic design standards by referencing large amounts of qualitative data from the region around the Korean Peninsula. Full article

We explored the usage of a response modification factor and overstrength factor for analyzing brittle or ductile failure of anchor system. Parametric studies on the tension and shear behaviors of anchor systems were compared in terms of elastic and ductile design using tuned Gyeongju earthquake data (ca. 0.3 g). We evaluated the yields of concrete anchors in terms of ductile failure and reviewed the various anchors, anchor attachments, and facilities and equipment that ensure anchor safety and functionality. The pseudo-static pushover test and elastic/inelastic dynamic tests revealed that a ductile design reduces the seismic demand relatively efficiently. As the DS-0050 design standards are based on strength design, no displacement limit for non-structural facilities/equipment is imposed. Despite the advantages of ductile design, large displacements of equipment or facilities during seismic action can cause permanent deformation and fall-out of major compartments; also, rapid functional recovery may be difficult. Thus, displacement limits for non-structural equipment or facilities should be included in the design code. Full article

The interest in the seismic performance of nuclear power plants has increased worldwide since the Fukushima Daiichi Nuclear Power Plant incident. In Korea, interest in the seismic safety of nuclear power plants has increased since the earthquake events in Gyeongju (2016) and Pohang (2017). In Korea, studies have been conducted to apply seismic isolation systems to ensure seismic safety while minimizing the design changes to nuclear power plants. Nuclear power plants with seismic isolation systems may have a higher seismic risk due to the failure of the piping system in the structure after a relatively large displacement. Therefore, it is essential to secure the seismic safety of pipes for the safe operation of nuclear power plants. The seismic safety of pipes is determined by seismic fragility analysis. Seismic fragility analysis requires many seismic response analyses because it is a statistical approach to various random variables. Typical numerical conditions affecting the seismic response analysis of pipes are the convergence conditions and mesh size in numerical analysis. This study examined the change in the seismic safety of piping according to the numerical conditions. The difference in the seismic response analysis results of the piping according to the mesh size was analyzed comparatively. In addition, the change in the seismic fragility curve of the piping according to the convergence conditions was investigated. Full article

In general, the stone pagoda structures with discontinuous surfaces are vulnerable to lateral forces and are severely damaged by earthquakes. After the Gyeongju earthquake in 2016 and the Pohang earthquake in 2017, numerous stone pagoda structures were damaged due to slippage, rotation, and the separation of stacked stone. To evaluate seismic resistance of masonry stone pagoda structures, we analyzed the seismic behavior of stone pagoda structures using the shaking table test. Shaking frequency, permanent displacement, maximum acceleration, rocking, and sliding were assessed. Responses to simulations of the Bingol, Gyeongju, and Pohang earthquakes based on the Korean seismic design standard (KDS 41 17 00) were analyzed for return periods of 1000 and 2400 years. We found that the type of stylobate affected the seismic resistance of the stone pagoda structure. When the stylobates were stiff, seismic energy was transferred from lower to upper regions of the stone pagoda, which mainly resulted in deformation of the upper region. When the stylobates were weak, earthquake energy was absorbed in the lower regions, which was associated with large stylobate deformations. The lower part of the tower body was mainly affected by rocking, because the structural members were slender. The higher part of the stone pagoda was mainly affected by sliding, because the load and contact area decreased with height. Full article

In Korea, the earthquakes in Gyeongju (2016) and Pohang (2017) have led to increased interest in the seismic design of nonstructural elements. Among these, the suspended ceiling can cause personal injury and property damage. In addition, most suspended ceilings that are used in Korea neither have seismic design details nor meet the current seismic design standards. There are two seismic design methods for suspended ceilings using a perimeter clip and a brace. In the United States and Japan, seismic design of ceilings is typically used, but the concepts of applying and installing braces are different. This is because the typical ceiling systems are different in the United States and Japan. In this study, a brace-applied ceiling system that is suitable for a suspended ceiling with a steel panel was applied in the indirect suspended ceiling mainly used in Korea. In addition, the seismic performance was verified through a shaking table test. All the specimens were applied with anti-falling clips that are designed to prevent the panels from falling, and they satisfy KDS 41 17 00, which is a Korean seismic design life safety standard. Without considering these factors, the performance level is lower than a nonseismic designed ceiling, which is not properly designed or constructed. Full article

Background: The aim of this study was to evaluate the impact of the 2016 Gyeongju Earthquake on the stress perception, depressive symptoms, and health-related quality of life (HRQoL) among Gyeongju residents. Methods: This study was a secondary analysis of the 2015–2017 Korean Community Health Survey undertaken in the disaster area, Gyeongju, and in controlled areas, Sangju and Yangju, which had varying seismic intensities. Pearson’s chi-square test, ANCOVA and two-way ANOVA were performed. Results: The stress perception rate and anxiety/depression in the 5th dimension of the EuroQul-five-dimensions three-level version (EQ-5D-3L) in Gyeongju was significantly higher in 2017 than in 2016. As for the HRQoL, the controlled regions showed a tendency to increase in 2017 rather than in 2016, while Gyeongju had no significant differences during 2015 and 2017. As a result, Gyeongju had the lowest HRQoL in 2017. Conclusion: Mental health in the disaster area after the 2016 earthquake was worse, and the HRQoL of Gyeongju residents was relatively lower than the control regions. Based on the results of the study, government agencies should remain interested in developing a post-disaster psychological support program for disaster survivors at a community level. Full article

Since 2016, the frequency and scale of earthquakes have been rapidly increasing in South Korea. In particular, the damage caused by the Gyeongju and Pohang earthquakes has attracted considerable attention since 2017, leading to changes in social insensitivity to safety and the perception of seismic damage to facilities. However, the current risk assessment technology for earthquake-damaged buildings is subjective and inaccurate, as it is based on visual inspection for a limited time. Accordingly, this study focuses on improving the method of analysis of disaster-damaged buildings. To this end, the study analyzes the risk factors of earthquake-damaged buildings by comparing point cloud data using 3D scanning technology with Building Information Modeling (BIM) spatial information, which is based on the existing design information. To apply this technology, existing design information was acquired through BIM modeling of the existing 2D design drawings of Building E in the Daeseong Apartment Complex (located in Heunghae-eup, Pohang City). This study is expected to contribute to improving the efficiency of measurement technology for earthquake-damaged buildings by analyzing old buildings’ BIM-based 3D modeling visualization information without drawing information, and thus improving the accuracy of seismic damage risk measurement by scanning point cloud data. Full article