受水平循环荷载影响的斜桩p-y曲线构建及应用

p-y曲线法是分析水平受荷桩基承载变形特性的主要方法,利用p-y曲线法的关键在于构建合理的p-y曲线。在砂土地基中开展了2组共10根水平受荷斜桩模型试验,其中2根斜桩仅分级施加了水平静力荷载,其余8根斜桩先施加了不同幅值的单向水平循环荷载,然后再分级施加水平静力荷载。试验测试了10根斜桩的砂面处桩身横向位移及桩身应变,根据桩身应变计算得到了桩身弯矩,在此基础上根据Euler-Bernoulli梁理论得到了桩侧土抗力及相应的桩身水平位移,构建了承受水平单向循环荷载后再承受水平静力荷载时斜桩的双曲线型p-y曲线,并给出了斜桩初始地基反力模量及桩侧极限土抗力的确定方法。用上述构建的双曲线型p-y曲线计算了本文模型试验及文献中模型试验斜桩的响应,发现利用所构建的p-y曲线得到的计算结果与实测结果整体上吻合较好,说明本文构建的双曲线型p-y曲线是合理可行的。最后利用p-y曲线计算了承受单向水平循环荷载后再承受水平静力荷载斜桩的桩身位移及桩身内力,计算结果表明:(1)相对于斜桩桩顶自由,桩顶固支能有效地减小斜桩的桩身横向位移、桩身弯矩及剪力;(2)在单向水平循环荷载作用下,正斜桩桩顶横向位移、 桩身最大弯矩及剪力均小于负斜桩;(3)无论是正斜桩还是负斜桩,桩顶横向位移、桩身剪力随着抗弯刚度增加而减小,而桩身最大弯矩随着抗弯刚度增加而增加。     

水平偏心荷载下斜桩群桩受力性状的离心机模型试验

为研究斜桩群桩在水平偏心荷载下的受力性状,在砂土中开展了一系列离心机模型试验,着重对比了直桩群桩和斜桩群桩抵抗水平及偏心荷载的不同特性。详细介绍了模型试验的装置、方法以及内容。试验结果表明：水平荷载偏心距大小对群桩水平承载力有一定的影响,但是对群桩扭转承载力的影响较小。对于直桩群桩,在试验范围内小偏心距（4.3倍桩径）加载对应的水平承载力大于零偏心距（即纯水平加载）及大偏心距（7.1倍桩径）加载的水平承载力。相同条件下,斜桩群桩抵抗水平、偏心及扭转荷载的能力显著强于直桩群桩。水平偏心荷载下,斜桩群桩中各基桩的桩顶水平位移相互差异较直桩群桩更大,且该差异随偏心距的增加而增大;在多向荷载的共同作用下,基桩桩顶剪力与桩顶位移方向有所不同。水平荷载下斜桩群桩中的基桩轴力显著大于直桩群桩。斜桩群桩较好地发挥了基桩的轴向承载能力,从而能够更有效地抵抗水平荷载。     

斜桩的承载能力分析

斜桩以及由斜桩组成的群桩主要应用于桥梁、深水港区和大型输电线路基础等。文章以斜桩作为研究对象,从斜桩承载力影响因素研究单斜桩工作特性。主要得到以下一些结论:1)竖向荷载作用下,随着桩身倾斜度、地面荷载、土质不均匀程度增大,斜桩的沉降量相应增大;2)结合斜桩刚度及斜桩基础形式综合考虑,中等刚性负斜桩的水平承载能力较好;随土体位移层厚度的增加,桩身主动侧部分的土抗力逐渐减小。     

组合扁梁楼盖水平荷载作用下承载性能分析

为了研究组合扁梁楼盖在水平荷载作用下的承载性能和有效宽度,采用有限元分析软件建立了钢—混凝土组合扁梁整体楼盖三维实体有限元模型,并进行了相应的计算分析.计算结果表明:钢—混凝土组合扁梁楼盖具有较大的水平刚度和较好的空间作用,组合扁梁楼盖在水平荷载情况下有效宽度较竖向荷载作用时小.建议进行组合扁梁整体楼盖试验,进一步研究其有效宽度取值.     

Influence mechanism of vertical-horizontal combined loads on the response of a single pile in sand

Pile foundations are used to support both vertical and horizontal loads in many geotechnical projects, such as the coastal and offshore engineering. The responses of piles under vertical-horizontal combined loading are separately analyzed and then superposed in current design practice. This simplified analysis approach does not take the coupling effect of the combined loads into consideration. The research on this topic is limited and the results reported to date are inconclusive with regard to the influence of vertical loads on the horizontal response of piles. In this paper, a series of centrifuge model tests under different vertical-horizontal combined loading conditions was performed to investigate the influence rules and mechanism of the combined loads on the response of piles in sand. The vertical load is shown to densify the soil near the pile and therefore decrease the horizontal displacement and bending moment of the pile: this is termed the “soil densification effect”. The vertical load induces an additional bending moment of the pile due to the lateral deformation of the pile: this is termed the “P-Δ effect”. The soil densification effect plays a dominant role in the early horizontal loading while the P-Δ effect is strengthened as the horizontal loads increases. These compound effect of these two seemingly opposing effects is a decrease in the bending moment of the pile decrease first then increase as the horizontal load increases. Additional settlement of the pile is caused by horizontal loading and isa positively correlated with the pre-vertical loads.     

船撞作用下斜桩基础动力响应研究

东海大桥100MW海上风电示范项目中风机采用斜桩基础,必须考虑船撞作用。本文利用有限元方法,研究了斜桩基础在船撞作用下的动力响应。模拟不同工况,研究船舶吨位、船舶速度、倾斜角、桩径、桩周土体等因素对桩基的动力响应的影响。研究表明:船舶吨位和船舶速度对斜桩的动力学响应影响最大;桩的倾斜角会影响最大桩项位移,最优倾斜角约为10°;在既定的土质条件下,桩径增大到某一值后,桩基动力响应基本不变;土体较软时,桩身的最大应力较小,但最大桩顶位移较大。因此,进行斜桩设计时,必须在理论分析的基础上,选取合适的倾斜角与桩径。本文研究结果对斜桩基础在考虑船撞作用下的设计和施工有一定参考价值。     

砂土中竖向和水平荷载共同作用下的单桩承载特性研究

水平荷载引起桩体水平位移,导致桩侧摩阻力发生变化,从而影响单桩的竖向承载特性;竖向荷载影响桩周土体抗力,并随着桩身挠曲变形而产生附加弯矩,从而影响单桩的水平承载特性。利用室内模型试验研究了砂土中单桩在竖向和水平荷载共同作用下的受力和变形特性。试验结果表明:预先施加竖向荷载有利于单桩水平承载力的提高和水平位移的减小;预先施加水平荷载对桩身上部桩侧阻力的发挥有减小作用,但水平荷载的增大对桩端阻力的发挥有促进作用,总体上表现为预先施加水平荷载削弱了单桩的竖向承载力;单桩水平荷载引起的最大弯矩位置在地面以下约5d~7d处,水平荷载对桩身弯矩和桩侧摩阻力的影响主要集中在地面以下0~10d的深度范围内。结合已有研究成果和理论分析,验证了试验成果的合理性并从理论上分析了砂土中竖向和水平荷载共同作用下的单桩承载机理。     

输电线路掏挖式基础在倾斜荷载作用下的特性

通过数值模拟对输电线路竖向和倾斜掏挖式基础在不同倾角荷载作用下的承载特性和内力分布进行分析。结果表明,直掏挖基础在小于10°的倾斜荷载作用下竖向承载力变化不大,随着荷载倾角的增加,竖向承载力明显减小。在相同倾角的荷载作用下,正斜掏挖式基础的竖向承载力要大于负斜掏挖式基础,直掏挖基础居中。同时,正斜掏挖式基础的弯矩和剪力均要小于负斜掏挖基础。掏挖式基础的倾角与荷载倾角相同情况下的基础受力最合理,不但可以保证基础承载力,而且基础所受弯矩几乎为零。     

桥梁群桩基础非线性静力计算模型及拟静力试验研究

 线弹性地基反力法(m法)仅适用于正常使用时桥梁桩基础变位较小的情况,但在强震作用下基础的变位较大。为了研究桩基础在地基土及桩身进入非线性状态下的水平承载能力及变形特性,通过群桩基础缩尺比例模型,采用拟静力试验研究桩基础的破坏机制、承载能力、变形性能以及滞回特性。提出水平荷载作用下群桩基础的非线性静力计算模型,在该模型中采用分布PMM塑性铰模拟变轴力作用下桩身的弹塑性,采用美国API规范给出的p-y曲线、t-z曲线以及q-z曲线模拟地基土的非线性(其中,p为桩侧土水平抗力,y为水平位移,t为桩周土竖向摩阻力,q为桩端土竖向抗力,z为桩土竖向相对位移)。研究结果表明：(1) 本文提出的分析模型与模型试验结果吻合较好;(2) 可采用Clough退化双线性模型模拟桩基础的滞回特性;(3) 桩身受力薄弱部位在桩顶以下0～4倍桩径范围内。研究结果可为应用能力谱法评价桩基础的抗震性能提供参考。     

斜坡基桩的斜坡空间效应及其水平承载特性研究

为研究水平荷载作用下斜坡基桩的斜坡空间效应对其承载特性的影响,设计并完成了不同坡度及水平荷载作用角度下斜坡基桩室内模型试验,测得了桩顶荷载位移曲线及桩身弯矩分布。结果分析表明：水平荷载相同时,桩顶水平位移及桩身最大弯矩均随坡度增加呈非线性增大,随水平荷载作用角度增加而呈线性减小;基桩水平极限承载力却随坡度增加而减小,随水平荷载作用角度增加而增大。坡度每增加30°,桩顶水平位移约增大1.3~1.9倍,桩身最大弯矩增大约17%~30%;水平荷载作用角度每增加30°,桩顶水平变形减小约25%~30%,桩身最大弯矩减小约6%~11%。斜坡基桩的桩身最大弯矩位于地面以下3~6倍桩径范围内,坡度越大桩身最大弯矩位置越深。分析得到了基桩水平极限承载力拟合公式,可以为斜坡基桩设计提供参考。     

Monopilegründungen von Offshore‐Windenergieanlagen – Zum Ansatz der Bettung

Monopile foundations for Offshore‐Wind Power Plants – approach of subgrade reaction. The large moments and horizontal forces and their cyclic occurrence represent a special challenge to the prognosis of the deformations of Monopiles as a foundation of offshore wind energy plants. The conventional procedures for the computation of the horizontal pile bearing capacity and deformation, subgrade reaction procedure and API procedure, are compared with the results of a 3D‐FE analysis for a system with exemplary dimensions, soil conditions and loads. It is shown that the conventional procedures for the prognosis of the deformations in the serviceability limit state, thus clearly underneath the maximum load, for this example are insufficient. The distribution of the subgrade reaction modulus over the depth is sufficiently approximated with none of these procedures. Moreover the change of the subgrade reaction modulus is investigated for several cycles swelling and alternated loads. The modulus of subgrade reaction, referred to the initial pile position, changes especially under swelling loads for each loading cycle. The displacement of the pilehead still increases after 20 cycles. The modulus of subgrade reaction derived from the oedometric soil stiffness does not produce an accurate prognosis of the pile deformation particularly for cyclic loads. For this purpose further investigations are necessary.     

对称双斜桩桩基础竖向承载力模型试验研究

对称双斜桩基础是斜桩基础用于建(构)筑物的基本基础形式。通过对桩身竖向倾角分别为0°、5°、10°、15°和20°的对称双斜桩基础模型试验,研究竖向荷载作用下对称双斜桩基础的承载特点。研究发现,对称双斜桩基础在竖向荷载作用下,随着桩身倾角的增加,当桩身对竖向的倾角在5°～10°时,其竖向承载力比直桩基础大,当桩身对竖向的倾角超过10°时,其竖向承载力随桩身倾角的增加逐渐减小,并小于直桩基础的承载力;根据该模型试验,对称双斜桩基础当桩身对竖向的倾角在5°～10°内是最优的。     

倾斜桩承受竖向荷载能力的分析

从倾斜桩受竖向荷载这一主要受荷形式入手,运用有限元分析软件MARC分析了倾斜桩在荷载作用下的承载性状,研究了在不同倾斜度下桩身的应力分布以及桩顶的Q—S曲线,得到了较合理的结果,结合工程实例验证了该分析方法的可行性。     

中密砂土地基中H-T组合作用下单桩承载特性研究

为探讨中密砂土地基中桩顶水平力(H)与扭矩(T)组合作用单桩的承载特性,研制了适合于室内砂箱模型试验的H-T组合加载装置,并通过对比试验获得不同H-T大小组合与加载顺序(H→T或T→H)下的桩身内力变形与承载力,及其对桩身承载特性的相互影响曲线,结果表明：相比单一受荷时的水平或扭转极限承载力(Hu或Tu),H-T组合作用会导致桩身承载力减小,且H→T要比T→H的影响要明显,如先施加2/3Tu时桩身水平承载力减小约12.4%,而先施加2/3Hu后的桩身扭转承载力减幅达48.5%,故不能简单基于叠加原理评估组合受荷时的承载力。在此基础上,引入能反映水平力对桩身扭转承载力影响的桩侧扭转土抗力放大因子αTH,基于杆系有限元和m法建立了考虑桩周土约束及H-T耦合效应的桩身单元综合刚度矩阵,进而用MATLAB编制了H-T组合受荷桩的改进杆系有限元法计算程序,并将其结果与模型试验值进行对比分析。     

粗粒土应力诱导各向异性真三轴试验研究

使用河海大学最新研制成功的真三轴仪,对粗粒土进行不同主应力方向上的单向加荷试验。结果表明,在σ1、σ2、σ3方向上单向加荷时,加荷向变形都为压缩,而侧向变形较为复杂。当在σ1或者σ2方向上单向加荷时,σ3方向上都是发生膨胀,而另一个侧向(即σ2或σ1方向上)没有明显变形;当在σ3方向上单向加荷时,两个侧向(即σ1、σ2方向上)都几乎没有变形。分析认为:剪切作用增强即应力状态接近破坏面,会发生侧向膨胀;反之,剪切作用减弱,则无侧向膨胀产生或侧向膨胀较小。对σ3方向单向加荷的情况研究表明,该应力路径下,p、q、b这3个量的变化都是使试样的应力状态远离破坏面,剪切作用减弱,因此侧向膨胀很小或没有。所试验的粗粒土在一般应力条件下各向异性性质显著。     

不同包裹角度下GFRP复合桩水平承载特性研究

玻璃纤维增强复合材料(Glass Fiber Reinforced Polymer)是由玻璃纤维和基体材料按照一定比例混合而成的高性能材料,具有轻质高强、耐腐蚀和抗疲劳的优点。GFRP复合桩是利用GFRP筋代替钢筋,并且在桩身包裹GFRP布的一种新型桩基形式。为了研究在桩身表面粘贴不同角度的GFRP单向布对GFRP复合桩水平承载性能的影响。通过室内模型试验,研究了在桩身表面分别按照30°、45°和60°包裹GFRP单向布,对单桩的水平承载力和抗弯刚度的影响。利用ABAQUS有限元软件建立模型,对不同包裹角度GFRP复合桩的水平承载力进行数值模拟。试验结果表明:随着包裹角度的增加,单桩的水平承载力和抗弯刚度随之增加,桩身的弯矩则减小少。在桩顶承受2 000 N的水平荷载作用时,GFRP布按60°包裹的GFRP复合桩的水平位移比按30°包裹减小了21.8%,桩身截面的最大弯矩减小了16.7%。增大GFRP单向布在桩身的包裹角度,可以提高GFRP复合桩的水平承载力。     

Frequency- and intensity-dependent impedance functions of laterally loaded single piles in cohesionless soil

This paper investigates the frequency-dependent pile-head impedance characteristics of a model soil-pile foundation system under large amplitude loads, inducing soil yielding. Testing was conducted on a scaled single pile embedded in sand under a 1g condition. A laminar shear box mounted on a unidirectional shaking table was used to house the soil-pile foundation system. Quasi-static loads and dynamic loads were applied to obtain the force–displacement relationships and pile-head impedance functions, respectively, through the pile head connected to a loading actuator providing fixity to the pile head in all directions, except horizontal. In the quasi-static case, loads with three different velocities were applied to study the rate-dependent characteristics of the lateral bearing capacity of the pile. The Stereo-PIV system was employed to measure the surface soil displacement around the pile. The lateral bearing capacity changed with the loading velocity, but the soil near the pile showed a consistent failure pattern despite a significant change in velocity. Lateral pile-head dynamic impedance functions were obtained for low-to-high amplitude harmonic loading for a wide range of frequencies. The dynamic stiffness was seen to converge to that of the secant static stiffness with an increase in the amplitude of the dynamic loading for all the excitation frequencies.     

塑料套管现浇混凝土桩倾斜对承载性能影响的模型试验研究

 通过模型试验研究竖直桩与倾斜角度为5°,8°,10°和15°倾斜桩的承载性能,分析倾斜对塑料套管现浇混凝土桩(以下简称TC桩)单桩承载力、桩顶沉降、桩身水平位移、桩身弯矩、桩身轴力及侧摩阻力和端阻比的影响。模型试验结果表明：(1) 当TC桩倾斜度不大于8°时,对承载力和桩顶沉降影响不明显,对于倾斜10°,15°的桩,承载力明显降低;(2) 倾斜桩桩身水平位移和弯矩主要发生于1/3桩长范围内,且均随着荷载和倾角的增加而增大;(3) 竖直桩及各倾斜桩的侧摩阻力随深度的增加呈先增大后减小的趋势,随着倾角的增大桩极限侧摩阻力的平均值略有增大,侧摩阻分担比较大;(4) 端阻力和端阻比基本随荷载的增加而增加,随倾角的增加而减小。采用Origin软件应用Sigmoidal函数拟合,得出模型桩极限承载力随桩体倾角的计算公式,并根据现场实测数据,给出现场应用时修正系数的取值范围。     

Test and numerical simulation of partially encased composite columns subject to axial and cyclic horizontal loads

Partial encased composite (PEC) members with thin steel plates and three types of constructional detailing are studied. Six pieces of PEC column specimens were tested under constant vertical load and cyclic horizontal loads. A numerical FE model is established. In the model, the in-filled concrete is decomposed as transverse and longitudinal springs, considering the functions and the properties of the concrete in two directions. This model simplifies the numerical computation with high efficiency, and acquires a satisfied agreement with test results in both capacity and deformability of the PEC member. The parametrical study by the FE model is performed. By tests and numerical analysis, it is found that though local buckling of thin plate of H steel is a crucial factor, when the compressively axial load does not surpass the encased steel capacity, the PEC could behave quite well under cyclic horizontal loads. No distinguished difference in three kind details was observed, so that PEC member could be built in a simple way.     

大口径挖孔灌注桩水平承载力试验分析与研究

本文结合工程实践，介绍了大口径人工挖孔灌注桩水平承载力的试验方法、成果整理与分析、水平承载机理研究。试验结果表明：桩周土的性质是影响单桩水平承载力和性状的主要因素。