Bridge Performance Evaluation Based On Monitoring Data And Multi-scale Finite Element Model Analysis

How to ensure the safety performance and long-life requirements of important engineering structures is the focus of civil engineering.Temperature plays an important role in the safety performance of bridge structures.Owing to the effect of solar radiation and other environmental effects,the nonlinear temperature gradient is formed on the girder cross-section of long-span bridges,which produces a significant temperature effect.The phenomenon of stress concentration may be appeared on bridge local structural components,and a great deformation is caused.It may eventually lead to structural performance deterioration and local damage.Research indicates that the temperature induced stress caused by the nonlinear temperature gradient is even greater than the structural stress caused by vehicle load and wind load.It can be seen that the temperature plays a great role in the safety performance of bridge structures.In summary,it is very important to assess the safety performance of long-span bridges.For evaluating the safety performance of bridges,an accurate finite element model is needed,so this paper focus on geometric topology,boundary condition and mechanical parameter to update the accuracy of the finite element model.The research of the paper includes the multi-scale finite element method for temperature stress analysis of local components of bridges is used to elevate the geometric topological form of the model,the bridge longitudinal constraint stiffness identification method based on temperature and displacement monitoring data is used to enhance the boundary conditions of the model,and the multi-model finite element analysis method based on Markov Chain Monte Carlo(MCMC)sampling and response surface technique is used to upgrade the mechanical parameters of the model.The main studies of the paper are as follows.(1)The monitoring data of two long-span steel box girder bridges,including a cable-stayed bridge and a suspension bridge,were analyzed.The statistics analysis includes the temperature distribution,displacement-temperature correlation,strain-temperature correlation,and cable forcetemperature correlation.Based on the basic assumption that the temperature variation along the longitudinal direction of the girder of the long span bridge is very small and the statistical law of no transverse temperature gradient along the crosssection of the box girder with wind fairing components,it is concluded that the temperature field of a long span steel box girder bridge with wind fairing components can be analyzed with a one-dimensional vertical temperature gradient.The longitudinal displacement of the beam increases with the increase of temperature and decreases with the decrease of temperature.The two have a strong linear correlation.However,there is a time delay effect of temperature,and the lag time is about 1 hour.In addition,the correlation between temperature and strain of the girder under one-day solar radiation and the correlation under one year seasonal temperature variation wereanalyzed respectively,and it was found that the strain and the temperature were significantly correlated.Cable force is less affected by temperature.(2)Bridge temperature-induced stress analysis were carried out based on multi-scale finite element method and monitoring data.By modeling local components such as U-shape stiffeners in the overall model,the geometric and topological forms of actual bridges can be accurately described.The temperature field of Sutong long-span steel box girder cable-stayed bridge was analyzed in this paper.The boundary conditions of temperature field can be determined by two parameters,absolute radiation temperature and compositive heat transfer coefficient.The temperature field finite element model of Sutong bridge was established,and the nonlinear temperature distribution along the girder crosssection was obtained.The calculated results are in good agreement with the measured temperatures.In addition,the calculation results of temperature field could be used as load in the finite element model of subsequent analysis of stress field.In the overall model,the traditional finite element method is difficult to analyze the local components,such as steel box girder's U-shape stiffener.In this paper,the multi-scale finite element method was used to analyze the temperatureinduced stresses of local components.The multi-scale method was verified by finite element models of a cantilever plate and a box girder bridge.The results show that the multi-scale finite element model is closer to the real value than the traditional finite element model,and greatly improves the computational efficiency.Finally,the multi-scale finite element analysis method was applied to Sutong bridge,and the internal components of the box girder were considered in detail,such as Ushape stiffener and longitudinal truss.And traditional elements were used to simulate the structure of cable towers and cables.The substructures were integrated to form a multi-scale finite element model of Sutong bridge to analyze the temperature-induced displacement and temperature-induced stress in stress field.The results show that the temperature-induced displacement and the temperature-induced strain calculated by the multi-scale model agree well with the measured values,and it can effectively improve the computation efficiency and solve the problem of analyzing local components in the whole bridge model.(3)Longitudinal restraint stiffness identification of long-span bridges based on temperature monitoring data.The selection of boundary conditions is an important factor affecting the accuracy of finite element analysis.In this paper,a longitudinal constraint stiffness identification method based on temperature and displacement monitoring data was proposed to identify longitudinal boundary conditions.Identified longitudinal constraint stiffnesses were substituted into the finite element model of a long-span suspension bridge,and the calculated values and measured values of displacements at the end of the girder were compared.The results show that the longitudinal displacements are more accurate considering the longitudinal constraint stiffness.(4)Uncertainty analysis of bridge multi-model based on MCMC sampling and response surface technology were carried out.The mechanical parameters directly affect the results of finite element analysis.However,with the increase of structure service time,the structural performance will gradually degenerate,and the uncertainty of structural mechanical parameters including elasticity modulus,density,etc.will also increase.Multi-model can be used to analyze the uncertainty of bridge structure.In this paper,a multi-model analysis method based on MCMC sampling and response surface methodology was proposed.Based on the idea of multi-model,the MCMC sampling theory was used to sample the key parameters of the structure,and multiple finite element models with uncertainties in covering structural parameters were established.The amount of computation will be greatly increased by multi-model method.For complex bridge models,multi-model analysis is difficult to carry out by ordinary computers.In order to improve the computational efficiency,response surface methodology was introduced in the analysis of multi-models,and the mathematical relationship between structural uncertainty parameters and structural responses was constructed by using second order response surface.By using the response surface model instead of the finite element model,the computational efficiency is greatly improved,and the method of multi-model can really be applied to practical structures.