基于环境激励的藏式古城墙动力特性研究  

Research on the dynamic characteristics of Tibetan ancient city wall based on ambient excitation

作　　者：刘威 杨娜[1,2] 白凡[1,2] 常鹏[1,2] Liu Wei;Yang Na;Bai Fan;Chang Peng(School of Cinil Engineeing,Beijing Jiaotong University,Beijing 100044,China;Beijing's Key Laboratory of Structural Wind Engineering and Urban Wind Envionmend,Beijing Jaotong University,Beijing 00044,China)

机构地区：[1]北京交通大学土木建筑工程学院,北京100044 [2]北京交通大学结构风工程与城市风环境北京市重点实验室,北京100044

出　　处：《土木工程学报》2021年第4期45-56,共12页China Civil Engineering Journal

基　　金：国家自然科学基金(51778045)。

摘　　要：藏式古城墙具有很高的历史文化价值,但历经数百年风雨侵蚀后,普遍存在较严重的病害,影响其安全性能。为获取藏式古城墙的动力特性,进而为藏式古建筑性能的精准评估提供重要依据,采用环境激励法对某藏式古城墙进行现场动力测试。基于环境激励数据,利用协方差驱动的随机子空间法进行模态参数识别。通过一经典算例验证该方法识别模态参数的精度。同时结合随机减量技术及协方差随机子空间方法,得到城墙平面外振动的频率、振型与阻尼比。最后,考虑阻尼比机理复杂、识别误差较大的问题,基于卡美罗下界(Cramer-Rao lower bound)对城墙阻尼比进行进一步精确估计,从而得到变异性更小的阻尼比识别结果。以E段城墙为例,卡美罗下界法比基于随机减量技术的随机子空间法、节约时域法识别阻尼比的离散性更小,变异系数分别从0.273、0.290减小到0.046。The ancient Tibetan city wall has high historical and cultural value,but after hundreds of years of wind and rain erosion,its safety performance is significantly affected by some serious defects.To obtain the dynamic characteristics of the Tibetan ancient wall and accurately evaluate the performance of Tibetan ancient buildings,an ambient vibration test was carried out on an ancient Tibetan wall.Based on the ambient excitation data,the covariance-driven stochastic subspace method was used to conduct the identification of modal parameters.Furthermore,the accuracy of the method in identifying modal parameters was verified based on one classical case.By combining the covariance-driven stochastic subspace identification method and the random decrement technique,the frequency,mode shape and damping ratio of the out-of-plane vibration of the city wall were obtained.Finally,in view of the complex mechanism of the damping ratio and the large recognition error of identification,the damping ratio of the city wall was further accurately estimated based on the Cramer-Rao lower bound,and then the results of damping ratio with less variability were obtained.With the wall segment E taken as an example,the Cramer-Rao lower bound method produced the damping ratios with smaller dispersion than the stochastic subspace method based on the random decrement technique as well as the STD method,and the coefficient of variation was reduced from 0.273 and 0.290 to 0.046,respectively.

关 键 词：藏式古城墙 环境激励 模态识别 随机子空间 阻尼比 卡美罗下界 

分 类 号：TU361[建筑科学—结构工程] TU363