幂函数剪切模量成层土非线性地震反应的半解析算法

运用文献[1]所建议的动态应力一应变关系及其推广的Masing加卸载准则,考虑土料在地震等产生的不规则加载条件下的非线性滞回特征,将增量法与相应场地地震线性反应解析解[2]相结合,提出了该动力非线性方程的半解析时域算法,基于改进的一维剪切梁模型,对剪切模量是其深度的某一幂函数的成层非均质土层,建立了求解土体地震反应的非线性分析技术。针对文献[2]中的土层剖面,做了计算、分析和讨论。     

求解薄板频率特性的边界元法解析研究

根据弹性薄板理论和振动理论,运用边界元法(BEM)分析了薄板弯曲自由振动的频率特性,从薄板自由振动的微分方程式出发,采用动态基本解推导出其相应的边界积分方程式,计算中对边界积分方程进行缩减,应用频率扫描的方法研究薄板的动态特性,准确、有效地得到了其相应的固有频率、给出的数值算例证明了本文的方法简单、可行,且具有良好的解析计算精度。     

广义Voigt土模型基于虚土桩法的桩基纵向振动

在桩侧土广义Voigt模型条件下,研究成层土中黏弹性桩在纵向振动荷载作用下的动力特性。将桩底截面范围内有限层桩底土模拟为虚土桩,建立虚土桩-土、桩-土耦合振动模型,采用广义Voigt体模型建立桩、虚土桩与桩侧土的纵向振动动力方程。利用桩-土、虚土桩-土的耦合接触条件求解动力方程,得到桩顶频域响应解析解和时域响应半解析解。通过对虚土桩参数的研究检验桩底土对桩顶动力响应的影响,得到一系列的桩顶速度导纳曲线及时域反射波曲线。     

圆弧状多层沉积谷地在平面SV波入射下的动力响应

利用波函数的Fourier-Bessel级数展开法,推导出了含任意多个圆弧状沉积层的谷地在平面SV波入射下稳态动力响应的解析解,并分析了该级数形式的解析解随着截断项数的收敛问题.其结果表明,该级数解能够在一个非常宽的频带范围内收敛;通过在简化条件下与现有其他解析解的比较,验证了该解析解的正确性;并利用该解析解,以稳态地面运动的位移幅值和相位差为基本参数,在一个较宽的频带范围内讨论了谷地中沉积介质的成层性对地面运动的影响,其结果表明对于多层谷地而言,当入射波频率较高时,散射波之间的干涉显著并且出现了能量聚焦现象.     

地面运动的平均周期对单自由度和多自由度体系的非弹性动力反应的影响

主要研究地面运动的频率成分在非弹性需求下对单自由度（SDF）和多自由度（MDF）钢架结构的作用。通过对文献进行详细的审查,识别出最能代表地面运动频率成分的指标。选择地面运动的平均周期（Tm）是由于它能区别各种不同地面运动的频谱形态及其与震级、距离和场地特征的关系。首先使用一组128次地面运动的记录根据L对单自由度体系在特定延性水平时的非弹性位移要求进行研究。然后通过采用相同的地面运动资料做增量动力分析,把研究扩展到多自由度系统,评价Tm对各种工程需求参数的影响。得到的结果表明,对于单自由度体系,当弹性周期（Te）与Tm的比值低于1时,位移将增大。对于多自由度体系,结果证明了高阶振型对于基底剪力的影响和当Tm接近结构的高阶振型周期时,对最大层间侧移的影响变得更加显著。对单自由度体系和多自由度体系,在非弹性水平较高时这些观测更为明显。研究结果对于欧洲抗震设计法是尤为重要的。     

移动荷载作用下轨道地基的位移反应

将车辆荷载等效为移动的动点荷载,地基等效为弹性半空间,利用改进的圆心位移影响函数法求解了轨道路基的竖向位移反应的解析解,探讨了离车辆荷载距离、车辆荷载振动频率、速度对位移的影响规律。研究表明离振源距离的增加,位移函数收敛的值逐渐减小;频率对位移的变化有明显的影响,位移函数收敛的趋势随频率的增大而变快,并且变化的幅度随频率的增大而越来越大;在速度为160公里/小时范围内,竖向位移对速度的影响规律不明显。     

高层建筑电梯平衡重体系的动力特性与地震反应分析

本文在文献[2,1]所建立的平衡重体系运动方程的基础上,对高层建筑电梯系统中平衡重体系的动力特性进行了探讨,给出了求解该体系自振频率的近似方法,通过对一幢14层建筑内的平衡重体系进行的大量地震反应分析,研究了其动力反应沿建筑物高度变化的一般规律,给出了最大反应所处的位置。本文的工作为实施和推广文献[1]所提出的平衡重体系的抗震控制措施奠定了理论基础。     

正弦行波激励下单层偏心框架结构扭转响应的解析解

文中针对单层偏心框架结构,利用正弦行波激励研究了质量偏心率和激励频率对偏心框架结构行波扭转响应的影响规律.建立了行波激励下单层偏心框架结构的振动方程,采用相对运动法求解给出了正弦行波激励下单层偏心框架结构楼板的质心平动位移和转角位移以及楼板扭矩和柱剪力的解析解.计算了一个钢筋混凝凝土单层偏心框架结构的峰值楼板扭矩和峰值...     

基础隔震耗能结构基于Kanai-Tajimi谱的随机响应简明解法研究

针对在Kanai-Tajimi谱激励下设置广义Maxwell阻尼器的多自由度基础隔震耗能结构进行响应分析比较复杂的问题，提出一种求解响应的简明解法。首先，联立广义Maxwell阻尼器本构方程与原结构运动方程，重构结构运动方程；其次，利用复模态法将运动方程解耦获得了系列响应的特征值以及复模态参与系数，进而获得结构系列响应的统一表达式；最后，计算激励功率谱与响应功率谱的二次正交式，获得了结构响应0～2阶谱矩及方差的简明解析解。算例计算了一多自由度结构响应的方差及0～2阶谱矩，将计算结果与虚拟激励法进行比较，证明本文所提方法的正确性，同时具有更高的计算效率。     

拉索端部弹性约束振动控制研究(Ⅱ)——试验验证

在索端沿轴向设置弹性约束,对拉索振动轴向被动控制进行了试验研究。研究了支座移动对拉索振动频率的影响;验证了弹性约束对拉索振动的减振效果,讨论了阻尼系数和弹簧刚度对减振效果的影响;最后验证文献[10]中理论研究的正确性。     

Free vibration and transient response of thick and thin plates using the finite element method

An isoparametric quadrilateral plate bending element is used for the free and forced vibration analysis of both thick and thin plates. Plates of rectangular, circular and triangular planform are analysed and excellent results are obtained. The element performance is assessed by comparison with analytical solutions based on Mindlin's thick plate theory, three-dimensional elasticity solutions and solutions based on thin plate theory.     

钢结构建筑钢板外部震动下承载力有限元分析

传统钢结构建筑钢板外部震动下承载力分析方法,是基于总体钢板结构以及受力特征,获取载荷同振动频率间的关系,实现承载力的分析,并未对钢板同混凝土间的应力-应变关系进行分析,导致分析结果存在较高的偏差。提出新的钢结构建筑钢板外部震动下承载力有限元分析方法,将钢结构建筑钢板横截面简化成混凝土的矩形截面和波纹钢板的工字形梁截面,采用ANSYS有限元软件中的CONTACI2接触单元仿真分析钢板同混凝土两者的影响,分析混凝土及钢板的应力-应变关系、界面模块的应力-滑移关系,采用力平衡迭代法获取外部震动下钢板荷载增量;在上述基础工作上采用有限元软件,对外部震动下钢结构建筑钢板实施有限元接触单元建模及承载力分析。实验结果表明,该方法能够实现钢结构建筑钢板外部震动下承载力有限元分析,并且分析结果具有准确性高和效率高的优点。     

Shifting natural frequencies of plates through preforming

Through an energy formulation and the use of a large deflection theory, it is shown that if a thin plate has a slight initial preform, and if its edges are constrained against in–plane displacements, then all of the natural frequencies of the plate will be shifted upward. For a uniform thin plate, the amount of frequency shift depends on the type of boundary conditions and the ratio of the amplitude of preform to the thickness of the plate. Examples of square and rectangular plates preformed in the shape of their first mode shapes are presented. The method holds the promise of shifting or essentially removing a troublesome vibration mode.     

Output only modal identification and structural damage detection using time frequency ＆ wavelet techniques

The primary objective of this paper is to develop output only modal identifi cation and structural damage detection.Identif ication of multi-degree of freedom(MDOF) linear time invariant(LTI) and linear time variant(LTV—due to damage) systems based on Time-frequency(TF) techniques—such as short-time Fourier transform(STFT),empirical mode decomposition(EMD),and wavelets—is proposed.STFT,EMD,and wavelet methods developed to date are reviewed in detail.In addition a Hilbert transform(HT) approach to determine ...     

Sloshing response of layered liquids in rigid tanks

The sloshing action of layered liquids in rigid cylindrical and long rectangular tanks is investigated, considering both their free vibrational characteristics and their response to a horizontal component of base shaking. Special attention is given to the maximum surface displacement induced by the base motion. The analysis is formulated for systems with N superimposed layers of different thicknesses and densities, and is illustrated by a numerical example. In addition, comprehensive numerical data are presented for two-layered and some three-layered systems which elucidate the underlying response mechanisms and the effects and relative importance of the numerous parameters involved. It is shown that for each horizontal natural mode of vibration, there are N distinct vertical modes, the frequencies of which are lower than the natural frequency of a homogeneous liquid of the same total depth. It is further shown that the maximum surface sloshing displacement of the base-excited layered system is typically larger than that of the corresponding homogeneous system, and that the results for the long rectangular and cylindrical tanks are quite similar.     

拟协调四节点板弯曲单元在薄板振动分析中的应用

本文以文〔１〕构造的拟协调板弯曲单元为基础，横向剪切应变假设中采用沿厚度二次分布，将其应用于薄板固有振动分析，求解前ｎ阶固有频率，结果表明该单元具有良好的数值特性。     

Frequency domain substructural identification for arbitrary excitations

Structural identification based on analysis of vibration signals is usually formulated as an optimization problem. Nevertheless, identifying a structural system as a whole often involves a great number of unknowns and degrees of freedom, resulting in considerable convergence difficulty and expensive evaluation of objective function. To handle these issues, this paper aims to propose a frequency domain substructural identification method applicable to arbitrary excitations. This is done by introducing the exponential window method in the formulation so that the effect caused by initial condition is alleviated without using zero padding. The proposed identification method is verified through both numerical and experimental studies. It is shown that significant reduction in computer time can be achieved in addition to remarkable identification accuracy. The experimental study also indicates that the proposed strategy is effective in identifying small structural changes. Copyright © 2011 John Wiley & Sons, Ltd.     

Vertical vibration of three-dimensional rigid foundations on layered media

A numerical method of analysis is presented for the determination of the steady-state vertical vibration of rigid foundations with arbitrary three-dimensional geometries resting on the surface of a layered soil medium. The method utilizes the flexibility concept applied to steady-state periodic problems and it is solved in the frequency domain. The accuracy of the method is verified by comparison with several published solutions for massless, smooth rigid rectangular foundations on a homogeneous, isotropic elastic half-space. Parametric solutions are presented to study the dynamic behaviour of massless, smooth rigid rectangular foundations on a homogeneous, elastic stratum.     

Vibration of vertical rectangular plate in contact with water on one side

In this paper, the vibratory characteristics of a rectangular plate in contact with water on one side are studied. The elastic plate is considered to be a part of a vertical rectangular rigid wall in contact with water, the edges of which are elastically restrained and parallel to those of the rigid wall. The location and size of the plate on the rigid wall may vary arbitrarily. The water with a free surface is in a rectangular domain infinite in the length direction. The effects of free surface waves, compressibility of the water and the hydrostatic water pressure are neglected in the analysis. An analytical‐Ritz method is developed to analyse the interaction of the plate–water system. First of all, by using the method of separation of variables and the method of Fourier series expansion, the exact expression of the motion of water is derived in the form of integral equations including the dynamic deformation of the plate. Then the Rayleigh–Ritz approach is used to derive the eigenfrequency equation of the system via the variational principle of energy. By selecting beam vibrating functions as the admissible functions of the plate, the added virtual mass incremental (AVMI) matrices for plate vibration are obtained. The convergency studies are carried out. The effects of some parameters such as the depth and width of water, the support stiffnesses, location and aspect ratio of the plate and the plate–water size and density ratios on the eigenfrequencies of the plate–water system are investigated. Several numerical examples are given. The validity of AVMI factor approach is also confirmed by comparing the AVMI factor solutions with the analytical‐Ritz solutions. The results show that the approach presented here can also be used as excellent approximate solutions for rectangular plates in contact with water of infinite width and/or infinite depth. Copyright © 2000 John Wiley & Sons, Ltd.