• Journal of the Earthquake Engineering Society of Korea
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• v.20 no.4
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• pp.235-243
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• 2016

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)

• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.4
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• pp.65-77
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• 2007

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.

• Journal of the Earthquake Engineering Society of Korea
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• v.20 no.4
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• pp.257-268
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• 2016

In the companion papers (I, II), site-specific response analyses were performed at more than 300 domestic sites and a new site classification system and design response spectra (DRS) were proposed using the results of the site-specific response analyses. In this paper, the proposed site classification system and the design response spectra are compared with those in other seismic codes and verified by different methods. Firstly, the design response spectra are compared with the design response spectra in Eurocode 8, KBC 2016 and MOCT 1997 to estimate quantitative differences and general trends. Secondly, site-specific response analyses are carried out using $V_S$-profiles obtained using field seismic tests and the results are compared with the proposed DRS in order to reduce the uncertainty in using the SPT-N value in site-specific response analyses in the companion paper (I). In addition, site coefficients from real earthquake records measured in Korean peninsula are used to compare with the proposed site coefficients. Finally, dynamic centrifuge tests are also performed to simulate the representative Korean site conditions, such as shallow depth to bedrock and short-period amplification characteristics. The overall results showed that the proposed site classification system and design response spectra reasonably represented the site amplification characteristic of shallow bedrock condition in Korea.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1998.10a
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• pp.345-352
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• 1998

Free-field ground motion during earthquake is significantly affected by the local site conditions and the behavior of structure is influenced by ground motion, it is essential to perform the reliable site characterization and to determine the site specific earthquake response. In this study, case study of site specific ground response evaluation was performed at Inchon area. Step by step procedures for site characterization and one-dimensional site response analysis were introduced and the importance of site specific analysis was verified.

• Journal of the Earthquake Engineering Society of Korea
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• v.20 no.4
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• pp.245-256
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• 2016

In the companion paper (I - Database and Site Response Analyses), site-specific response analyses were performed at more than 300 domestic sites. In this study, a new site classification system and design response spectra are proposed using results of the site-specific response analyses. Depth to bedrock (H) and average shear wave velocity of soil above the bedrock ($V_{S,Soil}$) were adopted as parameters to classify the sites into sub-categories because these two factors mostly affect site amplification, especially for shallow bedrock region. The 20 m of depth to bedrock was selected as the initial parameter for site classification based on the trend of site coefficients obtained from the site-specific response analyses. The sites having less than 20 m of depth to bedrock (H1 sites) are sub-divided into two site classes using 260 m/s of $V_{S,Soil}$ while the sites having greater than 20 m of depth to bedrock (H2 sites) are sub-divided into two site classes at $V_{S,Soil}$ equal to 180 m/s. The integration interval of 0.4 ~ 1.5 sec period range was adopted to calculate the long-period site coefficients ($F_v$) for reflecting the amplification characteristics of Korean geological condition. In addition, the frequency distribution of depth to bedrock reported for Korean sites was also considered in calculating the site coefficients for H2 sites to incorporate sites having greater than 30 m of depth to bedrock. The relationships between the site coefficients and rock shaking intensity were proposed and then subsequently compared with the site coefficients of similar site classes suggested in other codes.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.707-714
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• 2009

The design response spectrum generally used in Korea is decided by the site coefficients determined by deterministic methodology, while it is based on probabilistic seismic hazard analysis. The design response spectrum has to be made using probabilistic method which includes uncertainties of ground motions and ground properties for coincide with probabilistic methodology of seismic hazard analysis. In this study probabilistic site coefficients were developed, which were defined by the results of site response analysis using a set of ground motion that was compatible with present seismic hazard map. The design response spectrum defined by probabilistic seismic coefficients resulted in lower spectrum in long period area and larger spectrum in short period area. Also, the maximum spectral accelerations in site class D and site class E were lower than one in site class C while in the previous design response spectrum the maximum spectral acceleration increased from site class A to E.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2006.03a
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• pp.113-124
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• 2006

Despite the site classification method was improved in the previous study, the response spectrum would be required to be modified by adjusting the integration interval to calculate the site coefficients because the response spectra did not match well the average spectral accelerations obtained by site response analyses in the range of long periods. In this paper, new response spectra for each site categories were determined by adjusting the integration interval of long-period site coefficient $F_{v}$ from $0.4{\sim}2.0$ to $0.4{\sim}1.5$ second. It matched well the average spectral accelerations and new response spectrum, and it was also improved compared to the current site classification system.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.2 s.48
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• pp.63-71
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• 2006

In the companion paper (II, Development of Site Classification System), new size classification system based on site periods $(T_G)$ was recommended for legions of shallow bedrock depth in Korea. Despite the site classification method was improved, the response spectrum would be required to be modified by adjusting the integration interval to calculate the site coefficients because the response spectra did not match well the average spectral accelerations obtained by site response analyses in the range of long periods. In this paper, new response spectra for each site categories were determined by adjusting the integration interval of long period site coefficient $F_v\;from\;0.4{\sim}2.0\;to\;0.4{\sim}1.5$ second. It matched well the average spectral accelerations and new response spectrum, and it was also improved compared to the current she classification system.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.10a
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• pp.154-162
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• 2005

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 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. 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 ($F_a$ and $F_v$) and the fundamental site periods, and site coefficients were grouped based on site periods in the regions of shallow bedrock. The standard deviations of the proposed method was reasonable compared to site classification based on $V_{S30}$. Finally, new site classification system is recommended based on site periods for regions of shallow bedrock depth in Korea.

• Earthquakes and Structures
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• v.10 no.5
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• pp.1233-1251
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• 2016

In this paper, it is aimed to determine the stochastic response of a suspension bridge subjected to spatially varying ground motions considering the geometric nonlinearity. Bosphorus Suspension Bridge built in Turkey and connects Europe to Asia in Istanbul is selected as a numerical example. The spatial variability of the ground motion is considered with the incoherence, wave-passage and site-response effects. The importance of site-response effect which arises from the difference in the local soil conditions at different support points of the structure is also investigated. At the end of the study, mean of the maximum and variance response values obtained from the spatially varying ground motions are compared with those of the specialised cases of the ground motion model. It is seen that each component of the spatially varying ground motion model has important effects on the dynamic behaviour of the bridge. The response values obtained from the general excitation case, which also includes the site-response effect causes larger response values than those of the homogeneous soil condition cases. The variance values calculated for the general excitation case are dominated by dynamic component at the deck and Asian side tower. The response values obtained for the site-response effect alone are larger than the response values obtained for the incoherence and wave-passage effects, separately. It can be concluded that suspension bridges are sensitive to the spatial variability of ground motion. Therefore, the incoherence, the wave-passage and especially the site-response effects should be considered in the stochastic analysis of this type of engineering structures.