Study On Damage Alarming And Condition Assessment Method For Railway Truss Bridge

Bridge construction has made remarkable achievements along with the rapid development of Chines railway especially high-speed railway.The safety of bridge is the premise of the normal running of railway transportation system.In order to get the real-time bridge heath condition and avoid the occurrence of disastrous accidents,it's quite necessary to establish complete and reliable structural health monitoring system and research on the method of damage alarming and damage identification,which is of great significance for the development of Chinese bridges.Based on the monitoring project of Xiangtan Bridge,several key technical issues related to structural health monitoring are studied,including service condition assessment based on monitoring data,method for damage alarming and damage quantitative identification.The main research contents and conclusions are as follows:(1)The monitoring items and emphasis as well as principle of the measuring points are confirmed according to the structural style and the historical damages of the bridge.The subsystems of the monitoring system are studied.(2)The method for distinguishing abnormal signal and signal filtering are studied.The operation condition of the first and second span truss bridge are evaluated based on time-domain and frequency-domain analysis of the measured monitoring data.(3)Wavelet energy entropy is proposed to achieve bridge damage alarming.Firstly,the advantage of wavelet energy entropy are analyzed by detecting the singularity of two types of singular signals and the measured singular signals.Then,the numerical model of simply supported truss bridge is built,and the vertical acceleration of the bridge under moving loads along with sudden damage is calculated.The damage moment is precisely detected by the wavelet energy entropy of acceleration signal.The damage alarming index of wavelet energy entropy is quite effective.(4)A quantitative damage identification method is proposed for truss bridges based on the frequency response function and model updating.The objective functions are constructed with the correlation of frequency response function(COFRF)between measuring points.The damage located at different member bar can be precisely identified by model updating method.The applicability of the model updating method for gusset plate damage is also studied.It's shown that the proposed method can also precisely identify the damage of gusset plate.