• Journal of the Korean GEO-environmental Society
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• v.12 no.1
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• pp.81-87
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• 2011

The characteristics of vertical to horizontal ratio of response spectrum from 20 recent earthquakes were analysed. Response spectrum of 260 horizontal and 130 vertical ground motions were normalized by peak ground acceleration at each resonance frequency from 0.1 to 50Hz. It has been identified that the ratio of vertical to horizontal response spectrum has strong dependancy on epicentral distance and resonance frequency. The ratio of vertical to horizontal response spectrum for the 0-50km epicentral distance group are larger than 2/3 values, which is a standard engineering rule-of-thumb V/H=2/3, at resonance frequency above 7-8Hz. All the 3 groups such as 50-100, 100-150- and 150-200km epicentral distance have shown larger values of vertical to horizontal ratio than 2/3 at resonance frequency above 15Hz and also are larger than 2/3 at resonance frequency below 8-10Hz. Even though there are differences in specific resonance frequency values which depend on the epicentral distance group, we should be careful of seismic design of vertical component of the structures winch are located within the range of about 200km distance. form the potentially seismic causative faults.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1989.04a
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• pp.5-10
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• 1989

In this study, the basic concept of design response spectrum is briefly revi-ewed. To generate the artificial earthquake acceleration, the method of superpo-sition of cosine waves is used. Theoretical developments using F.F.T. and spect-ral density function are compared. The amplitude was derived by use of the peak factor and the phase angle is d-erived by use of Monte Carlo simulation. To smoothen the match, the calculated pseudo velocity respon-se spectrum is compared with input pseudo velocity response spectrum at a set of control frequencies. With the modified spectral density function, a new acceleration and pseudo velocity response spectrum are generat-ed.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1997.04a
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• pp.62-66
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• 1997

확률론적 방법을 적용하여 국내의 4개 원전 부지의 설계지진을 분석하였다. 본 연구에서 사용된 방법은, 지금까지 원전 부지의 안전성 분야에서 적용되어 왔던 기존의 확률론적 재해도분석과는 다른 새로운 방법으로서, 기준확률의 분석과 제어지진의 결정을 위한 지진재해도 분해의 두 과정으로 구성된다. 분석에 사용된 지진원과 지진활동 특성값은 기존의 확률론적 지진재해도 분석에 사용되었던 입력자료이다. 이로부터 계산된 기준확률은 스펙트럼 가속도 감쇄식에 크게 좌우되는 것으로 나타났다. 기준확률1.0$\times$10-5에 대하여, 4개 원전 부지의 제어지진은 평균거리가 13~26kg, 평균 규모가 5.7~6.1 사이에 분포하는 것으로 나타났다. 이 값은 단지 현재의 입력자료에 근거하였을 때의 결과로서, 값 자체의 수치적인 의미보다는 전체적인 분석 과정을 검토하고 또한 현재의 입력자료와 새로운 방법이 조합되었을 때 산출되는 결과의 대략적인 수준을 파악하는데 더 큰 의미가 있다.

• The Journal of Engineering Geology
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• v.25 no.2
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• pp.201-213
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• 2015

Site effects resulting in the amplification of earthquake ground motion are strongly influenced not only by the subsurface soil conditions and structure, but also by the surface topography. Yet, over the last several decades, most studies of site-specific seismic responses in Korea have focused primarily on the seismic amplification associated with geologic and soil conditions. For example, the effects of local geology are now well established and have been incorporated into current Korean seismic design codes, whereas topographic effects have not been considered. To help address this shortcoming, two-dimensional (2D) seismic site response analyses, using finite element (FE) ground modeling with three different slope angles, were performed in order to assess the site effects of surface topography. We then compared our results, specifically peak ground acceleration (PGA) and acceleration response spectrum, to those of one-dimensional (1D) FE model analyses conducted alongside our study. Throughout much of the upper slope region, PGAs and spectral accelerations are larger in the 2D analyses than in the 1D analyses as a result of the topographic effect.

• Journal of the Earthquake Engineering Society of Korea
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• v.9 no.1 s.41
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• pp.1-7
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• 2005

The optimal seismic retrofitting of NPP(Nuclear Power Plant) cabinet structures that contain seismic category 1 relays was studied in this paper. During earthquake event, the failure modes of relays are not appeared in form of structural failure, but are appeared in form of contact chatter of relay. Therefore, the retrofitting of cabinet has to be aimed at the reducing of the structural response, such as acceleration. In this study, the optimal characteristic values of dampers were searched by ${\mu}$-GA (micro-Genetic Algorithm) scheme for several installation patterns. To keep accuracy and efficiency of analysis, the structural models of cabinet were considered as a frame structure. The responses of structure were obtained inform of acceleration response spectra derived from the results of nonlinear time history analysis including damping nonlinearity. The objective function of the optimum procedure was constructed based on the maximum ratio of maximum spectral value and target GERS (General Equipment Ruggedness Spectra). The results show the good improvements of fitness for adequate retrofitting pattern. Especially, the improvements of fitness were remarkable when the values of damping exponents are low.

• Journal of the Korean earth science society
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• v.37 no.1
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• pp.40-51
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• 2016

The problem has been pointed out that the domestic design response spectrum does not reflect site amplification, particularly in the high frequency bands, including the fact that site specific response spectrum from the observed ground motions appears relatively higher than design response spectrum. Among various methods, this study applied H/V spectral ratio of ground motion for estimating site amplification. This method, originated from S waves and Rayleigh waves, recently has been extended to Coda waves and background noise for estimating site amplification. For limited time of periods, 4 electric substation sites had operated seismic stations at two separate locations (bedrock and borehole) within each substation site. H/V spectral ratio of S wave, Coda wave, and background noise, was applied to 36 accelerations of 3 macro earthquakes (Odaesan, Jeju and Gongju earthquakes), larger than magnitude 3.4. observed simultaneously at each bedrock location within 4 electric substation sites. Site amplifications at the bedrock location of 4 sites were compared among S wave, Coda wave energy, and background noise, and then compared to the previous results from the borehole location data. The site classification was also tried using resonancy frequency information at each site and location. The results suggested that all the electric substation sites showed similar site amplification patterns among S wave, Coda wave, and background noise. Each station showed its own characteristics of site amplification property in low, high and specific resonance frequency ranges. Comparison of this study to other results using different method can give us much more information about dynamic amplification of domestic sites characteristics and site classification.

• Journal of Convergence for Information Technology
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• v.11 no.9
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• pp.130-137
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• 2021

The characteristics of forced vibration by an external excitation force having a frequency were analyzed according to the amplitude and frequency of the excitation force. To obtain displacement, velocity, and acceleration, numerical analysis was performed to obtain the frequency response, and in particular, each FRF(Frequency Response Function) was analyzed to reveal the location of the system natural frequency and excitation frequency in the frequency domain. In the vibration model caused by external excitation, the natural frequency and distribution of the surrounding excitation mode in displacement, velocity and acceleration FRF. The FRF was also shown in the power spectrum and FRF of real and imaginary parts. The external excitation force was approximated with the excitation force of a sine wave by giving the amplitude and frequency, the mode generated by this excitation force could be distinguished. After numerical analysis by changing the equivalent mass, damping and stiffness, the forced vibration response characteristics by external excitation force were systematically analyzed.

• Journal of Convergence for Information Technology
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• v.12 no.3
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• pp.151-157
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• 2022

The purpose of this study was to investigate the frequency characteristics of forced vibration considering the vehicle progress. And the vibration characteristics in frequency domain that occur, when vehicle passes the bump, were analyzed. The responses such as displacement, velocity and acceleration were obtained through numerical analysis, and FFT processing was performed to analyze the frequency response function(FRF) characteristics. In particular, the location of vehicle eigenmodes and external excitation modes was clearly shown and analyzed. In the forced vibration model by external force, the behavior of the eigenmode in power spectrum and real and imaginary parts were also analyzed. The mode characteristics were also analyzed in each FRF. It was approximated by assuming total excitation force by considering the exciting frequency using impulse and sine wave forces, which can give the amplitude and frequencies. The response characteristics of forced oscillations having different mass, damping and stiffness have been systematically discussed.

• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.1 s.53
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• pp.59-65
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• 2007

Site classification of IBC and KBC is based on the ft-kips unit system and is not friendly for the linear interpolation of the site coefficients due to the implicit relationship between a site class and site coefficients, defining a site class by the range of the soil properties, not by a single soil property. Also, the site class definition of KBC has too wide range of soil properties for each soil class. making the structural engineers difficult to estimate the site coefficients for the diverse soil layers. In this study, a new site classification in SI unit system was proposed for the seismic design codes of KBC etc., and the comparison of the site coefficients of $F_{a}\;and\;F_{v}$ was also performed to investigate the possibility of the linear interpolation of the site coefficients with the proposed new site classification. According to the study results, it was more reasonable for the linear interpolation of the site coefficients to utilize the proposed new site classification considered the Sl unit system and the soil characteristics of the 30m soil layer beneath the shallow embedded foundation, and the linear interpolation of the acceleration coefficients for the design spectrum can be performed more reasonably defining the site coefficients for the representative shear wave velocities of each site class. With the study results, a new site classification, and the linear interpolation permitted acceleration coefficients fer the design spectrum were proposed for the modification of the seismic design regulations of KBC.

• Journal of the Earthquake Engineering Society of Korea
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• v.13 no.4
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• pp.15-23
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• 2009

An experimental study was performed to evaluate seismic reduction performance and the applicability of 2-dimensional floor isolation system to the main control room of a nuclear power plant. A lead-rubber bearing (LRB) and a friction pendulum system (FPS) were designed and fabricated for a 2-dimensional floor isolation system. A partial experimental model of a main control room with the LRB and FPS was tested using a shaking table. The experimental model consisted of a control panel, a 2.5m${\times}$2.5m access floor, and four LRB and FPS. The artificial time histories based on the horizontal floor response spectrums (OBE, SSE) of the main control room were used as earthquake input signals. Compared to the non-isolated system, the seismic response of experimental models using a 2-dimensional floor isolation system showed considerable seismic reduction performance against an earthquake.