Dynamic Behaviour Of Piles Research Articles

Dynamic behavior of pile foundations under vertical and lateral vibrations

ABSTRACTPile foundations supporting machines, buildings under seismic effect, and wind turbines are subjected to dynamic loads. Under such conditions, there is a necessity to evaluate the dynamic behavior of piles. Therefore, a 3D numerical modeling technique is needed to consider the complicated dynamic interaction between the piles and soil (pile-soil interaction) and between adjacent piles in the same group (pile-soil-pile interaction). To validate the results of 3D numerical simulation of piles, the results obtained from the numerical model has been compared to the measurements of a selected case study. The 3D finite element model has also been used to evaluate the impedance parameters and induced peak displacements. The study is performed for single piles and pile groups. The different techniques to model the piles are evaluated. In addition, the effect of related parameters, such as excitation force frequency (f), soil modulus of elasticity (Es), pile slenderness Ratio (L/D), dimensionless spacing ratio (S/D) and pile group size (ng) have been studied.

Irregular Wave Effects on Dynamic Behavior of Piles

The paper presents computer-aided numerical analyses which are utilized to investigate the dynamic behavior of piles under wind-generated irregular wave loads. A pile is modeled as a single-degree-of-freedom system. The equation of motion of the system is numerically integrated using a fourth order Runge–Kutta method. The equation of motion includes shape function that is obtained approximately. It is needed to compare the solutions with another method to determine the approximation leads whether significant differences or not. For this purpose the dynamic behavior of structure is modeled by the Time History Tool of SAP 2000 and the results compared with those found by a single-degree-of-freedom system. Irregular wave is represented with equivalent regular waves with two different approaches; based on either superimposed multi-sinusoidal wave (Loading I) or significant wave (Loading II), utilizing the energy spectrum. Wave forces are obtained from Morrison Equation. The analyses account for a soil-pile interaction in a simplified way. As the lateral ground pressure changes by delving deep into the ground, soil spring stiffness also changes. Those forces are calculated separately for different depths and taken into account in both analyses. Lateral displacement of the employed pile varying with the time is obtained from analyses for Loading I and Loading II. Critical results are obtained from which loading is determined. Finally, the frequencies of the external loads and natural frequency of pile are compared to examine whether the resonance came true or not.

지반-말뚝 시스템에 대한 3차원 동적 수치 모델링 기법 개발

말뚝의 동적 거동은 지반-말뚝의 동적상호작용, 지반의 비선형성, 지반-말뚝 시스템의 공진 현상 등 많은 요소가 상호 작용을 하므로 매우 복잡하다. 그러므로, 말뚝의 동적 거동을 수치해석으로 정확히 모사하려면 많은 노력과 시간이 필요하다. 본 연구에서는 기존의 범용 수치해석 프로그램인 FLAC 3D를 활용하면서도 해석시간을 크게 감소 시킬 수 있는 새로운 모델링 기법을 개발하였다. 본 기법은 전체 해석 영역을 근역 지반과 원역 지반으로 나누고 지반-말뚝 동적상호작용에 영향을 받지 않는 원역 지반을 요소망으로 모델링하는 대신 원역 지반의 지반 운동 시간이력을 근역 지반의 경계 조건에 입력 하중으로 적용하는 기법이다. 이 수치 모델링에서 지진파의 강도가 클 때 일어나는 지반의 비선형 거동을 모사하기 위하여 이력 감쇠 모델을 이용하여 접선 탄성 계수를 전단 변형률의 함수 값으로 입력하였으며, 지반과 말뚝 사이의 분리 현상을 모사하기 위하여 지반-말뚝 경계 요소를 도입하였다. 이 방법은 기존의 방법과 비교하여 해석 결과의 정확성을 유지하면서 해석 시간을 1/3로 감소시켰다. 제안된 수치해석 방법으로 예측한 1g 진동대 모형 실험의 원형 거동은 원형으로 환산한 모형 실험 결과와 유사하게 나타났다. The dynamic behavior of piles becomes very complex due to soil-pile dynamic interaction, soil non-linearity, resonance phenomena of soil-pile system and so on. Therefore, the proper numerical simulation of the pile behavior needs much effort and calculation time. In this research, a new modeling method, which can be applied to the conventional finite difference analysis program FLAC 3D, was developed to reduce the calculation time. The soil domain in this method is divided into a near-field region and a far-field region, which is not influenced by the soil-pile dynamic interaction. Then, the ground motion of the far-field is applied to the boundaries of the near-field instead of modeling the far-field region as finite meshes. In addition, the soil non-linearity behavior is modeled by using the hysteretic damping model, which determines the soil tangent modulus as a function of shear strain and the interface element was applied to simulate the separation and slip between the soil and pile. The proposed method reduced the calculation time by as much as one third compared with a usual modeling method and maintained the accuracy of the calculated results. The calculated results by the proposed method showed a good agreement with the prototype pile behavior, which was obtained by applying a similitude law to the 1-g shaking table test results.

Dynamic behavior of piles embedded in transversely isotropic layered media

Dynamic behavior of single pile embedded in transversely isotropic layered media is investigated using the finite element method combined with dynamic stiffness matrices of the soil derived from Green's function for ring loads. The influence of soil anisotropy on the dynamic behavior of piles is examined through a series of parametric studies

Dynamic response of single piles embedded in transversely isotropic layered media

AbstractDynamic response of single piles embedded in transversely isotropic layered media is investigated using the finite element method combined with dynamic stiffness matrices of the soil derived from Green's functions for ring loads. The influence of soil anisotropy on the dynamic behaviour of piles is examined through a series of parametric studies.

Dynamic behaviour of piles during impact driving : Proc Ninth Southeast Asian Geotechnical Conference, Bangkok, 7–11 December 1987 V2, P6.219–6.228. Publ Bangkok: Southeast Asian Geotechnical Society, 1987

Dynamic behaviour of piles during impact driving : Proc Ninth Southeast Asian Geotechnical Conference, Bangkok, 7–11 December 1987 V2, P6.219–6.228. Publ Bangkok: Southeast Asian Geotechnical Society, 1987

Dynamic behaviour of single piles under strong harmonic excitation

Dynamic experiments were conducted on large-scale model piles in sand subjected to strong horizontal and vertical excitation. The theoretical response curves are calculated using DYNA2 and PILAY2 computer codes, and using also for the vertical direction, the theory of nonlinear vibration. The theoretical curves are compared with the experimental results. The dynamic behaviour of the pile is presented as frequency response curves for displacement, stiffness, dashpot constants, and damping ratios. The influence of excitation intensity, repeated loading, and cap contact with soil on the dynamic behaviour of single piles is investigated. Key words: dynamics, vibration, piles, foundations, nonlinear vibration, testing, deep foundations.