三向受压混凝土的动态特性研究

为探究混凝土在三向受压状态下的动态特性,利用自行研制的大型多功能三轴材料试验机,进行不同应变速率(10^-5/s、10^-4/s、10^-3/s、10^-2/s)下混凝土不同定侧压比(1:1、2:1、3:1、4:1)的动态真三轴抗压试验,研究了混凝土在动态抗压下的强度和变形特性。结果表明:混凝土在三向受压状态下表现出明显的应变率效应,峰值应力随着应变速率的增加先减小后增大,峰值应力减小最大幅度为5.42%而后开始增大,最大增幅为18.22%。而峰值应力随着侧压比的增大而增大,到达3:1时应力速率敏感性降低。混凝土的峰值应变在低侧压比(1:1和2:1)时随着应变速率的增加而减小,而在侧压比较高(3:1和4:1)时先减小再增大。随着应变速率的增加,裂纹开始从骨料处产生,塑性应变增大,导致峰值应变增大;在动态加载条件下,峰值应变随着侧压比的增大有先增大后减小的趋势。较高侧压比时混凝土的弹性模量随着应变速率的增加具有增大的趋势,最大增幅为240.66%。应力-应变曲线上升段随着应变速率增大越来越陡峭。试件的破坏形态随着侧压比的增大从柱状破坏变为斜剪破坏。     

基于修正压力场理论的再生混凝土梁抗剪承载力计算方法研究

基于修正压力场理论分析有腹筋再生混凝土梁的剪切破坏机理,建立了更接近有腹筋再生混凝土梁实际受力的抗剪模型,并通过考虑再生骨料有效粒径和受箍筋作用下的裂缝宽度与构件裂缝处应力的联系,分析了再生骨料咬合力对梁斜截面抗剪性能的影响,提出了再生混凝土梁极限抗剪承载力的计算方法。此外,本文将理论结果与课题组自制的6根再生混凝土梁的抗剪承载力试验结果进行了对比,理论值与试验值吻合较好,验证了本文方法的有效性,从而为设计人员提供了一种预测再生混凝土梁极限抗剪承载力的计算方法。     

Determination of Chloride Content in Different Types of Cement Using Laser-Induced Breakdown Spectroscopy

The characterization and accurate determination of the chloride content in cement/concrete is very important for the assessment of the durability and safety of a concrete structure. The available analytical techniques are relatively expensive and time consuming. In this study, a laser-induced breakdown spectroscopy (LIBS) system was used for determination of elemental composition in three different types of cement samples. The plasma was generated by focusing a pulsed Nd: YAG laser at 1064 nm on the cement samples. The concentrations of different elements of significance for structural stability in cement samples were determined. The evaluation of the potential and the capabilities of LIBS as a rapid tool for characterization of cement samples is discussed. The optimum LIBS setup and experimental conditions to detect and measure chloride in building materials are reported. The LIBS results were compared with the results obtained using a standard analytical technique such as inductively coupled plasma emission spectroscopy (ICP–ES). The limits of detection were determined, and calibration curves were measured. The results of this investigation indicate the reliability of LIBS to characterize different cement samples and to assess the chloride content in these cements.     

冲击作用下的摩擦力效应实验研究

针对摩擦力效应产生的机理, 本文设计了三种不同尺寸的试件进行SHPB实验, 得到了摩擦力效应对实验的定量影响, 在此基础上对混凝土的DIF进行了修正研究, 为混凝土抗冲击工程设计提供了参考依据. 关键词： 冲击 混凝土 SHPB 摩擦力     

高强混凝土立方强度尺寸效应的分析计算

对55组高强混凝土立方强度实测数据作了分析,并给出了计算公式.表明高强混凝土立方强度尺寸效应不同于普通混凝土.     

Behavior of concrete cylinders confined by a carbon composite 3. Deformability and the ultimate axial strain

Results of an experimental investigation into the mechanical properties of concrete cylinders confined by a carbon-epoxy composite wrapping are presented. It is shown that, for all the con fined con crete spec i mens tested, the loading paths in the normalized stress space follow a single master curve, what ever the concrete strength and confinement intensity. At stresses in the confined concrete exceeding the strength of plain concrete, the tangent modulus was found to depend on the slope angle of the master curve and the asymptotic value of the differential Poisson ratio (the first derivative of the lateral strain with respect to the axial one). Formulas for predicting the ultimate axial strain and the tangent modulus are derived and compared with the corresponding fib (fédération internationale du béton) recommendations. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 4, pp. 433–448, July–Au gust, 2006.     

Behavior of concrete cylinders confined by carbon-composite tapes and prestressed yarns 1. Experimental data

The results of a comprehensive test program for the mechanical behavior of round concrete specimens confined by carbon-fiber epoxy tapes and prestressed carbon yarns are reported. Five different concrete batches of compressive strength from 20 to 100 MPa and the confinement of various thickness and pretension level were investigated. The specimens, which were subjected to monotonic or repeated compressive loadings, showed a nonlinear stress-strain behavior with a significant ductility and increased ultimate strength, in contrary to the brittle behavior of plain concrete. The limit of linearity on the stress-strain diagrams of the confined concrete roughly coincided with the ultimate strength of plain concrete. Above this limit, the damage accumulation and plastic deformations proceeded in the confined specimens. This fact was evidenced by the increasing slope of deformation diagrams in unloadings and repeated loadings and by the pronounced residual strains. The limit of linearity could be raised significantly by pretension of the carbon yarns during their winding. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 1, pp. 21–44, January–February, 2006.     

Deformational Properties of Polymer Concrete during Long-Term Exposure to Water

Changes in the elastic and viscoelastic (creep) characteristics of polymer concrete and its structural components (polyester resin, unfilled or filled with diabase flour) during a long-term exposure to water at 20°C were studied. Modeling the structural changes in polymer concrete with time showed an increase in the relative volume content of pores filled with water and a decrease in that of unfilled pores. Based on the free-volume concept and the data on swelling due to moistening and shrinkage due to physical aging of the binder, a rather accurate estimate of the time-moisture reduction function for polymer concrete was obtained. The function was found to be nonmonotonic: the interval of increase was followed by an interval of decrease.     

An elastic micro-structural continuous damage model

The paper formulates a micro-structural continuous damage theory describing an anisotropic damage field. The model can be reduced to some of the major models well known at present, and the numerical analyses are compared with the experimental data of the concrete specimen under uniaxial tension and compression.     

钢筋混凝土箱梁开裂后剪力滞效应的研究

本文用级数分析方法分析了钢筋混凝土箱梁开裂后的剪力滞效应,推得了剪滞应力公式.根据应力公式,本文还探讨了剪力滞效应随配筋率ρ等的变化情况.