Load And Resistance Modeling And Reliability Evaluation For Operational Bridges Based On Long-Term Monitoring Data

In our country,the condition assessment for the technical condition of in-service bridge structures is still based on experience,with low probability level.It does not match with the probability design method adopted in the design stage.Compared with the proposed bridge in the design stage,the service environment and structural response of the in-service bridge are real and can be measured and recorded.However,how to accurately and efficiently extract information that affects structural safety based on these recorded data,establish a probabilistic evaluation method for in-service bridges and evaluate the safety status of the structure is a challenging research topic.This paper conducts research on the state assessment of in-service bridge structures using theoretical analysis,numerical statistics,finite element simulation and model tests,etc.In order to assess the in-service bridge structure,this paper identifies the actual load and resistance of the bridge structure from the data recorded by the structural health monitoring system.The main research content and results are as follows:1)Based on WIM data and extreme value theory,a lane load evaluation model containing only two parameters of virtual concentration and vehicle distance is established.Based on the WIM data of the cable-stayed bridge in the main channel of the Shanghai Yangtze River Bridge,the mathematical statistical characteristics of vehicle weight,vehicle speed,and wheelbase are analyzed from the perspective of data driving.Through the measured data,model tests and finite element analysis,it can be known that in the overall calculation,the multi-parameter single-vehicle model can be simplified to a single-parameter virtual concentrated force.A fleet model composed of multiple variables such as axle load,wheelbase,and clear distance between vehicles can be simplified to a fleet load model that only contains two random variables,virtual concentration and distance between vehicles.The virtual concentrated force can be expressed by multiplying the weight of the vehicle by a proportional coefficient related to the length of the load effect influence line.The vehicle weight model can be established through the POT model based on the GPD distribution.2)Based on the natural environment and structural response data obtained by monitoring,this paper established the overall temperature field model of different components(regions)of the bridge and the structural temperature load model of the steel box girder without concrete deck.This paper also analyzed the characteristics of the wind field at the bridge site.The overall temperature field of different components(regions)of the bridge is quite different.The "box effect" and the material together affect the distribution of the temperature field.The "box effect" causes the atmospheric temperature in the steel box girder to be much higher than the ambient temperature and higher than the design value.And it is also the "box effect" that causes the atmospheric temperature in the tower to be lower than the ambient temperature and lower than the design value.For the structural temperature of the steel box girder without concrete deck,it is proposed that the triangular distribution of the structural temperature load is more suitable.Finite element calculations show that the stress under this triangular temperature load is greater than the response under the design load.For the analysis of the wind field at the bridge site,it can be seen that the wind speed and the longitudinal and transverse turbulence intensity values at the bridge deck are all less than the design value.3)The cable force obtained from the monitoring is used as the verification load,t,the Bayesian method is used to establish the resistance model,and the resistance degradation function is introduced to modify the resistance model.The in-service bridges experience the effects of various loads(verification loads)during bridge operation.The results of these verification loads are shown as structural responses,so the distribution function of the structural response can be substituted for the distribution function of the comprehensive verification loads.Studies have shown that the structural resistance established only by Bayesian method considering the verification loads will increase with time(verification loads),which is not consistent with the actual situation.Introducing the resistance degradation function to modify the Bayesian model,the resistance obtained is more practical and convenient for application.4)Comparative analysis of the uncertain factors affecting the structural design and the existing structure evaluation,the recommended values of the target reliability index of the existing bridge structure are given.Two methods for structural safety assessment are given—reliability index method and limit state method.Based on the analysis of the uncertain factors that affect the reliability of the existing structure,as well as the target reliability index of the building structure and bridge structure design stage,combined with the target reliability index of the existing building structure evaluation,this paper recommends that the target reliability index of the in-service bridge structure be selected to be one order of magnitude(0.5)lower than the target value in the design stage.The reliability index method and the limit state method are used to evaluate the safety of the key cables.The calculation results show that the results obtained by the two methods are basically the same,and the service life of the cables is greater than the service life required by the specification(20 years).The calculation results also show that the long stay cable has a higher degree of redundancy than the short stay cable in the early stage of the stay cable service.