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1.
Elastic/plastic deformations in frictional materials under moving surface loads are investigated. The static and kinematic shakedown theorems are used to obtain estimates of the critical shakedown load for plane strain deformations under trapezoidal surface load distributions and for three-dimensional deformations under loads distributed over circular areas. It is shown that the material can fail either by incremental collapse or in cyclic or alternating collapse modes. 相似文献
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Lower bound dynamic shakedown theory is a limit state method. It is employed herein to investigate the safety, which is associated with permanent displacement, of slopes under repeated dynamic loads, mainly earthquakes. An efficient numerical method, previously applied to the static shakedown of pavements, is extended to the dynamic shakedown of slopes in this study. It is shown that dynamic shakedown, unlike other limit state methods, is able to consider the dynamic properties of both the load and subsoil. The effect of the soil strength parameters and dynamic features of the soil and loads are examined thoroughly and some illustrative examples are employed. The short-term and long-term behavior of slopes under seismic loads are studied as well, comparing results of the present study with the well-known displacement method of Newmark. 相似文献
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30多年来,国际上的道路设计原理及方法逐渐从传统经验法向运用理论框架方面转变。但这些理论框架主要基于土和粒状材料的弹性假设,从而限制了材料塑性性能的发挥。安定分析基于弹塑性理论,可以确定结构在循环或变值荷载作用下的最大承载力,因此,能够被运用于道路承受交通荷载的问题。阐述了安定理论的概念以及两种经典安定定理,回顾了道路安定分析方法的创始及发展过程,包括与试验结果的比较,讨论了残余应力在道路中的分布、两种求解道路安定荷载极限的方法,以及与塑性极限分析的比较,并把一种下限安定分析方法应用于多层柔性路面的设计,最后展望了道路安定理论未来的发展方向。 相似文献
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Modelling of rutting of two flexible pavements with the shakedown theory and the finite element method 总被引：1，自引：0，他引：1
Cyrille Chazallon Georg Koval Pierre Hornych Fatima Allou Saida Mouhoubi 《Computers and Geotechnics》2009
This paper presents a finite element program, for the modelling of rutting of flexible pavements. In its present version, the program incorporates a permanent deformation model for unbound granular materials based on the concept of the shakedown theory developed by Zarka for metallic structures under cyclic loadings and has been used to estimate the permanent deformations of unbound granular materials (UGM) subjected to traffic loading. The calculation is performed in two steps: the first step consists in modelling the resilient behaviour of the pavement in 3D, using non-linear elastic models, to determine the stress field in the pavement. Then stress paths are derived and used to calculate the permanent deformations and the displacements, using a Drucker–Prager yield surface. An application to the prediction of the permanent deformations of experimental pavements with an unbound granular base, tested on the LCPC pavement testing facility is presented. 相似文献
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Nowadays, the problem of rutting of flexible pavements linked to permanent deformations occurring in the unbound layers is taken into account only by mechanistic empirical formulas. Finite element modelling of realistic boundary value problems with incremental rheological models will lead to unrealistic calculation time for large cycle numbers. The objective of the authors is to present a simplified model which can be used to model the flexible pavements rutting with the finite elements framework. This method is based on the shakedown theory developed by Zarka which is usually associated to materials like steels. It has been adapted for granular materials by introducing a yield surface taking into account the mean stress influence on the mechanical behaviour and a dependency of the hardening modulus with the stress state. The Drucker–Prager yield surface has been used with a non‐associated flow rule. Comparisons with repeated load triaxial tests carried out on a subgrade soil have been done. These comparisons underline the capabilities of the model to take into account the cyclic behaviour of unbound materials for roads. Finally, a discussion, dealing with the use of the simplified method within a finite element modelling of a full‐scale experiment, is presented. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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粗粒土填料被广泛应用于铁路基床填料中,直接承受轨道结构传递的列车动循环荷载的长期作用,研究其在列车动荷载作用下的动力行为特征及塑性变形特性可为路基状态评估、沉降控制提供思路。采用GDS动三轴试验系统对铁路基床表层的粗粒土填料动力响应开展研究,通过引入塑性应变率和安定理论,将不同频率、围压、循环动应力比等条件下路基填料的轴向塑性应变的发展规律划分为塑性安定、塑性蠕变和增量塑性破坏3种类型,并确定了塑性安定和塑性蠕变状态的临界动应力水平。研究表明：粗粒土填料的临界循环应力比随着围压的增大而增大,随着荷载频率的增加而减小。通过对试验结果的拟合分析,提出了以围压为变量的临界动应力经验公式,为合理评估列车荷载作用下路基任意深度的动力稳定提供了理论依据。 相似文献
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Previous work on three‐dimensional shakedown analysis of cohesive‐frictional materials under moving surface loads has been entirely for isotropic materials. As a result, the effects of anisotropy, both elastic and plastic, of soil and pavement materials are ignored. This paper will, for the first time, develop three‐dimensional shakedown solutions to allow for the variation of elastic and plastic material properties with direction. Melan's lower‐bound shakedown theorem is used to derive shakedown solutions. In particular, a generalised, anisotropic Mohr–Coulomb yield criterion and cross‐anisotropic elastic stress fields are utilised to develop anisotropic shakedown solutions. It is found that shakedown solutions for anisotropic materials are dominated by Young's modulus ratio for the cases of subsurface failure and by shear modulus ratio for the cases of surface failure. Plastic anisotropy is mainly controlled by material cohesion ratio, the rise of which increases the shakedown limit until a maximum value is reached. The anisotropic shakedown limit varies with frictional coefficient, and the peak value may not occur for the case of normal loading only. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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针对交通移动荷载,基于第一动力安定性理论预测了弹塑性半无限空间动力安定性下限值。通过建立无限元边界的三维动力有限元模型,研究了移动荷载作用下弹塑性半无限空间的动应力分布,构造了稳态动应力下的残余应力场,基于残余应力场的构造提出了动力安定性下限值的预测方法,分析了交通动应力下的安定性下限值以及车辆移动速度对安定性的影响,同时分析了均布荷载和Hertz荷载分布对动力安定性下限值的影响。当荷载移动速度低于Rayleigh波速时,安定性极限值随着速度的增加而增加,而当速度超过Rayleigh波速时,随着速度的增加而减小。研究还发现,当荷载和总重相等时采用圆形均布荷载和Hertz荷载的安定性极限值较为相似。 相似文献
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最优含水率下红层泥岩作为高速铁路路基填料的适用性已经在西南地区得到了初步验证,但饱和状态下红层泥岩填料的累积变形特性仍不明确。为此,开展了不同围压及动应力下饱和红层泥岩填料的动三轴试验,讨论了围压和动应力对填料累积变形特性的影响。结果表明：不同动应力幅值下,饱和红层泥岩填料的等效模量随振次增加,先迅速减小后趋于稳定。稳定后填料的等效模量具有应力水平相关性,随围压增大而增大,随动应力比增大而呈指数减小。不同动应力幅值下,填料变形可分为塑性稳定型、塑性蠕变型和增量破坏型3种类型。填料应变随振次增加而不再处于稳定阶段的应力状态定为塑性稳定界限应力状态。动应力进一步增加后,填料应变速率发生突增,对应的应力状态为塑性蠕变界限应力状态;塑性稳定与塑性蠕变界限应力状态对应的动应力比均低于静强度,且随围压增加呈指数衰减的规律。基床表层如用红层泥岩作填料,应考虑降雨的影响,并采取排水和改良措施以提高路基稳定性。 相似文献
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A finite element algorithm is presented to evaluate the dynamic response of pavements including aircraft-guideway-foundation interaction. The pavement-foundation system is modeled by a series of thick plate elements supported by discrete springs and dashpots at the nodal points representing the viscoelastic foundation. The moving aircraft loads are represented by masses each supported by a spring and dashpot suspension system and having a specified horizontal velocity and acceleration. The accuracy of the algorithm is verified by comparing the finite element solution with available analytical results. A parametric study is conducted to determine the effects of various parameters on the dynamic response of pavements to moving loads. 相似文献
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循环荷载下路基红黏土临界应力水平分析 总被引：4，自引：0，他引：4
根据设计改装的循环动单轴压缩试验,研究不同含水率、不同轴向应力水平、不同循环加载次数、不同应力加载路径条件下路基土的塑性力学行为,并结合shakedown概念,界定了循环动荷载作用下红黏土的安定界限（shakedown limit）和临界应力水平,系统地分析了影响循环动荷载作用下路基土力学行为的因素和永久变形的发展趋势,以及路基土在循环载荷作用下的力学行为发展规律。通过试验结果的分析,把红黏土的塑性变形分为稳定、破坏和临界3个阶段,并按3个阶段划分出可接受状态和不可接受状态,由此确定路基红黏土在循环荷载作用下的临界应力水平为41.8 %。 相似文献
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重载铁路路基比普通铁路和高速铁路要承受更大的动力荷载,路基本体的动力变形更加明显。重载铁路路基的核心层绝大部分为粗粒土,为了探讨重载铁路路基粗粒土填料在列车往复荷载作用下的变形和强度特性,开展了一系列大型动三轴试验,探讨了不同动应力幅值、不同围压、不同含水率对粗粒土土样累积变形的影响,分析了不同静强度和围压时动强度的特点,并根据粗粒土土样在不同围压和动应力作用下的变形规律,即增大围压或减小动应力有助于增强土体稳定,提出了基于累积变形发展趋势的路基粗粒土变形稳定界限状态和判别准则,并给出了判别准则参数。研究结果对重载铁路路基的动力变形稳定性评价和基于动力变形控制的路基设计具有参考价值。 相似文献
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The cyclic behaviours of embedded offshore structures under different cyclic loading levels are related to the cyclic shakedown and degradation of the surrounding soils. In the present study, a damage-dependent bounding-surface model based on a newly proposed hardening rule was developed to predict the cyclic shakedown and degradation of saturated clay and the effect of the initial anisotropic stress state. By extending the Masing’s rule to the bounding-surface plasticity theory, the stress reversal point is taken as the generalised homological centre of the bounding surface. With movement of the generalised homological centre, at lower stress amplitudes, the cyclic process ends at a steady state, and cyclic shakedown is reached. At higher stress amplitudes, a damage parameter related to the accumulated deviatoric plastic strain is incorporated into the form of the bounding surface, which is hence able to contract to model degradations in stiffness and strength. To take into account the effects of initial anisotropic conditions on the cyclic behaviour of soils, an initial anisotropic tensor is introduced in the bounding surface. The developed model is validated through undrained isotropic and anisotropic cyclic triaxial tests in normally consolidated and overconsolidated saturated clay under both one-way and two-way loadings. Both cyclic shakedown and degradation are well reproduced by the model, as is the anisotropy effect induced by the initial anisotropic consolidation process. 相似文献
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海底缓坡场地地震侧移数值分析方法 总被引：2，自引：0，他引：2
地震动使海底倾斜土层软化、液化并产生永久变形和位移。基于有限元理论,提出一种海底缓坡场地地震引起水平侧移的数值计算方法,将波浪荷载简化为恒定压力荷载和初始孔压,采用二维有效应力动力有限元分析方法进行液化分析,同时由模量软化理论得到土层在地震动各时段的模量,通过非线性静力方法计算软化、液化引起的水平侧移。由算例分析了土层坡度、液化层及上覆非液化层厚度、波浪荷载等因素对侧移的影响,通过对比分析表明了该方法的有效性,可为近海工程场地地震地质灾害评价提供参考数据。 相似文献
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Groundwater levels vary with precipitation and other environmental impacts, rendering wetting and drying cycles in parts of a slope. It may be quite disadvantageous, as groundwater has been implicated as a crucial controlling factor in slope stability. The wetting–drying cycles can be considered as cyclic loads for the slope. In such cases, a shakedown analysis is appropriate for the long‐term safety evaluation. This paper presents an upper bound shakedown analysis method based on strong version of Koiter's theorem to evaluate slope stability. An element integration method is employed to provide limit and shakedown safety factors for the slope. For plane slip surfaces or logarithmic spiral slip surfaces, the validity of the method is verified by two documented examples. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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车辆动荷载是引起路面损坏的最主要原因。目前国内外相关研究多集中于单一车辆对路面结构所产生的动荷载,实际上路面结构所承受的是车流荷载,而且车流在行驶过程中各车辆的车速和车辆之间的距离会产生变化,但关于这方面的研究甚少。针对这一工程实际问题,采用微观交通流模型中的跟车模型来模拟车流行驶过程中各车辆的速度以及它们之间车距的变化,车辆振动模型采用1/4车身结构的两自由度模型,并根据国家标准GB7031-86[1]规定生成路面轮廓的时域信号。最后分析了某水泥混凝土路面在生成的车流荷载作用下的动力响应,为研究车流荷载作用下路面结构动力响应提供了基础性成果。 相似文献
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岩石破坏的机理再认识 总被引：1，自引：0，他引：1
岩石的各种强度准则一直是解释岩石或岩体破坏机理的主要理论。此外,从流变现象出发,通过数值模拟、实验对照、理论分析、进一步对岩石破坏机理的解释进行了探讨,认为受力岩石或岩体内差异流动变形也是导致岩石破坏的原因。 相似文献
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通过对取自新疆克拉玛依风城油田重油储层的油砂进行室温和高温三轴固结排水压缩试验,研究了油砂基本力学和热学性质。研究结果表明：在常温试验条件下,油砂的偏应力-应变曲线可分为弹性阶段、塑性阶段和软化阶段,高温试验条件下则首先会出现压密阶段,不同围压下的体积应变变化规律显著不同;油砂的弹性模量和泊松比均与固结压力有较好的线性关系;高温对油砂的峰值强度、残余强度、泊松比和弹性模量影响很小;油砂的内摩擦角为34°,大小与粗粒土相近,凝聚力为0.47 MPa;油砂的热膨胀系数随围压的增大而增大,环向膨胀系数远大于轴向膨胀系数;围压?3 =5 MPa时存在临界温度,使得油砂的变形在低于或高于临界温度时表现出不同的特点,当温度小于临界温度时,试件的环向变形、轴向变形、体积变形均随温度的升高线性膨胀;当温度大于临界温度时,试件的环向变形、轴向变形、体积变形均随温度的升高线性收缩。最后将风城油砂的性质与加拿大Athabasca和Cold Lake两处的油砂进行了对比,发现3个地区的油砂在强度、变形等方面有很多相似之处,这对风城重油资源的开采具有重要的指导意义。 相似文献