• Journal of the Earthquake Engineering Society of Korea
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• v.5 no.3
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• pp.19-27
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• 2001

In this seismic analyses of structures, it is well recognized that the effects of soil-structure interaction can not be ignored and seismic responses of a structure taking into account the stiffnesses of a foundation-soil system show the significant difference from those with a rigid base. However, current seismic analyses of apartment building structures were carried out with the rigid base ignoring the characteristics of the foundation and the properties of the underlying soil. In this study, seismic analyses of wall-slob type apartment buildings which have a particular structural type were carried out taking into account the soft soil layer comparing seismic response spectra of a flexible base with those of a rigid base and UBC-97. Low-rise or middle height wall-slab type apartment buildings built on the deep soft soil layer showed a rigid body motion with the reduced seismic responses due to the base isolation effect, indicating that it is considerably safe but uneconomical to utilize the design spectra of UB-97 for the seismic design of wall-slab type apartment buildings due to conservative design.

• Advances in Computational Design
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• v.9 no.2
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• pp.81-96
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• 2024

Modeling and analyzing the dynamic behavior of fluid-soil-structure interaction problems are crucial in structural engineering. The solution to such coupled engineering systems is often not achievable through analytical modeling alone, and a numerical solution is necessary. Generally, the Finite Element Method (FEM) is commonly used to address such problems. However, when dealing with coupled problems with complex geometry, the finite element method may not precisely represent the geometry, leading to errors that impact solution quality. Recently, Isogeometric Analysis (IGA) has emerged as a preferred method for modeling and analyzing complex systems. In this study, IGA based on Non-Uniform Rational B-Splines (NURBS) is employed to analyze the seismic behavior of concrete gravity dams, considering fluid-structure-foundation interaction. The performance of IGA is then compared with the classical finite element solution. The computational efficiency of IGA is demonstrated through case studies involving simulations of the reservoir-foundation-dam system under seismic loading.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.10 no.2
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• pp.103-112
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• 1990

This study examines the characteristics of soil behavior which includes many uncertainties in seismic design, evaluates the dynamic soil properties and studies the soil-structure interaction to generalize the applicability and economy of the available sites. An example analysis is performed for soil-structure system response assuming a containment structure built on site which includes soil layers using both elastic halfspace analysis and FEM analysis against the seismic loads from the actual design. This exercise is performed as a part of the safety analysis and economic assessment of the nuclear power plant built on soils. It includes the preparation of computer program capable of incorporating large nonlinearity in the analysis, resonable evaluation procedures to determine input soil data. Nonlinear FEM analysis of Seed and Idriss model is found suitable for the accurate analysis of dynamic response of soils. Linear FEM analysis using dynamic soil properties at strain level obtained by one-dimensional seismic response, and elastic half-space analysis using dynamic soil properties at strain level under static loads are recommended to evaluate the dynamic soil properties.

• Structural Engineering and Mechanics
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• v.15 no.6
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• pp.717-733
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• 2003

A time domain method is presented for soil-structure interaction analysis under seismic excitations. It is based on the finite element formulation incorporating infinite elements for the far field soil region. Equivalent earthquake input forces are calculated based on the free field responses along the interface between the near and far field soil regions utilizing the fixed exterior boundary method in the frequency domain. Then, the input forces are transformed into the time domain by using inverse Fourier transform. The dynamic stiffness matrices of the far field soil region formulated using the analytical frequency-dependent infinite elements in the frequency domain can be easily transformed into the corresponding matrices in the time domain. Hence, the response can be analytically computed in the time domain. A recursive procedure is proposed to compute the interaction forces along the interface and the responses of the soil-structure system in the time domain. Earthquake response analyses have been carried out on a multi-layered half-space and a tunnel embedded in a layered half-space with the assumption of the linearity of the near and far field soil region, and results are compared with those obtained by the conventional method in the frequency domain.

• Structural Engineering and Mechanics
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• v.61 no.4
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• pp.527-538
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• 2017

The evaluation of the loss-of-support conditions of frictional beam-to-column connections using simplified numerical models describing the transverse response of a portal-like structure is presented in this paper considering the effects of the seismic-hazard disaggregation. Real earthquake time histories selected from European Strong-motion Database (ESD) are used to show the effects of the seismic-hazard disaggregation on the beam loss-of-support conditions. Seismic events are classified according to different values of magnitudes, epicentral distances and soil conditions (stiff or soft soil) highlighting the importance of considering the characteristics of the seismic input in the assessment of the loss-of-support conditions of frictional beam-to-column connections. A rigid and an elastic model of a frame of a precast industrial building (2-DoF portal-like model) are presented and adopted to find the minimum required friction coefficient to avoid sliding. Then, the mean value of the minimum required friction coefficient with an epicentral distance bin of 10 km is calculated and fitted with a linear function depending on the logarithm of the epicentral distance. A complete parametric analysis varying the horizontal and vertical period of vibration of the structure is performed. Results show that the loss-of-support condition is strongly influenced by magnitude, epicentral distance and soil conditions determining the frequency content of the earthquake time histories and the correlation between the maxima of the horizontal and vertical components. Moreover, as expected, dynamic characteristics of the structure have also a strong influence. Finally, the effect of the column nonlinear behavior (i.e. formation of plastic hinges at the base) is analyzed showing that the connection and the column are a series system where the maximum force is limited by the element having the minimum strength. Two different longitudinal reinforcement ratios are analyzed demonstrating that the column strength variation changes the system response.

• Structural Engineering and Mechanics
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• v.40 no.6
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• pp.763-782
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• 2011

Results from nonlinear time-history analyses of wall-frame structural models indicate that the condition of vulnerable foundations -for which uplifting and reaching the bearing capacity of the supporting soil can occur before yielding at the base of the shear walls- may not be necessarily detrimental to the drift response of buildings under strong ground motions. Analyses also show that a soil-foundation system can inherently have deformation capacity well in excess of the demand and thus act as a source of energy dissipation that protects the structural integrity of the shear walls.

• Steel and Composite Structures
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• v.17 no.6
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• pp.803-824
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• 2014

The dynamic characterization is important in making accurate predictions of the seismic response of the hybrid structures dominated by different damping mechanisms. Different damping characteristics arise from the construction of the tower with different materials: steel for the upper part; reinforced concrete for the lower main part and interaction with supporting soil. The process of modeling damping matrices and experimental verification is challenging because damping cannot be determined via static tests as can mass and stiffness. The assumption of classical damping is not appropriate if the system to be analyzed consists of two or more parts with significantly different levels of damping, such as steel/concrete mixed structure - supporting soil coupled system. The dynamic response of structures is critically determined by the damping mechanisms, and its value is very important for the design and analysis of vibrating structures. An analytical approach capable of evaluating the equivalent modal damping ratio from structural components is desirable for improving seismic design. Two approaches are considered to define and investigate dynamic characteristics of hybrid tower of cable-stayed bridges: The first approach makes use of a simplified approximation of two lumped masses to investigate the structure irregularity effects including damping of different material, mass ratio, frequency ratio on dynamic characteristics and modal damping; the second approach employs a detailed numerical step-by step integration procedure in which the damping matrices of the upper and the lower substructures are modeled with the Rayleigh damping formulation.

• Earthquakes and Structures
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• v.7 no.2
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• pp.233-250
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• 2014

In this paper, a three dimensional soil-structure interaction (SSI) is numerically simulated using finite element method in order to analyse the foundation moments in annular raft of tall slender chimney structures incorporating the effect of openings in the structure and the effect of soil flexibility, when the structure-soil system is subjected to El Centro (1940) ground motion in time domain. The transient dynamic analysis is carried out using LS-DYNA software. The linear ground response analysis program ProShake has been adopted for obtaining the ground level excitation for different soil conditions, given the rock level excitation. The radial and tangential bending moments of annular raft foundation obtained from this SSI analysis have been compared with those obtained from conventional method according to the Indian standard code of practice, IS 11089:1984. It is observed that tangential and radial moments increase with the increase in flexibility of soil. The analysis results show that the natural frequency of chimney decreases with increase in supporting soil flexibility. Structural responses increase when the openings in the structure are also considered. The purpose of this paper is to propose the need for an accurate evaluation of the soilstructure interaction forces which govern the structural response.

• Journal of Korean Society of Steel Construction
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• v.18 no.2
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• pp.173-180
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• 2006

The seismic responses of a building are affected by the base soil conditions. In this study, linear time-history seismic analysis and nonlinear pushover static seismic analysis were performed to estimate the base shear forces of 3-, 5-, and 7-story steel buildings, considering the rigid and soft soil conditions. Foundation soil stiffness, based on the equivalent static stiffness formula, is used for the damper, one of the Link elements in SAP 2000. The base shear forces of the steel buildings, estimated through time-history analysis using the general-purpose structural-analysis program of SAP 2000, were compared with those calculated using the domestic seismic design code, the UBC-97 design response spectrum. and pushover static nonlinear analysis. The steel buildings designed for gravity and wind loads showed elastic responses with a moderate earthquake of 0.11 g, while the elastic soft-soil layer increased the displacement and the base shear force of the buildings due to soil-structure interaction and soil amplification. Therefore, considering the characteristics of the soft-soil layer, it is more reasonable to perform an elastic seismic analysis of a building's structure during weak or moderate earthquakes.

• Geomechanics and Engineering
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• v.39 no.3
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• pp.317-331
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• 2024

Sand liquefaction caused by earthquakes is one of the serious threats to underground stations. The change in groundwater level may have a great influence on the seismic behavior of underground stations buried in sand foundations. In this paper, a 3D numerical model for the soil-structure interaction system was established by applying the fully nonlinear finite difference program FLAC^3D. The impact of different groundwater levels on the seismic behavior of underground stations was explored in numerical analyses. The fluid-solid coupling and different seismic intensities were taken into consideration in the model. The numerical results demonstrate that the decrease of groundwater level significantly restrains the uplift of the underground station and the liquefaction of the site. The dynamic soil pressure around the sidewall under a higher water table is larger than that under a low water table. Under the earthquake, the ground peak acceleration increases as the groundwater level decreases. For the station structure, the decrease of groundwater level is unfavorable to the shear resistance of the middle columns. However, the effect of different groundwater levels on the axial stress of the middle columns is relatively small. The research results can be used as a reference for the seismic design of subway stations shallowly buried in the sand foundation with different groundwater levels.