Research On Damage Identification And Fracture Impact Effects Of Suspenders In Suspension Footbridges

Suspension footbridges are compact,economical,practical,and aesthetically unique,mainly composed of main cables,bridge towers,stiffening beams,anchors,slings,and bridge decks.From the perspective of the force analysis,the pedestrian loads are transmitted to the main cables through hangers,and then transmitted to the foundation through anchorages and towers,thereby achieving pedestrian access.When the hanger of the suspension footbridge was damaged or even broken due to fatigue and other reasons,it may lead to serious consequences.This study investigated a suspension bridge in a scenic region.The finite element models were established by Midas and Ansys software respectively,to analyze the static and dynamic properties of the structure after the damage and fracture of the hanger.The main contents and conclusions are as follows:(1)By comparing with the measured natural frequency,the finite element model was verified,and the stress values of the hangers and the main cables in the bridge completion state were obtained.Robustness analysis was conducted through structural response sensitivity,and the "critical hanger" of the greatest impact was obtained by the constraints such as the axial force of the main cable,the displacement and bending moment of the suspended beam;(2)By investigating the "critical hanger",the influence of hanger damage and fracture on the stress,internal force and deformation of the hangers,suspended beam and main cables was analyzed.It was found that the influence range of hanger damage was only limited to the range of 1 to 2 hanger spacing on both sides of the damaged hanger position;(3)The changes of natural frequency,modal curvature and modal curvature difference of the suspension footbridge after hanger damage were analyzed.It was found that the modal curvature difference could be used as the damage index to obtain better accuracy.Based on the modal curvature difference,the location and damage degree of the damaged hanger could be effectively identified by the hierarchical identification method;(4)The dynamic response time history of the remaining hangers,main cables and suspended beam after the instantaneous break of a single hanger and two adjacent hangers were analyzed.The static and dynamic redistribution coefficients,vibration amplitude and dynamic amplification coefficients were analyzed.It was found that the impact effect of the adjacent hangers on the same side was the largest after the hanger was broken,and the influence on the side hangers was small.The envelope diagrams of the static and dynamic redistribution coefficients and dynamic amplification coefficients after the fracture of the hanger were drawn.It was found that the static redistribution coefficient SR of the hanger at each position was about50 %,the dynamic redistribution coefficient DR was about 100 %,and the dynamic amplification coefficient was between 1.9 and 2.5.The fitting curve of the dynamic amplification coefficient of the hanger at each position was acquire.