共查询到20条相似文献，搜索用时 15 毫秒
1.
The finite strip method is extended to the free vibration of rectangular plates continuous in one or two directions. A subroutine has been written for the computation of beam functions for continuous beams over any number of intermediate rigid supports and with simply supported or clamped end conditions. The standard finite strip method can thus be applied to plates continuous in both directions using the computed beam functions. The frequencies of 2 × 2 and 3 × 3 continuous panels with many different end conditions have been computed. The computations are also checked against published solutions and the accuracy is shown to be excellent. 相似文献
2.
混凝土桥梁在工作过程中会产生裂缝,为分析移动荷载对开裂混凝土桥梁结构刚度的影响,对开裂梁动力响应进行分析。建立简支T梁桥有限元模型,并将移动荷载施加至有限元模型中。根据简支T梁桥破坏横向分布位置和强度的不同,研究不同工况下各梁荷载横向分布及不同移动速度对裂缝扩展宽度的影响。结果表明,数值模拟结果能较好地验证计算模型的准确性;在较大的移动荷载作用下,混凝土开裂,导致结构刚度减小、位移增大;随着移动荷载和速度的增加,开裂时间增加,结构刚度降低,持续时间增加,位移增大,使结构响应呈现明显非线性。 相似文献
3.
Maria Anna De Rosa 《地震工程与结构动力学》1989,18(3):377-388
The dynamical properties of a foundation beam on a Winkler soil have been recently discussed by using the power series method14 and the finite element method.15, 17 – 19 The first method can be applied only if the Winkler soil is linearly distributed along the whole span: on the contrary, the second method is more general, but it requires considerable computational efforts. In this paper a recently developed discretization method has been shown to be particularly well suited for dynamic analysis of foundation beams, in the presence of second order destabilizing effects. The procedure is based on the Hamilton principle, and the equation of motion is deduced from the corresponding Lagrange equations. According to the proposed method, the structure is reduced to a set of rigid bars, connected together by elastic cells. The convergence of the method is shown to be quite rapid, so that a small number of Lagrangian coordinates has to be introduced, and the resulting eigenvalue problem can be easily solved. Numerical comparisons are also performed with the available data of the literature, and the agreement is shown to be excellent. Two particularly unusual cases are illustrated, in order to emphasize the method's peculiarities. Finally, the influence of the axial forces on the fundamental vibration frequency is discussed, both for conservative and non-conservative forces. 相似文献
4.
总结了6种半主动控制算法,采用黏滞阻尼器,对一座三跨简支梁桥进行了不同地震动输入下的半主动控制地震反应计算分析,比较分析了不同地震动输入和半主动控制算法对简支梁桥地震反应控制效果的影响。结果表明,半主动控制能有效地减小桥梁结构的大部分地震反应,同时可能会放大另外部分地震反应,这与地震动输入密切相关,不同地震动输入下的控制效果各不相同。所提六种半主动控制算法中,算法2、5、6对该简支梁桥地震反应的减震效果相对最好,这与各种算法的阻尼器耗能大小有关。 相似文献
5.
Praveen K. Malhotra 《地震工程与结构动力学》1995,24(12):1591-1607
An approximate method is presented for the analysis of earthquake induced uplifting in base plates of unanchored liquid-storage tanks that are supported directly on flexible soil foundations. The method takes due account of the non-linearities arising from the continuous variation of base contact area, membrane action and plastic yielding in the base plate. First, an ‘exact’ solution is presented for a uniformly loaded flexibly supported prismatic beam, uplifted by a concentrated force applied at one end. A series of such beams are later used in an approximate model of the base plate. The method is highly efficient and believed to be accurate for the level of uplifts encountered in practice. The results are presented for a range of foundation stiffness, representing loose sandy soils to rigid concrete mat. It is shown that, for the same overturning base moment, the flexibly supported tanks, in comparison with the rigidly supported tanks, experience significantly smaller axial compressive stress, but larger base uplift, foundation penetration, plastic rotation at plate boundary and hoop compressive stress in the tank wall. 相似文献
6.
A numerical method is shown to analyse the dynamic elastic-plastic responses of those structures with known elastic solutions. The displacement at one point at time t caused by a unit load applied at another point at zero time, called dynamic influence coefficient, is calculated from the known elastic solutions. Incremental plastic strain is accounted for by a set of additional incremental loads, so the stiffness matrix and the eigenvectors do not vary with time. From the incremental load including that caused by the incremental plastic strain, the displacement vs. time of the structure is obtained. This method is applied to simply supported beams with bilinear stress-strain relations with different strain-hardening rates and to a simply supported elastic-ideally plastic rectangular plate. This procedure can be extended to structures with no available known analytical elastic solutions. For these structures, the elastic solutions can be obtained by the finite element method. 相似文献
7.
A semi-analytical approach for analyzing ground vibrations caused by trains moving over elevated bridges 总被引：3，自引：0，他引：3
A semi-analytic approach is presented for the three-dimensional analysis of ground vibrations induced by trains moving over elevated bridges. The train is modeled as two sets of moving loads, with one for the front wheels and the other for the rear ones, the elevated bridge as a series of elastically supported beams, and the ground as a viscoelastic half space. Three key elements are considered in the solution: (1) the analytic solution for the vibration of an elastically supported beam under a series of moving loads, (2) the impedance of the foundation–soil system, and (3) Green's function for an elastic half space under a harmonic point load. Such an approach allows us to consider the structural dynamics of the elevated bridge, the foundation–soil interaction, and the wave propagation characteristics in the half space. From the numerical examples studied, the proposed approach was demonstrated to be accurate and efficient. The framework of analysis described herein can be generalized to solve problems with complex foundations and layered soils. 相似文献
8.
9.
《Journal of Atmospheric and Solar》2000,62(7):541-552
The purpose of this paper is to discuss the properties of electron beams formed by cyclotron interactions between radiation belt electrons and a quasi-monochromatic whistler wave packet from a ground-based VLF transmitter. The beams are formed due to trapping of the electrons at the forward edge of the wave packet, their acceleration inside the wave packet, the escape of the accelerated electrons from the moving backward edge of the wave packet, and their following free motion in an inhomogeneous magnetic field. A combination of these processes provides the main features of the spatial-temporal evolution of the beams which are investigated both analytically and numerically. It is shown that one or two beams can appear at one point at the same time, and that the density of the beams increases during their expansion. Motion of the pumping wave packet in the inhomogeneous magnetic field provides the variations of the initial velocity and position of the beam injection which change the spatial and temporal gradients of the parallel velocity of the beam, in contrast with the case of the pure adiabatic motion of an individual electron. Such a behaviour can be significant for the generation of secondary emissions. Numerical calculations demonstrate a wide variety of the spatio–temporal patterns of the beam parallel velocity depending on the plasma and wave packet parameters. It is shown that the most significant parameters which determine the beam characteristics are the wave packet length about the equator, its group velocity, and the initial energy and pitch angle of the electrons. 相似文献
10.
This paper addresses the elastic dynamic response of simply supported bridges to ground motion in their transverse direction. The interaction between superstructure and support flexibilities is studied in a systematic manner for symmetric spans. The bridges are modelled as beams with uniformly distributed mass and elasticity, simply supported at the ends by elastic springs. It is shown that a dimensionless stiffness index, which reflects the relative stiffness of the superstructure compared to the stiffness of the substructure, completely defines the dynamic mode shapes of the model. Useful closed‐form expressions, based on approximate shape functions, are derived for the dynamic parameters of the first mode, and their accuracy is assessed. The effect of the stiffness index on these dynamic parameters is investigated. Numerical case studies are presented to illustrate the use of proposed equations in the seismic analysis of bridges. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
11.
It is well known that axial force – bending moment interaction (N–M interaction) affects to a large extent the cyclic inelastic behaviour of structural elements, especially columns in framed structures, with reduction in bending capacity and loss of available ductility. A few studies have also shown that significant inelastic axial shortening affects the response of column elements subjected to medium–high levels of axial loads and cyclic bending. This paper is primarily aimed at evaluating the effects of column N–M interaction on the inelastic seismic response of steel frames. By considering the contemporaneous action of vertical loads, due to gravity, and of horizontal seismic excitation, it is shown that the progressive axial shortening of adjacent columns may differ substantially, thus inducing significant relative settlements at the ends of the connecting beams and, then, remarkable amplifications in beam plastic rotations. An evaluation of additional beam plastic rotations induced by column N–M interaction is carried out for real structures by investigating the inelastic response of steel frames designed according to European standards under horizontal and vertical earthquake excitations. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
12.
Jiahao Lin Guizhen Song Yong Sun F. W. Williams 《Soil Dynamics and Earthquake Engineering》1995,14(4)
In this paper, a direct Ritz method is presented for analysing the responses of non-uniform shear beams subjected to the action of an evolutionary random seismic excitation. Because of the use of a pseudo ground acceleration, time-dependent random responses can conveniently be calculated by solving a set of deterministic equations of motion. These responses include power spectral densities, variances and higher spectral moments of any required responses of the beam. A non-uniform beam example was solved and the time-dependent variances and second spectral moments of both the beam-top displacement and the beam-base shear force are given to show the simplicity and effectiveness of the method, which can also easily be applied to other continuous elastic structures. 相似文献
13.
高温下受弯钢梁的弹塑性弯扭屈曲分析 总被引：1，自引：0，他引：1
基于弹塑性理论,通过建立钢梁截面的弯矩曲率关系作弯矩作用平面内的弹塑性分析等几个步骤,对火灾高温作用下受弯简支钢梁在弹塑性阶段的弯扭屈曲性能变化进行了分析,给出了钢梁的临界屈曲弯矩的计算表达式。通过算例分析了钢梁弹塑性阶段临界屈曲弯矩随温度的变化,并利用ANSYS有限元软件模拟了钢梁在火灾燃烧不同时刻的竖向变形。结果表明,随着温度的升高,钢梁弹塑性阶段的临界弯矩呈现出逐渐降低的趋势,而其竖向变形则逐渐增大,文中对这2个变量在不同温度条件下的具体变化情况分别进行了详细的分析和描述。 相似文献
14.
研究了高强钢绞线网-高性能砂浆加固钢筋混凝土梁的抗低速冲击性能,利用落锤冲击试验法对4根简支钢筋混凝土梁进行对比试验研究,其中1根为普通梁,3根为加固梁,通过分析加固前后梁的破坏形态,结合挠度变化、钢筋的应变以及加速度的时程曲线,对比得到了钢筋混凝土梁加固后的抗冲击性能。研究结果表明：加固后钢筋混凝土梁的抗冲击能力显著提高,钢绞线和砂浆作为外加层,不仅增加了梁的抗弯剪能力和刚度,提高了结构的耗能能力,而且限制了裂缝的发展,使梁的整体性和延性更好;在相同冲击作用下,钢绞线直径的增加能适当提高结构的抗冲击性能。 相似文献
15.
A general method is outlined for the determination of natural frequencies of cylindrical shells with any boundary conditions when the effects of rotatory inertia and transverse shear deformation are included in the analysis. This is applied to cylindrical shells with both ends clamped. It is shown that the inclusion of these effects tends to have a greater effect upon frequencies of cylindrical shells with clamped ends than it does for corresponding shells with simply supported ends, for which numerical results are available. The authors suggest an empirical relation, which together with the latter results enables rapid estimates to be made of the effects of rotatory inertia and shear deformation on the frequencies of a wide range of cylindrical shells with clamped ends. An assessment of the accuracy of the theory with these effects included is made by comparing frequencies with values from a three-dimensional elasticity theory, but this comparison has to be restricted to cylindrical shells with simply supported ends. 相似文献
16.
斜交桥梁由于其不规则的结构形式使其受力规律与规则桥梁相比具有特殊性和复杂性,在地震作用下梁体的平动与转动存在弯扭耦合效应,导致结构动力响应分析复杂。针对斜交桥梁的结构特点,建立包含桩土相互作用的三维有限元模型,在考虑水平双向地震作用下,采用反应谱法及时程分析法对京包高速公路某互通式斜交桥梁进行地震反应分析。结果表明:互通式简支斜交桥梁的地震响应受地震动输入方向的影响较大,在考虑碰撞效应后,碰撞涉及结构部位的地震位移显著增加,地震内力也出现较大差异,即说明在斜交桥梁抗震设计时有必要适当考虑地震动输入方向和梁端与墩台及相邻梁端的碰撞效应。 相似文献
17.
基于Winkler地基模型及Euler - Bernoulli梁理论,建立了Winkler地基上有限长梁的非线性运动方程.运用Galerkin方法对运动方程进行一阶模态截断,得到离散的非线性振动方程,利用多尺度法求得该系统1/3次亚谐共振的一阶近似解.分析了长细比、弹性模量、地基刚度、阻尼、密度等参数对其亚谐共振幅频响... 相似文献
18.
The non-linear steady state vibration of shallow arch beams is studied by a finite element method based on the principle of virtual work. Both the free and forced periodic vibrations are considered. The axial and flexural deformations are coupled by the induced axial force along the beam element. The spatial discretization is achieved by the usual finite element method and the steady state nodal displacements are expanded into a Fourier series. The harmonic balance method gives a set of non-linear algebraic equations in terms of the vibrating frequency and the Fourier coefficients of nodal displacements. The non-linear algebraic equations are solved by the Newtonian algorithm iteratively. The combined algorithm is called the incremental harmonic balance method. The importance of the conditions of completeness and balanceability is presented. Since the non-linearity is essentially softening, different orders of internal resonances between two modes can occur repeatedly. Isolated response curves are possible and are connected to the bifurcation of a particular excited mode. 相似文献
19.
The characteristics of transverse free vibration of a tapered Timoshenko beam under an axially conservative compression resting on visco-Pasternak foundations are investigated by the interpolating matrix method. The research is executed in view of a three-parameter foundation which includes the effects of the Winkler coefficient, Pasternak coefficient and damping coefficient of the elastic medium. The governing equations of free vibration of a non-prismatic Timoshenko beam under an axially conservative force resting on visco-Pasternak foundations are transformed into ordinary differential equations with variable coefficients in light of the bending rotation angle and transverse displacement. All the natural frequencies orders together with the corresponding mode shapes of the beam are calculated at the same time, and a good convergence and accuracy of the proposed method is verified through two numerical examples. The influences of foundation mechanical characteristics together with rotary inertia and shear deformation on natural frequencies of the beam with different taper ratios are analyzed. A comprehensive parametric numerical study is carried out emphasizing the primary parameters that describe the dynamic property of the beam. 相似文献
20.
随着交通网络向偏远地区辐射,桥梁结构会不可避免的出现靠近断层的情况,受到近断层地震动的影响显著。为了研究近场地震作用下简支梁桥的搭接长度需求,基于ANSYS平台建立了简支梁桥的弹塑性分析模型。通过动力响应分析、弹塑性分析和抗剪能力分析,探讨了近场地震动的脉冲效应对简支梁桥搭接长度的影响。研究表明：近场地震动的脉冲效应放大了结构的地震响应,脉冲型地震和非脉冲地震作用时的最大墩梁相对位移分别为115.1 cm和41.5 cm;两类地震作用时的最大剪力分别为1 892.5 kN和1737.8 kN,最大剪力剪切强度比为0.82;当PGA≥0.4 g时,脉冲型地震作用下桥墩底部塑性铰区的最大转角超过极限转角,桥墩发生破坏,而非脉冲型地震PGA=1.0 g时的塑性铰转角小于极限转角;当PGA=1.0 g时,塑性铰破坏前墩梁相对位移为37 cm,占规范搭接长度的41.8%,近场地震作用下简支梁桥的搭接长度需求满足规范要求。 相似文献