Research On The Method Of Evaluating The Stress State Of Self-anchored Suspension Pedestrian Overpass With 3D Point Cloud Model

Self-anchored suspension bridge is a system of cooperative force of cables,beams,towers and suspenders.The stress of each component is closely related.For example,the vertical deformation of the main beam will cause the change of the suspender cable force,and then the spatial position and stress of the main cable and the main tower will change accordingly,that is to say,the spatial displacement of the self-anchored suspension bridge will seriously affect the overall stress of the bridge.Therefore,analyzing the stress state of the bridge based on the deformation data of each member of the self-anchored suspension bridge within a certain period of time has been the focus of bridge health monitoring,but at present,there is no research to clarify the relationship between the deformation of each component and its internal force change value.At present,the traditional methods of deformation detection,such as precise total station and physical sensor,have the disadvantages of single point measurement and embedded sensor,while 3D laser scanning technology can measure the overall spatial position of the bridge at any time,which makes up for the shortcomings of the traditional measurement method,and provides the possibility to make full use of the deformation data of various components of the bridge to evaluate the state of the bridge.Therefore,in order to clarify the relationship between the deformation of each component of the self-anchored suspension bridge and the change of its internal force,and to find a new method of stress state evaluation,this paper combines 3D laser scanning technology with the stress state evaluation of self-anchored suspension bridge,and proposes a method to obtain the deformation data of self-anchored suspension bridge by using 3D point cloud model,and then inversely derive the horizontal force of the main cable,the force of the suspensions and the changes of the two.The specific research contents and results are as follows:(1)A theoretical method of stress analysis based on deformation data is established.Aiming at the common self-anchored suspension footbridges in the city,a theoretical method is established to calculate the horizontal force of main cable,suspender force and the tension change value of main cable and suspender by using the parameters of axial compression deformation and vertical deformation of main beam,vertical deformation of main cable and vertical deformation of tower top.(2)Assessing the stress status of a pedestrian overpass.Taking the pedestrian overpass of Taixing Road in Tianjin as an example,the point cloud data of two times before and after of one year were obtained by a 3D laser scanner;the axial and vertical deformation of the main beam,the vertical deformation of the cable and the vertical horizontal deformation of the tower top were calculated by processing point cloud data.Then the above theoretical method was used to calculate the tension of the main cable and the boom during the two scans of the bridge and the changes in both of them during one year of operation.(3)Finally,Midas-civil software is used to simulate the pedestrian overpass and single cable plane suspension bridge to verify the accuracy of the theoretical method,and the results of the finite element method and the theoretical method are compared.The results show that the error between the two is small,and the accuracy of the theoretical method is high.