Safety Status Analysis Of Long Span PC Continuous Box Girder Based On Long-term Monitoring Data

Transportation is an important guarantee for the national economic development.As an important link,the structural safety of Bridges has been paid more and more attention during the operation period.However,the regular manual inspection is difficult to assess the bridge safety status in real time,with the development of computer technology and intelligent technology,the bridge health monitoring system arises at the historic moment,it provides strong data support for structural security status monitoring and evaluation,effectively avoid the occurrence of safety accidents.This paper combines the research status and engineering practice experience of bridge health monitoring system at domestic and abroad,based on a bridge in service in Liaoning province,and studied a series of problems such as the establishment of monitoring system,the analysis of data,the setting of early warning threshold value and the method of state evaluation.The main research content and results are as follows:(1)Firstly,the paper introduces the research background and significance,and summarizes deficiencies of health monitoring system and status assessment that still exist.(2)It established a health monitoring system for large span PC continuous box girder,and introduced the functions of each subsystem,the selection of sensors and the layout of measuring points,then verified system reliability through load test data.(3)It analyzed the overall change trend,difference of measurement points and data correlation of each monitoring project,and determined the safety state of the structure preliminarily,and understand the characteristics of structural response changes during the operational period based on 2017 annual monitoring data,these provide the basis for the establishment of early warning threshold and state evaluation.(4)According to the characteristics of the project and the requirements of the early warning system,a multi-index hierarchical early warning system based on time series is established,The hierarchical warning threshold are based on the statistic value of the index monitoring,the monitoring value of the load test under the most unfavorable conditions,the theoretical calculation value of the finite element model and the normative limit value.It proposed a new early warning method by combined with the characteristics of strain monitoring data: the influence of temperature load was removed through linear fitting,and the load strain of vehicle was separately warned.(5)An assessment system of structural security state is established based on analytic hierarchy process(AHP).Firstly,the related theories of traditional AHP are introduced,including the establishment of AHP,the determination of initial weight,and the calculation of the evaluation value of the underlying indicators;secondly,the principle of variable weight is introduced and the problem of variable weight equilibrium coefficient is studied to make up for the short board effect;a new method to calculate the initial weight of deflection and strain measurement points is introduced,based on the damage sensitivity theory;in the end,the improved variable weight analytic hierarchy process is used to evaluate the safety condition of the box girder of the main bridge,it makes the evaluation result reasonable and close to the real state of the structure.