不同应变速率下再生混凝土单轴受压力学性能研究

设计并完成60个再生混凝土棱柱体试块,利用电液伺服万能试验机对设计强度等级为C30,C40的2种再生混凝土试块进行应变速率为10-5/s~10-2/s范围内的单轴受压本构关系试验,得到不同应变速率下的应力-应变全曲线。通过试验特征点及应力应变关系曲线,分析应变速率与应力应变关系和混凝土抗压后破坏形态、强度、弹性模量等关系。试验结果表明:随着应变速率的增加,应力-应变全曲线形状基本无变化,而抗压强度、峰值应变等则呈显著增长趋势,当应变速率为10-2/s时,设计强度等级为C30,C40再生混凝土的抗压强度较准静态(10-5/s)抗压强度分别提高12.5%,14.2%,峰值应变分别提高16.97%,17.92%,弹性模量则受应变速率的影响较小。     

高应变率受压荷载下准各向同性碳纤维复合增强层压板的破环分析

对准各向同性纤维复合材料的动态抗压强度进行试验和数字模拟。采用分离式霍普金森压杆,在应变率400/s左右进行准各向同性层压板的平面压缩试验。与静态值相比,准各向同性层压板的动力强度大大增强。采用ABAQUS软件中实体8结点单元C3D8I和作者自定义的8结点界面单元建立有限元模型。界面单元连接三维实体单元来模拟复合材料层,其包括允许初始剥离和扩展的粘结破坏模式。假定模型在这些条件下的破坏现象主要取决于界面的剥离,这一结论通过试验得到验证。试验显示所有的准各向同性层压板几乎劈裂成完整的几块。模型结果与试验结果十分吻合,证实了假设:层内破坏不是准各向同性层压板破坏的主要原因。     

大理岩单轴压缩过程的强度确定及其应变率影响

大理岩试件单轴压缩过程中 ,其破坏面在上下两个端面附近有剪切破坏的痕迹。根据此现象进行强度确定 ,其结果与三轴压缩过程的强度值基本一致。随着应变率的增长 ,大理岩表现出 C值增大 ,φ值减小的趋势。     

Influence of Curing Stress on One-Dimensional Yielding of Cement-Admixed Bangkok Clay at High Water Content

The influence of curing stress on the one-dimensional compression characteristics of cement-admixed clay at high water content is investigated by oedometer tests, with special attention paid to the primary vertical yield stress. From the test results, the stress acting during the formation of cementation plays an important role in the one-dimensional compression characteristics of cement admixed clay. The stress compresses the treated clay and results in an increase in the vertical yield stress. For the cement-admixed clay studied, the effect of the curing stress inherently reflects on the after-curing void ratio. Therefore, the primary vertical yield stress in one-dimensional compression is a function of the after-curing void ratio and the ratio of the clay water content to the cement content ratio.     

上海粘性土局部化变形的平面应变试验研究

采用可量测局部变形的平面应变仪 ,对上海粘性土原状土样进行固结不排水平面应变压缩条件下局部化变形的试验研究 ,试验表明 :上海原状粘性土在固结不排水平面应变压缩试验过程中 ,确实存在局部化变形 ,土样经历了变形分叉、偏应力峰值、剪切带破坏到残余偏应力等阶段的渐进性破坏过程 ,定性提出上海原状粘性土局部化变形的一些规律     

钢筋混凝土轴心受压柱非线性设计

对普通箍筋轴心受压柱进行非线性分析时,由于混凝土的应力-应变曲线有下降段,当混凝土先达峰值应力后进入下降段,而钢筋尚未屈服,钢筋和混凝土不能同时达到各自的极限承载力,柱的承载力不能由两种材料的承载力简单叠加。密排环箍轴心受压柱是典型的常规三轴受压,可用三轴强度准则进行计算,计算结果偏于保守。     

Effects of Reinforcement type and Loading History on the Deformation of Reinforced Sand in Plane Strain Compression

To evaluate the effects of reinforcement type in terms of stiffness, viscous property, rupture strength, shape and loading history on the stress-strain behaviour during primary, sustained and cyclic loading of reinforced sand, a series of drained plane strain compression tests were performed on Toyoura sand. The sand specimens were reinforced with two types of polymer geogrid as well as two types of metal grid, having largely different stiffness values and surface conditions. Despite that the effects of reinforcement type on the overall stress-strain characteristics of reinforced sand and their rate-dependency are significant during primary loading, the effects are much smaller than the difference in the stiffness of reinforcement. The effects of reinforcement type on the global unloading behaviour and the residual strain by cyclic loading during otherwise global unloading are generally insignificant or negligible. The residual strains by cyclic loading of reinforced sand became substantially small by preloading as well as pre-sustained loading and pre-cyclic loading at higher load levels. With this procedure, polymer geosynthetic reinforcement, which is much more extensible and viscous than metal reinforcement, can be used to reinforce soil structures allowing very limited residual deformation.     

A Simple and Unified One-Dimensional Model to Describe Various Characteristics of Soils

A simple and unified constitutive model for soils, considering various effects such as the influences of density, bonding, time dependent behavior and others, is presented in this paper. The elastoplastic behavior of over consolidated non-structured soils under a one-dimensional stress condition is firstly presented by introducing a state variable that represents the influence of density (stage I). To describe the one-dimensional stress-strain behavior of structured soils, attention is focused on density and bonding as the main factors that affect the response of this type of soil, because it can be considered that soil a skeleton structure which is in a looser state than that of a normally consolidated soil is formed by bonding effects (stage II). Furthermore, a simple method is presented which allows for other soil characteristics to be considered, such as time and temperature dependency, and the effect of suction in unsaturated soils. Experimental observations show that the normally consolidated line (NCL) in the void ratio—stress relation (e.g., e-ln σ curve) shifts depending on the change of strain rate, temperature, suction and others (stage III). The validation of the model at stages I and II is demonstrated by simulating one-dimensional consolidation tests for normally consolidated, over consolidated and natural clays. The applicability of the model at stage III is verified not only by the simulations of time-dependent behavior of clays in one-dimensional element tests but also by the soil-water coupled finite element analysis of oedometer tests as a boundary value problem. The extension from one-dimensional models to three-dimensional models is easily achieved by defining the yield function using stress invariants instead of one-dimensional stress ‘σ’ and by assuming an appropriate flow rule in stress space. The details of the modeling in general three-dimensional stress conditions will be described in another paper (Nakai et al., 2011).     

受压花岗岩砂质粘性土结构性的试验及研究

通过引入应力综合结构势来分析花岗岩砂质粘性土的结构性.以深圳宝安区新龙园二期工程施工工地的砂质粘性土为例,对土样进行原状、饱和、重塑状态下的压缩试验,得到结构性参数曲线,得出含水量、干密度及压力的变化对砂质粘性土的结构性有显著影响的结论.     

含有机质粉质粘土的压缩试验与性状分析

通过重铬酸钾法测定了取自南京河西地区土样的有机质含量在5％-10％之间,判定其为有机质土。根据比较南京地区一般粉质粘土的物理力学指标,发现有机质土的含水率、孔隙比、压缩系数都远大于南京地区一般粉质粘土,说明该土样属于高孔隙比、高液限、高压缩性土,且随着土样中有机质含量的增大,其含水率、孔隙比、液塑限、压缩性逐渐增大。后又采取上述有机质土进行压缩-回弹再压缩试验研究,土样的残余变形比弹性变形大得多。     

三面高温时高强混凝土轴心受压柱强度和变形试验研究

通过 1 2根三面高温时钢筋混凝土轴心受压柱在不同温度下的试验 ,研究了高强混凝土 (C60 )轴心受压柱在不均匀温度场下的力学性能 ,并与普通强度混凝土 (C3 0 )轴心受压柱进行了比较。试验结果表明 ,在不均匀温度场下的高强混凝土轴心受压柱强度和变形与温度、箍筋用量、荷载温度途径及预加荷载水平有关     

Proposal of a Simple Method for Assessing the Susceptibility of Naturally Deposited Clay Grounds to Large Long-Term Settlement due to Embankment Loading

A simple method that utilizes the results of laboratory tests has been proposed for determining the susceptibility of soft clay grounds to large residual consolidation settlement due to embankment loading. It was found that there is a possibility of large long-term settlement if the sensitivity and compression index ratios of the clay material that constitutes the ground are equal to or more than 8.0 and 1.5, respectively. The compression index ratio is defined in this paper as the ratio (Cc/Ccr) of the steepest gradient of the compression curve of an undisturbed sample to that of the remolded sample. Through the SYS Cam-clay model, an elasto-plastic constitutive model that describes the actions of the soil skeleton structure, it was found that clays with large sensitivity and compression index ratios are characterized by initially highly structured soils and that decay/upgradation of the structure can easily occur due to plastic deformation. In addition, by following Schmertmann's graphic method for in-situ compression curve (1953), this paper proposes a method of deducing the in-situ initial conditions from the results of laboratory consolidation tests on undisturbed samples. These investigations revealed not only that large delayed settlement is facilitated in clays, which have higher degrees of structure and faster rates of structural decay, but also that the Δe method and other simple methods of predicting settlement may underestimate the amount of settlement.     

电控气动油门操纵装置

气动油门操纵系统,在工程机械中较为常用,它的原理如图１所示,是靠气动阀通断,控制单作用气缸,从而控制油门的开度,改变发动机的转速。随着工程机械各种性能的不断完善,这种气动油门操纵系统,逐渐显示出它的局限性,这种局限性主要表现在以下几个方面： （１）不少工程机械需要在驾驶室、车尾部、转台上操纵室、载人平台多个位置控制油门,如果油门操纵不连续,操作就会不方便,直接影响整车性能的发挥; （２）发动机由怠速到最高转速的变化是瞬间完成的,造成对发动机、取力器等各工作装置的冲击,缩短了它们的使用寿命; （３）…     

非线性有限元模拟中的应力、应变关系

提出一种方法,可以确定直至结构破坏时,与单元长度相关的应力、应变关系,并适用于有限元分析模型。采用已测出的表面位移计算结构直至破坏时的应变。从颈缩处已测出的力和横截面面积可以推导出应力的数值。此外,由于光学测量的数字特性,将应变的参考长度清晰地定义为像素的函数。在数值模拟中有限单元的长度与这个参考长度相等。此法可以对拉伸试验进行精确的数值模拟,除非在结构破坏时曲线无法拟合,或者缺少根据所取的分隔尺寸来调整材料关系的迭代方法。精确的材料关系有助于提高非线性数值模拟的准确性。     

纤维增强复合材料约束下圆形混凝土柱应力-应变全曲线简化模型

在国内外关于FRP(纤维增强复合材料)约束圆形混凝土柱的研究基础上，对FRP约束中必须考虑的相关参数即侧向约束刚度、约束强度、未约束混凝土的峰值应变、软化段界定等作了分析。提出新的三折线简化模型，并考虑到了上述参数的影响。与试验数据进行比较分析，结果表明该模型与试验数据吻合较好，该模型结构形式简单，参数取值方便。     

深厚软黏土层上路堤堆载的数值模拟

在我国广泛分布着深厚海相、湖相软土层,其表现为高含水量、高孔隙比、高压缩性和低强度,故在深厚软土层上修建路堤面临着巨大的挑战。由此,结合修正剑桥模型,对软黏土层上的路堤堆载进行了数值模拟,研究了堆载作用下不同填土高度时黏土层内的位移场及应力场,坡脚处土体水平位移的发展规律,并以此作为最大填土高度的一个判断依据。数值模拟结果表明:坡趾处最大水平位移发生在地下2 m处,最大填土高度与模型路堤结果接近。     

木材装卸运输车液压行走系统研究

介绍了林场木材装卸运输车的液压行走系统,建立了系统的数学模型。数字仿真及实测结果表明,系统响应快速、控制精度高,越野性能好,高效节能。     

分级加荷条件下正常固结软土的不排水强度确定

本文提出了分级加荷条件下正常固结软土不排水强度确定的试验法和理论法，指出了它们各自存在的问题和解决办法。     

高层建筑单桩竖向抗压静载试验分析

以清远市某高层住宅工程为背景,从单桩竖向抗压静载试验的设备配置、加载方案、承载力判定依据和检测结果等方面入手,系统阐明了桩基承载能力检测成套技术的控制要点,并结合数值模拟技术,分析了桩基极限承载力和桩土挤压效应,力求为今后的高层建筑单桩竖向抗压静载试验和计算提供借鉴。     

浅谈PHC管桩张拉控制应力

简述了用于PHC管桩的PC钢棒的特性,探讨了目前生产PHC管桩时张拉控制应力存在的问题以及解决的方法与措施。