• Journal of the Korean Geotechnical Society
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• v.38 no.12
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• pp.91-101
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• 2022

The 1995 Kobe earthquake caused a massive damage to the Port of Kobe. Therefore, it was pointed out that it was impossible to design port structures for Level II (Mw 6.5) earthquakes with quasi-static analysis and Allowable Stress Design methods. In Japan and the United States, where earthquakes are frequent, the most advanced design standards for port facilities are introduced and applied, and the existing seismic design standards have been converted to performance-based design. Since 1999, the Korean Port Seismic Design Act has established a definition of necessary facilities and seismic grades through research on facilities that require seismic design and their seismic grades. It has also established a performance-based seismic design method based on experimental verification. In the performance-based seismic design method of the breakwater proposed in this study, the acceleration time history on the surface of the original ground was subjected to a fast Fourier transform, followed by a filter processing that corrected the frequency characteristics corresponding to the maximum allowable displacement with respect to performance level of the breakwater and the filtered spectrum. The horizontal seismic coefficient for the equivalent static analysis considering the displacement was calculated by inversely transforming (i.e., subjected to an inverse fast Fourier transform) into the acceleration time history and obtaining the maximum acceleration value. In addition, experiments and numerical analysis were performed to verify the performance-based seismic design method of breakwaters suitable for domestic earthquake levels.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.1C
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• pp.43-52
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• 2006

Despite several constitutive models have been proposed and applied, it is still difficult to choose a suitable model and to estimate adequate analysis parameters. Furthermore, a cyclic shear behavior under the volume change caused by the seepage is more complex. None of the constitutive model is available at present in the expression of the cyclic behavior of soil under an additional volume change condition by seepage. Therefore, a new geotechnical hybrid simulation system which can control the pore water immigration was developed. The system enables a quantitative evaluation of the residual deformation such as lateral spreading and settlement caused by the liquefaction. The seismic responses in a one-dimensional slightly inclined multilayered soil system are taken into consideration, and the soils are governed by both equation of motion and the continuity equation. Furthermore, the estimation and the selection of the soil parameter for the representation of the strong nonlinearity of the material are not required, because soil behaviors under the earthquake motions are directly introduced instead of a numerical soil constitutive model. This paper presents the concept and specifications of the system. By applying the system to an example problem, the permeability effect on the seismic response during cyclic shear is studied. The importance of the volume change characteristics of sandy soil during and after cyclic shear is shown in conclusion.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.3
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• pp.205-216
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• 2024

Recently, seismic Probabilistic Safety Assessment (PSA) methods have been developed for process plants, such as gas plants, oil refineries, and chemical plants. The framework originated from the PSA of nuclear power plants, which aims to assess the risk of reactor core damage. The original PSA method was modified to adopt the characteristics of a process plant whose purpose is continuous operation without shutdown. Therefore, a fault tree, whose top event is shut down, was constructed and transformed into a Bayesian Network (BN), a probabilistic graph model, for efficient risk-informed decision-making. In this research, the fault tree-based BN from the previous research is further developed to consider the multi-hazard of earthquake-induced fire and explosion (EQ-induced F&E). For this purpose, an event tree describing the occurrence of fire and explosion from a release is first constructed and transformed into a BN. And then, this BN is connected to the previous BN model developed for seismic PSA. A virtual plot plan of a gas plant is introduced as a basis for the construction of the specific EQ-induced F&E BN to test the proposed BN framework. The paper demonstrates the method through two examples of risk-informed decision-making. In particular, the second example verifies how the proposed method can establish a repair and retrofit strategy when a shutdown occurs in a process plant.

• Journal of the Korean Geotechnical Society
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• v.21 no.4
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• pp.65-70
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• 2005

Many case histories of re-liquefaction phenomena seem to support the idea that sand deposits, if they once have been liquefied, could be reliquefied again by a subsequent earthquake even though the earthquake is smaller than the previous one. The magnitude of the strains induced in the initial liquefaction has a significant influence on the resistance of the sample to re-liquefaction. The deposits undergoing liquefaction experience large shear strain during liquefaction. And this previous strain changes the microstructure into highly anisotropic structure such as columnlike structure and connected voids. This type of anisotropy is so unstable that it can reduce re-liquefaction resistance. It is blown that the extent of anisotropic structural change depends on the gradation characteristics of ground. The purpose of this study is to estimate the correlation between the gradation characteristics of the sand and the ratio of re-liquefaction resistance to liquefaction resistance. In this study, 1-g shaking table tests were carried out on five different kinds of sands. During the tests the values of excess pore pressure at various depths and surface settlements were measured. Re-liquefaction resistances were not affected by the initial void ratio and the effective confining pressures, and the deposits of all test sands which had once been liquefied were reliquefied in the cyclic loading number below 1 to 1.5. The ratio of re-liquefaction resistance to liquefaction resistance linearly decreased as $D_{10}/C_u$ increased, and was constant as about 0.2 above the value of $D_{10}/C_u$, 0.15 mm.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.4
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• pp.759-768
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• 2015

The ground motions of large dimensional structures such as long span bridges at different stations during an earthquake, are inevitably different, which is known as the ground motion spatial variation effect. There are many causes that may result in the spatial variability in seismic ground motion, e.g., the wave passage effect due to the different arrival times of waves at different locations; the loss of coherency due to seismic waves scattering in the heterogeneous medium of the ground; the site amplification effect owing to different local soil properties. In previous researches, the site amplification effects have not been considered or considered by a single-layered soil model only. In this study, however, the ground motion amplification and filtering effects are evaluated by multi-layered soil model. Spatially varying ground motion at the sites with different number of layers, depths, and soil characteristics are generated and the variation characteristics of ground motion time histories according to the correlation of coherency loss function and soil conditions are evaluated. For the bridge system composed of two unit bridges, seismic behavior characteristics are analyzed using the generated seismic waves as input ground motion. Especially, relative displacement due to coherency loss and site effect which can cause the unseating and pounding between girders are evaluated. As a result, considering the soil conditions of each site are always important and should not be neglected for an accurate structural response analysis.

• The Journal of Engineering Geology
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• v.23 no.4
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• pp.435-445
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• 2013

Since design response spectrum does not reflect local soil characteristics, site specific response spectrum of observed ground motions appears relatively higher than design response spectrum at high frequency range. These problems have been pointed out from the domestic seismic design industry. Among various estimation methods, this study used the method H/V ratio of ground motion for estimating site amplification. This method has been extended to background noise, Coda waves and S waves recently for estimating site amplification. This study applied this method to the background noise and Coda wave energy. This study analysed more than 267 background noises from 15 macro earthquakes including main Fukuoka earthquake (2005/03/20, M=6.5) and then compared to results from S waves, at 8 main domestic seismic stations. The results showed that most of the domestic seismic stations gave similar results to those from S waves. Each station showed its own characteristics of site amplification property in low, high and specific resonance frequency ranges. Comparison of this study to other studies using different method can give us much information about dynamic amplification of domestic sites characteristics and site classification.

• Geotechnical Engineering
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• v.11 no.2
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• pp.139-156
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• 1995

A set of field investigations was performed to estimate accurately the predominant periods of seismic 8round motions and the attenuation characteristics of the seismic ground vibration. Predominant periods of ground motions were estimated from the measurement of the continuous microseismic vibratins of certain periods, inherent in the ground and in the buildings, utilizing the high sensitivity digital velocity seismometer consisting of 3-component geophones and a digital seismograph. Estimated predominant periods of microseismic vibraion of the ground(measured on'the ground surface) and the building (measured on the second floor) were in the range of 0.18~0.235 sec. and 0.26~0.31 sec. respectively. The subsurface structure of the site ground was surveyed by the seismic refraction method utilizing the digital seismicwave probing system. The ground structure was found to be a two-layered system : an upper top soil layer of 7m in thickness with the P-wave velocity of 662m1sec and a lower layer of silty-clayey soils with the P -wave velocity of 2210m1 sec. The attenuation characteristics of the seismic ground vibrations were determined by the amplitude decay measurement method us;ng the Seisgun, which produces strong artificial seismic energy. Measured spatial attenuation coefficients of the ground vibration in vertical(Z) longitudinal(X), transverse(Y) direction were 0.1137, 0.0025, and 0.0290 respectively. Estimated Spartial QP's (inverse of the specific dissipation constant w.r.t. shear waved of X, Y, and Z directions were in the range of 5.913~7.575, 32.371~41.452, 2.794~3.579 re spectively. This indicates that aseimic design of the structures on the site should take stronger consideration regarding the earthquake resistance characteristics of the structures against longitudinal ground motion.

• Journal of the Korean Geotechnical Society
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• v.35 no.4
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• pp.15-26
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• 2019

The stability of the gravity quay wall against earthquakes is evaluated on the basis of the allowable displacement of the wall. To estimate the displacement caused by external forces, empirical equations based on the Newmark sliding block method or numerical analysis are widely used. In numerical analysis, it is possible to analyze precisely a complicated site and structure, but difficult to set the appropriate parameters and environments; there are limitations in obtaining reliable results, depending on one's level of expertise. The Newmark method, with only seismic motions, is widely used because it is simpler than numerical simulations when estimating permanent displacement. However, the empirical equations do not have any parameters for the response characteristics and sliding block of the structure, and sliding blocks being assumed as rigid bodies does not consider the nonlinear behavior of the soil and interaction with the structure. Therefore, in order to evaluate the seismic stability of the gravity quay wall, a newly-developed empirical equation is needed to overcome the above-mentioned limitations. In this study, numerical simulations are performed to analyze the response characteristics of the backfill of the structure, and to propose an optimal method of calculating the active area. For this purpose, finite element analyses were performed to analyze the response characteristics, and stress-strain relationships for various seismic motions. As a result, the response characteristics, sliding block, and failure surface of the backfill vary depending on the input seismic motions.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.1
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• pp.59-66
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• 2021

The earthquakes are the natural disasters that can cause the most serious damage to civil structures. Therefore, various studies are being conducted to secure the safety of structures against earthquakes. Most studies on the safety or mechanism of civil structures during earthquakes are being conducted based on lab scale test, because real structure tests are impossible when considering the scale of civil structures. The scaling factor proposed by Iai is mainly cited, but when applying the scaling factor proposed by Iai, there are many difficulties in selecting the structural members necessary for the production of the lab scale model. This is because when applying the scaling factor proposed by Iai, the scaling factor must be applied to the elastic modulus, which is the material property of the structure. Therefore, a new method based on Iai's 's similarity law for determining scale factor is applied in this study where the material property of real structure is same as that of lab-scale model. Through the results of this study, it is considered that the characteristics of the structure calculated through the lab scale model test can more accurately reflect the characteristics of the real structure.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.36 no.2
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• pp.80-86
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• 2024

Large-scale earthquakes are occurring globally, especially in the South Asian crust, which is experiencing a state of tension in the aftermath of the 2011 East Japan Earthquake. Uncertainty and fear regarding the possibility of further seismic activity in the near future have been on the rise in the region. The National Disaster Management Research Institute has previously studied and analyzed the overflow characteristics of a tsunami and the rate of flood forecasting through tsunami numerical simulations of the East Sea of South Korea. However, there is currently a significant lack of research on the Southern Coast tsunamis compared to the East Coast. On the Southern Coast, the tidal difference is between 1~4 m, and the impact of the tides is hard to ignore. Therefore, it is necessary to analyze the impact of the tide propagation characteristics on the tsunami. Occurrence regions that may cradle tsunamis that affect the southern coast region are the Ryukyu Island and Nankai Trough, which are active seafloor fault zones. The Southern Coast has not experienced direct damage from tsunamis before, but since the possibility is always present, further research is required to prepare precautionary measures in the face of a potential event. Therefore, this study numerically simulated a hypothetical tsunami scenario that could impact the southern coast of South Korea. In addition, the tidal wave propagation characteristics that emerge at the shore due to tide and tsunami interactions will be analyzed. This study will be used to prepare for tsunamis that might occur on the southern coast through tsunami hazard and risk analysis.