温差影响下的局部滑移接触行为的研究

针对不同温度装配件间接触界面的局部滑移问题,建立了三维稳态热弹性局部滑移接触的半解析求解模型.基于热弹性理论与热传导方程,构建了半空间受热流载荷和力载荷作用下的频响函数并建立了相应的影响系数矩阵.借助离散卷积-快速Fourier变换等数学工具,实现了针对高温压头与热弹性半空间局部滑移接触问题的高效求解.接触界面间的热量传递满足Fourier热传导定律,并且黏/滑状态由Coulomb定律确定.基于该半解析模型分析了不同荷载及温差对表面法向压力分布、摩擦力分布、刚体位移及接触区黏/滑演化行为的影响.研究结果表明,当法向荷载和切向荷载一定时,温差的上升会导致接触区域的减小,引起接触面法向压力及摩擦力的峰值增大,并且会显著影响黏着区与滑移区的分布情况.     

基于表面阻抗张量的界面滑移波动态失稳分析

基于Stroh公式和表面阻抗张量理论,提出了研究界面滑移波动态失稳问题的一种新的方法．该方法将表面阻抗张量概念推广到复波速域,并将摩擦接触界面上的边界条件以表面阻抗张量表示．最终将边值问题化归为求解一个复多项式在单位圆内的根．以弹性半空间与刚体平面相对稳态摩擦滑移为例进行了详细的分析,导出了一个4次复特征方程并讨论了方程在单位圆内解的特性,给出了滑移界面波失稳条件的显式解析表达式．     

四阶流体在一个倾斜有局部滑移的非对称通道中作有热交换的蠕动流

分析研究滑移和热交换对四阶流体作磁流体动力学蠕动流的影响.首先建立模型的控制方程,然后在长波长的假设下,采用标准的摄动法近似值求解;给出的解包括:流函数、速度、压力梯度、温度和热交换系数的显式表达式;分析了滑移参数增大时泵输送性质的变化,及其潴留现象.进而对所出现的变化参数,得到了温度分布曲线和热交换系数;讨论了这些参数对所考虑流动特性的影响;并与以往发表的无滑移情况相比较,结果基本一致.     

FRP加固再生混凝土圆柱力学性能试验研究

通过混凝土圆柱轴心受压试验,研究了0%、50%、100%3种粗骨料取代率对再生混凝土圆柱抗压强度的影响以及碳纤维(CFRP)布或玄武岩(BFRP)布加固后圆柱的力学性能。试验结果表明:再生骨料取代率对再生混凝土圆柱的力学性能有一定影响,取代率为100%时,圆柱的抗压强度和极限应变均有所增加;而取代率为50%的再生混凝土的横向变形系数略低于天然骨料混凝土的横向变形系数。纤维增强型复合材料(FRP)加固再生混凝土能有效提高结构的承载能力和改善其变形性能,增加构件的延性;其中CFRP加固比BFRP加固效果更为显著。FRP加固再生混凝土与加固天然混凝土类似,其应力-应变曲线表现为明显的双线性,与所选模型计算结果符合良好。     

空间半参数变系数部分线性回归中的分位数估计

本文研究了空间数据变系数部分线性回归中的分位数估计. 模型中的参数估计量通过未知系数函数的分段多项式逼近得到, 而未知系数函数的估计量通过将参数估计量代入模型中并通过局部线性逼近得到. 文中推导了未知参数向量估计量的渐近分布, 并建立了未知系数函数估计量在内点及边界点的渐近分布. 通过Monte Carlo 模拟研究了估计量的有限样本性质.     

多釜串联模型停留时间分布方差的推导

简要分析了理想反应器的特点,并指出现实反应器与理想反应器的区别,介绍了多釜串联模型描述实际反应器的思想.针对多釜串联模型的停留时间分布的计算函数进行逐步的推导,以阶跃法对模型进行分析,采用数学归纳法和分部积分法等方法推导出了多釜串联模型无因次停留时间分布函数表达式;根据停留时间分布密度函数定义,推导出了无因次停留时间分布密度函数的表达式;根据概率中方差的定义,推导出了无因次方差的表达式.     

二参数广义Rayleigh分布

为了研究某些工程过程的寿命,需要一个能够适应这些过程性质的寿命模型.与简单模型相比,基于寿命分布的广义模型在建模过程中更具有直观的适用性和吸引力.本文介绍一个二参数广义Rayleigh分布,推导出了其矩生成函数和k阶矩的表达式,通过对样本点进行归一化,得到了它的近似分布函数、概率密度函数、生存函数、风险率函数等.在此基...     

BA模型的数学基础——纪念李国平院士吴新谋教授诞辰100周年

该文基于马氏链的概念和技巧, 给出了BA无标度网络模型稳态度分布存在性的严格证明, 并且从数学上重新推导了度分布的精确解析表达式. 此处所用的方法具有一定的普适性, 适用于更一般的无标度型复杂网络模型.     

变系数空间自相关模型的Bayesian-INLA估计

文章提出了一类变系数空间自相关模型(VCSAM)新的Bayesian-INLA估计方法.在这个模型中,响应变量具有空间自相关性,且包含变系数的非参数部分.尽管已有的工作对该模型已经进行了大量研究,但很少有研究使用贝叶斯方法提出高效求解模型的方法.因此基于上述动机,文章提出了基于B ayesian-INLA技术的方法,以寻求在VCSAM框架内代替MCMC方法的有效解决方案.变系数部分使用B-样条基函数的线性组合进行逼近,空间自相关系数采用M-H算法进行估计,并应用Bayesian-INLA技术来估计变系数函数和相关系数的后验分布.通过模拟研究,展示了文章提出的估计方法在同时处理空间依赖效应和空间非平稳性时的优势.此外,通过对波士顿房价数据的实证分析,展示了文章提出的估计方法优越的性能.     

随机数学建模方法在钢筋与混凝土粘结强度分析中的应用

本文主要利用随机建模的方法推导了均速加载的速率对粘结承载力影响量化表达的基本形式 .运用随机过程中的 Markov过程的方法得到了加载速率对粘结承载力 (平均粘结强度 )影响的量化表述 ,并综合考虑了钢筋锈蚀率的影响 ,且结合实际试验确定了一些未知参数 ,在此基础上分析了混凝土强度变化可能的影响 .     

Bond-slip behavior of CFRP plate-concrete interface

The paper deals with evaluation of the bond performance between a CFRP plate and concrete with respect to various compressive strengths of concrete and bond lengths of the CFRP plate as parameters. To consider stress conditions in the tensile zone of reinforced concrete (RC) structures, double-lap axial tension tests were conducted for eight specimens with CFRP plates bonded to concrete prisms. In addition, a simple linear bond-slip model for the CFRP plate/concrete joints, developed from the bond tests, was used. To verify the model proposed, a total of seven RC beams were strengthened with CFRP plates and tested in flexure employing various bond lengths, strengthening methods, and numbers of CFRP plates. A nonlinear finite-element analysis, with the bond–slip model incorporated in the DIANA program, was performed for the strengthened RC beams. Also, the results of flexural test and analytical predictions are found to be in close agreement in terms of yield and ultimate loads and ductility.     

Cracking Analysis of FRP-Reinforced Concrete Flexural Members

The paper is dedicated to the cracking analysis of FRP (Fiber-Reinforced Polymer)-reinforced concrete elements. A general nonlinear calculation procedure, based on the slip and bond stresses, is described and adopted for the prediction of the crack width and crack spacing in FRP-reinforced concrete beams. An analytical expression of the bond-slip law is estimated using the corresponding experimental results available in the literature. A numerical investigation is carried out and the influence of the mechanical and geometrical parameters of the material (bond-slip law, reinforcement ratio, concrete strength, diameter of rebars, etc.) on the crack formation is investigated. Referring to glass-FRP-reinforced concrete beams, a comparison between the theoretical predictions and experimental results is made. The results obtained are presented and discussed.     

Modeling of the Behavior of Concrete Tension Members Reinforced with FRP Rods

The paper is devoted to the analysis of cracking and deformability of concrete tension members reinforced with fiber-reinforced polymer (FRP) rods. A theoretical nonlinear model, derived from a cracking analysis founded on slip and bond stresses, is adopted for evaluating the crack width, crack spacing, and elongation of tension members. The procedure takes into account the local bond-slip law, experimentally determined by means of pullout tests, and allows us to evaluate the influence of tensile stiffening. The analysis is performed with considering all parameters influencing the behavior of tension members, such as the concrete strength, the kind of FRP rebars, the surface treatment of FRP rebars, and the concrete cover thickness. The theoretical predictions are compared with available experimental results, obtained on cylindrical concrete specimens reinforced with carbon FRP (CFRP) rods, and with predictions of the traditional models usually adopted for design purposes.     

On the macroscopic material behaviour of textile reinforced concrete undertensile loading

This paper concerns with the development of the macroscopic material behaviour of textile reinforced concrete (TRC) using an analytical approach. Therefore the heterogeneous structure of TRC is modelled on the mesoscopic level. The overall material behaviour on the macroscopic level is obtained by means of the homogenisation technique. The analytical approach is based on the micro mechanical solution for a single inclusion according to Eshelby . In extension of this solution for multidirectional reinforced concrete an effective field approximation is used. This approach considers the interactions between the different orientated rovings and the micro cracks in an average sense. For the mechanical modelling of the bond behaviour between roving and matrix after initiating of the macro cracking a slip based bond model with a multiple linear shear stress-slip relation is used. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A new model for the analysis of reinforced concrete members with a coupled HdBNM/FEM

As a truly boundary-type meshless method, the hybrid boundary node method (HdBNM) does not require ‘boundary element mesh’, either for the purpose of interpolation of the solution variables or for the integration of ‘energy’. In this paper, the HdBNM is coupled with the finite element method (FEM) for predicting the mechanical behaviors of reinforced concrete. The steel bars are considered as body forces in the concrete. A bond model is presented to simulate the bond-slip between the concrete and steels using fictitious spring elements. The computational scale and cost for meshing can be further reduced. Numerical examples, in 2D and 3D cases, demonstrate the efficiency of the proposed approach.     

FRP-strengthened reinforced concrete beams: a review and the assessment of cracking and deflection models

A review of some cracking and deflection models used for a structural analysis of FRP-strengthened reinforced concrete beams is presented, and, with reference to short-term deflections, a comparison between model predictions and experimental results is made. By using predictions provided by a nonlinear model derived from a cracking analysis, founded on slip and bond stresses, and experimental results for 63 FRP-strengthened beams, a modification of the well-known semi-empirical Branson’s formula to compute beam deflections is proposed. Finally, the efficiency of the modification is evaluated by comparison with experimental results.     

Experimetal study on the FRP-concrete bond behavior under repeated loadings

In this study, the effects of repeated loads on the FRP-concrete bond strength were investigated experimentally by direct pull out tests according to CSA S806-02. A conventional reinforcing steel bar and two types of glass-fiber-reinforced plastic (GFRP) bars were embedded in concrete and tested under four different loading patterns. The bond strength–slip curves of the bars were obtained and analyzed. The results showed that the maximum bond strengths under the repeated loads differed from those obtained under monotonic ones. In addition, noticeable differences in degradation of the bond strength with respect to the magnitude of slip were observed between the different bar types tested. On the basis of an image analysis of failure surfaces, they were attributed to the different bond failure mechanisms associated with the steel and GFRP bars.     

Behavior of Adhesively Bonded Concrete-CFRP Joints at Low and High Temperatures

This paper presents an evaluation of the results obtained from an initial study carried out at the IBMB, Technical University of Braunschweig, on the influence of temperature on adhesively bonded plate-concrete joint systems. The results of a theoretical model are also presented. The type of specimen used in this study is a three-point bending beam. The concrete specimens were prismatic in form, 100 × 100 × 700 mm without an internal steel reinforcement, strengthened at the intradoss with two types of UD CFRP lamina 20 mm wide and 590 mm long of thickness 1.4 mm for the E = 300 GPa type and 1.24 mm for the E = 175 GPa type. The plate-bonded specimens were designed to produce bending failure under a load, by not bonding the lamina and the concrete around the midspan of the specimens. The specimens were tested to failure at –100°, –30°, and +40°C after an approximately homogeneous temperature distribution within the concrete specimen has been reached. For comparison only, specimens of the same type were tested to failure at room temperature. The results obtained showed varying behavior of the bonded plate-concrete joint depending on variations in temperature. Furthermore, they showed different failure mechanisms. Greater reductions in the ultimate bond force were recorded for the test specimens strengthened with lamina having a high elastic modulus. A reasonable correlation was found between the experimental and theoretical results.     

Load-deflection analysis of concrete elements reinforced with FRP rebars

The behavior of fiber reinforced plastic (FRP) concrete elements under service conditions is analyzed. Taking into account the real constitutive law of materials and local bond-slip law which adequately describes the interaction between the FRP reinforcement and concrete, a numerical procedure is proposed for obtaining moment-curvature relationships for a cracked beam element. Using the moment-curvature laws, the load-deflection analysis of FRP concrete beams is carried out. To study the influence of geometric and mechanical parameters, a numerical investigation was carried out and the results obtained were compared with those from other methods and Codes. The results of the experimental investigation are described and compared with those of the proposed procedure; the comparison shows good agreement between the theoretical and experimental results.     

Partially connected composite beams

Analytical solutions to some boundary value problems for a steel-concrete composite beam with deformable shear connectors in the elastic range are presented. The obtained results show that the distribution of slip on the bond interface between the concrete slab and the steel girder is not a monotone function, even in the case of uniform loading on the composite beam. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)