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1.
The influence of inclined piles on the dynamic response of deep foundations and superstructures is still not well understood and needs further research. For this reason, impedance functions of deep foundations with inclined piles, obtained numerically from a boundary element–finite element coupling model, are provided in this paper. More precisely, vertical, horizontal, rocking and horizontal–rocking crossed dynamic stiffness and damping functions of single inclined piles and 2 × 2 and 3 × 3 pile groups with battered elements are presented in a set of plots. The soil is assumed to be a homogeneous viscoelastic isotropic half‐space and the piles are modeled as elastic compressible Euler–Bernoulli beams. The results for different pile group configurations, pile–soil stiffness ratios and rake angles are presented. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
2.
Most offshore platforms are supported on long and large-diameter piles with variable wall-thickness along the length, and soil properties varying with depth. The design and analyses of these piles are made by modelling the soil-pile system with a beam-on-Winkler foundation. Therefore, evaluation of appropriate soil-pile springs for use in such analyses is a matter of concern. Fundamental characteristics of dynamic lateral load-deflection relationships for piles were studied analytically considering the soil-pile-structure interaction under seismic loading conditions. The soil layer was assumed homogeneous, linearly elastic with hysteretic type material damping, and overlying a rigid base. A superstructure with multi-degrees of freedom was supported by a single vertical pile hinged at the rigid base. Parametric studies were carried out to identify the influence of the system parameters on the behaviour of the dynamic lateral load-deflection relationships of piles. The lateral load-deflection relationships vary considerably with depth and are influenced not only by the dynamic properties of soil but also by the structural properties of a pile and loading conditions. These lateral load-deflection relationships can be used to define the soil-pile springs for the seismic response analysis of a soil-pile-structure system, and the results can be extended to problems with soil profiles with layering and non-linearity. 相似文献
3.
The paper presents a numerical model for the dynamic analysis of pile groups with inclined piles in horizontally layered soil deposits. Piles are modelled with Euler–Bernoulli beams, while the soil is supposed to be constituted by independent infinite viscoelastic horizontal layers. The pile–soil–pile interaction as well as the hysteretic and geometric damping is taken into account by means of two‐dimensional elastodynamic Green's functions. Piles cap is considered by introducing a rigid constraint; the condensation of the problem permits a consistent derivation of both the dynamic impedance matrix of the soil–foundation system and the foundation input motion. These quantities are those used to perform inertial soil–structure interaction analyses in the framework of the substructure approach. Furthermore, the model allows evaluating the kinematic stress resultants in piles resulting from waves propagating in the soil deposit, taking into account the pile–soil–pile interactions. The model validation is carried out by performing accuracy analyses and comparing results in terms of dynamic impedance functions, kinematic response parameters and pile stress resultants, with those furnished by 3D refined finite element models. To this purpose, classical elastodynamic solutions are adopted to define the soil–pile interaction problem. The model results in low computational demands without significant loss of precision, compared with more rigorous approaches or refined finite element models. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
4.
《Soil Dynamics and Earthquake Engineering》2012,33(1):56-70
We present the development and calibration of a macroelement model that captures the response of piles in cohesionless soils subjected to biaxial lateral loading. The model is founded on actual physical mechanism of soil resistance and provides the framework for extending a uniaxial model to biaxial case by means of a single cross-stiffness parameter. Both upper and lower bounds for the cross-stiffness parameter are also presented. The model is calibrated and verified using three-dimensional finite element (FE) simulations of soil-pile interaction for uniformly prescribed displacement along the pile length. Comparison of predictions from uniaxial and biaxial models with the FE results for transient loading indicates that the response assuming no coupling between the two horizontal directions for biaxial loading can differ significantly from the ‘true’ response for some cases. Accounting for coupling in the lateral direction, the proposed model captures the transverse pile response with very good accuracy while retaining the simplicity and computational efficiency of macroelement formulations compared to 3D FE analyses. 相似文献
5.
Dynamic experimental studies on horizontal interaction factors for laterally loaded model soil–pile systems subjected to low-to-high amplitude pile head loading are reported, focusing on the effect of dynamics and local non-linearity. Results obtained from dynamic experiments with different amplitudes of harmonic lateral loading on instrumented model soil–pile systems conducted on a shaking table indicate that the resonance of soil–pile system shows a profound impact on the horizontal interaction factors. Furthermore, behavior of the soil–pile system becomes highly non-linear with increasing amplitude of loading, as the extent of local non-linearity around the pile increases. Consequently, group effects cannot be predicted by using established approximate equations based on the assumption of linear viscoelastic behavior. To this end, new semi-empirical equations are proposed for obtaining the horizontal interaction factors, as an extension of available approximate equations to incorporate the local non-linear behavior of soil–pile system for both small and large pile spacings. 相似文献
6.
Seismic behavior of inclined piles has been considered detrimental for years. However, recent researches show that battered piles can have a beneficial effect. In this framework, a series of centrifuge tests on an inclined pile group is performed. The analysis is based on the comparative response of two 2×1 simplified pile groups: one with vertical piles and the other with one vertical and one inclined pile. The response of these pile groups to repeated earthquakes or sinusoidal inputs is analyzed through the response frequencies, the envelop curves of bending moment profiles, the axial loads measured in both piles and the kinematic response of the cap. Results highlight that the effect of inclined pile is highly influenced by the frequency content of the input. In addition, the inclined pile induces non-negligible residual bending moments, higher horizontal stiffness at the pile cap and larger rotation. 相似文献
7.
Evidence of beneficial role of inclined piles: observations and summary of numerical analyses 总被引：1，自引：0，他引：1
Nikos Gerolymos Amalia Giannakou Ioannis Anastasopoulos George Gazetas 《Bulletin of Earthquake Engineering》2008,6(4):705-722
The behaviour under seismic loading of inclined piles embedded in two idealized soil profiles, a homogeneous and a non-homogenous
“Gibson” soil, is analysed with 3D finite elements. Two structures, modeled as single-degree-of-freedom oscillators, are studied:
(1) a tall slender superstructure (H
st = 12 m) whose crucial loading is the overturning moment, and (2) a short structure (H
st = 1 m) whose crucial loading is the shear force. Three simple two-pile group are studied: (a) one comprising a vertical pile
and a pile inclined at 25°, (b) one consisting of two piles symmetrically inclined at 25°, and (c) a group of two vertical
piles. The influence of key parameters is analysed and non-dimensional diagrams are presented to illustrate the role of raked
piles on pile and structure response. It is shown that this role can be beneficial or detrimental depending on a number of
factors, including the slenderness of the superstructure and the type of pile-to-cap connection. 相似文献
8.
根据已经完成的液化侧向扩展场地-群桩基础-上部结构体系大型振动台试验,在有限元软件OpenSees中建立了可液化倾斜场地振动台试验的有限元模型。通过与试验结果对比,验证了数值模型的可靠性。基于此,建立了典型水平和倾斜液化场地-桩基-桥梁结构体系的数值模型,讨论了双向地震作用下水平和倾斜场地体系地震响应的差异,结果表明:相比水平场地,倾斜场地超孔隙水压力在峰值阶段波动幅度更大,土体的侧向位移增加明显,尤其是在饱和砂土中部位置;倾斜场地中桩基础的破坏程度更大,可液化层中部桩基曲率最大可增大约13倍,桩身水平位移显著增加;而水平场地桥墩曲率比倾斜场地桥墩曲率大,建议在液化场地桩基设计中应考虑场地倾斜带来的影响。 相似文献
9.
Raked piles are believed to behave better than vertical piles in a laterally flowing liquefied ground. This paper aims at numerically simulating the response of raked pile foundations in liquefying ground through nonlinear finite element analysis. For this purpose, the OpenSees computer package was used. A range of sources have been adopted in the definition of model components whose validity is assessed against case studies presented in literature. Experimental and analytical data confirmed that the backbone force density–displacement (p–y) curve simulating lateral pile response is of acceptable credibility for both vertical and raked piles. A parametric investigation on fixed-head piles subject to lateral spreading concluded that piles exhibiting positive inclination impart lower moment demands at the head while those inclined negatively perform better at liquefaction boundaries (relative to vertical piles). Further studies reveal substantial axial demand imposed upon negatively inclined members due to the transfer of gravity and ground-induced lateral forces axially down the pile. Extra care must be taken in the design of such members in soils susceptible to lateral spreading such that compressive failure (i.e. pile buckling) is avoided. 相似文献
10.
A numerical analysis of pile driving for tapered piles is presented in this paper. A three-dimensional finite difference analysis for tapered angle and geometry effects has been used on pile driving response of tapered piles. The simulation considers an idealization for pile–soil system in drivability. The vertical pile is assumed to have linear and elastic behavior. It is also assumed that the soil is elasto-plastic material and its failure stage is controlled using the Mohr–Coulomb failure criterion. At the soil–pile contact surfaces along the pile shaft and pile toe, slip is allowed to occur during the driving procedure using interface elements. Quiet boundaries are used to prevent waves traveling in the lateral and vertical directions for the soil. Cylindrical, fully tapered, and semi-tapered piles were analyzed. The results obtained from numerical analyses were compared with those obtained from available laboratory tests and also other available numerical data, resulting in a satisfactory agreement. The results have shown that among piles of the same length and material volume, with increasing the taper angle from zero (representing a cylindrical pile), the driving stresses decrease and the permanent pile toe settlement (set) increases. These are interesting in pile driving and are on the safe side for driven piles and increasing the driving efficiency. It has also been found that the geometry of the pile can generally influence the pile drivability. Generally speaking, tapered and partially tapered piles offer better drivability performance than cylindrical piles of the same volume and length. 相似文献
11.
The analytical representation of dynamic soil reaction to a laterally-loaded pile using 3D continuum modeling is revisited. The governing elastodynamic Navier equations are simplified by setting the dynamic vertical normal stresses in the soil equal to zero, which uncouples the equilibrium in vertical and horizontal directions and allows a closed-form solution to be obtained. This physically motivated approximation, correctly conforming to the existence of a free surface, was not exploited in earlier studies by Tajimi, Nogami and Novak and leads to a weaker dependence of soil response to Poisson's ratio which is in agreement with numerical solutions found in literature. The stress and displacement fields in the soil and the associated reaction to an arbitrary harmonic pile displacement are derived analytically using pertinent displacement potentials and eigenvalue expansions over the vertical coordinate. Both infinitely long piles and piles of finite length are considered. Results are presented in terms of dimensionless parameters and graphs that highlight salient aspects of the problem. A detailed discussion on wave propagation and cutoff frequencies based on the analytical findings is provided. A new dimensionless frequency parameter is introduced to demonstrate that the popular plane-strain model yields realistic values for soil reaction only at high frequencies and low Poisson's ratios. 相似文献
12.
A simplified three-step procedure is proposed for estimating the dynamic interaction between two vertical piles, subjected either to lateral pile-head loading or to vertically-propagating seismic S-waves. The starting point is the determination of the deflection profile of a solitary pile using any of the established methods available. Physically-motivated approximations are then introduced for the wave field radiating from an oscillating pile and for the effect of this field on an adjacent pile. The procedure is applied in this paper to a flexible pile embedded in a homogeneous stratum. To obtain analytical closed-form results for both pile-head and seismic-type loading pile-soil and soil-pile interaction are accounted for through a single dynamic Winkler model, with realistic frequency-dependent ‘springs’ and ‘dashpots’. Final- and intermediate-step results of the procedure compare favourably with those obtained using rigorous formulations for several pile group configurations. It is shown that, for a homogeneous stratum, pile-to-pile interaction effects are far more significant under head loading than under seismic excitation. 相似文献
13.
14.
Nicos Makris 《地震工程与结构动力学》1994,23(2):153-167
A simple analytical solution is presented to calculate the single-pile response when excited by the passage of Rayleigh seismic waves. Closed-form expressions for the horizontal and vertical displacement distributions are presented for piles with finite or infinite length. The analytical results for both free-head and fixed-head piles are obtained through a dynamic Winkler model, with realistic frequency-dependent ‘springs’ and ‘dashpots’. The results of the presented method are in excellent agreement with results of a rigorous solution. It is shown that in vertical motion, the differences between pile and soil displacements are far more significant than in horizontal motion, and therefore, further work is needed to investigate the importance of pile-soil-pile interaction (group effects), because of the vertical component of Rayleigh seismic waves. 相似文献
15.
Zheng Li Sandra Escoffier Panagiotis Kotronis 《Bulletin of Earthquake Engineering》2016,14(3):673-697
Batter pile (or inclined pile) foundations are widely used in civil engineering structures. However, their behavior under dynamic loadings is not yet thoroughly understood. This paper presents an experimental work on the behavior of batter and vertical piles considering dynamic soil-pile-superstructure interactions. A series of dynamic centrifuge tests were performed using sinusoidal excitations. The influence of the base shaking (frequency content and amplitude) and of the height of the center of gravity of the superstructure is investigated. Seismic responses are analyzed considering the pile cap displacements and forces (total base shear, overturning and residual moments, axial forces). It is found that in certain cases batter piles play a beneficial role on the dynamic behavior of the pile foundation system. This novel experimental work provides an important database on the behavior of batter pile foundations under dynamic loadings. 相似文献
16.
This paper presents a parametric study that looks into the influence of pile rake angle on the kinematic internal forces of deep foundations with inclined piles. Envelopes of maximum kinematic bending moments, shear forces and axial loads are presented along single inclined piles and 2 × 2 symmetrical square pile groups with inclined elements subjected to an earthquake generated by vertically incident shear waves. Inclination angles from 0° to 30° are considered, and three different pile–soil stiffness ratios are studied. These results are obtained through a frequency–domain analysis using a boundary element–finite element code in which the soil is modelled by the boundary element method as a homogeneous, viscoelastic, unbounded region, and the piles are modelled by finite elements as Euler–Bernoulli beams. The rotational kinematic response of the pile foundations is shown to be a key factor on the evolution of the kinematic internal forces along the foundations. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
17.
Centrifuge modelling of raked piles 总被引：1，自引：1，他引：0
Sandra Escoffier Jean-Louis Chazelas Jacques Garnier 《Bulletin of Earthquake Engineering》2008,6(4):689-704
Inclined piles are prohibited by many codes in seismic areas. Nevertheless the battered effect has not yet been clarified
because very few data are available. The present work is a comparison, at reduced scale in the centrifuge, of the response
of two simplified pile groups: a 1 × 2 vertical piles and 1 × 2 pile group with one inclined pile. Two configurations are
considered: end-bearing and floating pile group, both with pile heads rigidly fixed with a massive cap. First, repeatability
tests under horizontal cyclic loading were performed on both floating pile groups. Secondly, repeated horizontal impact tests
were performed on both end-bearing pile groups. These impact tests, which highlight the influence of inclined piles on the
inertial response of a group, are a first step for the more complex analysis of the performance of such groups under seismic
loads where inertial and kinematic interactions are combined. The first part of this work revealed the influence of sand structure
around the inclined pile tip on the repeatability of the tests performed on floating pile groups. The second part highlighted
differences in the dynamic response between the two end-bearing pile groups through measurements of the pile cap acceleration,
the bending moment profile and the axial load in the piles. 相似文献
18.
本文对分层弹性地基中端承桩基础按Ｗｉｎｋｌｅｒ（温克尔）地基土模型，通过特性分析，建立了合理的力学模型，经过动力分析，给出了端承桩基础横向自由振动特性及在横向动力载荷与地震载荷作用下强迫反应的解析解。文中的解析公式为分层弹性地基中端承桩基础在横向动力载荷与地震载荷作用下的动力反应分析，提供了一种新的解析方法。 相似文献
19.
基于复刚度传递多圈层平面应变模型,研究考虑桩周土挤土效应时成层地基中楔形桩的纵向振动问题。首先根据桩周土体的纵向成层情况并考虑楔形桩的变截面特性,将桩土系统沿纵向划分为有限个微元段,对每个微元段的桩周土体建立复刚度传递多圈层平面应变模型,并通过剪切复刚度递推方法求得桩周土作用在桩身的剪切复刚度;然后将求得的剪切复刚度代入桩身纵向振动控制方程,运用Laplace变换技术和阻抗函数递推方法,推导得到考虑桩周土挤土效应时成层地基中楔形桩纵向振动时桩顶复阻抗的解析解;最后,采用参数研究方法在低频范围内分析挤土效应对桩顶复阻抗的影响及其规律。 相似文献
20.
The paper presents a numerical model for the analysis of the soil–structure kinematic interaction of single piles and pile groups embedded in layered soil deposits during seismic actions. A finite element model is considered for the pile group and the soil is assumed to be a Winkler‐type medium. The pile–soil–pile interaction and the radiation problem are accounted for by means of elastodynamic Green's functions. Condensation of the problem permits a consistent and straightforward derivation of both the impedance functions and the foundation input motion, which are necessary to perform the inertial soil–structure interaction analyses. The model proposed allows calculating the internal forces induced by soil–pile and pile‐to‐pile interactions. Comparisons with data available in literature are made to study the convergence and validate the model. An application to a realistic pile foundation is given to demonstrate the potential of the model to catch the dynamic behaviour of the soil–foundation system and the stress resultants in each pile. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献