The damage to structures during an earthquake can be varied depending on the frequency characteristics of seismic waves and the geological properties of the ground. Therefore, considering such attributes in the design ground motions is crucial. The Korean seismic design standard (KDS 17 10 00) provides design response spectra for various ground classifications. If required for time-domain analysis, ground motion time series can be either selected and adjusted from motions recorded at rock sites in intraplate regions or artificially synthesized. Ground motion time series at soil sites should be obtained from site response analysis. However, in practice, selecting suitable ground motion records is challenging due to the overall lack of large earthquakes in intraplate regions, and artificially synthesized time series often leads to unrealistic responses of structures. As an alternative approach, this study provides a case study of generating ground motion time series based on the hybrid broadband ground motion simulation of selected scenario earthquakes at sites in the Nakdonggang delta region. This research is significant as it provides a novel method for generating ground motion time series that can be used in seismic design and response analysis. For large-magnitude earthquake scenarios close to the epicenter, the simulated response spectra surpassed the 1000-year design response spectra in some specific frequency ranges. Subsequently, the acceleration time series at each location were used as input motions to perform nonlinear 1D site response analysis through the PySeismoSoil Package to account for the site response characteristics at each location. The results of the study revealed a tendency to amplify ground motion in the mid to long-period range in most places within the study area. Additionally, significant amplification in the short-period range was observed in some locations characterized by a thin soil layer and relatively high shear wave velocity soil near the upper bedrock.

Accurate seismic vulnerability assessment requires high quality and large amounts of ground motion data. Ground motion data generated from time series contains not only the seismic waves but also the background noise. Therefore, it is crucial to determine the high-pass cut-off frequency to reduce the background noise. Traditional methods for determining the high-pass filter frequency are based on human inspection, such as comparing the noise and the signal Fourier Amplitude Spectrum (FAS), f2 trend line fitting, and inspection of the displacement curve after filtering. However, these methods are subject to human error and unsuitable for automating the process. This study used a deep learning approach to determine the high-pass filter frequency. We used the Mel-spectrogram for feature extraction and mixup technique to overcome the lack of data. We selected convolutional neural network (CNN) models such as ResNet, DenseNet, and EfficientNet for transfer learning. Additionally, we chose ViT and DeiT for transformer-based models. The results showed that ResNet had the highest performance with R2 (the coefficient of determination) at 0.977 and the lowest mean absolute error (MAE) and RMSE (root mean square error) at 0.006 and 0.074, respectively. When applied to a seismic event and compared to the traditional methods, the determination of the high-pass filter frequency through the deep learning method showed a difference of 0.1 Hz, which demonstrates that it can be used as a replacement for traditional methods. We anticipate that this study will pave the way for automating ground motion processing, which could be applied to the system to handle large amounts of data efficiently.

일반적으로 속도 펄스를 가진 지반운동이 속도 펄스가 없는 지반운동에 비하여 구조물에 보다 큰 손상을 줄 수 있다고 알려져 있다. 지진가속도기록으로부터 속도 펄스의 유무의 판정과 이를 정량화하는 연구가 현재 많이 진행되어 오고 있다. 기존 지진기록들을 단 층으로 떨어진 거리를 기준으로 원거리 지진과 근거리 지진으로 구분하였다. 또한, 근거리 지진은 속도 펄스의 유무를 정량화하여 펄 스를 가진 지진과 펄스를 가지지 않은 지진으로 구분하였다. 최종적으로 각 지진그룹별로 40개의 원거리지진, 40개의 속도 펄스를 가 진 근거리 지진과 40개의 속도 펄스를 가지지 않은 근거리 지진을 선정하였으며, 총 120개 지진가속도 기록을 지진취약도 평가를 위 한 지진해석에 사용하였다. 세 그룹의 지진을 이용하여 납-고무받침과 탄성받침을 가진 두 종류의 예제교량에 대한 지진응답을 평가 하여 확률론적 지진요구도 모델을 작성하였다. 확률론적 지진요구도 모델을 이용하여 지진취약도 해석을 수행하여 속도 펄스의 유무 에 따른 지진취약도 영향을 분석하였다. 지진파의 속도 펄스 유무에 따른 지진취약도 곡선의 비교 결과로부터, 속도 펄스를 가진 지진 의 지진취약도가 속도 펄스가 없는 지진의 지진취약도가 약 3배~5배 정도 정도 크게 나타난다. 이는 속도 펄스를 가진 지진의 경우가 그렇지 않은 지진의 경우에 비하여 교량의 손상 피해가 크다는 것을 의미한다.

According to several seismic design standards, a ground motion time history should be selected similar to the design response spectrum, or a ground motion time history should be modified by matching procedure to the design response spectrum through the time-domain method. For the response spectrum matching procedure, appropriate seed ground motions need to be selected to maintain recorded earthquake accelerogram characteristics. However, there are no specific criteria for selecting the seed ground motions for applying this methodology. In this study, the characteristics of ground motion time histories between seed motions and spectral matched motions were compared. Intensity measures used in the design were compared, and their change by spectral matching procedure was quantified. In addition, the seed ground motion sets were determined according to the response spectrum shape, and these sets analyzed the response of nonlinear and equivalent linear single degrees of freedom systems to present the seed motion selection conditions for spectral matching. As a result, several considerations for applying the time domain spectral matching method were presented.

2004년 5월 29일 발생한 울진해역지진(Mw 5.1)과 관련된 대기 인프라사운드 신호가 철원(진앙 거리 321 km) 및 대전(256 km) 관측소에 기록되었다. 신호의 지속시간은 수 분 이상이며, 음원 방향을 지시하는 후방-방위각은 28 o 이상의 큰 변화를 보였다. 역-투사 방법과 신호 감쇄 보정 결과, 인프라사운드 신호는 삼척-울진-포항까지 연결되는 약 4,600 km2 면적의 지반운동으로 발생하였으며, 음원 최대 크기(BSP)는 11.1 Pa로 계산되었다. 이 결과는 최대지반가속 도(PGA) 자료로 계산한 음원 최대 크기(PSP)와도 부합하고 있으며, 지진 발생 당시 인프라사운드 신호 탐지를 가능케 했던 최소 지반운동은 ~3.0 cm s−2 이상으로 확인되었다. 울진해역지진이 비록 동해 해역에서 발생하였지만, 진앙과 가 까운 강원도 남부-경상북도의 고지대를 따라 전파한 표면파의 지반운동으로 회절 인프라사운드가 효과적으로 발생한 것으로 해석된다. 인프라사운드 관측을 통한 원거리 지진 지반운동 특성 추정 방법은 지진관측망이 설치되어 있지 않거나 관측소 수가 적은 지역을 대상으로 활용이 가능할 것이다.

액체저장탱크의 지진 거동은 유체-구조물 상호작용에 의해 복잡하게 나타나므로, 이 시스템의 지진응답과 피해를 정확하게 예측 하기 위해서는 이를 엄밀히 고려하여야 한다. 이 연구에서는 유체-구조물 상호작용을 엄밀히 고려하여 양방향 수평 지반운동이 작용 하는 직사각형 액체저장탱크의 지진응답 해석을 수행하고 그 응답 특성을 분석하고자 한다. 이를 위해 지진하중 작용 시 발생하는 유체 동수압을 유한요소 기법을 사용하여 산정하고, 이 동수압을 구조물의 유한 요소에 작용하여 전체 시스템의 동적 거동을 모사한다. 예제 직사각형 액체저장탱크의 지진응답 해석을 통하여 대상 시스템의 동적 거동은 양방향 수평 지반운동이 작용하는 방위각에 의해 유의미한 영향을 받음을 확인할 수 있다. 그러므로 직사각형 액체저장탱크의 내진설계를 수행하거나 내진성능을 검토할 때는 이러한 특성을 고려하여야 할 것이다.

The stochastic point-source model has been widely used in generating artificial ground motions, which can be used to develop a ground motion prediction equation and to evaluate the seismic risk of structures. This model mainly consists of three different functions representing source, path, and site effects. The path effect is used to emulate decay in ground motion in accordance with distance from the source. In the stochastic point-source model, the path attenuation effect is taken into account by using the geometrical attenuation effect and the inelastic attenuation effect. The aim of this study is to develop accurate equations of ground motion attenuation in the Korean peninsula. In this study, attenuation was estimated and validated by using a stochastic point source model and observed ground motion recordings for the Korean peninsula.

In a seismic design, a structural demand by an earthquake load is determined by design response spectra. The ground motion is a three-dimensional movement; therefore, the design response spectra in each direction need to be assigned. However, in most design codes, an identical design response spectrum is used in two horizontal directions. Unlike these design criteria, a realistic seismic input motion should be applied for a seismic evaluation of structures. In this study, the definition of horizontal spectral acceleration representing the two-horizontal spectral acceleration is reviewed. Based on these methodologies, the horizontal responses of observed ground motions are calculated. The data used in the analysis are recorded accelerograms at the stations near the epicenters of recent earthquakes which are the 2007 Odeasan earthquake, 2016 Gyeongju earthquake, and 2017 Pohang earthquake. Geometric mean-based horizontal response spectra and maximum directional response spectrum are evaluated and their differences are compared over the period range. Statistical representation of the relations between geometric mean and maximum directional spectral acceleration for horizontal direction and spectral acceleration for vertical direction are also evaluated. Finally, discussions and suggestions to consider these different two horizontal directional spectral accelerations in the seismic performance evaluation are presented.

The site coefficients in the common requirements for seismic design codes, which were promulgated in 2017, were reevaluated and the standard design spectrum for soil sites were newly proposed in order to ensure the consistency of the standard design spectra for rock and soil sites specified in the common requirements. Using the 55 ground motions from domestic and overseas intraplate earthquakes, which were used to derive the standard design spectrum for rock sites, as rock outcropping motions, site response analyses of Korean soil were performed and its ground-motion-amplification was characterized. Then, the site coefficients for soil sites were reevaluated. Compared with the existing site coefficients, the newly proposed short-period site coefficient Fa increased and the long-period site coefficient Fv decreased overall. A new standard design spectrum for soil sites was proposed using the reevaluated site coefficients. When compared with the existing design spectrum, it could be seen that the proposed site coefficients and the standard design spectrum for soil sites were reasonably derived. They reflected the short-period characteristics of earthquake and soil in Korea.

Current seismic design provisions such as ASCE 7-10 provide criteria for selecting ground motions for conducting response history analysis. This study is the sequel of a companion paper (I – Ground Motion Selection) for assessment of the ASCE 7-10 criteria. To assess of the ASCE 7-10 criteria, nonlinear response history analyses of twelve single degree of freedom (SDF) systems and one multi-degree of freedom (MDF) system are conducted in this study. The results show that the target seismic demands for SDF can be predicted using the mean seismic demands over seven and ten ground motions selected according to the proposed method within an error of 30% and 20%, respectively

For estimating the seismic demand of buildings, most seismic design provisions permit conducting linear and nonlinear response history analysis. In order to obtain reliable results from response history analyses, a proper selection of input ground motions is required. In this study, an accurate algorithm for selecting and scaling ground motions is proposed, which satisfies the ASCE 7-10 criteria. In the proposed algorithm, a desired number of ground motions are sequentially scaled and selected from a ground motion library without iterations.

In low to moderate seismic regions, there are limited earthquake ground motion data recorded from past earthquakes. In this regard, th e Gyeongju earthquake (M=5.8)occurred on September 12, 2016 produces valuable information on ground motions. Ground motions w ere recorded at various recording stations located widely in Korean peninsula. Without actual recoded ground motions, it is impossible t o make a ground motion prediction model. In this study, a point source model is constructed to accurately simulate ground motions rec orded at different stations located on different soil conditions during the Gyeongju earthquake. Using the model, ground motions are ge nerated at all grid locations of Korean peninsula. Each grid size has 0.1°(latitude)x0.1°(longitude). Then a contour hazard map is constr ucted using the peak ground acceleration of the simulated ground motions

Currently, researches are being actively conducted in assessing seismic performance of nuclear facilities in USA and Europe. In particular, applying this technique of assessing seismic performance to design of isolation systems in nuclear power plants is being performed and then ASCE 4 Draft (2013) is being revised accordingly in the United States. In order to satisfy the probabilistic performance objectives described by seismic responses with certain confidence levels (ASCE 43, 2005), the probability distributions of these responses have to be defined. What is the minimum number of input ground-motions to obtain the probability distribution precise enough to represent the unknown actual distribution? Theoretical basis, for how to determine the minimum number of input ground-motions for given a logarithmic standard deviation to approximate the unknown actual median of the log-normal distribution within a range of error at a certain level of confidence, is introduced by Huang et al. (2008). However, the relationship between the level of confidence and the range of error is not stated in the previous study. In this paper, based on careful reviews on the previous work, the relationship between the level of confidence and the range of error is logically and explicitly stated. Furthermore, this relationship is also applied to derive the minimum number of input ground-motions in order to approximate the unknown actual logarithmic standard deviation. Several recommendations are made for determining the minimum number of input ground-motions in probabilistic assessment on seismic performance of facilities in nuclear power plants.

It is important to select proper ground motions for obtaining accurate results from response history analyses. The purpose of this study is to propose an accurate and efficient method that does not require excessive computation for selecting and scaling ground motions to match target response spectrum mean and variance. The proposed method is conceptually simple and straightforward, and it does not use a simulation algorithm that requires a sophisticated subroutine program. In this method, the desired number of ground motions are sequentially scaled and selected from a ground motion library. The proposed method gives the best selection results using Sum of Square Error and has the smallest value(=0.14). Also, The accuracy and consistency of the proposed method are verified by comparing the selection results of the proposed method with those of existing methods.

이 연구에서는 3축 방향 지반운동이 작용하는 지반-구조물 상호작용계의 비선형 지진응답 해석을 수행한다. 비선형 거동 이 예상되는 구조물과 지반의 근역은 비선형 유한요소에 의해 모형을 구성한다. 기하학적 형상과 재료 성질이 균일하고 선 형 거동을 가정하는 원역지반은 무한 영역으로의 에너지 방사를 정확히 고려할 수 있는 3차원 perfectly matched discrete layer에 의해 수치 모형을 구성한다. 이와 같은 지반-구조물 상호작용계의 수치모형을 사용하여 3축 방향 지반운동이 작용 하는 비선형 지진-구조물 상호작용계의 지진응답해석을 수행한다. 3축 방향 지반운동이 작용하는 경우에는 입력 지반운동의 특성에 따라 시스템의 응답이 우세하게 발현되는 방향이 존재하고 그 수준 또한 정밀한 지진응답해석을 통해 산정하여야 한 다. 이 연구의 해석기법은 구조물과 지반의 재료 비선형 거동, 기초와 지반 경계면에서의 경계 비선형 거동 등 다양한 비선 형 지반-구조물 상호작용 해석에 확장 적용할 수 있을 것이다.

이 연구에서는 3축 방향 지반운동이 작용하는 지반-구조물 상호작용계의 비선형 지진응답 해석을 수행한다. 비선형 거동이 예상되는 구조물과 지반의 근역은 비선형 유한요소에 의해 모형을 구성한다. 기하학적 형상과 재료 성질이 균일하고 선형 거동을 가정하는 원역지반은 무한 영역으로의 에너지 방사를 정확히 고려할 수 있는 3차원 perfectly matched discrete layer에 의해 수치 모형을 구성한다. 이와 같은 지반-구조물 상호작용계의 수치모형을 사용하여 3축 방향 지반운동이 작용하는 비선형 지진-구조물 상호작용계의 지진응답해석을 수행한다. 3축 방향 지반운동이 작용하는 경우에는 입력 지반운동의 특성에 따라 시스템의 응답이 우세하게 발현되는 방향이 존재하고 그 수준 또한 정밀한 지진응답해석을 통해 산정하여야 한다. 이 연구의 해석기법은 구조물과 지반의 재료 비선형 거동, 기초와 지반 경계면에서의 경계 비선형 거동 등 다양한 비선형 지반-구조물 상호작용 해석에 확장 적용할 수 있을 것이다.

This study is the sequel of a companion paper (I. Algorithm) for assessment of the seismic performance evaluation of structure using ground motions selected by the proposed algorithm. To evaluate the effect of the correlation structures of selected ground motions on the seismic responses of a structure, three sets of ground motions are selected with and without consideration of the correlation structure. Nonlinear response history analyses of a 20-story reinforced concrete frame are conducted using the three sets of ground motions. This study shows that the seismic responses of the frames vary according to ground motion selection and correlation structures.

It is important to select an accurate set of ground motions when conducting linear and nonlinear response history analyses of structures. This study proposes a method for selecting ground motions from a ground motion library with response spectra that match the target response spectrum mean, variance and correlation structures. This study also has addressed the determination of an appropriate value for the weight factor of a correlation structure. The proposed method is conceptually simple and straightforward, and does not involve a simulation algorithm. In this method, a desired number of ground motions are sequentially selected from first to last. The proposed method can be also used for selecting ground motions with response spectra that match the conditional spectrum. The accuracy and efficiency of the proposed procedure are verified with numerical examples.

Considering a rigorously fluid-structure interaction, a method for an earthquake response analysis of a floating offshore structure subjected to vertical ground motion from a seaquake is developed. Mass, damping, stiffness, and hydrostatic stiffness matrices of the floating offshore structure are obtained from a finite-element model. The sea water is assumed to be a compressible, nonviscous, ideal fluid. Hydrodynamic pressure, which is applied to the structure, from the sea water is assessed using its finite elements and transmitting boundary. Considering the fluid-structure interaction, added mass and force from the hydrodynamic pressure is obtained, which will be combined with the numerical model for the structure. Hydrodynamic pressure in a free field subjected to vertical ground motion and due to harmonic vibration of a floating massless rigid circular plate are calculated and compared with analytical solutions for verification. Using the developed method, the earthquake responses of a floating offshore structure subjected to a vertical ground motion from the seaquake is obtained. It is concluded that the earthquake responses of a floating offshore structure to vertical ground motion is severely influenced by the compressibility of sea water.

Structures in a nuclear power system are designed to be elastic even under an earthquake excitation. However a structural component such as an isolator shows inelastic behavior inherently. For the seismic assessment of nonlinear structures, response history analysis should be performed. In this study, the response of base isolation system was analyzed by response history analysis for the seismic performance assessment. Firstly, several seismic assessment criteria for a nuclear power plant structure were reviewed for the nonlinear response history analysis. Based on these criteria, the spectrum matched ground motion generation method modifying a seed earthquake ground motion time history was adjusted. Using these spectrum matched accelerograms, the distribution of displacement responses of the simplified base isolation system was evaluated. The resulting seismic responses excited by the modified ground motion time histories and the synthesized time history generated by stochastic approach were compared. And the response analysis of the base isolation system considering the different intensities in each orthogonal direction was performed.