共查询到19条相似文献，搜索用时 171 毫秒
1.
《地震工程与工程振动》2016,(3)
在考虑大直径桩尺寸效应及桩端土应力扩散效应情况下,进行了非均质土中大直径桩的纵向振动研究。利用Rayleigh-Love杆理论,考虑大直径桩桩身的横向惯性效应;引入扩散虚土桩模型模拟桩端土对桩身的支承作用;桩侧土考虑径向非均质,采用复刚度传递多圈层平面应变模型——以此建立桩-土耦合振动系统的简化模型。结合边界条件、初始条件和连续条件,推导得出大直径桩桩顶速度的频域解析解和时域半解析解。通过各种工况下相关参数对桩顶动力响应的影响分析,得出非均质土中大直径桩的振动规律。 相似文献
2.
基于平面应变简化假定的桩扭转振动理论精度研究 总被引：3，自引：1，他引：2
利用拉普拉斯变换对考虑桩土耦合扭转振动条件下,桩顶受到任意激振扭矩作用的端承桩桩顶频域及时域响应进行解析求解,推导求得了桩顶位移、速度频域响应,桩顶复阻抗的解析表达式和半正弦脉冲激励作用下的桩顶时域响应半解析解;将本文所得理论解与基于平面应变假定的桩基扭转耦合振动的频域解和时域解进行了全面对比研究,具体比较范围涉及土层对桩的局部复阻抗、桩顶复频响应、速度导纳、桩顶复刚度和桩顶时域响应等方面,并得到若干重要结论。研究成果校核了平面应变假定在桩基扭转振动理论研究中的合理运用,为进一步了解桩土耦合振动的内在机理提供理论支持。 相似文献
3.
假设桩周土层为成层黏弹性体,土体材料阻尼为黏性阻尼,从三维轴对称角度出发,对任意激振扭矩作用下,成层土中完整桩与土扭转耦合振动时的桩顶振动特性进行了理论研究.首先建立定解问题,然后利用拉氏变换求解得到其振动角位移的形式解,并利用桩土接触界面处的连续条件来考虑桩土耦合作用,使用桩段阻抗函数的传递性进行逐层递推求解,最终得到桩顶频域和时域响应的理论解.通过参数影响分析研究发现,成层土中桩顶复刚度主要受上部土层动力特性及性质影响;随着上层土模量增大桩顶复刚度的刚度部分也相应增大,阻尼部分相应减小.成层土由于土层模量变化,桩的导纳曲线有大峰夹小峰循环的特征.当上层土模量大于下层土模量时,在土层分界面时域波形与初始脉冲反向,反之则同向,土模量突变导致的时域波形的特征反射较平缓,幅度不大. 相似文献
4.
成层粘弹性土中桩土耦合纵向振动时域响应研究 总被引：10，自引：3，他引：7
从三维轴对称角度出发,采用粘性阻尼粘弹性连续土介质模型,考虑桩土相互作用效应,对成层土中桩土纵向耦合振动时的桩顶时域响应进行了解析研究。求解时,首先建立定解问题,然后利用拉氏变换先对底部土层进行求解得到其振动位移形式解,然后利用桩土接触界面连续条件来考虑桩土耦合作用,分析底层土中桩段的动力反应,然后利用桩段阻抗函数的传递性,进行逐层递推求解,最终得到桩顶时域和频域响应的半解析解。通过参数影响分析和与工程实测曲线的对比,讨论分析了成层土中桩土耦合振动的响应特性,验证了本文解。基于本文研究可为桩基抗震、防震设计、桩基动力检测提供新的理论支持。 相似文献
5.
工程上广泛采用基于Winkler模型的层状地基反力系数法对桩土水平动力响应进行分析,该方法忽略了地基土剪切作用的影响,与工程实际有一定偏差。另外,对桩土的非线性相互作用和如扩底桩、楔形桩等变截面桩问题常用的传递矩阵法或中心差分法,计算过程较为繁琐。基于Pasternak地基模型和Adomian分解方法,提出一种考虑地基土剪切作用的桩土水平动力相互作用近似计算方法,该方法计算简便且结果精度较高,对变截面桩问题有很好的适用性;并基于该方法,对扩底桩水平动力响应问题和影响因素进行分析。结果指出,扩底半径和上部桩周土弹性模量对扩底桩水平动力响应影响较大,随着扩底半径的增加和桩周土弹性模量的增大,扩底桩水平振动位移幅值逐渐减小。另外,在较低频率的荷载激励下,应考虑土层对桩的剪切作用。 相似文献
6.
均匀土-桩基-结构相互作用体系的计算分析 总被引：14，自引：4，他引：14
本文以结构－地基动力相互作用振动台模型试验为基础，结合通用有限元软件ANSYS，对均匀土－桩基－结构动力相互作用体系进行了三维有限元分析。计算中土体采用等效线性模型，利用面－面接触单元考虑土体与结构交界面的状态非线性，计算与试验得出的规律基本一致。桩基与土体间发生了脱开再闭合和滑移现象。桩身应变幅值分布呈桩顶大、桩尖小的倒三角分布，角桩的应变幅值较大，边排中桩和中桩的应变幅值较小。桩土接触压力幅值呈桩顶小、桩尖大的三角形分布。在沿振动方向的三排桩中，边排桩的滑移比中排桩的滑移量大。通过计算分析与试验的对照研究，验证了采用的计算模型与分析方法的合理性，为结构－地基相互作用的进一步研究奠定了基础。 相似文献
7.
通过对群桩-土-偏心结构相互作用体系振动台试验,分析了结构偏心效应对相互作用体系自振特性、地基振动和桩基变形的影响规律。试验结果表明:地基土的加入使得相互作用体系前两阶自振频率相差增大,平扭振动耦联程度降低,体系阻尼比明显增加;结构偏心效应增大了角桩的加速度响应,高出同深度边桩测点10～15%,桩身振动频率特性较场地土有明显差别;角桩变形幅度较边桩更为突出,桩长范围内角桩应变峰值始终大于边桩测点,两者相差在桩顶附近达到最大;桩间土承担了部分扭转效应,角桩较边桩应变增幅约为对应位置筏板位移增幅的一半;土的动力放大特性与以往研究规律相近,结构偏心效应对地基整体振动产生的影响不很明显;桩土界面动力响应与筏板平动位移时程相对应,且随深度的增加而逐步增大。 相似文献
8.
液化场地桩-土-桥梁结构地震相互作用振动台试验数值模拟方法研究 总被引：1，自引：0，他引：1
直接针对大型振动台模型试验,建立液化场地桩-土-桥梁结构地震相互作用数值模拟的二维分析模型和计算方法。根据桩基平面应变假定,将空间桩体转换成平面板桩,并考虑桩的尺寸效应;基于桩截面节点位移协调条件和平衡力系等效原理,建立四结点梁单元刚度矩阵且对Timoshenko梁杆单元刚度矩阵进行增广修正,以考虑桩的横向尺寸影响桩周土位移场分布的尺寸效应。根据有效应力原理进行土动反应分析,采用满足M asing准则的修正双曲线模型描述土动力变形的本构关系,同时考虑因孔压上升造成土体软化而对土动力性能的影响,由迭代法处理土的动力非线性。采用并联弹簧-阻尼器模拟计算域人工边界,以考虑边界波的反射作用对体系动力反应的干扰和土粘滞阻尼的影响。采用W ilson-θ逐步积分法计算体系的地震反应。通过与试验结果的对比分析,评估数值模拟的建模途径和计算方法的可靠性。 相似文献
9.
《地震工程与工程振动》2015,(3)
在桩侧土广义Voigt模型条件下,研究成层土中黏弹性桩在纵向振动荷载作用下的动力特性。将桩底截面范围内有限层桩底土模拟为虚土桩,建立虚土桩-土、桩-土耦合振动模型,采用广义Voigt体模型建立桩、虚土桩与桩侧土的纵向振动动力方程。利用桩-土、虚土桩-土的耦合接触条件求解动力方程,得到桩顶频域响应解析解和时域响应半解析解。通过对虚土桩参数的研究检验桩底土对桩顶动力响应的影响,得到一系列的桩顶速度导纳曲线及时域反射波曲线。 相似文献
10.
考虑地基土液化影响的桩基高层建筑体系地震反应分析 总被引：5，自引：2，他引：5
本文建立了土体－结构体系地震反应分析的混合有限元法，并研究了地基土液化对地震反应的影响。本方法把土体－结构体系简化为一个完整的体系，该体系由梁（柱）单元、剪切杆单元、刚体单元、平面四边形等参单元与三角形单元、界面单元的任意组合来模拟。桩与上部结构材料视为线弹性体，土介质视为非线性材料。土的静应力－应变关系之间的非线性用邓肯一张模型来描述；土的动应力－应变关系之间的非线性和振动孔隙水压力对土的软化效 相似文献
11.
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
12.
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
13.
Horizontal impedance functions of inclined single piles are measured experimentally for model soil-pile systems with both the effects of local soil nonlinearity and resonant characteristics.Two practical pile inclinations of 5° and 10° in addition to a vertical pile embedded in cohesionless soil and subjected to lateral harmonic pile head loadings for a wide range of frequencies are considered.Results obtained with low-to-high amplitude of lateral loadings on model soil-pile systems encased in a laminar shear box show that the local nonlinearities have a profound impact on the horizontal impedance functions of piles.Horizontal impedance functions of inclined piles are found to be smaller than the vertical pile and the values decrease as the angle of pile inclination increases.Distinct values of horizontal impedance functions are obtained for the ’positive’ and ’negative’ cycles of harmonic loadings,leading to asymmetric force-displacement relationships for the inclined piles.Validation of these experimental results is carried out through three-dimensional nonlinear finite element analyses,and the results from the numerical models are in good agreement with the experimental data.Sensitivity analyses conducted on the numerical models suggest that the consideration of local nonlinearity at the vicinity of the soil-pile interface influence the response of the soil-pile systems. 相似文献
14.
A new model named double-shear model based on Pasternak foundation and Timoshenko beam theory is developed to evaluate the effect of a forced harmonic vibration pile to its adjacent pile in multilayered soil medium. The double-shear model takes into account the shear deformation and the rotational inertia of piles as well as the shear deformation of soil. The piles are simulated as Timoshenko beams, which are embedded in a layered Pasternak foundation. The differential equation of transverse vibration for a pile is solved by the initial parameter method. The dynamic interaction factors for the layered soil medium are obtained by the transfer matrix method. The formulation and the implementation have been verified by means of several examples. The individual shear effects of soil and piles on the interaction factors are evaluated through a parametric study. Compared to Winkler model with Euler beam, the present model gives much better results for the dynamic interaction of piles embedded in stiff soil with small slenderness ratios. Finally, the effect of a forced long pile to a short pile embedded in multilayered soil medium is studied in detail. 相似文献
15.
Interpretation from large-scale shake table tests on piles undergoing lateral spreading in liquefied soils 总被引：2，自引：0，他引：2
M. Cubrinovski T. Kokusho K. Ishihara 《Soil Dynamics and Earthquake Engineering》2006,26(2-4):275-286
Results from a benchmark test on full-scale piles are used to investigate the response of piles to lateral spreading. In the experiment, two single piles, a relatively flexible pile that moves together with the surrounding soil and a relatively stiff pile that does not follow the ground movement have been subjected to large post-liquefaction ground displacement simulating piles in laterally spreading soils. The observed response of the piles is first presented and then the results are used to examine the lateral loads on the pile from a non-liquefied soil at the ground surface and to evaluate the stiffness characteristics of the spreading soils. The measured ultimate lateral pressure from the crust soil on the stiff pile was about 4.5 times the Rankine passive pressure. The back-calculated stiffness of the liquefied soil was found to be in the range between 1/30 and 1/80 of the initial stiffness of the soil showing gradual decrease in the course of lateral spreading. 相似文献
16.
基于OpenSees数值分析平台,建立了群桩-土-桥墩非线性数值分析模型。模型中桩-土水平向相互作用和桩-土竖向相互作用、桩底-土竖向相互作用分别通过p-y、t-z与q-z零长度弹簧单元模拟。模型中同时考虑了群桩效应与纵筋在墩底的应变渗透和粘结滑移的影响。结合群桩基础拟静力试验结果,对数值模型的准确性进行了验证,在此基础上对土体参数特性对桩基滞回性能的影响规律进行了分析。结果表明:所建立的数值分析模型可对群桩基础滞回曲线和骨架曲线进行较为准确的模拟分析,验证了模型的可靠性。反复荷载作用下,前桩处土体的反应明显大于中桩处;土体由软黏土变为硬黏土时,墩顶侧向承载力与刚度显著增加,但土体的非线性反应减弱。 相似文献
17.
斜交桥梁由于其不规则的结构形式使其受力规律与规则桥梁相比具有特殊性和复杂性,在地震作用下梁体的平动与转动存在弯扭耦合效应,导致结构动力响应分析复杂。针对斜交桥梁的结构特点,建立包含桩土相互作用的三维有限元模型,在考虑水平双向地震作用下,采用反应谱法及时程分析法对京包高速公路某互通式斜交桥梁进行地震反应分析。结果表明:互通式简支斜交桥梁的地震响应受地震动输入方向的影响较大,在考虑碰撞效应后,碰撞涉及结构部位的地震位移显著增加,地震内力也出现较大差异,即说明在斜交桥梁抗震设计时有必要适当考虑地震动输入方向和梁端与墩台及相邻梁端的碰撞效应。 相似文献
18.
Simple formulas are derived for the dynamic stiffness of pile group foundations subjected to horizontal and rocking dynamic loads. The formulations are based on the construction of a general model of impedance matrices as the condensation of matrices of mass, damping, and stiffness, and on the identification of the values of these matrices on an extensive database of numerical experiments computed using coupled finite element–boundary element models. The formulations obtained can be readily used for the design of both floating piles on homogeneous half‐space and end‐bearing piles and are applicable for a wide range of mechanical and geometrical parameters of the soil and piles, in particular for large pile groups. For the seismic design of a building, the use of the simple formulas rather than a full computational model is shown to induce little error on the evaluation of the response spectra and time histories. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
19.
为研究抗滑桩合理桩间距以及荷载传递机制,首先以桩侧摩阻力为拱脚时的破裂面推导出以桩身为拱脚时的破裂角计算公式;然后引入对数螺旋线法确定桩间土体的滑移深度,以土拱效应为基础建立计算模型,求解考虑桩间土体滑移深度的合理桩间距表达式;最后对桩间净距的主要影响因素进行分析,包括滑坡推力、黏聚力、桩截面宽度以及高度。研究结果表明：由桩身和桩侧摩阻力同时作为土拱拱脚更符合实际受力状态,同时求得的土拱拱圈厚度和矢高小于以桩身为拱脚条件下相应值而大于以桩侧摩阻力为拱脚条件下的相应值,并且随桩埋深的增加而增大。 相似文献