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1.
建立了横-竖立体加筋（H-V筋）地基的有限元模型,通过分析地基中的竖向应力分布、水平向位移分布以及筋-土界面相互作用,发现横-竖立体加筋地基中的竖向应力在筋材下方出现扩散和重分布,并逐渐向土体下部传递,使得土体中整体的应力分布更加均匀;同时,横-竖筋材中的竖筋类似于一个侧壁,其提供的垂直侧向力约束了介于竖筋间的土体,限制了土体的侧向水平位移,使得地基中筋材上部土体的侧向水平位移变小。基于有限元模拟对横-竖立体加筋地基加固机制的认识,将横-竖立体筋视为作用在地基上的一维弹性地基梁,通过弹性地基梁理论,根据弗拉曼解推导求解了横-竖立体加筋地基中任意一点竖向附加应力的计算表达式。将模型计算结果与有限元模拟所得结果进行对比发现两者吻合良好。 相似文献
2.
水平荷载下导管架平台桩基础的非线性有限元分析 总被引：2，自引：0，他引：2
导管架平台桩基础的控制荷载主要为风荷载、波浪荷载、地震荷载等水平荷载,为研究水平荷载下导管架平台桩基础的承载特性,采用非线性有限元分析方法对水平荷载下桩-土之间的相互作用进行研究,提出了有效模拟桩基水平承载特性的有限元模型,分析了模型桩的刚度、直径、土质参数中水平土压力系数、剪胀角对桩基承载特性的影响及水平荷载下群桩承载特性,并将有限元计算结果与API规范及模型试验结果进行对比。研究结果表明,非线性有限元分析方法分析水平荷载下桩-土相互作用是可行的,计算结果可为导管架平台的桩基设计提供参考。 相似文献
3.
长短桩复合地基中,地震发生时,短桩在降低长桩所受剪力和弯矩影响中起到重要作用。本研究对弹性地基中的钢管桩基础实行了静态有限元分析,以及动态离心模型试验,通过桩径、桩长、桩间距等参数进行剪切波速,长桩剪力弯矩的对比分析,得到一种新的水平向群桩效应系数计算方法,并通过对模型建筑物的模拟,验证了该方法的有效性与实用性。结果表明,静态有限元数值模拟分析和离心模型试验结果有较好拟合,不同震级作用下通过该方法均能给出较为合理的系数。本文结果可为长短桩复合桩基的抗震性能提供重要参考,实际工程中,通过调整桩径,桩长,短桩数量等参数,可以提出更为合理的设计施工方案。 相似文献
4.
地震荷载作用下桩-土-结构相互作用问题在桥梁抗震研究中越来越受到重视。本文结合工程实例,利用有限元仿真软件ADINA,建立桩-土-结构相互作用的有限元实体分析模型。选取三种时程波作为地震荷载,对在地震作用下桩-土-结构相互作用对桩的沉降位移,桩侧摩阻力和有效应力的影响进行了分析研究,对桩基设计提出了较为合理的建议。 相似文献
5.
考虑桩-土作用的高速列车-桥梁地震响应分析 总被引：1，自引：0，他引：1
基于空间梁单元有限元法,建立了两种高速铁路多跨简支梁桥的全桥空间分析模型,一种是包括桩基的列车-桥梁模型,给出成层土的动力阻抗,采用改进的Penzien模型模拟桩-土作用;一种是不考虑桩-土作用的墩底固结的列车-桥梁模型;分析了两种模型的自振特性,计算了两种模型在不同车速、墩高、地震强度、不同地震波等工况下的地震反应。计算结果表明,桥梁横向位移、加速度主要受到低频成分的影响,这部分频率与其底部地震波相互反馈,改变了地基运动的频谱组成,使接近于桥梁结构自振频率的分量获得加强,考虑桩-土作用后,横向位移/加速度增加较大;桥梁竖向振动频率受桩-土作用影响较小,随墩高和车速的增加梁体竖向位移增加不大,梁体竖向加速度受高频成分的影响较大,这些高频主要由车辆荷载和轨道不平顺引起。 相似文献
6.
This paper presents a non‐linear interface element to compute soil–structure interaction (SSI) based on the macro‐element concept. The particularity of this approach lies in the fact that the foundation is supposed to be infinitely rigid and its movement is entirely described by a system of global variables (forces and displacements) defined in the foundation's centre. The non‐linear behaviour of the soil is reproduced using the classical theory of plasticity. Failure is described by the interaction diagram of the ultimate bearing capacity of the foundation under combined loads. The macro‐element is appropriate for modelling the cyclic or dynamic response of structures subjected to seismic action. More specifically, the element is able to simulate the behaviour of a circular rigid shallow foundation considering the plasticity of the soil under monotonic static or cyclic loading applied in three directions. It is implemented into FedeasLab, a finite element Matlab toolbox. Comparisons with experimental monotonic static and cyclic results show the good performance of the approach. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
7.
桩基会由于隧道或基坑开挖、打桩顺序不当等原因而倾斜。实际工程中经常遇到桩局部倾斜的情况,例如上段桩发生弯曲与倾斜,下段桩则仍然保持竖直。在已经完成的整体倾斜桩现场试验及有限元分析基础上,建立了桩身局部倾斜的有限元模型,对局部倾斜桩的承载力进行有限元分析。分析结果表明：算例条件下相同竖向荷载作用时,垂直度在5 %以内的局部倾斜桩的桩顶沉降均小于竖直桩的桩顶沉降;垂直度超过5 %时局部倾斜桩的桩顶沉降大于竖直桩的桩顶沉降。相同竖向荷载作用下垂直度为7 %以内局部倾斜桩的桩顶沉降均小于相同垂直度整体倾斜桩的桩顶沉降,超过7 %后局部倾斜桩的桩顶沉降大于整体倾斜桩的桩顶沉降。对于局部倾斜桩,由上段倾斜桩传递到垂直度转折点处的轴力将对下段竖直桩产生水平向推力。当垂直度转折点深度在反弯点以下时,水平向推力将导致下段竖直桩产生更大的反向挠曲变形和弯矩,使竖向荷载作用下桩顶水平位移增加,使桩更易于因为水平弯曲变形过大而破坏。 相似文献
8.
The driving response of thin‐walled open‐ended piles is studied using numerical simulation of the wave propagation inside the soil plug and the pile. An elastic finite element analysis is carried out to identify the stress wave propagation in the vicinity of the pile toe. It is found that the shear stress wave has the highest magnitude above the bottom of the soil plug. Below the bottom of the soil plug, the vertical stress wave has the highest magnitude. Although the shear stress wave propagating in the radial direction is similar in magnitude to the vertical stress wave at the bottom of the soil plug, it decays rapidly while travelling downwards. The highest vertical stress at the bottom of the soil plug appears after the vertical stress wave interacts with the shear stress wave travelling in the radial direction. Initially, the vertical stress wave propagates with the dilation wave velocity in both the radial and vertical directions. After it interacts with the shear stress wave, the vertical stress wave starts to propagate with the shear wave velocity in the radial direction and with the axial wave velocity downwards. It is concluded that at the bottom of the soil plug, the interaction between the waves travelling in radial and vertical directions is important. The capabilities of several one‐dimensional pile‐in‐pile models to reproduce the driving response given by a two‐dimensional axisymmetric finite element model is studied. It is seen that when the base of the soil plug fails, a one‐dimensional pile‐in‐pile model can be used to achieve results in agreement with the finite element model. However, when the pile is unplugged, where the base of the soil plug does not fail, a reduced finite element mesh that permits the radial wave propagation inside the soil plug must be used. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
9.
This paper presents a non‐linear soil–structure interaction (SSI) macro‐element for shallow foundation on cohesive soil. The element describes the behaviour in the near field of the foundation under cyclic loading, reproducing the material non‐linearities of the soil under the foundation (yielding) as well as the geometrical non‐linearities (uplift) at the soil–structure interface. The overall behaviour in the soil and at the interface is reduced to its action on the foundation. The macro‐element consists of a non‐linear joint element, expressed in generalised variables, i.e. in forces applied to the foundation and in the corresponding displacements. Failure is described by the interaction diagram of the ultimate bearing capacity of the foundation under combined loads. Mechanisms of yielding and uplift are modelled through a global, coupled plasticity–uplift model. The cyclic model is dedicated to modelling the dynamic response of structures subjected to seismic action. Thus, it is especially suited to combined loading developed during this kind of motion. Comparisons of cyclic results obtained from the macro‐element and from a FE modelization are shown in order to demonstrate the relevance of the proposed model and its predictive ability. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
10.
This paper presents a finite element procedure for the analysis of consolidation of layered soils with vertical drain using general one‐dimensional (1‐D) constitutive models. In formulating the finite element procedure, a Newton–Cotes‐type integration formula is used to avoid the unsymmetry of the stiffness matrix for a Newton (Modified Newton) iteration scheme. The proposed procedure is then applied for the consolidation analysis of a number of typical problems using both linear and non‐linear soil models. Results from this simplified method are compared with those from a fully coupled consolidation analysis using a well‐known finite element package. The average degree of consolidation, excess porewater pressure and average vertical effective stress are almost the same as those from the fully coupled analysis for both the linear and non‐linear cases studied. The differences in vertical effective stresses are tolerable except for the values near the vertical drain boundaries. The consolidation behaviour of soils below a certain depth of the bottom of vertical drain is actually one‐dimensional for the partially penetrating case. Therefore, there are not much differences in whether one uses a one‐dimensional model or a three‐dimensional model in this region. The average degree of consolidation has good normalized feature with respect to the ratio of well radius to external drainage boundary for the cases of fully penetrating vertical drain using a normalized time even in the non‐linear case. Numerical results clearly demonstrate that the proposed simplified finite element procedure is efficient for the consolidation analysis of soils with vertical drain and it has better numerical stability characteristics. This simplified method can easily account for layered systems, time‐dependent loading, well‐resistance, smear effects and inelastic stress–strain behaviour. This method is also very suitable for the design of vertical drain, since it greatly reduces the unknown variables in the calculation and the 1‐D soil model parameters can be more easily determined. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
11.
覆盖层上土石坝非线性动力响应分析的地震波动输入方法 总被引：1，自引：0，他引：1
较多已建和待建的土石坝直接修筑于覆盖层上,合理描述土石坝与覆盖层之间的动力相互作用对大坝抗震安全评价至关重要。基于等效荷载和人工边界的地震波动输入方法能较好地反映出结构-地基之间的相互作用并得到了广泛应用。等效荷载和人工边界参数在均质线弹性地基条件下易于获得,而对于覆盖层地基,土体动力非线性特性给求解带来很大困难。鉴于此,首先根据覆盖层侧向边界的位移模式,发展了能高效、精确地获取多向地震动垂直入射时均质或成层覆盖层自由场非线性动力响应的简化模型;结合能动态实时获取地基材料参数的非线性人工边界,发展了一套覆盖层上土石坝非线性动力响应分析的地震波动输入方法。算例表明,发展的地震波动输入方法可大大减小计算网格量,并能较好地反映覆盖层对地震动频谱特性的影响且具有较高的精度。 相似文献
12.
在二维剖面上,抗滑桩两侧岩土体规模及形态差异导致桩两侧静止侧压力的合力不等,且合力作用点也不在同一水平线上,这直接影响作用于抗滑桩上的弯矩与剪力。滑体在重力作用下存在整体滑动及侧向膨胀两种效应：当滑动面倾角较小时,侧向膨胀效应占优势,抗滑桩的设计荷载应依据桩两侧静止侧压力合力之差;当滑动面倾角较大时,滑动效应占主导地位,抗滑桩的设计荷载可根据各种条分法来确定。此外,通过有限单元法算例说明数值计算方法是求解静止侧压力的有效工具。 相似文献
13.
为研究近断层脉冲地震动中竖向加速度对砂土场地液化的影响,基于有限元平台OpenSees开发的边界面塑性本构模型,建立了动单剪单元试验模型和饱和砂土三维有限元模型。选取台湾Chi-Chi地震中10条具有速度脉冲特性的地震波,对比分析了水平双向脉冲波与三向脉冲波作用下土柱竖向位移、循环应力比、孔压比及等效循环周数的差异性,继而明确了脉冲地震动中竖向加速度对砂土液化的影响规律。研究表明,三向脉冲地震波中竖向加速度分量对场地永久位移值影响较小,但使永久位移的发展持时明显增大;土柱循环应力比受竖向地震动影响较小,因此分析脉冲地震动对场地剪切特性的影响时,可将三向脉冲地震动简化为水平双向地震动;考虑竖向地震动的三向脉冲地震波引起的孔压比变化幅度较大,孔压消散时间较长;三向脉冲地震波对应的等效循环周数较大,地震动发展持时长,可认为竖向加速度对场地液化有促进作用。 相似文献
14.
柔性基础下群桩复合地基荷载传递规律及计算 总被引：11，自引：2，他引：9
复合地基沉降及荷载传递规律的研究是复合地基理论中一项非常重要的研究内容,然而对群桩复合地基的沉降及荷载传递规律的研究,在理论上很不成熟。在采用文[1]推荐的竖向变形模式及文[2]推荐的径向变形模式的基础上,利用弹性理论及桩-土位移协调条件建立了桩及桩周土的控制微分方程,并由此推导出了柔性基础下群桩复合地基加固区内桩及桩周土压缩量计算的解析式,同时得出了桩、桩周土中竖向应力及桩侧剪应力计算的解析式。通过算例将该方法所得结果与有限元结果进行了对比,同时也与模型实验结果进行了比较。算例及模型实验结果均表明：该方法对分析柔性基础下群桩复合地基的荷载传递规律及加固区的变形具有足够的精度,且该法计算工作量小,便于工程应用。 相似文献
15.
砂土液化导致的地基侧向大变形是地震中许多重要的工程设施和建筑物破坏的主要原因之一。简要介绍了可进行液化大变形分析的散粒体材料本构模型--应变空间多机构CG模型,基于FLIP ROSE程序平台,建立了预测和研究倾斜地基砂土液化导致侧向大变形的二维有限元数值分析方法。采用该模型对相同工况的土工动态离心模型试验进行了模拟,通过对比超孔隙水压力、剪切波水平加速度以及地基侧向位移发现,数值预测与试验结果吻合良好,从而验证了该有限元数值分析模型的可靠性。最后利用该数值分析模型预测了倾斜率不同的地基受到相同剪切波作用时,倾斜地基不同深度产生的侧向位移。预测结果显示,随着地基深度的减小,倾斜率对于地震液化导致倾斜地基侧向大变形的影响越来越显著。 相似文献
16.
考虑蠕变性土工格栅加筋挡土墙应力与变形有限元分析 总被引：4，自引：1，他引：4
土工格栅加筋挡土墙在岩上加固工程中得到了广泛应用。采用粘弹塑性流变模型考虑地基和填士的流变性，采用作者所建议的绎验型粘弹性本构模型考虑土工格栅的蠕变性，对于土工格栅加筋挡土墒发展了非线性有限元数值分析方法，通过变动参数的对比计算与分析探讨了逐层填筑过程、加筋长度及间距布置方式等因素对土工格栅加筋挡土墙长期变形与应力特性的影响。计算与分析表明：填筑过程对面板侧向变形、格栅拉力与应变及地基中水平位移与竖向沉降具有较大的影响；加筋使墙后填土应力重新分布；面板位移、格栅拉力及应变在经历一段时间后趋于稳定状态。 相似文献
17.
水平荷载作用下PCC桩复合地基工作性状 总被引：5，自引：1，他引：4
利用河海大学岩土所自行研制开发的大型试验模型槽进行PCC桩水平承载足尺试验,实测得到了水平荷载作用下桩身弯矩分布。利用三维弹塑性有限元方法,研究了PCC单桩与等截面实心圆桩、PCC桩复合地基与等截面实心圆桩复合地基在水平荷载作用下的工作性状,对其桩身弯矩和水平位移的分布规律进行了比较,分析了竖向荷载、褥垫层厚度、基础埋深和置换率对PCC桩复合地基桩身性状的影响。研究表明,PCC桩复合地基在水平荷载作用下,随着竖向荷载、褥垫层厚度、基础埋深和置换率的增加,其桩身弯矩和水平位移随之减小。因此,在PCC桩复合地基设计时可以通过适度调整这些影响参数来减小水平荷载作用下的桩身弯矩和水平位移,确保桩身的安全。 相似文献
18.
刚性桩复合地基桩体抗震性能分析 总被引：2，自引：0，他引：2
建立三维有限模型,分别采用振型分解反应谱法和时程分析法研究刚性桩复合地基的抗震性能,并根据相似理论,建立刚性桩复合地基群桩模型,采用模型拟动力试验,对其进行了地震作用下桩体响应规律试验研究,并对其在不同方法下的结果进行了对比分析,结果表明：无论是弯矩值还是剪力值,都是角桩最大,其次是边桩,再次是中心桩;不同分析方法所得的位移值相差不大,位移分布比较均匀;而且通过观察试验现象、分析试验和理论数据可见刚性桩复合地基具有良好的抗震性能;模型动力试验方法用于研究刚性桩复合地基的抗震性能是可行的,并且可推广应用到类似性的其他复合地基的抗震性能试验研究。 相似文献
19.
《Geomechanics and Geoengineering》2013,8(3):185-194
In this paper, a model for the analysis of footings having finite flexural rigidity resting on a granular bed on top of stone columns improved saturated soft (clayey) soil has been proposed. Soft soil has been modeled as a Kelvin–Voigt body to represent its time dependent behavior. Pasternak shear layer has been used to represent the granular layer and the stone columns have been idealized by means of nonlinear Winkler springs. Nonlinear behavior of granular fill, soft soil and stone columns has been invoked by means of hyperbolic constitutive relationships. Governing differential equations for the soil–foundation system have been obtained and finite difference method has been adopted for solving these, using the Gauss-elimination iterative scheme. Detailed parametric study for a combined footing has been carried out to study the influence of parameters, like magnitude of applied load, flexural rigidity of footing, diameter of stone column, spacing of stone column, ultimate bearing capacity of granular fill, poor foundation soil and stone column, relative stiffness of stone columns and degree of consolidation, on flexural response of the footing. 相似文献
20.
竖向立柱是基坑逆作法设计的关键环节之一,而动态施工下侧向约束则是决定立柱稳定承载力的主要因素。针对逆作施工中立柱的轴压稳定问题,采用有限元方法获得立柱轴压屈曲荷载,进而通过杆件欧拉公式反推获得立柱计算长度系数。采用线性特征值屈曲分析研究地基土分步开挖、侧向约束动态变化下竖向立柱的承载力和稳定性,提出了竖向立柱稳定承载力分析时计算长度系数的拟合公式。非线性屈曲分析考虑了几何大位移的影响,通过施加初始几何缺陷获得立柱屈曲后的平衡路径。结果表明,含初始缺陷的立柱实际承载力一般要比特征值屈曲荷载小,且初始缺陷幅值越大,立柱的稳定承载力越小。 相似文献