空冷风机桥架疲劳寿命分析

基于现场实测风机桥架振动响应,采用风机调幅扰力模型进行结构动力响应分析.根据不同工况下疲劳危险点的名义应力时程,采用雨流计数法和各工况年运行频次调查结果编制疲劳载荷谱.通过Miner损伤累积准则和p-S-N关系对风机桥架进行疲劳损伤分析,给定疲劳破坏的损伤阈值,所得疲劳寿命满足设计使用年限的要求.采用Goodman、Gerber和Soderberg模型考虑平均应力影响时的疲劳寿命略有降低.     

地震自动速报信息在桥梁监测警报系统中的应用

介绍地震自动速报信息系统与桥梁监测警报系统的构成,通过将地震自动速报技术与强震动观测技术相结合,形成一套既有强震动观测功能又能接收处理即时地震信息的桥梁监测报警系统,应用结果显示,能丰富强震动观测系统的功能,为桥梁管理提供更多决策支持.     

A base isolation system for bridges subjected to seismic disturbances

The study reported in this paper investigates the feasibility of developing an active base isolation system for the protection of bridges subjected to earthquakes. The proposed system incorporates spherical supports, cams and springs which can be optimally designed to minimize the transmissibility of the seismic disturbances to the bridge. The considered example shows that the proposed design is implementable and can provide an order of magnitude reduction in the maximum stress resulting from seismic waves acting on the bridge in the transverse or longitudinal direction. Since the system performance is highly dependent on the rapid unlocking of the cams in the event of a seismic disturbance, careful consideration should be given to the design of a reliable cam release control. This can be achieved by spring loading each cam such that it would be normally unlocked. A hydraulic actuator would be used to force it to rotate to the locking position under fluid pressure which would be constantly maintained at the design level during normal conditions. The actuator would be equipped with a quick response release valve for rapidly releasing the pressure and consequently unlocking the cam as soon as an earthquake is detected. Copyright © 2002 John Wiley & Sons, Ltd.     

Effect of variation of normal force on seismic performance of resilient sliding isolation systems in highway bridges

In this study, a series of shaking table tests are carried out on scaled models of two seismically isolated highway bridges to investigate the effect of rocking motion and vertical acceleration on seismic performance of resilient sliding isolators. In addition, performance of RSI is compared with system having solely natural rubber bearings. Test results show that variation of normal force on sliders due to rocking effect and vertical acceleration makes no significant difference in response of RSI systems. In addition, analytical response of prototype isolated bridge and the model used in experiments is obtained analytically by using non‐linear model for isolation systems. It is observed that for seismically isolated bridges, dynamic response of full‐scale complex structures can be predicted with acceptable accuracy by experiments using a simple model of the structure. Copyright © 2005 John Wiley & Sons, Ltd.     

基于形状与纹理特征的高分辨率SAR影像桥梁目标自动提取方法

基于高分辨率SAR影像中桥梁目标特征的分析,提出了一种桥梁目标自动提取方法。首先使用多影像时序平均法对SAR影像进行预处理,去除SAR影像噪声;再使用阈值法对水体分割;最后采用形状特征与纹理特征相结合的方法提取桥梁目标。本方法在提取效果上明显优于传统桥梁目标提取方法,其提取准确率可达87.5%。证明本文方法在面向高分辨率雷达影像的桥梁目标自动提取应用上的可靠性和可行性。     

顾及观测点坐标精度的非线性拟合模型

推导出考虑了平面坐标误差情况下的曲面拟合模型的参数估计及其精度评定公式。此方法简单,易用程序实现,并可应用于曲线、曲面、数字地面模型、地壳垂直形变和多面函数拟合模型的参数估计中。结果表明,在曲面拟合模型中顾及平面坐标的精度,将使拟合精度及参数精度显著提高。     

基于GAMIT／GLOBK的海潮对跨海大桥GPS控制网影响初探

利用高精度GPS后处理软件GAMIT／GLOBK对厦门集美跨海大桥B级GPS控制网的实测数据进行处理,分析海潮对GPS控制网的影响,指出海潮改正对近海短时间GPS观测高程方向的影响可达数厘米。     

三维激光扫描的龙柱倾斜观测方法

针对城市高耸建筑物倾斜观测作业时间长、信息量少的问题,将三维激光扫描技术应用到城市高耸建筑物变形监测领域,探讨对无观测标志、不可或不便攀登的城市高耸建筑物进行倾斜观测的施测方法。以龙柱为例,制定了可行的测量方案,并采用高斯曲面拟合算法对其表面进行拟合,精确计算出龙柱的倾斜量,且与全站仪倾斜观测结果进行对比。结果表明,该方法可以快速、全面的获取观测对象的整体信息,且能够满足高耸建筑物倾斜观测的精度要求。     

白水河大桥场区黄土地基湿陷性分析

以白水河大桥施工场地黄土地层为研究对象,分析场地黄土的湿陷系数、自重失陷系数与深度的关系,湿陷量、自重湿陷量与深度的关系,研究得出场区的黄土湿陷特点:研究区地貌单元属河谷阶地区,地处阶地前缘斜坡处,发生湿陷的地层为上更新统风积黄土、古土壤及中更新统风积黄土层。湿陷性黄土主要有轻矿物、重矿物和粘土矿物组成。黄土的化学组成主要为SiO_2,其次为Al_2O_3,Fe_2O_3和CaO等,但黄土湿陷性的发生与黄土的矿物组成及化学组成关系较小。综合分析研究区黄土湿陷性影响因素,认为湿陷性主要影响因素为含水状态,应力状态等。对比分析湿陷系数,湿陷量随深度的变化规律:随着计算深度的增加,湿陷量、湿陷系数均呈先增加后减少趋势。最终判定研究区地基湿陷等级为Ⅲ级,为严重湿陷。该研究成果对工程建设中遇到的黄土湿陷的分析及其治理具有重要意义。     

苏通大桥形变的GPS动态监测

针对目前大桥监测的现状及各种监测方法的优缺点,该文结合苏通大桥运营情况,研究了GPS动态监测的原理、系统组成、坐标转换及监测注意事项,并对其进行了GPS动态监测试验。采集了桥面沿轴线方向、横向及竖向位移数据,对大桥在温度、风荷、车载等因素影响下的运营期大桥响应情况进行了分析。表明大桥轴线方向位移与温度正相关,1/4跨处相关系数为0.859;竖向位移与温度负相关,1/4跨处相关系数-0.817。并对数据进行了频谱分析,分析结果表明频谱没有明显变化;大桥各方向振幅在安全范围内,表明运营期的大桥十分健康;同时也表明GPS动态系统监测结果是可靠的。