径向基神经网络GPS高程转换方法

针对GPS高程转换问题,给出了基于径向基神经网络转换GPS高程的模型。用实际观测数据对该模型进行了试验,结果表明,用径向基神经网络转换GPS高程精度高于二次拟合法和BP神经网络法。径向基神经网络能够有效克服BP神经网络局部极小值的缺点,并且具有较高的收敛速度,在GPS高程转换方面具有广阔应用前景。     

水工地下大洞径断面开挖轮廓线监理检测

隧洞断面开挖放样是直接为施工服务的,而检测工作是监理人员必须的工作。监理人员结合测量仪器和计算工具,依据具体的施工图纸进行隧洞断面开挖检测验收,检查开挖断面尺寸,核定超挖部分回填混凝土量。本文就海原县石峡口水库水工建筑物地下大洞径隧洞断面开挖后的检测计算方法作了论述,找出了解决该问题的办法,希望为类似工程监理及施工工作起到抛砖引玉的作用。     

Coupled wellbore erosion and stability analysis

This paper extends earlier work on sand erosion and presents an attempt to couple sand erosion to mechanical damage of rock around a wellbore. Porosity which evolves in time and space as surface erosion progresses, is chosen as the coupling parameter. Both rock elasticity and strength (cohesion) are assumed to depend on porosity in such a way that the material becomes weaker with increasing porosity. The mathematical model, consists of erosion equations, mixture flow equations and stress equilibrium equations, is solved numerically by Galerkin finite element method. Numerical results suggest that erosion, resulting in sand production, is high close to the free surface. Erosion is accompained by changes in porosity and a significant permeability increase. Erosion in the vicinity of the wellbore induces alterations in the mechanical behaviour of the medium. Weakening of rock stiffness leads to severe alteration of both effective stresses and pore pressure near the cavity. Since cohesion decreases with increasing porosity, one can also identify the time instant at which rock mechanical failure starts. © 1998 John Wiley & Sons, Ltd.     

CALCULATING THE DYNAMIC STIFFNESS MATRIX OF 2-D FOUNDATIONS BY DISCRETE WAVE NUMBER INDIRECT BOUNDARY ELEMENT METHODS

Apart from some special cases, calculating the dynamic stiffness matrix of foundations on a layered half-space, especially for embedded foundations, is computationally expensive. An efficient method for two-dimensional foundations in a horizontally layered soil media is presented in this paper. This method is based on indirect boundary element methods and uses discrete wave number solution methods for calculating Green's functions for displacements and analytical methods for the integrations over the boundary. For surface foundations, the present method applies at all frequencies. For embedded foundations or for constructing energy transmitting boundaries, because the free-field part is modelled by boundary elements and the excavated part is modelled by finite elements, the present method applies only at low frequencies for the spring coefficients (the real parts of the dynamic stiffness matrix) but applies at all frequencies for the damping coefficients (the imaginary part of the dynamic stiffness matrix) for undamped sites. The novelty of the method can be used for three-dimensional foundations. © 1997 by John Wiley & Sons, Ltd.     

Spring-dashpot-mass models for foundation vibrations

The foundation on deformable soil, which, in general, radiates energy, can be represented in structural dynamics as a simple spring-dashpot-mass model with frequency-independent coefficients. For the two limiting cases of a site, the homogeneous half-space and the homogeneous layer fixed at its base, the coefficients are specified in tables for varying parameters such as ratios of dimensions and Poisson's ratio. Rigid foundations on the surface and with embedment are considered for all translational and rotational motions. In a practical analysis of soil–structure interaction this dynamic model of the foundation is coupled directly to that of the structure, whereby a standard dynamics program is used. © 1997 by John Wiley & Sons, Ltd.     

Seismic behaviour of confined masonry walls

The results of tests of plain and confined masonry walls with h/l ratio equal to 1·5, made at 1:5 scale, have been used to develop a rational method for modelling the seismic behaviour of confined masonry walls. A trilinear model of lateral resistance–displacement envelope curve has been proposed, where the resistance is calculated as a combination of the shear resistance of the plain masonry wall panel and dowel effect of the tie-columns’ reinforcement. Lateral stiffness, however, is modelled as a function of the initial effective stiffness and damage, occurring to the panel at characteristic limit states. Good correlation between the predicted and experimental envelopes has been obtained in the particular case studied. The method has been also verified for the case of prototype confined masonry walls with h/l ratio equal to 1·0. Good correlation between the predicted and experimental values of lateral resistance indicates the general validity of the proposed method. © 1997 John Wiley & Sons, Ltd.     

任意刚性基础竖向动阻抗的简化计算

对于均质弹性半空间上的任意形状的刚性明置和埋置基础,其动刚度和阻尼系数的确定,已有很多这方面的研究。通常基础的任意形状用其外包的规则几何形状代替原有的不规则基础形状,以达到确定动刚度和阻尼系数的目的,而且这两个参数的确定仅仅是对单独刚性基础的,无法考虑相邻基础对其产生的影响。针对上述两方面不完善之处作了进一步探讨,引入相邻基础动力相互作用因子的概念,并利用地基为平面应变假定以求之。推荐的方法经验证,非常准确。     

带双腹板顶底角钢连接初始刚度研究

初始连接刚度在节点刚度分类和钢结构地震分析中占有很重要的地位,因此研究连接的初始刚度很有现实意义。主要研究带双腹板顶底角钢连接初始刚度的确定方法以及影响其性能的主要因素。     

盾构隧道下穿管道施工引起的管-土相互作用研究

采用Loganathan公式研究了盾构隧道下穿管道施工引起的地下管道处土体竖向位移,利用考虑土中剪力传递的Pasternak模型模拟管-土相互作用,运用修正Vlasov模型中的迭代流程计算出Pasternak模型的关键参数——弹性系数k与剪切系数gs。将计算结果与已有文献结果及工程监测数据进行对比,深入分析了迭代求解k、gs值的Pasternak模型与传统模型的计算差异,并进一步研究了土中剪力、管道与隧道的夹角、土体弹性模量及隧道半径的变化对管-土相互作用的影响。研究结果表明：迭代求解的k、gs值能提升Pasternak模型的精确度;土中剪力对管道竖向位移计算值的影响可达15.3%;随着管道与隧道夹角的减小,管道的竖向位移增大、弯矩减小;土体弹性模量与隧道半径的增大均会增加管道的竖向位移和弯矩。     

考虑尺寸效应的近海桥梁天然橡胶隔震支座力学性能老化时变规律研究

目前天然橡胶支座（NRB）的性能研究大多未考虑尺寸效应,在前期开展的近海桥梁隔震支座和材料老化时变规律研究的基础上,同时考虑支座直径尺寸变化和老化作用时间的影响对NRB的性能进行研究。首先采用ABAQUS有限元软件对不同直径尺寸NRB的性能进行分析,得到了NRB性能随直径尺寸的变化规律;然后结合前期老化作用对NRB及其橡胶材料性能时变规律的影响研究成果,分析了直径尺寸及老化作用时间共同作用下,NRB性能的变化规律,并通过ABAQUS有限元分析,验证了该变化规律的准确性。结果表明:NRB的水平刚度和竖向刚度均随其直径尺寸的增大呈正比例增大趋势;NRB水平刚度比和竖向刚度比均随老化作用时间的增长呈线性增大趋势;且直径为150mm的NRB在实际环境老化60a后,其水平刚度和竖向刚度的增长幅度分别为:30.8%和16.41%,由此可见老化作用时间对NRB水平刚度的影响较显著,对其竖向刚度的影响较小。研究内容可为隔震桥梁结构中支座缩尺模型试验的相关设计提供参考,并为将实验室缩尺橡胶隔震支座的相关成果较好地应用于实际工程计算及设计中提供依据。