剪切变形对基桩P-Δ效应的影响

给出了小剪切变形下的基桩P-Δ效应和大剪切变形下支座P-Δ效应计算的杆单元刚度矩阵方程。假定杆单元弯曲变形位移函数为三次幂函数,剪切变形函数为线性函数,根据有限元法一般原理,推导了一种同时计入竖向力径向剪切分力剪切变形和水平力剪切变形的P-Δ效应杆单元刚度方程,推导了一种仅计入竖向力径向剪切分力剪切变形而忽略水平力剪切变形的P-Δ效应杆单元刚度方程,推导了一种仅计入水平力剪切变形而忽略竖向力径向剪切分力剪切变形的P-Δ效应杆单元刚度方程。计入水平力剪切变形而忽略竖向力径向剪切分力剪切变形的P-Δ效应杆单元可良好的模拟支座在大剪切变形下的偏心工作特性,能实时计入其偏心弯矩影响,为实时计入支座偏心特性的结构动静力分析提供了理论支撑。最后通过自编MATLAB程序进行算例分析,结果表明,计入支座大剪切变下的P-Δ效应后,基桩内力位移和地基土压力均显著增大。基桩自身剪切变形对桩身内力位移和地基土压力影响较小,可以忽略。     

水平荷载作用下单桩的虚拟桩解法及参数

根据Muki&Sternberg的虚拟桩方法,将水平荷载作用下单桩的问题分解为弹性半空间扩展土和一根虚拟桩的叠加,其中虚拟桩的弹性模量等于桩的弹性模量与土的弹性模量之差。基于水平位移协调条件推导出求解桩土间相互作用所需要的第二类Fredholm积分方程,通过广义胡可定律推导出该积分方程间断点的显式解,从而提高了Fredholm积分方程的数值计算精度并简化了计算程序的编写,根据Mindlin解推导出位移影响函数,简化了位移函数的推导过程。参数分析表明,桩土弹性模量比对单位水平力作用下桩身最大弯矩的位置有明显的影响,随着桩刚度的增加,桩身最大弯矩的位置随之加深。     

竖向荷载下弹性支承直墙拱反弯点理论分析

在工程实践中,直墙拱应用较多。由于拱脚位移的存在,合理假设拱脚约束为转角约束、竖向约束和水平弹性约束,应用力法推导出了在弯矩、剪力和轴力共同作用下直墙拱沿弧长的弯矩公式。研究了竖向均布荷载、竖向三角形荷载和竖向集中力荷载作用下,直墙拱沿弧长的弯矩分布及反弯点形成的规律;发现在3种荷载作用下,使得拱脚弯矩为零时的圆心角依次减小。取弹簧支座刚度为等效的下端固支、上端允许水平位移的直墙的抗推刚度,得出了随着直墙高度增加,圆弧拱拱顶弯矩增大而拱脚弯矩减小的变化规律。在直墙拱的设计中,建议选取合适的直墙高度和使得圆弧拱拱脚弯矩为零的圆心角大小,从而有利于提高结构抗弯承载力及拱脚抗剪承载力。     

红层泥岩桩岩接触面本构模型试验及数值模拟

桩-岩（土）接触面力学特性的研究是桩基承载机理研究的基础。通过红层泥岩桩岩接触面大型直剪试验,研究了红层泥岩桩岩接触面的力学特性,结果表明：接触面剪应力先随剪切位移增大而增大,在达到峰值后,剪应力随着剪切位移增大而降低,并最终趋于稳定值,应力应变曲线呈现出应变软化的特征。根据剪切试验结果,推导出桩岩接触面应变软化本构方程。利用fish语言对FLAC^3D中自带的理想弹塑性接触单元进行二次开发,并应用开发的模型对桩岩接触面直剪试验进行了数值模拟,分析剪应力与剪切位移之间的关系,证明了该本构能够较好地模拟接触面间的应变软化特性。     

水平荷载作用下斜坡刚性桩非线性分析

在综合分析现有水平荷载作用下桩基分析方法的基础上,建立了考虑桩侧土体受力状态的斜坡刚性桩力学模型;根据极限平衡原理,建立横向荷载作用下斜坡刚性桩弯矩和应力平衡方程;引入考虑斜坡影响的p-y曲线方法,提出了综合考虑桩侧土体极限承载力与水平抗力系数沿深度呈线性增加的侧向极限承载力与土体抗力承载力系数计算方法,同时,将该方法应用于计算实例,通过与已有有限元和理论计算方法对比分析,计算结果验证了本文方法的合理性与可行性;并利用该方法,分析了斜坡坡角、桩土接触面系数以及地基水平抗力系数对斜坡刚性桩承载特性的影响因素。分析表明:斜坡的坡角、桩土接触面系数对侧向荷载作用下斜坡刚性桩的荷载位移曲线影响明显,而桩侧土的抗力系数对侧向荷载作用下斜坡刚性桩的荷载位移曲线影响不明显。     

Vector form intrinsic finite element analysis based on fine beam model

精细梁不同于Euler梁和Timoshenko梁,该模型在考虑剪切变形的同时还考虑了横向弯曲时截面转动产生的附加轴向位移及横向剪切变形影响截面抗弯刚度后产生的附加横向位移。推导了适用于向量式有限元分析的精细梁单元应变和内力表达式,采用FORTRAN自编了向量式有限元程序。对悬臂梁、两端固支梁和门式框架进行了算例分析,对比了采用不同梁单元模型下结构的竖向位移。结果表明：当高跨比较小时,3种梁单元的竖向位移相差不大;当高跨比较大时,精细梁单元的竖向位移较Euler梁和Timoshenko梁明显增大,表明剪切变形及刚度折减引起的附加轴向位移、附加横向位移不能忽略。精细梁单元模型对高跨比较大的梁进行分析可望得到更精确的结果。     

简谐SH波作用下管桩的振动特性

在一维波动模型的基础上得到了简谐SH波作用下桩周土和桩芯土的位移。在三维轴对称的情况下,运用势函数和分离变量法求解了简谐水平集中荷载和SH波引起的管桩桩周土和桩芯土的振动问题,得到了桩周土和桩芯土的径向位移和环向位移。考虑管桩土动力相互作用和管桩土的连续性边界条件对简谐水平集中荷载和SH波作用下管桩的振动进行了研究,得到了管桩桩顶的动力放大因子。通过数值算例分析可知,简谐SH波作用下管桩存在共振现象;管桩管壁过薄宜导致桩基失稳;相同外径情况下采用管桩要比实芯桩的抗震性能更好。     

采用块体-界面体系的砌体结构简化细观模型

基于ABAQUS装配式建模构架,提出了一种砌体结构的简化细观模型。该建模方法将块体砂浆界面及砂浆层统一采用块体间的界面来代替。界面属性包括法向和切向的力学参数,用来模拟砌体的剪压及受拉行为。界面的法向受拉采用粘性力学参数赋值,并通过与轴心受拉本构模型的等效,推导得出控制界面损伤演化速率的无量纲指数α的计算方程。剪压复合受力模型基于剪摩理论建立,通过粘性属性和库伦摩擦赋值。当剪压复合受力构件处于高轴压比时,通过块体的非线性属性实现了主压应力为主控的损伤阀值。按照该方法进行剪压相关性和砖墙剪切失效的试验仿真模拟,模拟得出的失效形态及力-位移曲线与试验结果基本相符。     

考虑滑移和剪切变形的单箱双室组合箱梁剪力滞效应

为准确分析单箱双室组合箱梁的剪力滞效应,考虑钢混凝土的界面滑移效应和钢腹板的剪切变形,针对顶底板和翼板定义不同的剪力滞翘曲位移函数,基于能量变分法推导出单箱双室组合箱梁剪滞效应的控制微分方程及其闭合解。以单箱双室组合箱梁算例为基础,利用该方法分析其剪力滞效应的规律,结果表明：在同时考虑滑移和剪切变形时,组合箱梁的挠度比初等梁理论解大,且其挠度随界面滑移刚度的增大而减小;组合箱梁在均布荷载作用下,滑移量与荷载值近似成正比关系;在相同条件下,钢箱梁底板的剪力滞效应较混凝土顶板显著。     

固结煤矸石抗剪强度特征试验

依据现场大型剪切试验和室内直剪试验,研究了固结煤矸石的抗剪强度特性。试验剪应力-剪位移过程曲线表明,一定含水率条件下的固结煤矸石呈现明显的粘塑性体力学特性。以现场大型剪切试验煤矸石作为试样配料进行了室内直剪试验,分析了含水率和密实度对良好固结煤矸石试样剪应力-剪位移试验曲线以及抗剪强度参数的影响,在此基础上探讨了试样内煤及其它细颗粒的状态变化对固结煤矸石抗剪强度的弱化作用机理,最后对比分析了现场大型剪切试验抗剪强度参数值和室内直剪试验抗剪强度参数值的差异及其产生的主要原因。     

Dynamic Response Analysis of High-rise Pile Cap-soil-structure under the Wave and Earthquake Action

Finite element software was used to simulate the internal force and deformation of high-rise pile cap-soil-structure under the wave and earthquake action. Meanwhile, wave force was calculated by using Morison equation, and the mechanical behavior of structure was simulated by inputing horizontal El-Centro wave. Then, the initial state and the state of the largest positive and negative acceleration were selected to study the structure according to the time history curve, and the displacement, bending moment, shear and axial force changes of pile foundation under wave and earthquake action were discussed, which was compared and analyzed with the structural response under the action of earthquakes solely. The result shows that the moment of front row of piles is biggest, and the force of pile bolck is the most dangerous; the axial force of the corner piles is the largest, and one of the center piles is the smallest under the action of wave and earthquake. When the wave forces and seismic forces are in the same direction, the displacement, moment, and shear force of pile bolck will be increased, on the contrary, the displacement, moment, and shear force of pile bolck will be decreased.     

Technical Economy Analysis on Selection of Structure About Soldier Pile

Based on silt geological condition, aimed at cantilever pile and pile-anchor, using method of beam on elastic foundation ,through multiple combinations of pile spacing, diameter, embedded-depth at different levels of excavation depth, the impaction is discussed on the greatest displacement, maximum bending moment, the largest shear forces of supporting structure, and in different excavation, bolt locations impact on maximum horizontal displacement, the greatest moment of medial and lateral bending moment, the biggest shear force of pile and the axial force of bolt. By deformation control standards of supporting structure, the law and technically feasible program is found. Then combined with construction method of pile and current quota, technical economy is performed to find the economic plan and give suggestion to the project.     

Y形偏心支撑高强钢框架结构抗震性能

在Y形偏心支撑高强钢框架结构抗震性振动台试验的基础上,建立了试验试件的有限元模型,并验证了分析的正确性。设计了一个9层的Y形偏心支撑高强钢框架结构,以耗能梁段长度、耗能梁段腹板高厚比、高跨比为参数,对9层结构进行了非线性动力时程分析,研究了以上参数对结构抗震性能的影响。研究结果表明,改变耗能梁段长度、高跨比对结构层间侧移、耗能梁段性能、框架柱弯矩、耗能能力均有不同程度的影响,对框架柱轴力、基底剪力无显著影响;改变耗能梁段腹板高厚比对结构耗能能力有影响,对结构层间侧移、耗能梁段性能、框架柱受力、基底剪力无显著影响,并给出了相关设计建议。     

Stability Behavior of Shuttle-Shaped Steel Lattice Columns With Bending Moment

The stability behavior of shuttle-shaped steel lattice columns subject to combined axial force and bending moment was examined through elastic buckling analysis and geometrically and materially nonlinear analysis. Firstly, the concept of section stiffness variation ratio is proposed for shuttle-shaped lattice columns and the elastic buckling behavior is discussed. Then, the effect of bending moment on the stability behavior of lattice columns is investigated, with the emphasis on the development of axial stress, bending stress and shear stress. The influence of column component spacing and diaphragm thickness on the stability bearing capacity is also analyzed. It is shown that the elastic buckling mode of the lattice column is dependent on its section stiffness variation ratio; for lattice columns with C-shaped buckling mode, the reduction in stability bearing capacity caused by bending moment is smaller than that of columns with S-shaped buckling mode; the maximum stability bearing capacity of the lattice column can be achieved by adjusting the column component spacing, and the spacing corresponding to the maximum capacity is basically consistent with the critical spacing for transformation of C-shaped buckling mode and S-shaped mode; and it is more effective to increase the thickness of columns with S-shaped buckling mode to get larger bearing capacity.     

Effect of Shear Lag on Structural Behaviours in Indeterminate Box Girders

A finite element method considering interaction betwee bending and shear lag deformation was proposed and the finite element formulations including the effect of shear lag was deduced. The effect of shear lag on structural behaviours in indeterminate box girders was studied in detail based on the proposed method. Firstly, the shear lag effects on deflection and the shear lag coefficients were analyzed for both determinate and indeterminate beams. The results obtained by using the proposed method were compared with those by using the analytical method. Finally, the effect of shear lag on redistribution of internal forces including shear force, bending moment, and additional bending moment due to shear lag in indeterminate box girder bridges was studied. It is found that the effects of shear lag on deflection and stresses at a cross section are obvious for both determinate and indeterminate beams, while the effect of shear lag on internal forces in indeterminate box girder bridges is small and may be neglected.     

Simple Shear Test of Interface between Sand and Structure under High Stress

By using a simple shear apparatus that is developed from RMT-150B,a series of simple shear tests of interface between saturated sand and structure under high normal stress were carried out to study constitutive law and shearing stiffness of interface to provide some theoretical evidences for design and calculation of projects concerned with mechanical problem of interface.In test,sand was consolidated in upper shearing box firstly,then,shear was started and testing data was recorded under high and constant normal stress.During the process,sand can deform relatively freely.It is shown that the relation curve between shear stress and shear displacement under high normal stress in simple shear tests is different from that in direct shear tests,and the complete shearing deformation process of interface under high stress can be described as a nonlinear elastic-perfect plastic form;Weibull distribution with three parameters can overcome the mathematical deficiencies of hyperbola in NEPP.The new model which is established by substituting Weibull distribution for the hyperbola of NEPP better agrees with the testing data.The regressive results of the initial shearing stiffness demonstrate that the linear function is slightly better than power function to express the relation between the initial shearing stiffness and normal stress.Based on the new interface model,the formula of tangential shearing stiffness is proposed,meantime,the change trend of tangential shearing stiffness of the new model is compared with that of NEPP.     

五星形桩与圆桩水平承载性能对比模型试验研究

五星形桩是一种横截面异形桩,是在圆桩的基础上向内切割5个圆弧,形成截面类似五星形的异形桩。按其截面性质分为周长最大化五星形桩F₁、周长面积比最大化五星形桩F₂两种桩型,为掌握五星形桩的水平承载性能进行了与圆桩的对比模型试验研究。试验用土为干砂,砂雨法土样制作,模型桩为预制钢筋混凝土桩,相似比为1∶8。模型试验桩包括：五星形桩F₁、五星形桩F₂、与五星形桩F₂截面周长相同的圆桩C₁、与五星形桩F₂截面面积相同的圆桩C₂。由于五星形桩水平承载性能具有方向性,试验采用理论计算中水平承载力最大的方向施加水平荷载,试验结果表明：F₁、C₁和F₂的水平极限承载力相当,但F₂的截面面积最小,仅为C₁的0.44倍;与C₂相比,F₂的水平极限承载力是其1.63倍,可见,合理截面形式的五星形桩可以提供更大的水平承载能力;五星形桩与圆桩弯矩分布规律基本一致,都在4倍直径左右（五星形桩为外接圆直径）达到最大,但五星形桩截面面积小,抗弯刚度不足,容易折断,总体水平承载性能不及截面周长相同的圆形桩,但优于截面面积相同的圆形桩。     

Yield Displacement Calculation Method of High-Strength Concrete Shear Wall

It is assumed that concrete compressive stress of the cross-section compression zone is linear distribution when the cross-section of high-strength concrete shear wall reaches yield situation. Based on the plane section assumption, the yield curvature formula of shear wall section is obtained by using moment - curvature analysis method. The parameters affecting yield curvature of high-strength concrete shear wall are studied by using the yield curvature formula. The results show that longitudinal reinforcement yield strain is the most vital factor of the yield curvature in addition to axial load ratio. When axial load ratio is larger, both wing walls of shear wall section have larger impact. The yield curvature formula is presented, considering the impact of axial load ratio, boundary reinforcement yield stress and both ends of wing walls of shear wall section based on the regression analysis of calculation results. On this basis, the vertex yield displacement formula of high-strength concrete shear wall is proposed, and the calculation results of formula correspond well to the vertex yield displacement experimental values of the 12 high-strength concrete cantilever wall. The formula is also suited for the vertex yield displacement of comment concrete shear wall.