• Journal of the Earthquake Engineering Society of Korea
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• v.19 no.2
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• pp.63-74
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• 2015

This study investigated the influence of probabilistic variability in stiffness and nonlinearity of soil on response of nuclear power plant (NPP) structure subjected to seismic loads considering the soil-structure interaction (SSI). Both deterministic and probabilistic methods have been employed to evaluate the dynamic responses of the structure. For the deterministic method, $SRP_{min}$ method given in USNRC SRP 3.7.2(2013) (envelope of responses using three shear modulus profiles of lower bound($G_{LB}$), best estimate($G_{BE}$) and upper bound($G_{UB}$)) and $SRP_{max}$ method (envelope of responses by more than three ground profiles within range of $G_{LB}{\leq}G{\leq}G_{UB}$) have been considered. The probabilistic method uses the Latin Hypercube Sampling (LHS) that can capture probabilistic feature of soil stiffness defined by the median and the standard deviation. These analysis results indicated that 1) number of samples shall be larger than 60 to apply the probabilistic approach in SSI analysis and 2) in-structure response spectra using equivalent linear soil profiles considering the nonlinear behavior of soil medium can be larger than those based on low-strain soil profiles.

• Structural Engineering and Mechanics
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• v.58 no.6
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• pp.1045-1075
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• 2016

Shallow footings are one of the most common types of foundations used to support mid-rise buildings in high risk seismic zones. Recent findings have revealed that the dynamic interaction between the soil, foundation, and the superstructure can influence the seismic response of the building during earthquakes. Accordingly, the properties of a foundation can alter the dynamic characteristics (natural frequency and damping) of the soil-foundation-structure system. In this paper the influence that shallow foundations have on the seismic response of a mid-rise moment resisting building is investigated. For this purpose, a fifteen storey moment resisting frame sitting on shallow footings with different sizes was simulated numerically using ABAQUS software. By adopting a direct calculation method, the numerical model can perform a fully nonlinear time history dynamic analysis to realistically simulate the dynamic behaviour of soil, foundation, and structure under seismic excitations. This three-dimensional numerical model accounts for the nonlinear behaviour of the soil medium and structural elements. Infinite boundary conditions were assigned to the numerical model to simulate free field boundaries, and appropriate contact elements capable of modelling sliding and separation between the foundation and soil elements are also considered. The influence of foundation size on the natural frequency of the system and structural response spectrum was also studied. The numerical results for cases of soil-foundation-structure systems with different sized foundations and fixed base conditions (excluding soil-foundation-structure interaction) in terms of lateral deformations, inter-storey drifts, rocking, and shear force distribution of the structure were then compared. Due to natural period lengthening, there was a significant reduction in the base shears when the size of the foundation was reduced. It was concluded that the size of a shallow foundation influences the dynamic characteristics and the seismic response of the building due to interaction between the soil, foundation, and structure, and therefore design engineer should carefully consider these parameters in order to ensure a safe and cost effective seismic design.

• Korean Journal of Soil Science and Fertilizer
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• v.46 no.6
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• pp.487-493
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• 2013

The effects of long-term fertilization on soil biological properties and microbial community structure in the plough layer in a rice paddy soil in southern Korea were investigated in relation to the continuous application of chemical fertilizers (NPK), straw based compost (Compost), combination these two (NPK + Compost) for last 40 years. No fertilization plot (Control) was installed for comparison. Though fertilization significantly improved rice productivity over control, the long-term fertilization of NPK and compost combination was more effective on increasing rice productivity and soil nutrient status than single application of compost or chemical fertilizer. All fertilization treatments had shown significant improvement in soil microbial properties, however, continuous compost fertilization markedly increased soil enzyme and microbial activities as compared to sole chemical fertilization. Results of microbial community structure, evaluated by EL-FAME (ester-linked fatty acid methyl esters) method, revealed big difference among Control, NPK, and Compost. However, both Compost and Compost+NPK treatments belonged to the same cluster after statistical analysis. The combined application of chemical fertilizer and organic amendments could be more rational strategy to improve soil nutrient status and promote soil microbial communities than the single chemical fertilizer or compost application.

• Earthquakes and Structures
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• v.13 no.6
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• pp.561-572
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• 2017

Seismic base isolation has been accepted as one of the most popular design procedures to protect important structures against earthquakes. However, due to lack of information and experimental data the application of base isolation is quite limited to nuclear power plant (NPP) industry. Moreover, the effects of inelastic behavior of soil beneath base-isolated NPP have raised questions to the effectiveness of isolation device. This study applies the wavelet analysis to investigate the effects of soil-structure interaction (SSI) on the seismic response of a base-isolated NPP structure. To evaluate the SSI effects, the NPP structure is modelled as a lumped mass stick model and combined with a soil model using the concept of cone models. The lead rubber bearing (LRB) base isolator is used to adopt the base isolation system. The shear wave velocity of soil is varied to reflect the real rock site conditions of structure. The comparison between seismic performance of isolated structure and non-isolated structure has drawn. The results show that the wavelet analysis proves to be an efficient tool to evaluate the SSI effects on the seismic response of base-isolated structure and the seismic performance of base-isolated NPP is not sensitive to the effects in this case.

• Journal of the Earthquake Engineering Society of Korea
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• v.18 no.3
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• pp.125-132
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• 2014

In this study, a series of dynamic centrifuge tests were performed for a soil-foundation-structural interaction system in dry sand with various embedded depths and superstructure conditions. Sinusoidal wave, sweep wave and real earthquake were used as input motion with various input acceleration and frequencies. Based on the results, a natural period and an earthquake load for soil-structure interaction system were evaluated by comparing the free-field and foundation accelerations. The natural period of free field is longer than that of the soil-foundation-structure system. In addition, it is confirmed that the earthquake load for soil-foundation-structure system is smaller than that of free-field in short period region. In contrast, the earthquake load for soil-foundation-structure interaction system is larger than that of free-field in long period region. Therefore, the current seismic design method, applying seismic loading of free-field to foundation, could overly underestimate seismic load and cause unsafe design for long period structures, such as high-rise buildings.

• Steel and Composite Structures
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• v.51 no.1
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• pp.93-101
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• 2024

This paper presents an experimental and analytical study on a steel slit damper designed as an energy dissipative device for earthquake protection of structures considering soil-structure interaction. The steel slit damper is made of a steel plate with a number of slits cut out of it. The slit damper has an advantage as a seismic energy dissipation device in that the stiffness and the yield force of the damper can be easily controlled by changing the number and size of the vertical strips. Cyclic loading tests of the slit damper are carried out to verify its energy dissipation capability, and an analytical model is developed validated based on the test results. The seismic performance of a case study building is then assessed using nonlinear dynamic analysis with and without soil-structure interaction. The soil-structure system turns out to show larger seismic responses and thus seismic retrofit is required to satisfy a predefined performance limit state. The developed slit dampers are employed as a seismic energy dissipation device for retrofitting the case study structure taking into account the soil-structure interaction. The seismic performance evaluation of the model structure shows that the device works stably and dissipates significant amount of seismic energy during earthquake excitations, and is effective in lowering the seismic response of structures standing on soft soil.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.5
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• pp.1-12
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• 2010

This study presents a finite element analysis method that can accurately evaluate the nonlinear behaviour of structures affected by shallow soft subsoils and the soil-structure interaction. A two-dimensional finite element model that consists of a structure and shallow soft subsoil was used. The finite element model was used for a nonlinear time domain analysis of the OpenSees program. A parametric study was performed to investigate the effects of soil shear velocities, earthquake input motions, soft soil depth, and soil-structure interaction. The result of the proposed nonlinear finite element analysis method was compared with the result of an existing frequency domain analysis method, which is frequently used for addressing nonlinear soil behavior. The result showed that the frequency domain analysis, which uses equivalent secant soil stiffness and does not address the soil-structure interaction, significantly overestimated the response of the structures with short dynamic periods. The effect of the soil-structure interaction on the response spectrum did not significantly vary with the foundation dimensions and structure mass.

• Korean Journal of Soil Science and Fertilizer
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• v.47 no.4
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• pp.242-248
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• 2014

We have five soil series of pan soils in South Korea out of 391 series: Gangreung, Bugog, Yeongog, Jangweon, and Pogog. Productivity decreases in pan soils as pan horizons impede percolation and capillary rise of water and interrupt root extension. This study was performed to investigate pedogenic processes of pan soils mainly located in footslope and river terrace by analyzing physicochemical properties and soil micro-morphology. Korean pan soils belong to Alfisols, Ultisols, or Inceptisols and have udic or aquic soil moisture regime, mesic temperature regime, and mixed mineral substances. Texture of pan horizons selected for the present study was mainly silty clay loam with clay contents ranging from 26.3 to 45.3%. Bulk density of the pan horizons ranged from 1.4 to $2.1Mg\;m^{-3}$ and their soil structure were subangular or angular structure. In terms of micro-morphological structure, Bt horizon of Gangreung series was formed as platy and striated b-fabric structure possibly affected by uplift of coastal terrace following clay sedimentation by flood. Jangweon series showed micro-morphology of massive structure and crystallic b-fabric as macropores between coarse debris established by debris fall in slope were filled with silt-sized particles. The Bt horizons having massive structure and striated b-fabric in Yeongog, Pogog, and Bugog series implies that those horizons experienced horizontal mass flow after clay accumulation.

• Structural Engineering and Mechanics
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• v.13 no.6
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• pp.615-638
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• 2002

This paper presents a method of seismic analysis for a cylindrical liquid storage structure considering the effects of the interior fluid and exterior soil medium in the frequency domain. The horizontal and rocking motions of the structure are included in this study. The fluid motion is expressed in terms of analytical velocity potential functions, which can be obtained by solving the boundary value problem including the deformed configuration of the structure as well as the sloshing behavior of the fluid. The effect of the fluid is included in the equation of motion as the impulsive added mass and the frequency-dependent convective added mass along the nodes on the wetted boundary of the structure. The structure and the near-field soil medium are represented using the axisymmetric finite elements, while the far-field soil is modeled using dynamic infinite elements. The present method can be applied to the structure embedded in ground as well as on ground, since it models both the soil medium and the structure directly. For the purpose of verification, earthquake response analyses are performed on several cases of liquid tanks on a rigid ground and on a homogeneous elastic half-space. Comparison of the present results with those by other methods shows good agreement. Finally, an application example of a reinforced concrete tank on a horizontally layered soil with a rigid bedrock is presented to demonstrate the importance of the soil-structure interaction effects in the seismic analysis for large liquid storage tanks.

• Korean Journal of Soil Science and Fertilizer
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• v.46 no.6
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• pp.474-481
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• 2013

Understanding the microbial community structure of agricultural soils is important for better soil management in order to improve soil quality. Phospholipid fatty acid analysis has been popularly used in determining the microbial community structure in different ecosystems. The microbial community structure of paddy soil under long-term fertilizer treatments was investigated after 45 years using PLFA analysis. Treatments were control (no fertilization, Con), compost (COM), NPK, NPK+compost (NPKC), PK, NK, and NP. Soil chemical properties were mainly affected by the addition of compost and inorganic P fertilizer. Total nitrogen and organic matter contents were significantly higher in treatments with compost while available $P_2O_5$ and exchangeable calcium were significantly higher in treatments with added inorganic P fertilizer. It was found that microbial communities were responsive to the different fertilizer treatments. PLFA results showed that the soils were dominated by gram-negative bacteria, followed by the actinomycetes, then gram-positive bacteria, and fungi. Principal component analysis of the soil chemical properties and PLFA composition proved to be a more reliable tool because it was more responsive to the changes in soil chemical properties.