• Journal of the Earthquake Engineering Society of Korea
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• v.25 no.5
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• pp.223-232
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• 2021

The spatial variation characteristics of seismic motions at the nuclear power plant's site and structures were analyzed using earthquake records obtained at the Fukushima nuclear power plant during the Great East Japan Earthquake. The ground responses amplified as they approached the soil surface from the lower rock surface, and the amplification occurred intensively at about 50 m near the ground. Due to the soil layer's nonlinear characteristics caused by the strong seismic motion, the ground's natural frequency derived from the response spectrum ratio appeared to be smaller than that calculated from the shear wave velocity profile. The spatial variation of the peak ground acceleration at the ground surface of the power plant site showed a significant difference of about 0.6 g at the maximum. As a result of comparing the response spectrums at the basement of the structure with the design response spectrum, there was a large variability by each power plant unit. The difference was more significant in the Fukushima Daiichi site record, which showed larger peak ground acceleration at the surface. The earthquake motions input to the basement of the structure amplified according to the structure's height. The natural frequency obtained from the recorded results was lower than that indicated in the previous research. Also, the floor response spectrum change according to the location at the same height was investigated. The vertical response on the foundation surface showed a significant difference in spectral acceleration depending on the location. The amplified response in the structure showed a different variability depending on the type of structure and the target frequency.

• Nuclear Engineering and Technology
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• v.49 no.4
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• pp.825-837
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• 2017

Due to the severe impacts of recent earthquakes, the use of seismic isolation is paramount for the safety of nuclear structures. The diversity observed in seismic events demands ongoing research to analyze the devastating attributes involved, and hence to enhance the sustainability of base-isolated nuclear power plants. This study reports the seismic performance of a seismically-isolated nuclear reactor containment building (NRCB) under strong short-period ground motions (SPGMs) and long-period ground motions (LPGMs). The United States Nuclear Regulatory Commission-based design response spectrum for the seismic design of nuclear power plants is stipulated as the reference spectrum for ground motion selection. Within the period range(s) of interest, the spectral matching of selected records with the target spectrum is ensured using the spectral-compatibility approach. NRC-compliant SPGMs and LPGMs from the mega-thrust Tohoku earthquake are used to obtain the structural response of the base-isolated NRCB. To account for the lack of earthquakes in low-to-moderate seismicity zones and the gap in the artificial synthesis of long-period records, wavelet-decomposition based autoregressive moving average modeling for artificial generation of real ground motions is performed. Based on analysis results from real and simulated SPGMs versus LPGMs, the performance of NRCBs is discussed with suggestions for future research and seismic provisions.

• Journal of the Korean Geophysical Society
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• v.3 no.3
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• pp.193-200
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• 2000

The attenuation characteristics($Q^{-1}$) are important factors representing the physical properties of the Earth interiors, and are essential for the quantitative prediction of strong ground-motion. Based on 156 earthquakes including 76 single-station record on the seismic station located Deok-jung Ri, southeastern Korea, we made the simultaneous measurement of P and S wave attenuation($Q_P^{-1}\;and\;Q_S^{-1}$) by means of extended coda-normalization method. Estimated $Q_P^{-1}\;and\;Q_S^{-1}$ decreased from $1{\times}10^{-2}\;and\;9{\times}10^{-3}$ at 1.5 Hz to $6{\times}10^{-4}\;and\;5{\times}10^{-4}$ at 24 Hz, respectively. This can be expressed by $Q_P^{-1}=0.01\;f^{-1.07}\;and\;Q_S^{-1}=0.01\;f^{-1.03}$ which indicate strong frequency dependence.

• Earthquakes and Structures
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• v.15 no.5
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• pp.453-462
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• 2018

Damages to buildings affected by a near-fault strong ground motion are largely attributed to the vertical component of the earthquake resulting in column failures, which could lead to disproportionate building catastrophic collapse in a progressive fashion. Recently, considerable interests are awakening to study effects of earthquake vertical components on structural responses. In this study, detailed modeling and time-history analyses of a 12-story code-conforming reinforced concrete moment frame building carrying the gravity loads, and exposed to once only the horizontal component of, and second time simultaneously the horizontal and vertical components of an ensemble of far-field and near-field earthquakes are conducted. Structural responses inclusive of tension, compression and its fluctuations in columns, the ratio of shear demand to capacity in columns and peak mid-span moment demand in beams are compared with and without the presence of the vertical component of earthquake records. The influences of the existence of earthquake vertical component in both exterior and interior spans are separately studied. Thereafter, the correlation between the increase of demands induced by the vertical component of the earthquake and the ratio of a set of earthquake record characteristic parameters is investigated. It is shown that uplift initiation and the magnitude of tensile forces developed in corner columns are relatively more critical. Presence of vertical component of earthquake leads to a drop in minimum compressive force and initiation of tension in columns. The magnitude of this reduction in the most critical case is recorded on average 84% under near-fault ground motions. Besides, the presence of earthquake vertical components increases the shear capacity required in columns, which is at most 31%. In the best case, a direct correlation of 95% between the increase of the maximum compressive force and the ratio of vertical to horizontal 'effective peak acceleration (EPA)' is observed.

• Journal of the Earthquake Engineering Society of Korea
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• v.22 no.3
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• pp.175-184
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• 2018

In this paper, comparative analysis of the 9.12 Gyeongju and 11.15 Pohang earthquakes was conducted in order to provide probable explanations and reasons for the damage observed in the 11.15 Pohang earthquake from both earthquake and structural engineering perspectives. The damage potentials like Arias intensity, effective peak ground acceleration, etc observed in the 11.15 Pohang earthquake were generally weaker than those of the 9.12 Gyeongju earthquake. However, in contrast to the high-frequency dominant nature of the 9.12 Gyeongju earthquake records, the spectral power of PHA2 record observed in the soft soil site was highly concentrated around 2Hz. The base shear around 2 Hz frequency was as high as 40% building weight. This frequency band is very close to the fundamental frequency of the piloti-type buildings severely damaged in the northern part of Pohang. Unfortunately, in addition to inherent vertical irregularity, most of the damaged piloti-type buildings had plan irregularity as well and were non-seismic. All these contributed to the fatal damage. Inelastic dynamic analysis indicated that PHA2 record demands system ductility capacity of 3.5 for a structure with a fundamental period of 0.5 sec and yield base shear strength of 10% building weight. The system ductility level of 3.5 seems very difficult to be achievable in non-seismic brittle piloti-type buildings. The soil profile of the PHA2 site was inversely estimated based on deconvolution technique and trial-error procedure with utilizing available records measured at several rock sites during the 11.15 Pohang earthquake. The soil profile estimated was very typical of soil class D, implying significant soil amplification in the 11.15 Pohang earthquake. The 11.15 Pohang earthquake gave us the expensive lesson that near-collapse damage to irregular and brittle buildings is highly possible when soil is soft and epicenter is close, although the earthquake magnitude is just minor to moderate (M 5+).

• Korean Journal of Applied Biomechanics
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• v.19 no.2
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• pp.337-345
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• 2009

The purpose of this study were to find out the differences in kinematic variables of racket movement by performing the tennis serve. Three top male tennis players participated in this study. Three synchronized high-speed cameras were used to record the service action of top players for Three dimensional video analysis. The results of this study showed that (1) the velocity of the tennis racket at impact is important to the generation of racket velocity to Y-axis. This result indicates that forward motion and upward movement of the racket; (2) with respect to racket angular velocity at impact, the fast angular momentum of X-axis is important to generate the velocity of the tennis ball. This result indicate upward movement of the racket with a strong flexor of wrist joint; (3) the velocity of the tennis ball was influenced by the change of angular linking the Z-axis to -X-axis. This result indicates that the high velocity of the tennis ball is obtained from having the racket unitedly moving to the direction of the bill's flight at the acceleration interval and acquiring the distance of acceleration with the racket head vertically to the ground at the back scratching.