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1.
混凝土灌注桩中混含硫酸盐的时变分布规律 总被引：2，自引：0，他引：2
硫酸盐环境下,为模拟混凝土灌注桩施工时混入的硫酸盐在桩中的时变分布行为,基于Fick第二定律并结合初始条件与边界条件,应用分离变量法,建立硫酸盐在桩中的时变分布模型。通过算例将本文解与传统解进行比较,并进一步探讨了硫酸盐扩散分布的影响因素和影响规律。结果表明,传统解用于分析混凝土灌注桩桩中硫酸盐扩散有局限性,而本文解相对于传统解具有一定的优势。混凝土灌注桩半径越小,应用传统解分析灌注桩中硫酸盐时变分布误差较大,同时,误差随时间增大。硫酸盐在混凝土灌注桩中的时变分布呈沙漏形,沿半径方向x=0处和桩表面处扩散行为明显,在x=0处附近区域,初始第一年扩散速率较快,在后续的50 a内扩散速率显著减小,但每10 a的平均速率基本相同。扩散系数和初始浓度梯度对硫酸盐在混凝土灌注桩中的时变分布影响较大。 相似文献
2.
Defects detection in the inner surface of pipes based on inverse heat conduction problem 总被引：1，自引：0，他引：1
It is a typical ill posed inverse heat conduction problem to estimate the geometry boundary of the inner surface of pipe by the temperature of outer surface. With the establishment of a two dimensional steady model for pipe with irregular inner surface, the inverse problem is transformed into a direct problem and an optimization problem. Based on the temperature at the outer surface obtained from the infrared thermography and the variation of the object function, the conjugate gradient method (CGM) is introduced into the geometry problem. With the numerical analysis of three typical defects, the effects of the measurement errors, choice of the initial value, boundary conditions and number of discrete temperature points are discussed and the proposed methodology is approved. 相似文献
3.
Considering the three-dimensional inhomogeneity of soil surrounding the pile, the response of non-uniform viscoelastic pile under axial dynamic loading is studied. Firstly, combining the boundary condition, the complex stiffness of axial different soil layers are obtained by the complex stiffness transfer model of radial multi-zone plane strain. Then, the analytical solution of dynamic response at pile top in frequency domain is proposed by solving the dynamic equation of non-uniform viscoelastic pile section one by one from the bottom up to the top, and the relevant semi-analytical solution response in time domain is adopted by the convolution theorem and the Inverse Fourier Transform. At last, the effect of parameters of pile and soil are investigated to get the nature of the dynamic response of pile top in frequency domain and time domain. 相似文献
4.
The Fick diffusion equation is widely used to describe mass transfer in a particlea droplet or a liquid layer in a chemical reactorwhere the definition domain of the diffusive equation is limitedbecause it is decided by the scale of those particles or droplets.The diffusive equation with a definition domain of certain length has no analytic solutions unless the series solution.Soto obtain approximate solutions of a diffusive equation is of theoretical and practical significance.After an assumption of constant concentration variance ratio is made and substituted for the presumption of constant concentration frequently used in kinetics of multi-phase reactiona detail process to deal with diffusion equation based on steady state approximation is givenand the approximate solutions of the diffusive equation with the second boundary condition and the third boundary condition are obtained in the meantime.The method to deal with diffusion equation by steady state approximation may be applied to many fields in engineering. 相似文献
5.
To investigate the effect of consolidation soft soil, three groups of model tests were designed. The first group was PVC pile-net composite foundation, the second was pile-cap-net composite foundation, and the third was PVC and sand pile composite foundation. Butter was coated and plastic membrane was covered on inner side wall of model cast to reduce border effect. The gauges were glued with epoxy on the surface of the model with PVC piles and geogrids to measure the stress of PVC piles and geogrids. Soil pressure cells were installed in the middle of piles and the top of the sand piles, and dial indicators were installed in the middle of road and road shoulder to measure deformations. It is that shown: 1) as for the distribution of the road settlement and the differential settlement, the settlements of the third group are the largest and those of the second group are the least; 2) in terms of the stress ratio of PVC pile and soil, the values of the first group and the third group are similar, while the value of the second group is much larger; 3) the change of geogrid strain is disorderly. There are periodic peaks in the strain of geogrid of pile top and periodic troughs in the soil between the piles. The geogrid strain of the second group measured in the corresponding spot is much larger than those of the other two groups. The results of three groups of tests illustrate that if the condition is permitted, it would be the best to adopt the scheme of pile-cap-net composite foundation, which has better reinforcement effect for soft soil. 相似文献
6.
Based on the technique proposed by Muki & Sternberg, a rigorous analytical method for calculating the interaction factor between two piles with different lengths, diameters and properties is presented. The pile group in layered soils is calculated by using the principle of superposition. The validity of the presented method has been verified through comparing with those from other existing solutions. A parametric analysis is made to study the pile group settlement and the loads shared by the individual pile. The proposed interaction factors of pile-pile can consider the strengthening effect of intervening piles. The proposed method can be used to analyze the large pile group. 相似文献
7.
The direct boundary integral equation of two-dimensional Laplace equation for Dirichlet problem is(con-sidered).It is deduced by Green's formula and the fundamental solution.The most-used numerical method for solving(direct) boundary integral equation is collocation method,and seldom have been used the Galerkin scheme in this case.The direct boundary integral eqution is changed into the variational eqution.Using linear element,it is solved by Galerkin boundary method.In the variational eqution double integrations shall be carried out.The paper presents the analytical formula to calculate the inner integration and the Gaussian quadrature is used for the outer integration. The numerical experimentation proved thefaesibility and the efficiency. 相似文献
8.
钢管混凝土FRP混凝土（SCFC）组合柱是新近提出的一种新型组合柱形式。提出考虑外钢管与FRP的双重约束效果,采用双剪统一理论分析了SCFC组合柱外钢管、外层混凝土、FRP管以及内层混凝土的应力状态,根据静力平衡条件得到了SCFC组合柱的轴压承载力计算公式,其与试验结果能够较好吻合。分析了含钢率、FRP与钢的相对配置率、FRP径厚比以及FRP管直径对轴压承载力提高系数的影响,结果表明：随着含钢率的增加、FRP与钢的相对配置率的提高以及FRP径厚比的减小,SCFC组合柱轴压承载力提高系数都有一定程度提高;内FRP管直径与外钢管边长之比在0.65~0.75之间时,轴压承载力增益效果较好。 相似文献
9.
Influence of Pile Driving on Soil Resistance in Clay 总被引：1，自引：0，他引：1
With the increase of platform size, pipe piles with super large diameter and deep penetration are increasingly used in practice. In order to make accurate prediction of pile drivability, it is essential to evaluate the change of the soil properties under pile driving exactly, and it is the premise to predict the pile bearing capacity after pile driving. In order to learn more about the change of clay properties during pile driving, analysis on the pile driving record of 36 piles in Bohai area is conducted. According to the analysis, the soil resistance in the clay layers decreases as the depth increases, and it is very different from that in the sand layer. The FEM method is used to discuss the mechanism of this decrease. The back analysis is carried out to get more information. The results show that the clay properties are affected by the dynamic effect. The undrained shear strength of clay approximately decreases with the increase of thickness of the layer linearly. At the same time, a prediction is conducted based on results, and the result is closer to the pile driving record than that calculated by method normally used today. 相似文献
10.
The process of chloride diffusion in concrete is time-dependent.The boundary element method (BEM) with a time-dependent diffusion coefficient is presented for chloride diffusion in concrete based on the suitable transformation of variables.The fundamental solution of the partial differential equation for time-dependent chloride diffusion in concrete is developed,and the compensation length of the diffusion field is defined as well as the compensation coefficient.The scheme of BEM with a time-dependent diffusion coefficient is developed.Two examples are given to demonstrate the accuracy and efficiency of the presented method and the rationality and the importance of the compensation length for the method. 相似文献
11.
考虑桩基的剪切变形影响,利用单广义位移深梁理论,建立了桩基m法的计算方法,导出了水平位移、转角、弯矩和剪力的初参数表达式和无量纲参数函数的统一表达式,根据桩底边界条件建立了初参数解的计算公式;给出了无量纲参数函数随换算深度和弯剪刚度比的变化图形。研究表明,换算深度小于3.0时,弯剪刚度比对无量纲参数函数影响较小,换算深度大于4.0时,弯剪刚度比对无量纲参数函数影响的趋势非常明显,桩基剪切变形的影响程度与桩的边界条件有关。算例结果表明,桩身的剪切变形有增大桩顶水平位移、提高弯矩零点位置、改变弯矩分布特征、扩大桩侧土压力大小等影响。 相似文献
12.
结合检测工况对测试数据的影响,对自平衡“精确转换法”进行改进,提出摩擦桩位移协调转换法和嵌岩桩的荷载协调转换法,实际应用结果说明两种转换方法合理。所得测试结果表明湄公河大桥桩基承载力符合设计要求;分析湄公河大桥试桩的侧摩阻力和端承力分布,嵌岩桩和摩擦桩纵向承载均以侧阻力为主。 相似文献
13.
Based on Biot's theory, the longitudinal vibrations of a single pile in saturated viscoelastic soil are investigated in the frequency domain subject to the harmonic load. By the Novak plane strain model, the control equations for the saturated viscoelastic soil are derived. Regarding the pile as the one-dimensional rod model, the vibration equation of the pile is established. Based on the continuity conditions of the pile and soil, the dynamic stiffness and dynamic damping of the pile top are obtained. It is compared with the solution for Novak, and the influence of different physical parameters of the pile and soil on the longitudinal vibrations of the soil and pile system is examined. It is shown that the dynamic characteristics of the pile in the dry soil as well as the saturated soil have some differences; the resonance effect of dynamic stiffness factor and equivalent damping is obvious weakening with the increase of the ratio of the length to radius of the pile. The resonance effect and natural frequency are increasing when the modulus ratio of the pile to soil increases; the interaction coefficient of the flow-solid and the damping ratio of soil skeleton have few influences on the responses. 相似文献
14.
enhanced pipe piles are made by centrifugal rotation and steam curing under high temperature, so it is very difficult to embed concrete strain gauges during making piles. A new method is used to embed concrete strain gauges in piles. Based on the static loading tests on enhanced pipe piles, the load transferring mechanism of enhanced pipe piles is studied through analysing axial load distribution, behaviors of skin resistance and base resistance of piles, and load sharing of rims of enhanced pipe piles. Experimental results show that when axial load acts on the top of enhanced pipe piles, the upper rims of enhanced pipe piles act on skin resistance of piles before the lower rims do, and the rims of enhanced pipe piles remarkably reinforce skin resistance of piles. 相似文献
15.
R. S. Kanwar 《Journal of Agronomy and Crop Science》1986,156(2):101-109
Analytical solutions were developed to describe the nonsteady-state transport of oxygen from the atmosphere into the soil media. These analyses are based on diffusion theory for oxygen diffusion in soils when oxygen is being consumed, either at a constant rate or consumption rate varies with time due to the biological and chemical processes occurring continuously in the soil media. The transport equations, and the initial and boundary conditions are set up to represent a field situation. Analytical solutions are obtained to calculate transient oxygen concentrations in the soil profile. The quantity of oxygen that might diffuse into the soil from atmosphere at any time, t, also can be found by using this method. Comparison with published data is made, and reasonably good agreement is obtained between oxygen concentrations at different depths and times computed from the analytical solutions and those actually measured. 相似文献
16.
为了准确评估带裂缝工作混凝土结构的耐久性能,针对氯离子在带裂缝混凝土中的扩散过程进行研究。提出了无损制备裂缝的方法,可高效易行地在混凝土侧面及内部产生裂缝。对带裂缝的水泥砂浆试件进行氯盐溶液浸泡试验,深入研究了单缝和双缝试件中氯离子的扩散作用,修正了氯离子的扩散系数,并对带裂缝混凝土的氯离子扩散过程进行了数值模拟。研究结果表明：氯离子会沿裂缝发展方向及垂直于裂缝发展方向扩散,随着水灰比的减小,砂浆试件的抗氯离子扩散性能明显提高,在一定范围内,当裂缝间距增大,双缝间的氯离子扩散交互影响作用明显减小,ANSYS软件的模拟结果与试验数据吻合良好。 相似文献
17.
Immersion in sodium chloride solution was adopted to periodically test chloride ion concentration at the surface of concrete and regression analysis was completed.And time dependent law of surface chloride ion concentration of concrete with time was investigated.Influences of sodium chloride solution concentration, water to cement ratio and fly ash content on size and accumulation rate of surface chloride ion concentration were also analyzed.It is found that surface chloride ion concentration gradually grows with the of time increase the of time and reaches a steady state finally.With the increase of sodium chloride solution concentration, surface chloride ion concentration reaches the steady state more quickly and then increases numerically.Bigger water to cement ratio means quicker accumulation of surface chloride ion concentration and greater surface chloride ion concentration.Fly ash replacement could fasten accumulation of surface chloride ion concentration and surface chloride ion concentration increases with the increase of fly ash content.An improved model was proposed by comparison and correction of current models. 相似文献
18.
The mechanism for chloride penetration in cracked concrete and its major impact factors were analyzed. As a result, a revised chloride diffusion model based on Fick's Law was built by dual porous medium model. Then several cracked reinforced concrete beams self-anchored with sustained flexural loads were immersed in the 5% NaCl solution with the condition of dry-wet cycles. After 15 times of dry-wet cycles, the rapid chloride testing (RCT) was used for the determination of chloride ion content of the powder at each cracked sections. The test results show that: 1) with the condition of dry-wet cycles, the chloride content will occur a peak in the surface 20mm concrete, so the depth for surface convection zone can be assumed to be 15~20 mm; 2) when the crack width is less than 0.3mm, the equivalent chloride diffusion coefficient increases steadily, which agrees well with model's prediction; when the crack width is larger than 0.3mm, the equivalent chloride diffusion coefficient augments rapidly and influence of convection on chloride penetration becomes more significant; 3) the deterioration factor for equivalent chloride diffusion coefficient in flexural cracked concrete is directly correlative with crack width, which can be expressed by second order power function or separate function. 相似文献
19.
A non-destructive method of evaluation of specific crack area was used to characterise microcracking in concrete prisms during uniaxial compression loading and unloading. Chloride profiles were also measured after the same concretes were exposed to chloride environment. The relation among microcracking, stress-strength ratio and chloride penetration of concrete were analysed based on the experimental results. Under compressive load, the apparent chloride diffusion coefficient decreases until about one third of the ultimate load. Further increase of compressive load improves the chloride diffusion coefficient again. There is a close link between microcracking and stress-strength ratio. The index of specific crack area can be used to indicate the microcracking and study chloride transport behaviour into concrete under the influence of microcracking. 相似文献
20.
Zeng Xin Xin Mingdao 《保鲜与加工》1991,(6):8-14
An implicit enthalpy solution is developed for analysis of one-dimensional conduction controlled phase change problems. The solution is based on separating the sensible and latent heat terms in an enthalpy formulation. By making the assumption of equal volume node-jumping,a variable time together with a fixed space grid is used to ensure that the phase boundary is always on a node point,so that the nonlinearity associated with the latent heat can be effectively dealt with via the source term. A freezing problem around a pipe with analytical solution is applied to demonstrate the effect of the present method. 相似文献