Dynamic identification of a reinforced concrete damaged bridge

The results of a series of harmonically forced tests carried out on a reinforced concrete single-span bridge subjected to increasing levels of damage are interpreted in this paper. The deck structure of the bridge consists of a slab and three simply supported beams. The damage is represented by a series of notches made on a lateral beam to simulate the effect of incremental concentrated damage. The variation of lower natural frequencies shows an anomalous increase in the transition from one intermediate damage configuration to the next ones. Vibration mode shapes show an appreciable asymmetry in the reference configuration, despite the nominal symmetry of the bridge. A justification of this unexpected dynamic behavior is presented in this paper. The analysis is based on progressive identification of an accurate finite element model of the reference configuration and on reconstruction of damage evolution from natural frequency and vibration mode measurements. Changes in modal curvature of the first two vibration modes evaluated along the main beams are successfully used to identify the location of the damage.     

桥式起重机动态分析与优化设计

用改进后的质量弹簧简化系统,分析了桥式起重机主要动态性能及结构参数的影响,并对桥式起重机动态指标进行了优化设计。     

Sensitivity and analysis GPS signals based bridge damage using GPS observations and wavelet transform

This paper uses GPS monitoring system on the Yonghe Bridge. After a year from re-construction of this bridge, cracks were pronounced 48.2 m far from the beginning of the abutment. To analyze the movements of bridge tower, the current operational safety, the cause of bridge cracks and sensitivity of GPS signals, and its movements were observed under different stress factors such as wind speed, temperature change and traffic loads. The observed lateral, longitudinal of bridge’s towers were studied. Two analytical methods namely; DWT and FT were used for the analysis of observation data. The analysis of test results indicates that: (1) The STFT is a significant step forward from the traditional FFT in terms of structural response analysis. (2) The sensitivity of GPS signals does not depend on the position of GPS antenna; and (3) the cracks of bridge deck bring out the frequency of the bridge tower movement transient characteristics.     

桥梁动态应变的压电传感和远程监测的研究

桥梁动态应变的远程监测对于确保桥梁安全运行具有十分重要的意义。以压电方程为基础，论述了采用压电片对桥梁的动态应变进行传感的理论和方法，得出了压电片的输出电荷与所传感的动态应变之间的理论关系式和工程应用中的传感计算公式，然后结合现代通讯技术，研制了基于公用电话交换网的远程监测系统，实际应用于红槽房大桥的动态应变监测中，并获得了满意的结果。     

Dynamic characteristics of a damaged plate

It is very important to well understand the dynamic characteristics of damaged structures to successfully develop or to choose a most appropriate structural damage identification method (SDIM) as the means of non-destructive testing. In this paper, the dynamic equation of motion for damaged plates is derived by introducing a damage distribution function, which may characterize the effective state of structural damages. It is found that structural damages may induce the coupling between modal coordinates. The effects of damages on the vibration characteristics of a plate depending on their locations, sizes, and magnitudes are numerically investigated in a systematic way. The numerical investigations are also given to the effects of damage-induced modal coupling on the changes in vibration characteristics and to the minimum number of natural modes required to predict sufficiently accurate vibration characteristics of damaged plates.     

LL680挠性剑杆织机动态特性测试研究

针对LL680挠性剑杆织机在高速化过程中遇到的振动过大等问题,通过对其进行动态特性的测试与分析,应用NI振动测试设备以及加速度传感器,找到振动的主要振源即为织机的凸轮箱,分析机械结构在结构动力学上的薄弱环节,得到通过对织机的主要支撑部件墙板优化设计,使得固有频率有所改变、着重加强其X方向的刚度以及对振源构件的优化等措施可以达到高速化效果的结论。为LL680高速化解决提供依据与方向。     

大位移桥梁伸缩缝的垂向动力学响应研究

以大位移桥梁伸缩缝为研究对象,应用动力学分析的理论方法,并结合数值计算,进行了垂向动力学研究。其中,建立了完整的垂向动力学理论模型,即模拟在行驶的汽车通过伸缩缝的整个过程中,汽车载荷的冲击对伸缩缝垂向振动的影响。并且结合载荷形式,对完整模型的方程组进行联立求解,计算了不同车速下伸缩缝的垂向振动响应。计算结果,用于对研究载荷的冲击系数以及大位移桥梁伸缩缝的关键部件结构参数,从而为伸缩缝的合理化设计提供理论依据。     

履带车辆动力传动系统扭振的测试与分析

论述了扭振测试的两种方法,即稳态测试方法和动态测试方法.在扫频分析理论的基础上,提出了扭振实车动态试验的条件和加速时间的要求,建立了试验测试系统,并对某型装甲履带车辆的动力传动系统进行了实车道路测试试验.通过对试验数据的分析处理,得到了车辆发生扭转共振时发动机的转速和谐次,为分析、评价车辆动力传动系统扭转振动的合理性提供了试验方面的依据.     

激光切割在汽车桥壳设计和加工中的应用

在桥壳设计和加工中 ,应用激光切割的方法改进冲裁下料工艺 ,较好地解决了传统冲裁下料工艺中存在的加工问题和质量问题 ,同时降低了生产成本、提高了加工效率。     

起重机桥架跨距改制工艺

起重机桥架作为大型焊接结构件,制造要求高,其改制具有典型意义。本文结合实例详细介绍了桥跨距改制的工艺方法和原理,阐述了不同解决方案的差别,以此说明如何制定合理的改制工序使可能报废的结构件达到新的使用要求。     

基于最小秩修正的结构损伤识别方法

提出一种改进的最小秩修正法.通过引入损伤定位向量,首先确定损伤单元的个数,再由最小秩修正法求解损伤程度.该方法较好地解决了运用最小秩修正法时必须采用正确的模态个数的问题.以一个平面桁架结构为例验证该方法,并对测量噪音的影响进行讨论.结果表明,所提方法是准确可靠的,且对测量噪音有很强的鲁棒性.     

Damage detection of damaged beam by constrained displacement curvature

Structural damage detection technique involves the problem of how to locate and detect damage that occurs in a structure by using the observed changes of its dynamic and static characteristics. The objective of this study is to present an analytical method for damage detection by utilizing displacement curvature and all static deflection data to be expanded from the measured deflection data. Utilizing the measured displacements as displacement constraints to describe a damaged beam, minimizing the change of the displacement vector between undamaged and damaged states, and neglecting the variation between the test data and the analytical results, the deflection shape and displacement curvature of the damaged beam can be estimated, and the damage can be detected by the curvature. The validity and effectiveness of the proposed method are illustrated through comparison with the experimental results of a simple cantilever beam test.     

动态称重系统计量误差的动态校正

本文讨论了称重系统在动态称重过程中产生计量误差的多种原因,提出了一种能改善动态称重系统性能、提高其测量精度的新的方法。该动态校正方法建立在动态补偿原理的基础上并且应用了一个模糊控制器。文中详细讲述了所使用的模糊控制器动态校正算法,相应的称重系统样机,并给出实际动态称重的结果。     

应变模态在斜拉索损伤诊断中的应用

应用应变模态方法对斜拉索的损伤识别进行了研究.通过对斜拉索在不同损伤工况下的数值仿真计算,探讨了应变模态方法用于斜拉索损伤识别的能力.结果表明:利用应变模态差曲线能准确识别斜拉索的损伤位置.并且,应变模态差曲线在斜拉索损伤单元处的跳跃幅值随单元损伤程度的增加而增大.所以,应变模态是对结构进行损伤诊断的较理想的损伤识别指标.     

起重机的动态分析方法

通过对动载系数演变过程的讨论，简要论述了国内、外起重机动态分析方法的应用情况和研究趋向。     

计入轴瓦变形的曲轴动应力和疲劳强度计算

采用动力学仿真软件ADAMS和有限元分析软件ANSYS,辅以手工编程相结合的方法,研究计入轴瓦变形时某四缸柴油机曲轴动应力分析和疲劳强度计算问题。解决计入轴瓦变形的曲轴—轴承系统动力学和摩擦学分析问题,得到动态油膜压力;采用ANSYS中的参数化编程语言APDL编写程序实现动态施加力边界条件,计算曲轴动应力;采用损伤积累理论计算曲轴疲劳强度。研究表明：计入轴瓦变形,主轴承最小油膜厚度大幅度下降,最大油膜压力大幅度上升,曲轴动力学响应和危险点的动应力也发生变化,曲轴疲劳寿命下降了15.6%。     

Finite element modeling of orthogonal micromachining of anisotropic pyrolytic carbon via damaged plasticity

Engineered features on pyrolytic carbon (PyC) have been demonstrated as an approach to improve the flow hemodynamics of the cardiovascular implants such as bileaflet mechanical heart valve. PyC also finds application in thermonuclear and missile components due to its unique directional thermal properties. However, very little work has been reported on modeling of machining/micromachining of PyC. Note that PyC is a brittle anisotropic material and its machining characteristics differ from plastically deformable isotropic materials. Consequently, this study is aimed at developing a finite element model to understand the mechanics of material removal in the plane of transverse isotropy (horizontally stacked laminae) of PyC. A damaged plasticity model has been used to capture the effect of material degradation under machining. Uniaxial tension/compression tests have been carried out to calibrate the damaged plasticity model. A cohesive element layer has been used between the chip layer and the bulk material to simulate the delamination/peeling effect. The model predicts cutting force and thrust forces at different set of process parameters. The orthogonal cutting model has been validated against the experimental data for different cutting conditions for cutting and thrust forces. In addition, the chip geometry has also been compared. The prediction error in the model lies between 9% and 27%. Parametric studies have also been performed to understand the effect of the machining parameters on the process response. It is found that use of the positive rake angle decreases the cutting forces up to 75%.     

纯电动桥梁检测维修车在高速铁路桥梁检测维护中的应用

介绍纯电力驱动技术桥梁检测维修车,该车采用C型整车结构,解决了桥梁断面复杂多变的问题,说明纯电动桥梁检测维修车在桥梁检测维修方面的可行性.     

XTR106在铂热电阻不平衡电桥测温中的应用

根据铂热电阻不平衡电桥测温的原理,铂热电阻的非线性和不平衡电桥的固有非线性给温度测量带来很大的非线性误差,XTR106主要用于桥路传感器线性化的两线制专用集成变送电路。本文介绍XTR106的工作原理及其在铂热电阻不平衡电桥测量中的应用。