내진설계기준의 지반분류체계 및 설계응답스펙트럼 개선을 위한 연구 - (I) 데이터베이스 및 지반응답해석

조형익,김동수,Cho, Hyung Ik,Satish, Manandhar,Kim, Dong Soo 한국지진공학회 2016 한국지진공학회논문집 Vol.20 No.4

Korea is part of a region of low to moderate seismicity located inside the Eurasian plate with bedrock located at depths less than 30 m. However, the spectral acceleration obtained from site response analyses based on the geologic conditions of inland areas of the Korean peninsula are significantly different from the current Korean seismic code. Therefore, suitable site classification scheme and design response spectra based on local site conditions in the Korean peninsula are required to produce reliable estimates of earthquake ground motion. In this study, site-specific response analyses were performed at more than 300 sites with at least 100 sites at each site categories of $S_C$, $S_D$, and $S_E$ as defined in the current seismic code in Korea. The process of creating a huge database of input parameters - such as shear wave velocity profiles, normalized shear modulus reduction curves, damping curves, and input earthquake motions - for site response analyses were described. The response spectra and site coefficients obtained from site response analyses were compared with those proposed for the site categories in the current code. Problems with the current seismic design code were subsequently discussed, and the development and verifications of new site classification system and corresponding design response spectra are detailed in companion papers (II-development of new site categories and design response spectra and III-Verifications)

시간영역에서 유한요소법을 이용한 지진시의 지반응답해석

류희룡,이재영,박영택,You, Hee-Yong,Lee, Jae-Young,Park, Young-Tack 한국농공학회 2006 한국농공학회논문집 Vol.48 No.6

The finite element method is a practical tool to compute the response of the irregularly layered soil deposit to the base-rock motions. The method is useful not only in estimating the interaction between the structure and the surrounding soil as a whole and the local behavior of the contacting area in detail, but also in predicting the resulting behavior of the superstructure affected by such soil-structure interactions. However, the computation of finite element analysis is marched in the time domain (TD), while the site response analysis has been carried out mostly in the frequency domain (FD) with equivalent linear analysis. This study is intended to compare the results of the TD and FD analysis with focus on the peak response accelerations and the predominant frequencies, and thus to evaluate the applicability and the validity of the finite element analysis in the site response analysis. The comparison shows that one can obtain the results very close to that of FD analysis, from the finite element analysis by including sufficiently large width of foundation in the model and further by applying partial mode superposition. The finite element analysis turned out to be well agreeing with FD analysis in their computed results of the peak acceleration and the acceleration response spectra, especially at the surface layer.

역사 지진 피해 발생 읍성 지역에 대한 부지 고유의 지진 응답 특성 평가

선창국 ( Chang Guk Sun ),정충기 ( Choong Ki Chung ),김동수 ( Dong Soo Kim ),김재관 ( Jae Kwan Kim ) 대한지질공학회 2007 지질공학 Vol.17 No.1

역사 지진으로 인해 성첩이 붕괴되었던 국내 두 읍성 지역에 대한 국부적 부지 효과를 평가하기 위하여, 현장 시추 조사 및 탄성파 시험을 통해 전단파속도(Vs) 주상을 포함한 지반 특성을 결정하고 이를 토대로 등가 선형 기법의 부지 응답 해석을 수행하였다. 대상 부지는 심도 30 m까지의 평균 전단파속도가 500~850 m/s의 분포를 보임에 따라 지반 분류 C와 B로 구분되었고, 부지 고유주기는 성벽과 성첩의 고유주기를 포함하는 범위인 0.06~0.16초의 단주기 분포를 보였다. 대상 영역에서의 부지 응답 해석 결과, 지반 분류 B와는 달리 대부분의 부지 조건인 지반 분류 C의 경우 부지 고유 지진 응답 특성인 단주기에서의 큰 증폭으로 인해, 국내 내진 설계 기준의 단주기(0.1~0.5초) 증폭계수 Fa와 중장주기(0.4~2.0초) 증폭계수 Fv는 각각 지반 운동을 단주기 영역에서는 과소평가하고 중장주기 영역에서는 과대평가함을 확인하였다. 이러한 부지 고유 응답 특성은 단주기 고유 응답을 보이는 성벽 구조물이 지진 발생 시 공진이 발생할 가능성이 높음을 의미하며, 그에 따라 역사 지진 피해 사례인 성첩 붕괴의 지배적인 영향 인자로서 작용했을 것으로 판단된다. In order to evaluate the local site effects at two town fortress areas in Korea where stone parapets were collapsed by historical earthquakes, site characteristics were assessed using site investigations such as borehole drillings and seismic tests. Equivalent-linear site response analyses were conducted based on the shear wave velocity (VS) profiles and geotechnical characteristics determined from site investigations. The study sites are categorized as site classes C and B according to the mean VS to 30 m ranging from 500 to 850 m/s, and their site periods are distributed in the short period range of 0.06 to 0.16 sec, which contains the natural period of fortress wall and stone parapet. From the results of site response analyses in the study areas, for site class C indicating most of site conditions, contrary to site class B, the short-period (0.1-0.5 sec) and mid-period (0.4-2.0 sec) site coefficients, Fa and Fv specified in the Korean seismic design guide, underestimate the ground motion in short-period band and overestimate the ground motion in mid-period band, respectively, due to the high amplification in short period range, which represent the site-specific seismic response characteristics. These site-specific response characteristics indicate the potential of resonance in fortress walls during earthquake and furthermore could strongly affect the collapse of parapets resulted from seismic events in historical records.

Comparison of Nonlinear Analysis and Equivalent Linear Analysis on 1D Site Response Analysis

( Yonghee Lee ),( Hak-sung Kim ),( Seok-chul Kim ),( Weon-hack Choi ) 대한지질공학회 2019 대한지질공학회 학술발표회논문집 Vol.2019 No.2

Equivalent linear and nonlinear analyses are the most common approaches to perform 1D site response analysis. Since these methods have inherent differences in analysis process (time domain, frequency domain), computed results yield different output. Equivalent linear analysis is a kind of linear analysis considering non-linearity and an approximation of hysteric soil behavior. Nonlinear analysis method is the hysteretic stress-strain response of soil and can represent more actual behavior rather than equivalent linear analysis. In this study 1D nonlinear analysis and equivalent linear analysis are performed with DEEPSOIL version 7.1 for 30 m soil depth. Shear modulus reduction and damping curve was used with Darendeli (2001) that has Ko is 0.5. Curve fitting for modulus reduction and damping function were performed with university of Illinois at Urbana-Champaign (MRDF-UIUC) model. Used soil model is pressure-dependent modified Kondner Zelasko (MKZ) and hysteretic unloading-reloading formulation follows non-masing rule in the nonlinear analyses. The thickness of each layer is 1 m. The used input motion is Northridge earthquake record (scaled from 0.05 g to 1 g). Analyses results show that ground behavior is very similar in the low peak ground acceleration (PGA) level but somewhat different in the high PGA level. In case of strong motion (i.e., PGA > 0.5 g) especially in the initial and decayed part, equivalent linear analyses results show under-prediction tendency but over-prediction tendency in the strong motion part. During strong motion part, soil stiffness decreased in the nonlinear analysis but is same in the equivalent linear analysis.

부지응답해석에 기반한 지반운동 선정 및 보정에 관한 고찰

황정현,목지욱,손현실,옥종호 한국구조물진단유지관리공학회 2020 한국구조물진단유지관리공학회 논문집 Vol.24 No.5

In the recent seismic design code KDS 41 17 00, selection and modification procedures of ground motions which are used for nonlinear dynamic analyses were adopted. However, its practical applications are still limited due to the lack of literatures. This paper introduces case studies which used site-response analyses to select and modify ground motions for nonlinear dynamic analyses. Based on the case studies, design criterion for site-response analyses were reviewed thoroughly in the viewpoint of practical applications. It was found that design requirements related with bedrock motions are too conservative that ground motions are selected and modified in the excessive manner. It is especially true for low-rise building structures with period ranges including acceleration-sensitive regions. Even though surface motions have shown appropriate responses, such building structures have to re-select and re-modify ground motions based on pre-analysis procedures rather than post-ones according to the current seismic design code. Also, it was observed that building structures with soft soils under strong ground motions need more comprehensive investigations on soil properties and efficient analysis methods in order to perform site-response analyses. This is due to the fact that lack of reliabilities on soil properties and analysis methods could result in unstable site-responses. 최신 내진설계기준 KDS 41 17 00에 비선형동적해석에 사용될 지반운동 선정 및 보정에 관한 절차가 반영되었으나 관련 문헌 부족으로 실무적 차원에서의 적용이 여전히 어려운 실정이다. 본 연구는 비선형동적해석 수행을 위한 지반운동을 선정하고 보정하기 위해 부지응답해석을 수행한 사례를 소개한다. 이에 근거하여, 현행 설계기준에 명기된 부지응답해석 관련 조항을 실무적용 차원에서 검토하였다. 그 결과 암반운동선정에 관한 설계조항이 지나치게 엄격하여 과도한 결과를 초래하는 것으로 나타났다. 이는 가속도 민감 구간을 포함한 관심주기범위를 지닌 저층 구조물일수록 더욱 부각되는 것으로 판단된다. 특히 표면지진파가 기준에 적합한 응답을 보였음에도 불구하고, 해석 전 절차의 암반운동선정과 관련된 조항으로 인해 해석 후 절차와 관계없이 지진파를 다시 선정 및 보정해야만 했다. 또한, 연약지반이거나 해당 지반에 강한 지진이 발생하는 경우에는 지반물성과 적절한 해석 기법을 올바르게 선정하기 위해 더욱 엄격한 조사가 선행되어야 한다고 판단된다. 지반물성과 해석기법에 관한 신뢰도가 조금이라도 문제가 있다면 설계용도로 사용하기에 부적합한 결과를 초래할 수 있기 때문이다.

Development of Site Classification System and Modification of Design Response Spectra Considering Geotechnical Characteristics in Korea

Kim, Dong-Soo,Yoon, Jong-Ku 한국지진공학회 2007 한국지진공학회논문집 Vol.11 No.4

Site response analyses were performed based on equivalent linear technique using shear wave velocity profiles of 162 sites collected around the Korean peninsula. The site characteristics, particularly the shear wave velocities and the depth to the bedrock, are compared to those in the western United States. The results show that the site-response coefficients based on the mean shear velocity of the top 30m (V_{S30}) suggested in the current code underestimates the motion in short-period ranges and overestimates the motion in mid-period ranges. The current Korean code based on UBC is required to be modified considering site characteristics in Korea for the reliable estimation of site amplification. From the results of numerical estimations, new regression curves were derived between site coefficients (F_{a}\;and\;F_{v}) and the fundamental site periods, and site coefficients were grouped based on site periods with reasonable standard deviations compared to site classification based on V_{S30}. Finally, new site classification system and modification of design response spectra are recommended considering geotechnical characteristics in Korea.

쌍계사 오층 석탑 부지의 지진 응답 특성 평가를 통한 1936년 지리산 지진 세기의 정량적 분석

선창국(Sun Chang-Guk),정충기(Chung Choong-Ki),김재관(Kim Jae-Kwan) 대한토목학회 2008 대한토목학회논문집 C Vol.28 No.3

한반도 남쪽 경계 부근에 위치한 지리산 내의 불교 사찰인 쌍계사에서 19361년 7월 4일 규모 5.0 지진이 발생하였다. 이 지진으로 인하여 쌍계사 경내 건축물과 구조물이 심각한 피해를 입었으며, 특히 지진시 사찰 내 오층 석탑의 탑두가 전도하여 추락하였다. 이 지진 피해 사례는 역사 지진 발생 이외의 강진 기록이 전무한 중진 지역의 한반도에서의 지반 운동 세기 평가에 유용하게 활용될 수 있다. 쌍계사 부지에서의 국부적 부지 효과 및 그에 따른 지반 운동을 평가하기 위하여, 시추와 크로스흘 및 SASW 시험과 같은 현장 탄성파 시험으로 구성된 종합적인 지반 조사를 사찰 경내에서 수행하였다. 조시된 지반 특성을 토대로, 다양한 지진파를 적용한 부지고유 지진 응답 해석을 0.044g부터 0.220g 범위의 여섯 가지 입력 암반 노두 가속도 수준으로 대표적 쌍계사 부지에 대해 일차원 등가선형 및 비선형 기법을 적용하여 실시하였다. 부지고유 지진 응답 결과로부터 쌍계사의 부지 주기 부근의 단주기 영역에서 증폭된 지반 운동을 확인할 수 있었다. 또한, 본 연구의 부지 응답 해석 결과와 선행 연구의 석탑 실물 크기 지진 시험 결과를 비교 분석하여 1936년 지리산 지진의 암반노두 지진 세기를 평가하였다. An earthquake of magnitude 5.0 occurred at Ssang-gye-sa, a Buddhist temple in Jirisan, located near the southern border of the Korean peninsula on 4 July 1936. It resulted in severe damage of several buildings and structures in Ssang-gye-sa. Particularly, the top component of a five-story stone pagoda in the temple was tipped over and fell down during the earthquake. This earthquake damage case would be usefully applied to estimating the intensity of ground motion in the Korean peninsula, a moderate seismicity region, where strong motion has never been recorded with the exception of historic seismic events. In order to estimate the local site effects and the corresponding ground motion at Ssang-gye-sa site, intensive site investigations including borehole drilling and in-situ seismic tests such as crosshole and SASW tests were performed in the temple area. Based on the site characteristics, site-specific seismic response analyses using various input motions were conducted for a representative Ssang-gye-sa site by means of both one-dimensional equivalent-linear and nonlinear methods with six input rock outcrop acceleration levels ranging from 0.044g to 0.220g. The resultant site-specific seismic responses indicated the amplified ground motions in the short-period range near the site period of Ssang-gye-sa. Furthermore, the intensity on rock outcrop of the 1936 Jirisan earthquake was estimated by making a comparison between the site responses analysis results in this study and the full-scaled seismic test of pagoda model in the prior study.

Analysis of Round Robin Test on Seismic Site Response Analysis

박두희,김진만 대한토목학회 2012 KSCE JOURNAL OF CIVIL ENGINEERING Vol.16 No.7

Site response analysis, widely performed in practice to estimate seismic site effects, requires multiple inputs regarding the dynamic soil properties. While comprehensive site-specific field and laboratory tests need to be performed for the proper characterization of a site, engineers are often given only limited information and are forced to work with uncertainties. A round-robin test on site response analysis was performed in Korea to evaluate the dispersion of the calculated responses originating from the uncertainties in soil characterization and from the method of analysis. The participants were intentionally given limited information, which represented a typical set of inputs given in practice. The participants were asked to predict the dynamic properties based on the given data, and to perform a series of site response analyses. This paper documents the variations in the predicted dynamic properties and the computed responses. The results showed that the prediction of the shear wave velocity was most important for the evaluation of the groundmotion propagation, while the type of analysis had only a secondary influence. Important guidelines for the prediction of dynamic properties are also given.

비선형 응답이력해석의 영향인자에 대한 사례연구 - 1989 Loma Prieta 지진 계측기록을 중심으로 -

유계항,이진선 한국지반공학회 2017 한국지반공학회논문집 Vol.33 No.12

As many seismic codes for various facilities are changed into a performance based design code, demand for a reliablenonlinear response-history analysis (RHA) arises. However, the equivalent linear analysis has been used as a standardapproach since 1970 in the field of site response analysis. So, the reliability of nonlinear RHA should be providedto be adopted in replace of equivalent linear analysis. In this paper, the reliability of nonlinear RHA is reviewed fora layered soil layer using Loma Prieta earthquake records in 1989. For this purpose, the appropriate way for selectingnonlinear soil models and the effect of base boundary condition for 3D analysis are evaluated. As a result, there isno significant differences between equivalent linear and nonlinear RHA. In case of 3D analysis, absorbing boundarycondition should be applied at base to prevent rocking motion of the whole model.

DEVELOPMENT OF NEW SITE CLASSIFICATION SYSTEM FOR THE REGIONS OF SHALLOW BEDROCK IN KOREA

Kim, Dong-Soo,Yoon, Jong-Ku Taylor Francis 2006 Journal of earthquake engineering Vol.10 No.3

<P> In the current Korean code, the site classification and the corresponding site coefficients were determined similar to the UBC 1997, which were revised based on the results from the investigation of the 1989 Loma Prieta earthquakes in the western United States. Since the site effects are directly dependent on the local site conditions, the use of site coefficients derived from earthquake records which occurred in different site conditions may mislead the earthquake ground motion. Therefore, it is important to compare the local site conditions in Korea to those in the western United States and assess their effects on site coefficients, for the reliable estimation of earthquake ground motions in Korea. In this paper, site response analyses were performed based on equivalent linear technique using the shear wave velocity profiles of 162 sites collected around the Korean peninsula. The site characteristics, particularly the shear wave velocities and the depth to the bedrock, are compared to those in western United States. The results showed that the site-response coefficients based on the mean shear velocity of the top 30 m (VS30) suggested in the current code underestimates the motion in short-period ranges and overestimates the motion in mid-period ranges. Also the current Korean code based on UBC is required to be modified considering site characteristics in Korea for the reliable estimation of site amplification. From the results of numerical estimations, new regression curves were derived between site coefficients (Fa and Fv) and the fundamental site periods, and site coefficients were grouped based on site period. The standard deviations of the proposed method were reasonable compared to site classification based on VS30. Finally, new site classification system was tentatively recommended based on site periods for regions of shallow bedrock depth in Korea.</P>