Second-Order Stiffness Matrix and Loading Vector of a Beam-Column with Semirigid Connections on an Elastic Foundation

The second-order stiffness matrix and corresponding loading vector of a prismatic beam–column subjected to a constant axial load and supported on a uniformly distributed elastic foundation (Winkler type) along its span with its ends connected to elastic supports are derived in a classical manner. The stiffness coefficients are expressed in terms of the ballast coefficient of the elastic foundation, applied axial load, support conditions, bending, and shear deformations. These individual parameters may be dropped when the appropriate effect is not considered; therefore, the proposed model captures all the different models of beams and beam–columns including those based on the theories of Bernoulli–Euler, Timoshenko, Rayleigh, and bending and shear.The expressions developed for the load vector are also general for any type or combinations of transverse loads including concentrated and partially nonuniform distributed loads. In addition, the transfer equations necessary to determine the transverse deflections, rotations, shear, and bending moments along the member are also developed and presented.     

An exact high order beam element

This work gives the exact stiffness coefficients for an high order isotropic beam element. The terms are found directly from the solutions of the differential equations that describe the deformations of the cross-section according to the high order theory, which include cubic variation of the axial displacements over the cross-section of the beam. The model has six degrees of freedom at the two ends, one transverse displacement and two rotations, and the end forces are a shear force and two end moments. Also given are the equivalent end forces and moments for several cases of loading along the member. The components of the end moments are investigated, and are found for exact results. Comparison is made with the Bernoulli-Euler and Timoshenko beam models.     

塔设备优化设计

从优化设计理论出发 ,对常压塔的强度优化和刚度优化进行了理论分析和实例计算 ,提出了较简便的优化设计计算方法     

Structural Damage Detection Using Empirical Mode Decomposition: Experimental Investigation

This paper presents an experimental investigation on the applicability of the empirical mode decomposition (EMD) for identifying structural damage caused by a sudden change of structural stiffness. A three-story shear building model was constructed and installed on a shaking table with two springs horizontally connected to the first floor of the building to provide additional structural stiffness. Structural damage was simulated by suddenly releasing two pretensioned springs either simultaneously or successively. Various damage severities were produced using springs of different stiffness. A series of free vibration, random vibration, and earthquake simulation tests were performed on the building with sudden stiffness changes. Dynamic responses including floor accelerations and displacements, column strains, and spring releasing time instants were measured. The EMD was then applied to measured time histories to identify damage time instant and damage location for various test cases. The comparison of identified results with measured ones showed that damage time instants could be accurately detected in terms of damage spikes extracted directly from the measurement data by EMD. The damage location could be determined by the spatial distribution of the spikes along the building. The influence of damage severity, sampling frequency, and measured quantities on the performance of EMD for damage detection was also discussed.     

Wave Propagation and Mode Localization in Simply Supported Multispan Beams with Couplers on Supports

The influences of couplers on wave propagation and mode localization in simply supported multispan beams with couplers consisting of lumped rotational stiffness and mass on supports are studied. A transfer matrix equation governing the vibrational wave propagation in the simply supported multispan beams with couplers is newly derived and simplified. The eigenvalue of the simplified transfer matrix shows that the larger stiffness or the larger mass of the coupler makes the internal coupling between spans weaker and so it makes the system more sensitive to mode localization. As the wave frequency or the eigenvalues of the system increases, the mass effect is increased while the stiffness effect is decreased. In a case considering the large stiffness and mass at the same time, there is a region with relatively wider passbands and narrower stop bands having small attenuation rates and the normal modes in it become delocalized ones. As an example structure, a simply supported two span beam with a coupler at the midspan is considered.     

4自由度并联机器人刚度分析

少自由度并联机构应用于机床上时要求具有很高的刚度,而少自由度并联机器人的刚度和机器人雅可比矩阵有很密切的关系。采用螺旋理论方法求出了4-RUC 4自由度并联机构的雅可比矩阵,推导出4自由度并联机器人的刚度计算公式和条件指数计算公式,分析了少自由度并联机器人在某一位置时(z=0)最大和最小刚度所在的方向,给出了这种4自由度并联机器人的最大和最小刚度曲线,通过曲线可以评价出此并联机构在各个方向上刚度大小,为这种机器人的应用和开发提供了有力的依据。     

滚齿工艺系统刚度研究

通过对YKX3132型滚齿机加工工艺系统的刚度进行分析研究，得到机床工艺系统的刚度计算公式。这对于滚齿切削用量的选择、滚齿加工误差的补偿、滚齿机床的设计与制造、提高齿轮滚切精度有一定的参考意义。     

PbMoO_4晶体的布里渊散射谱

报导了利用布里渊谱仪对PbMoO_4晶体进行90°和180°散射实验的测试结果。通过分析计算,得到了沿正z方向传播的声学波的声速和某些弹性参数。     

弱耦合对隔振效果的影响

本文从经典的二个对称面隔振理论入手,讨论了次级系统之间的耦合性,而后应用小参数法系统地推证了次级系统之间弱耦合对固有频率的影响,最后通过实例给出固有频率变化的参考值。     

四腿菱形变截面梁微加速度计结构设计与研究

在传统等截面双边四梁微加速度计结构上,以变极距式电容传感器为对象,设计一种菱形变截面梁.为增加梁的稳定性,满足加速度计对不同方向刚度要求,并提高灵敏度,建立加速度计数学理论模型,推导出灵敏度与刚度的关系.建立梁的纯弯曲模型,并基于静电驱动原理,推导出静电刚度公式,确定满足静电刚度小于机械刚度的条件下加速度计量程.结果显...