Dynamic Analysis And Model Updating Of Long-span Cable-stayed Bridge With Hybrid Girder

In the operating process, bridge structure would damage, as the result of design, construction, environment, overload and many other reasons, and the damage can affect the normal use and safety of the bridge structure. To ensure the safety of bridge structures, damage must be detected and identified, particularly for long-span bridges. Cable-stayed bridge attracts more and more attention in long-span bridges, for the superiority of their own characteristics and the super spanning capacity. It is important significant to studying the damage identification of long-span cable-stayed bridge. The precision of structural damage identification on the one hand is related to the finite element mode, the other is the identification method which is applied.This paper bases on the Jiujiang Yangtze River Highway Bridge which is an important part of the main line Fuzhou to Yinchuan in the national7918highway system, The girder of the bridge is consist of steel box girder,box concrete girder and the concrete combined section.This bridge is a half suspension system,it has two cable tower and the bridge cables are layouted by double cable plane close lock sector.This paper makes modal analysis on the bridge which is based on the preliminary established finite element mode,and the characteristics of the modal are as follows:1) The frequency is intensive,the frequency of the first20stepsis between0.10Hz and1.0Hz.2) The basic cycle is very long,the frequency of the first step is only0.1Hz as well as the circle is10s.3) The vibration model of the second step is the lateral bending of the main steel box girder.4) The symmetric vertical bending of the first step emerges in the third step of the whole vibration model.and the vibration models of the five of steps in the fist ten are the vertical bending.5) In the first twentieth vibration models,the vertical bendings of the girder emerge in the part of steel box girder.We take this basis for sensitivity analysis,and point out the sensitivity of the elastic modulus.1) The bridge to the sensitivity of the elastic modulus of the most sensitive mode for horizontal bending, followed by vertical bending;2) The elastic modulus of horizontal and vertical bending the sensitivity of the bending, along with the order time influence rising increase;3) The elastic modulus of each order horizontal bending sensitivity and vertical bending the most influence from the unit is located in vibration characteristics analysis this order horizontal bending or vertical bending mode maximum position;The method to the damage identification simulation of this bridge is using finite element model correction. Through the example of single damage, two damages and damages of more,we can see, based on the sensitivity of the model modification methods in no noise or small noise can better identify for damage location and damage size, but with the increase of the noise, can lead to misjudgment is more likely. And the finite element model updating with regularization can improve this shortcomings, it can recover the ill-posedness of the model updating process effectively and reduce the affection of measurement noise to avoid the misjudgment of structure damages.