• 한국지진공학회논문집
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• 제1권3호
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• pp.1-10
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• 1997

구조물 동적거동이 지반과 기초 특성에 따라 영향을 받는다는 것은 인식되었지만, 구조물 내진설계를 위한 설계규준이 지반의 본질적인 복잡성과 기초-지반체계에 대한 체계적인 연구부족으로 지반특성을 부분적으로만 반영하고 있어 불안전하거나 너무 안전한 결과를 초래한다. 이 연구에서는 전단파속도, 지반깊이, 기초 근입깊이 및 말뚝기초의 영향을 평가하여 구조물 내진해석을 위한 기초-지반체계의 운동학적 상호작용 영향을 고찰하였으며, 지반과 기초 특성을 고려한 합리적 내진해석을 위해 지반체계에 대한 수정된 분류기준을 제안하였다. 말뚝기초를 포함한 중형이나 대형 묻힌기초의 경우, 지초-지반체계의 운동학적 상호작용 영향을 고려하기 위해서는 기토밑 지반깊이를 최소한 60m 까지 고려해야하고, 말뚝유무에 관계없이 기초-지반체계의 회전운동도 구조물 내진해석에 포함되어야 한다.

• Earthquakes and Structures
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• 제23권4호
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• pp.353-361
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• 2022

The dynamic behavior of a single pile was investigated by using analytical and numerical studies. The focus of this study was to develop the dynamic p-y curve of a pile for pseudo-static analysis considering the shear wave velocity of the soil by using three-dimensional numerical analyses. Numerical analyses were conducted for a single pile in dry sand under changing conditions such as the shear wave velocity of the soil and the acceleration amplitudes. The proposed dynamic p-y curve is a shape of hyperbolic function that was developed to take into account the influence of the shear wave velocity of soil. The applicability of pseudo-static analysis using the proposed dynamic p-y curve shows good agreement with the general trends observed by dynamic analysis. Therefore, the proposed dynamic p-y curve represents practical improvements for the seismic design of piles.

• Earthquakes and Structures
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• 제3권3_4호
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• pp.495-506
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• 2012

An elasto-dynamic model for pile-soil-pile interaction together with a simple plate model is used in this study to assess the effect of flexible foundation slabs on the dynamic response of pile groups. To this end, different pile configurations with various slab thicknessesare considered in two soil media with low and high elastic moduli. The analyses include dynamic impedances and seismic responses of pile-group foundations. The presented results indicate that the stiffness and damping of pile foundations increase with thickness of the foundation slab; however, the results approach those for rigid slab as the slab thickness approaches twice the pile diameter for the cases considered in this study. The results also reveal that pile foundations with flexible slabs may amplify the earthquake motions by as much as 10 percent in the low to intermediate frequency ranges.

• Geomechanics and Engineering
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• 제27권5호
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• pp.465-479
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• 2021

One of the important causes of building and infrastructure failure, such as bridges on pile foundations, is the placement of the piles in liquefiable soil that can become unstable under seismic loads. Therefore, the overarching aim of this study is to investigate the seismic behavior of a soil-pile system in liquefiable soil using three-dimensional numerical FEM analysis, including soil-pile interaction. Effective parameters on concrete pile response, involving the pile diameter, pile length, soil type, and base acceleration, were considered in the framework of finite element non-linear dynamic analysis. The constitutive model of soil was considered as elasto-plastic kinematic-isotropic hardening. First, the finite element model was verified by comparing the variations on the pile response with the measured data from the centrifuge tests, and there was a strong agreement between the numerical and experimental results. Totally 64 non-linear time-history analyses were conducted, and the responses were investigated in terms of the lateral displacement of the pile, the effect of the base acceleration in the pile behavior, the bending moment distribution in the pile body, and the pore pressure. The numerical analysis results demonstrated that the relationship between the pile lateral displacement and the maximum base acceleration is non-linear. Furthermore, increasing the pile diameter results in an increase in the passive pressure of the soil. Also, piles with small and big diameters are subjected to yielding under bending and shear states, respectively. It is concluded that an effective stress-based ground response analysis should be conducted when there is a liquefaction condition in order to determine the maximum bending moment and shear force generated within the pile.

• 한국지진공학회논문집
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• 제5권3호
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• pp.1-8
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• 2001

교량 구성요소의 설계지진력은 현행 국내 도로교설계기준에 의하면 설계지진을 가하여 얻어진 탄성지진력을 구조형식에 따른 응답수정계수로 나눔으로써 결정되어진다. 말뚝기초가 채택된 교량시스템의 탄성지진력의 크기는 말뚝기초의 모형화 방법에 따라 크게 달라질 수 있다. 이 논문에서는 근사적이고 실용적인 말뚝기초의 모형화 기법을 제시하였다. 이 모형화 기법에서는 말뚝기초의 강도를 횡방향으로 반복하중을 가진 현장시험으로 얻은 말뚝-지반의 상호작용이 고려된 지반반력-변위 곡선을 이용한 말뚝의 수평방향 강도와 탄성 축변형은 물론 선단지지력 및 주변마찰력을 고려한 말뚝의 수직방향 강도로 나타내는 것이다. 예제 교량의 해석을 수행하여 제시된 절차가 타당성있고 적용 가능한 교량의 지진응답해석용 말뚝기초의 모형화 기법임을 검증하였다.

• Earthquakes and Structures
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• 제9권2호
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• pp.415-430
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• 2015

Integral abutment bridges have many advantages over bridges with expansion joints in terms of economy and maintenance costs. However, in the design of abutments of integral bridges temperature loads play a crucial role. In addition, seismic loads are readily transferred to the substructure and affect the design of these components significantly. Currently, the European and American bridge design codes consider these two load cases separately in their recommended design load combinations. In this paper, the importance and necessity of combining the thermal and seismic loads is investigated for integral bridges. A 2D finite element combined pile-soil-structure interactive model is used in this evaluation. Nonlinear behavior is assumed for near field soil behind the abutments. The soil around the piles is modeled by nonlinear springs based on p-y curves. The uniform temperature changes occurring at the time of some significant earthquakes around the world are gathered and applied simultaneously with the corresponding earthquake time history ground motions. By comparing the results of these analyses to prescribed AASHTO LRFD load combinations it is observed that pile forces and abutment stresses are affected by this new load combination. This effect is more severe for contraction mode which is caused by negative uniform temperature changes.

• Geomechanics and Engineering
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• 제34권5호
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• pp.529-545
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• 2023

The coupled soil-pile-structure seismic response is recently in the spotlight of researchers because of its extensive applications in the different fields of engineering such as bridges, offshore platforms, wind turbines, and buildings. In this paper, a simple analytical model is developed to evaluate the dynamic performance of seismically isolated bridges considering triple interactions of soil, piles, and bridges simultaneously. Novel expressions are proposed to present the dynamic behavior of pile groups in inhomogeneous soils with various shear modulus along with depth. Both cohesive and cohesionless soil deposits can be simulated by this analytical model with a generalized function of varied shear modulus along the soil depth belonging to an inhomogeneous stratum. The methodology is discussed in detail and validated by rigorous dynamic solution of 3D continuum modeling, and time history analysis of centrifuge tests. The proposed analytical model accuracy is guaranteed by the acceptable agreement between the experimental/numerical and analytical results. A comparison of the proposed linear model results with nonlinear centrifuge tests showed that during moderate (frequent) earthquakes the relative differences in responses of the superstructure and the pile cap can be ignored. However, during strong excitations, the response calculated in the linear time history analysis is always lower than the real conditions with the nonlinear behavior of the soil-pile-bridge system. The current simple and efficient method provides the accuracy and the least computational costs in comparison to the full three-dimensional analyses.

• 한국방재학회 논문집
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• 제11권2호
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• pp.93-101
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• 2011

국토의 70% 이상이 산지인 국내 지형 조건에서 도로, 철도 등 크고 작은 건설 공사에서는 필연적으로 사면이 형성된다. 그러나, 최근 국내외적으로 빈번히 발생하는 지진에 대한 사면안정 보강공법에 대한 연구는 전무한 실정이다. 이에 본 연구에서는 1 g 진동대 실험 및 등가정적해석을 이용하여 사면의 내진 보강공법으로써 억지말뚝의 적용성을 평가하고, 억지말뚝이 적용된 사면 및 억지말뚝의 지진시 거동을 분석하였다. 1 g 진동대 실험 결과로부터, 억지말뚝 보강 사면의 지진시 사면파괴 억지효과를 검증하였으며, 등가정적해석을 통해 억지 말뚝을 사면 하부 또는 상부보다 사면 파괴면의 중앙부에 말뚝을 설치했을 때 사면파괴 억지효과가 가장 큼을 알 수 있었다. 또한, 말뚝이 사면 중앙부에 설치되었을 경우, 말뚝의 중심 간격에 따른 안전율 변화를 등가정적해석으로부터 분석하였다.

• 한국지반공학회논문집
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• 제34권5호
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• pp.53-63
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• 2018

무리말뚝의 내진설계를 수행할 때 지반-말뚝 동적상호작용을 고려하는 것이 중요하다. 특히, 동적하중을 받는 무리말뚝의 횡방향 저항력은 무리말뚝 효과에 의하여 단일말뚝과 비교하여 감소한다. 그러나, 지금까지 지진하중을 받는 무리말뚝의 동적 무리말뚝 효과를 제안한 연구는 매우 부족한 실정이다. 그러므로, 본 연구에서는 건조 모래지반에 설치된 $3{\times}3$ 무리말뚝에 대한 동적 원심모형실험을 수행하여 무리말뚝 효과를 산정하였다. 이 무리말뚝 효과는 동적 p-y 곡선에서 극한 횡방향 지반반력과 지반반력계수에 대한 보정계수(multiplier)를 적용하여 고려하였다. 그리고, 본 연구에서 얻어진 동적 p-y 곡선을 Beam on Nonlinear Winkler Foundation 모델을 이용한 비선형 동해석에 적용하여 그 적용성을 검증하였다. 그 결과, 본 연구에서 제안한 무리말뚝의 보정계수가 원심모형실험 결과를 잘 모사할 수 있는 것으로 나타났다.

• Geomechanics and Engineering
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• 제29권2호
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• pp.155-170
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• 2022

An accurate analysis of structures supported on soft soils and subjected to seismic loading requires the consideration of the soil-foundation-structure interaction. An important aspect of this interaction lies with the energy dissipation due to soil material damping. Unlike advanced constitutive models that can induce energy loss, the use of simple elastoplastic constitutive models requires additional damping. The frequency dependent Rayleigh damping is a formulation that is frequently used in dynamic analysis. The main concern of this formulation is the correct selection of the target damping ratio and the frequency range where the response is frequency independent. The objective of this study is to investigate the effects of the Rayleigh damping parameters in soil-pile-structure and soil-inclusion-platform-structure systems in the presence of soft soil under seismic loading. Three-dimensional analyses of both systems are carried out using the finite difference software Flac3D. Different values of target damping ratios and minimum frequencies are utilized. Several earthquakes are used to study the influence of different excitation frequencies in the systems. The soil response in terms of accelerations, displacements and strains is obtained. For the rigid elements, the results are presented in terms of bending moments and normal forces. The results show that when the frequency of the input motion is close to the minimum (central) frequency in the Rayleigh damping formulation, the overdamping amount is reduced, and the surface spectral acceleration of the analyzed pile and inclusion systems increases. Thus, the bending moments and normal forces throughout the piles and inclusions also increase.