Predicting the Maximum Load of Reinforced-Concrete Pipe Columns

To simplify the calculation of the maximum load at which instability occurs for reinforced-concrete pipe columns under eccentric compression, a method based on the transformed cross-sectional area of the column and the concrete secant modulus of elasticity is proposed, consisting of an iterative process in which a sequence of lateral deflections is at column mid-height. The method assumes the deflected shape of the column as a half cosine wave. Analytical results were compared with experimental values obtained from 16 reinforced-concrete pipe columns. Using deflection at column mid-height recorded during the loading process, a typical load-deflection curve can be plotted and used to describe column behavior. The experimental results demonstrate that the failure of concrete columns is a process. The starting point is the cracking load point, when cracks are initiated in the concrete of the tensile zone of the critical cross-section of specimens. The maximum load point is the top of the failure process, and then the maximum bending moment occurs. The first point represents instability while the second one corresponds to the strength failure of the columns. The experimental results are close to the analytical values. The method is simple and can be used for stability analysis of reinforced-concrete pipe columns.     

A Method to Identify Flight Obstacles on Digital Surface Model

In modern low-altitude terrain-following guidance, a constructing method of the digital surface model (DSM) is presented in the paper to reduce the threat to flying vehicles of tall surface features for safef light. The relationship between an isolated obstacle size and the intervals of vertical- and cross-section in the DSM model is established. The definition and classification of isolated obstacles are proposed, and a method for determining such isolated obstacles in the DSM model is given. The simulation of a typical urban district shows that when the vertical- and cross-section DSM intervals are between 3 m and 25 m, the threat to terrain-following flight at low-altitude is reduced greatly, and the amount of data required by the DSM model for monitoring in real time a flying vehicle is also smaller. Experiments show that the optimal results are for an interval of 12.5 m in the vertical- and cross-sections in the DSM model, with a 1:10 000 DSM scale grade.     

Large Scale Analysis of Mechanical Properties in 3-D Fiber-Reinforced Composites Using a New Fast Multipole Boundary Element Method

Fiber-reinforced composites are commonly used in various engineering applications. The mechanical properties of such composites depend strongly on micro-structural parameters. This paper presents a new boundary element method (BEM) for numerical analysis of the mechanical properties of 3-D fiber-reinforced composites. Acceleration of the BEM is achieved by means of a fast multipole method (FMM), in allowing large scale simulations of a finite elastic domain containing up to 100 elastic fibers to be performed on one personal computer. The maximum number of degrees of freedom can reach a value of over 250 000. The effects of several key micro-structural parameters on the local stress fields and on the effective elastic moduli of fiber-reinforced composites are evaluated. The numerical results are compared with analytical predictions and good agreement is observed. The results show that the fast multipole BEM could be a prom- ising tool for further understanding of the mechanical behavior of such composites.     

Analytical Solution to the Density-Gradient Equation for MOS Quantum Tunneling

Engineering-oriented simulations of quantum mechanical tunneling are often based on density-gradient(DG) theory.This paper presents an analytical solution to the DG equation for quantum tunneling through an ultra-thin oxide in a MOS capacitor with an n+ poly-silicon gate obtained using the method of matched asymptotic expansions.Tunneling boundary conditions extend the approximation into the entire region of the poly-silicon gate,oxide barrier,and substrate.An analytical solution in the form of an asymptotic series is obtained in each region by treating each part of the domain as a separate singular perturbation problem.The solutions are then combined through ’matching’ to obtain an approximate solution for the whole domain.Analytical formulae are given for the electrostatic potential and the electron density profiles.The results capture the features of the quantum effects which are quite different from classical physics predictions.The analytical results compare well with exact numerical solutions over a broad range of voltages and different oxide thicknesses.The analytical results predict the enhancement of the quantum tunneling effect as the oxide thickness is reduced.     

Integral computation relating to rational curves based on approximate degree reduction

A new algorithm is presented for computing the volume of revolution, moment of area and centroid etc. , which are related to the integration of rational curves. In this algorithm rational curve with high degree is firstly approximated by those with lower degree through endpoint interpolation. And finally the closed form integration solution is derived for quadratic rational curve. The diminishing rate of the minimum norm of the perturbation vector needed by degree reduction is 0(2" ") when the interval is subdivided at the midpoint. Combining the subdivision with the degree reduction, we can obtain a faster convergence of integration approximation. A series of integral error bound functions which are fairly simple to compute are derived. The examples given in this paper show that this algorithm is a simple and time-saving method in computing with small tolerance.     

A new simulated annealing method of designing NMR biplanar shim coils

A new SA (simulated annealing) method is presented for the design of longitudinal shim coils for NMR (nuclear magnetic resonance) equipment. First, AGL (adaptive Gauss-Lobatto) quadrature used by the traditional SA method is analyzed. Two kinds of complete elliptic integrals are introduced to integrate the spatial magnetic field, which increases the computing speed by 13.3 times. Then, the system energy calculation is extended to the field of the z-axis. The results illustrate that the coil-set efficiency designed by the new SA method is 15% higher than that of the traditional one, and the field inhomogeneity is reduced from 1.20% to 0.49%. Finally, a prototype of coil assembly for NMR rock-core analyzer is built, and the experimental results are in good agreement with the theoretically calculated results.     

A Numerical Method for Cavity Identification in Beams on an Elastic Foundation

An analytical solution for the natural frequencies of a beam containing a cavity on an elastic foundation is presented. Based on the analytical solution, a numerical method for identifying cavities in the foundation is developed. The position and size of the cavities are identified by minimizing an objective function, which is formulated according to the difference between the computed and measured natural frequencies of the system. The conjugate gradient algorithm is adopted for minimizing the objective function. Some numerical examples are presented to demonstrate the applicability of the presented cavity determination method. The results show that the presented method can be used to identify the cavity position and size conveniently and efficiently.     

Calculation of Random Response Spectral Moments of Elastic-viscoelastic Combined Systems

In random vibration analysis, the importance of spectral moments of the response stems from their relevance to system performance prediction. Usually, spectral moments are obtained by the frequency domain method. In present paper, the random response spectral moments of elastic-viscoelastic combined systems are calculated by complex modal analysis in the time domain. The analytical form results are obtained for random response spectral moments of an elastic-viscoelastic combined system to a stationary white noise excitation. The method presented is simple and easy to apply. It is hoped that this study would pave a way for the analysis of reliability of elastic-viscoelastic combined systems subjected to random excitations.     

A liquid helium temperature target with a 10 K vapor shield for shock compression experiment in the environment condition of 100 Pa

The shock compression experiment of liquid helium is an available way to gain properties of specimen at high temperatures and pressures.Based on Fluent,a thermal insulation analysis and design of a liquid helium temperature target in the environment condition of 100 Pa for shock compression experiment is performed.Then,a cryogenic target with a 10 K helium vapor shield and a separated vacuum interval is particularly developed.A lowest temperature of 3.63 K and a stable temperature of 3.70 K in the specimen cavity with an accuracy of 0.1 K are obtained by means of continuous flow and vacuum cooling.Both time-consuming and temperature stability are well-suited to the requirements of the shock compression experiment.The results show that the calculated and experimental data well-matched each other.The simulation method may be effective and feasible for the optimal design of the cryogenic target.     

An element by element spectral element method for elastic wave modeling

The spectral element method which combines the advantages of spectral method with those of finite element method, provides an efficient tool in simulating elastic wave equation in complex medium. Based on weak form of elastodynamic equations, mathematical formulations for Legendre spectral element method are presented. The wave field on an element is discretized using high?order Lagrange interpolation, and integration over the element is accomplished based upon the Gauss?Lobatto?Legendre integration rule. This results in a diagonal mass matrix which leads to a greatly simplified algorithm. In addition, the element by element technique is introduced in our method to reduce the memory sizes and improve the computation efficiency. Finally, some numerical examples are presented to demonstrate the spectral accuracy and the efficiency. Because of combinations of the finite element scheme and spectral algorithms, this method can be used for complex models, including free surface boundaries and strong heterogeneity.     

双向偏压剪反复扭构件抗震性能试验研究

通过对 8根承受双向偏压力、剪力作用的钢筋混凝土柱在低周反复扭矩作用下的抗震性能试验 ,对钢筋混凝土复合受扭构件的破坏形态、滞回曲线、延性及耗能、承载力、刚度及滞回阻尼等特性以及轴压比、相对偏心距对它们的影响进行了分析 .并通过空间变角桁架理论推导出扭矩、轴压力、双向弯矩和双向剪力间的承载力相关公式 ,最后通过相关公式和试验结果拟合出极限扭矩实用计算公式 .分析表明公式计算值与试验值符合较好     

偏心构件受压计算分析

采用有限元法对钢筋混凝土偏心受压构件进行内力分析,通过算例对双向偏心受压和单向偏心受压两种计算方法进行了比较,并得出相应结论。     

外包钢管加固钢筋混凝土柱承载力试验研究

对利用外包钢管加固的钢筋混凝土柱承载力进行试验研究,测定了不同加固方法对其承载力的影响。试验和理论结果表明,外包钢管加固钢筋混凝土柱能够充分利用两种组成材料的受力性能,在截面面积增大不多的情况下大幅提高柱的承载能力。并提出其轴心受压和偏心受压的承载力经验公式。研究成果可为工程应用提供参考。     

钢筋混凝土L形截面柱曲率延性的研究

钢筋混凝土L形截面柱在不同荷载角下的力学性能差别很大，工程实践中应给予足够的重视。在充分考虑荷载角对L形截面柱曲率延性影响的基础上，提出两种曲率延性的概念。通过对10800根L形截面柱的曲率延性进行计算机模拟计算，分析了中和轴角、轴压比、混凝土强度、纵筋强度、体积配箍率、肢高肢厚比以及不等肢长等各种参数对其曲率延性影响，得出各因素对曲率延性的影响规律，建立了中和轴角曲率延性和荷载轴角曲率延性的计算公式，以供结构设计和工程实践参考。     

双向水平荷载作用下钢筋混凝土柱全过程分析

提出了一种用钢筋和混凝土单轴应力－应关系计算任意加载路径下钢筋混凝土柱荷载－位移关系的理论计算方法。其中考虑了钢筋的滑移变形和混凝土的塑性变形。通过对不同加载路径的９根试验进行试算，计算结果与试验结果吻合较好，表明本计算方法在实际应用中是可行的。     

基于损伤本构关系的钢筋混凝土双向压弯截面分析

基于混凝土材料的损伤本构关系和平截面假设，推导出钢筋混凝土双向压弯截面刚度矩阵的计算公式．为研究混凝土损伤本构关系对截面分析的影响，用推导的截面刚度矩阵进行钢筋混凝土双向压弯截面分析，理论结果与试验数据进行比较，二者吻合较好；并与用我国混凝土结构设计规范中的混凝土非线性分析本构关系分析的计算结果比较，二者计算结果相符．表明本文方法计算可行，并通过本文方法计算结果可以了解、评估结构内部的损伤分布情况．     

异形柱轴压比限值的简化计算方法

已往异形柱轴压比限值的计算均采用网格法进行截面积分.由于不规则截面不易划分网格,为此,文中提出一种截面不需划分网格计算异形柱轴压比限值的简化计算方法.基于平截面假设,采用一种新的简便的截面高斯积分法,对钢筋混凝土异形截面柱轴压比限值进行数值分析,并编制了相应的计算程序.将理论分析与其他文献分析结果比较,发现吻合较好.该简化计算方法无需迭代,计算简便直接.     

基于偏心距随机特性的混凝土偏心受压构件可靠度分析

现行规范在分析混凝土偏心受压构件时，对因轴力效应比值和弯矩效应比值不同而引起的偏心距随机特性考虑较少．针对此不足，在分析偏心距函数的变化规律的基础上．通过抽样统计得到偏心距的随机特性，然后完整考虑这些随机特性。采用Monte Carlo方法计算了大小偏心受压构件在不同荷载效应比值下的可靠度．计算结果表明，该方法能更加合理地反映出偏心受压构件的可靠度水平．     

带约束拉杆矩形钢管混凝土短柱延性计算

采用带约束拉杆矩形钢管混凝土的本构关系,建立了基于纤维模型法的模拟带约束拉杆矩形钢管混凝土短柱承载力-变形全过程曲线的非线性分析方法,计算结果与试验结果吻合良好。对带约束拉杆矩形钢管混凝土偏压短柱进行参数分析,回归了带约束拉杆矩形钢管混凝土短柱单向和双向偏压曲率延性系数的简化计算公式,公式的计算精度高,形式简单。     

带约束拉杆方形钢管混凝土短柱延性计算

采用带约束拉杆方形钢管混凝土的本构关系,建立了基于纤维模型法的模拟带约束拉杆方形钢管混凝土短柱承载力-变形全过程曲线的非线性分析方法,计算结果与试验结果吻合良好.利用经试验验证的计算程序对带约束拉杆方形钢管混凝土短柱的单向和双向偏压延性进行较系统的参数分析,回归了带约束拉杆方形钢管混凝土单向和双向偏压延性简化计算公式,公式的计算精度高,形式简单.