Von-Mises半无限空间结构安定理论研究

进行了Hertz载荷作用下Von-Mises半无限空间的安定性研究。基于静力安定定理,通过寻找最佳残余应力场建立了平面应变条件下严格的安定极限解析方法。避免了以往安定分析方法的大型数学规划的困难,摆脱了计算中的维数障碍。研究结果表明:严格的安定极限值随着材料屈服应力的提高而增大,但随着摩擦系数的增大而减小;临界残余应力场全部位于两个界限以内,并且相交于临界点。当摩擦系数较小时,临界点发生在表面以下,随着摩擦系数逐渐增大到0.3,临界点从下层逐渐上移到表面。研究成果对安定理论应用于高速铁路设计具有参考意义。     

正交异性道路的安定分析

基于弹塑性理论的安定分析能确定结构在循环荷载作用下的最大承载力,因此可被用于分析柔性道路结构在长期车辆荷载下的极限承载力(安定极限值)。但以往的安定分析通常假设道路材料为各向同性,从而忽略了材料各向异性对道路承载力的影响。本文在考虑材料弹塑性正交异性的情况下,采用静力安定定理并结合有限元数值模拟,估算成层道路结构的安定极限值。研究发现,假设材料各向同性可能过高估计了道路在长期车辆荷载下的极限承载力。     

移动简谐荷载作用下层状道路结构的安定下限分析

为了研究移动简谐荷载作用下层状道路结构的安定性问题,先通过傅里叶变换方法和数值积分求得三维层状道路结构在时间–空间域内的动力响应,然后考虑饱和土层的有效应力场而不是总应力场,对现有的静力安定理论和安定极限求解方法进行改进,提出了有效安定极限的概念,并与考虑总应力的安定极限求解方法进行了对比分析。此外,针对饱和土层选取不同的有效内摩擦角,分别研究了荷载移动速度、荷载频率以及道路面层刚度对层状道路结构的有效安定极限和有效临界深度的影响规律。结果表明：有效安定极限与考虑总应力的安定极限求解方法得到的安定极限有明显差异;而且在荷载移动速度较大时,有效临界深度比考虑总应力的安定求解方法得到的临界深度更深。有效安定极限的求解方法更适用于包含饱和土层的层状道路结构设计和安全评估。     

新型插盘式脚手架承载力影响因素分析

基于足尺试验得到的模型参数,建立新型插盘式脚手架的三维有限元模型.采用非线性分析方法研究几何形式和荷载类型对脚手架极限承载力的影响.分析表明:结构体系的第一阶屈曲模态为支撑屈曲;几何形式对新型插盘式脚手架体系的极限承载力有显著影响;三角形荷载作用下立杆的应力比大于矩形荷载和梯形荷载作用下的应力比;矩形荷载作用下的极限承载力大于梯形荷载和三角形荷载作用下的极限承载力.     

客运专线中V型刚构拱桥极限承载力研究

结合工程实例,运用有限元程序,采用弹性屈曲、几何非线性屈曲、几何和材料双重非线性屈曲三种方法对钢管混凝土拱桥的极限承载力进行了分析,并给出了影响拱桥极限承载力的主要参数,研究表明结构极限承载力与结构材料非线性的考虑与否、材料屈服应力的大小、荷载分布方式以及温度的变化有关联,对此类桥梁稳定性能的研究以及类似桥梁的设计有一定的参考价值。     

弹塑性有限元法在土工安性分析中的应用

将弹塑性有限元法与安定性分析的Melan静力型定理相结合发挥了一种土工极限分析与安定性分析的数值计算方法，依此可以预测一般土工结构的极限荷载和安定荷载，利用弹塑性分析求解弹塑性应力场与弹性应力场,造安定性分析所需的残余应力场，摆脱了传统分析方法中的大型规划运算，解决了计算的维数障碍问题，残余应力场的构造与土工结构的弹塑性分析同时进行，而且无需对屈服面进行线性化处理，求解的精度依赖于弹塑性分析，通过算例验证了分析方法与计算程序是可靠的，并利用此方法计算了极限荷载与安全荷载。     

海洋平台地基的极限分析与安定性分析

应用以Melan静力型安定定理为基础的弹塑性有限元数值方法，对海洋平台地基进行了变值加载条件下的安定性分析，同时，为便于比较，进行了静力极限分析。通过对海洋平台地基在各种荷载分量共同作用下的安定性分析，得到了地基在不同荷载组合模式下的安定荷载包络图。由此根据海洋结构上外载的可能变化模式可以确定地基的最可能失稳形式，从而评价复杂变值荷载作用下地基的稳定性。     

内气压对三种形式张弦气肋梁结构基本力学性能的影响

主要分析三种形式的张弦气肋梁结构在不同气压值作用下的基本力学性能和静力承载能力,利用ANSYS软件构建张弦气肋梁结构的有限元模型,对结构进行从充气构建预应力到承受荷载的全过程分析。首先分析结构在荷载态时不同气压值作用下的内力状态,再根据荷载-位移几何非线性分析讨论满跨均布荷载作用下不同气压值对结构静力极限承载力的影响,并根据结构的受力性能和极限承载力大小以及结构对气压值改变的敏感程度,比较了三种形式的张弦气肋梁结构的优劣,拟定合理的气压值。所得结论可为进一步研究和设计张弦气肋梁结构提供参考。     

新广州站内凹式索拱结构模型静力试验研究

新广州站站房屋盖采用一种新型预应力索拱-内凹式索拱结构,为了解该种结构的张拉成形过程、典型荷载工况下结构性能和结构极限承载力及破坏位置,分张拉成形、4种荷载工况的加载及2种典型荷载工况的极限加载3个阶段,对2榀内凹式索拱的1/3缩尺模型进行了静力试验,并将试验结果与有限元结果进行对比,有限元结果和试验值吻合较好。研究结果表明：张拉成形后索力和位形基本达到目标,确立的张拉原则可行,给出了快速确定初始张拉力的计算公式;设计工况下结构处于线弹性阶段,满跨分布荷载时主拱全截面受压,以受轴压力为主,而半跨分布荷载时以受弯为主,弯曲应力在主拱应力中的比重较大;半跨分布荷载对结构整体稳定最不利,其极限承载力较满跨分布荷载降低较大,前者在主拱弯矩最大的位置破坏,而后者在轴压力最大的拱脚附近破坏;索夹的连接形式及支座的抗推刚度对结构的承载能力影响很大。图13表4参10     

交通荷载作用下公路路面结构振动分析

为了研究路面结构的振动特性,基于2.5D有限单元方法建立了高速公路路面结构和下卧层地基在交通荷载作用下的三维耦合振动模型。通过计算分析了路面振动加速度的变化规律和路面结构的面层、基层和底基层中的应力分布,考虑了车辆运行速度、荷载振动频率、路面分层结构形式、路面材料和下卧层地基模量等因素的影响。结果表明：车辆运行速度和荷载振动频率对路面结构的振动响应有着显著影响;同时随着路面材料刚度的提高,路面结构振动会降低,在实际工程中可通过选用合适刚度的路面材料以获得路面性能的较大改善。     

Structural shakedown analysis by dual finite-element formulations

Starting from Melan's and Koiter's well-known theorems, the present paper establishes the lower and upper bound theorems for the shakedown load factor α, corresponding to a given load domain. In the case of a linear (or linearized) plastic condition, this leads to simple dual formulations enabling one to compute dual bounds for complex structures by means of finite-element and linear mathematical-programming techniques.     

Shakedown analysis and design in presence of limited ductility behaviour

The paper deals with discrete elastic-plastic structures subjected to variable repeated or cyclic loads, which are able to undergo only a limited amount of permanent deformation. By the methods of mathematical programming, the two main problems of shakedown theory, i.e. the evaluation of the shakedown safety factor of a given structure and the optimal shakedown design for a given load multiplier, are reformulated to take into account the limited ductility behaviour of the structure. The appropriate bounding technique used plays an essential role in obtaining a fairly unified approach to both problems, also in relation to the various types of deformation constraints which may be required in practice. To solve these constrained problems numerically, a solution method based on parametric linear programming is proposed and illustrated by means of some simple examples.     

长期循环荷载下饱和软黏土安定性模型

鉴于传统显式、隐式模型计算饱和软黏土长期循环荷载下轴向塑性累积应变的不足,在建立饱和软黏土总应力弹塑性模型基础上,考虑软黏土在长期小动应力比循环荷载作用下具有安定性特点,结合过应力模型及安定性理论提出计算饱和软黏土长期循环荷载下轴向塑性累积应变安定性本构模型.安定性模型能合理描述饱和软黏土循环荷载下的变形特性,模型只考...     

Optimal shakedown design of metal structures under stiffness and stability constraints

Optimal shakedown design of metal frame and truss-like structures is considered in this paper. Strength, stiffness and stability (only for trusses) constraints are included in non-linear mathematical models of volume minimization problems of structures. Stiffness conditions are realized by the restriction of structure deflections or nodal displacements, which can vary non-monotonically during the adaptation process. Determination of displacements is especially complicated if the variable repeated load is defined by variation bounds, which are not related to time. For trusses, stability constraints are related to recommendations of Eurocode 3 (EC3). Numerical examples concerning the calculation of frame and truss structures are presented. The results are valid for the small displacement assumptions.     

干湿交替对边坡长期安全性的影响

在自然条件下,边坡体内地下水位以上的部分岩土体经常处于干湿交替状态,这对其长期的安全性十分不利。在边坡所受到的全部或部分载荷发生往复变化的情况下,塑性理论要求采用安定分析来评价其安全性,而不是人们常用的、只适用于比例加载的极限分析。本文根据率形式的Koiter机动安定定理,提出了考虑地下水位往复变化情况的边坡安定上限分析方法。利用抗剪强度参数折减定义的安全系数,定量地计算载荷变化对边坡稳定性的影响。分析结果表明,干湿交替对边坡的长期安全性有较大的影响。     

Geometric effects on shakedown and ratchetting of axisymmetric cylindrical shells subjected to variable thermal loading

This paper presents results obtained from numerical simulations of the responses of an elastic-plastic thin cylindrical shell to fluctuating axisymmetric temperature in the presence of uniform axial stresses. The engineering situation considered has practical importance in nuclear reactors and has been the subject of a number of earlier studies. The main purpose is to assess quantitatively the influence of geometry changes, primarily due to plastic yielding, on shakedown and ratchetting (incremental collapse) phenomena. In particular, these phenomena are investigated with respect to both the stabilizing effects of tensile primary stresses on them, and their strong interference with elastoplastic buckling. The systematic evolutive analyses presented herein are also intended to critically assess the validity of earlier results (mainly condensed in the so-called Brussels diagrams) which have been established by simplified methods of shakedown based on the small deformation (no geometric effects) hypothesis.     

黑河水源调配中的Conflict解析法

跨际河流水源在多主体间调配的Conflict问题的协调与消除始终是关系资源合理利用、保护生态平衡的重要课题,以META—game理论为基础的Conflict数理解析方法,研究分析黑河流域水源调配中利益冲突的主体以及水源调配所涉及Conflict问题,利用META-game理论的Conflict数理解析方法,建立典型模型,然后通过模型,借助Conflict数理分析手段,对问题进行安定分析,寻求问题的答案——均衡解。最终提出Conflict问题消除的、能被矛盾各方接受的推荐方案,供决策部门选择。     

交通荷载应力路径下K_0固结软黏土变形特性试验研究

交通荷载作用下,软黏土路基土单元体上所受主应力的大小和方向是同时变化的,即在剪应力幅值改变的同时主应力轴连续旋转。针对该问题,利用GDS空心圆柱系统对K_0固结天然温州软黏土进行不排水大数目(10000次)循环扭剪试验,分析了K_0固结软黏土在考虑主应力轴旋转时不同动应力水平下的应变特性。试验结果表明:主应力轴旋转的存在将使土体内产生更高的孔压,并在轴向上产生额外变形,且随着扭剪应力的等幅增加,竖向应变和孔压的增加量将越来越大。考虑主应力轴旋转时不同动应力水平下K_0固结软黏土的变形发展模式有所不同,可由安定理论进行解释。确定了考虑主应力轴旋转下K_0固结温州软黏土的临界动应力水平——即门槛循环应力比、容许循环应力比和临界循环应力比的范围。提出可将容许循环应力比作为道路工程沉降控制的准则。与三轴试验结果相比,考虑主应力轴旋转时,道路设计中对动应力的控制应更为严格。     

Behaviour of footings on reinforced sand subjected to repeated loading – Comparing use of 3D and planar geotextile

This paper describes a series of laboratory model tests performed on strip footings supported on 3D and planar geotextile-reinforced sand beds under a combination of static and repeated loads. Footing settlement due to initial static applied load and up to 20,000 subsequent load repetitions was recorded, until its value becomes stable or failure occurred due to excessive settlement. The response under the first few cycles was found to be a significant behavioral characteristic of footings under repeated loads. The influence of various amplitudes of repeated load on foundations containing different numbers of planar geotextile layers and different heights of the 3D geotextile reinforcement were investigated. Most of the observed responses show plastic shakedown developing – that is a stable, resilient response is observed once incremental plastic strains under each load repetition have ceased to accumulate. The results show that the maximum footing settlement due to repeated loading is comparable for either planar- or 3D-reinforced sand and much improved over the settlement of unreinforced sand. The efficiency of reinforcement in reducing the maximum footing settlement was decreased by increasing the mass of reinforcement in the sand. On the whole, the results indicate that, for the same mass of geotextile material used in the tests, the 3D geotextile reinforcement system behaves more effectively than planar reinforcement as a retardant for the effects of dynamic loading. Thus, a specific improvement in footing settlement can be achieved using a lesser quantity of 3D geotextile material compared to planar geotextile.