• 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.

• Journal of Ocean Engineering and Technology
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• v.1 no.2
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• pp.52-59
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• 1987

극 지역용 중력식 해양구조물의 설계시 고려되어야 할 문제중의 하나가 구조물의 유빙(ice)과 충돌시 야기되는 foundation붕괴 현상인데, 본 논문에서는 정적 해석을 위해 sliding 및 bearing failure 현상에 대하여만 연구하였고, 또한 동적 해석을 위하여 soil과ice의 특성으로부터 structure-ice-soil의 상호 작용 운동 방정식을 설정하여 구조물과 ice의변위, 속도, 가속도와 ice force와 soil force의 history를 시간영역 해법으로 풀었다. 한 예제로 Beaufort Sea의 37 feet수심과 granular soil 상태에서 구조물의 최대변위는 0.4 feet이고 가속도는 약 0.3kg이며 이때 구조물이 sliding에 대하여 안전하다는 것이 입증되었다.

• Earthquakes and Structures
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• v.10 no.4
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• pp.939-963
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• 2016

According to the new directives about the rational and efficient use of energy, thermal bridges in buildings have to be avoided, and the thermal insulation (TI) layer should run without interruptions all around the building - even under its foundations. The paper deals with the seismic response of multi-storeyed reinforced concrete (RC) frame building structures founded on an extruded polystyrene (XPS) layer placed beneath the foundation slab. The purpose of the paper is to elucidate the problem of buildings founded on a TI layer from the seismic resistance point of view, to assess the seismic behaviour of such buildings, and to search for the critical parameters which can affect the structural and XPS layer response. Nonlinear dynamic and static analyses were performed, and the seismic response of fixed-base (FB) and thermally insulated (TI) variants of nonlinear RC building models were compared. Soil-structure interaction was also taken into account for different types of soil. The results showed that the use of a TI layer beneath the foundation slab of a superstructure generally induces a higher peak response compared to that of a corresponding system without TI beneath the foundation slab. In the case of stiff structures located on firm soil, amplification of the response might be substantial and could result in exceedance of the superstructure's moment-rotation plastic hinge capacities or allowable lateral roof and interstorey drift displacements. In the case of heavier, slenderer, and higher buildings subjected to stronger seismic excitations, the overall response is governed by the rocking mode of oscillation, and as a consequence the compressive strength of the XPS could be insufficient. On the other hand, in the case of low-rise and light-weight buildings, the friction capacity between the layers of the applied TI foundation set might be exceeded so that sliding could occur.

• Earthquakes and Structures
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• v.21 no.6
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• pp.563-576
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• 2021

The rocking foundation is effective for reducing structural seismic demand and avoiding overdesign of the foundation. It is crucial to evaluate the performance of rocking foundations because they cause plastic hinging in the soil. In this study, to derive optimized ground motion intensity measures (IMs) for rocking foundations, the efficiency of IMs correlated with engineering demand parameters (EDPs) was estimated through the coefficient determination using a physical modeling database for rocking shallow foundations. Foundation deformations, the structural horizontal drift ratio, and contribution in drift from foundation rotation and sliding were selected as crucial EDPs for the evaluation of rocking foundation systems. Among 15 different IMs, the peak ground velocity exhibited the most efficient parameters correlated with the EDPs, and it was discovered to be an efficient ground motion IM for predicting the seismic performance of rocking foundations. For vector regression, which uses two IMs to present the EDPs, the IMs indicating time features improved the efficiency of the regression curves, but the correlation was poor when these are used independently. Moreover, the ratio of the column-hinging base shear coefficient to the rocking base shear coefficient showed obvious trends for the accurate assessment of the seismic performance of rocking foundation-structure systems.

• Geomechanics and Engineering
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• v.21 no.1
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• pp.73-84
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• 2020

In the seismic design of bridges, formation of plastic hinges plays an important role in the dissipation of seismic energy. In the case of conventional fixed-base bridges, the plastic hinges are allowed to form in the superstructure alone. During seismic event, such bridges may be safe from collapse but the superstructure undergoes significant plastic deformations. As an alternative design approach, the plastic hinges are guided to form in the soil thereby utilizing the inevitable yielding of the soil. Rocking foundations work on this concept. The formation of plastic hinges in the soil reduces the load and displacement demands on the superstructure. This study aims at evaluating the seismic response of bridge pier supported on rocking shallow foundation. For this purpose, a BNWF model is implemented in OpenSees platform. The capability of the BNWF model to capture the SSI effects, nonlinear behavior and dynamic loading response are validated using the centrifuge and shake table test results. A comparative study is performed between the seismic response of the bridge pier supported on the rocking shallow foundation and conventional fixed-base foundation. Results of the study have established the beneficial effects of using the rocking shallow foundation for the seismic response analysis of the bridge piers.

• Structural Engineering and Mechanics
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• v.89 no.2
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• pp.121-133
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• 2024

In this paper, the performance of under-foundation isolators against generally annoying train-induced vibrations was examined experimentally. The effect of foundation type on the efficacy of such isolators was investigated for the first time. To this end, laboratory models including a soil container, soil, building with three types of foundation (i.e., single, strip, and mat), and isolator layer were employed. Through various dynamic tests, the effects of foundation type, isolation frequency, and the dominant frequency of train load on the isolator's performance were studied. The results demonstrated that the vibration level in the unisolated building with the strip and mat foundation was, respectively, 29 and 38% lower than in the building with the single foundation. However, the efficacy of the isolator in the building with the single foundation was, respectively, 21 and 40% higher than in the building with the strip and mat foundation. Furthermore, a lower isolation frequency and a higher excitation frequency resulted in greater isolator efficacy. The best vibration suppression occurred when the excitation frequency was close to the floor's natural frequency.

• Structural Engineering and Mechanics
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• v.66 no.5
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• pp.637-648
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• 2018

When the centers of mass and stiffness of a building do not coincide, the structure experiences torsional responses. Such systems can consist of the underlying soil and the super-structure. The underlying soil may modify the earthquake input motion and change structural responses. Specific effects of the input motion shall also not be ignored. In this study, seismic demands of asymmetric buildings considering soil-structure interaction (SSI) under near-fault ground motions are evaluated. The building is modeled as an idealized single-story structure. The soil beneath the building is modeled by non-linear finite elements in the two states of loose and dense sands both compared with the fixed-base state. The infinite boundary conditions are modelled using viscous boundary elements. The effects of traditional and yield displacement-based (YDB) approaches of strength and stiffness distributions are considered on seismic demands. In the YDB approach, the stiffness considered in seismic design depends on the strength. The results show that the decrease in the base shear considering soft soil induced SSI when the YDB approach is assumed results only in the center of rigidity to control torsional responses. However, for fixed-base structures and those on dense soils both centers of strength and rigidity are controlling.

• International Journal of High-Rise Buildings
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• v.9 no.4
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• pp.369-376
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• 2020

Given the importance of quickly recovering livelihoods and economic activity after an earthquake, the seismic performance of the pile foundation is becoming more critical than before. In order to promote seismic retrofit of the pile foundations, it is necessary to develop a method for evaluating the seismic performance of the pile foundation based on the experimental data. In this paper, we focus on the building that was suffered severe damage to the pile foundation, conduct simulation analyses of the building, and report the results of evaluating the dynamic characteristics when piles are damaged using a system identification method. As a result, an analysis model that can accurately simulate the behavior of the damaged building during an earthquake was constructed, and it was shown that the system identification method could extract dynamic characteristics that may damage piles.

• Earthquakes and Structures
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• v.25 no.2
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• pp.99-112
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• 2023

This paper investigates the influences of Soil-Structure Interaction (SSI) on the seismic behavior of two-dimensional reinforced concrete moment-resisting frames subjected to Far-Field Ground Motion (FFGM) and Near-Field Ground Motion (NFGM). For this purpose, the nonlinear modeling of 7, 10, and 15-story reinforced concrete moment resisting frames were developed in Open Systems for Earthquake Engineering Simulation (OpenSees) software. Effects of SSI were studied by simulating Beam on Nonlinear Winkler Foundation (BNWF) and the soil type as homogenous medium-dense. Generally, the building resistance to seismic loads can be explained in terms of Incremental Dynamic Analysis (IDA); therefore, IDA curves are presented in this study. For comparison, the fragility evaluation is subjected to NFGM and FFGM as proposed by Quantification of Building Seismic Performance Factors (FEMA P-695). The seismic performance of Reinforced Concrete (RC) buildings with fixed and flexible foundations was evaluated to assess the probability of collapse. The results of this paper demonstrate that SSI and NFGM have significantly influenced the probability of failure of the RC frames. In particular, the flexible-base RC buildings experience higher Spectral acceleration (Sa) compared to the fixed-base ones subjected to FFGM and NFGM.

• Geomechanics and Engineering
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• v.13 no.4
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• pp.601-619
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• 2017

Cantilever retaining wall movements generally depend on the intensity and duration of ground motion, the response of the soil underlying the wall, the response of the backfill, the structural rigidity, and soil-structure interaction (SSI). This paper investigates the effect of material properties on seismic response of backfill-cantilever retaining wall-soil/foundation interaction system considering SSI. The material properties varied include the modulus of elasticity, Poisson's ratio, and mass density of the wall material. A series of nonlinear time history analyses with variation of material properties of the cantilever retaining wall are carried out by using the suggested finite element model (FEM). The backfill and foundation soil are modelled as an elastoplastic medium obeying the Drucker-Prager yield criterion, and the backfill-wall interface behavior is taken into consideration by using interface elements between the wall and soil to allow for de-bonding. The viscous boundary model is used in three dimensions to consider radiational effect of the seismic waves through the soil medium. In the seismic analyses, North-South component of the ground motion recorded during August 17, 1999 Kocaeli Earthquake in Yarimca station is used. Dynamic equations of motions are solved by using Newmark's direct step-by-step integration method. The response quantities incorporate the lateral displacements of the wall relative to the moving base and the stresses in the wall in all directions. The results show that while the modulus of elasticity has a considerable effect on seismic behavior of cantilever retaining wall, the Poisson's ratio and mass density of the wall material have negligible effects on seismic response.