Deformation And Stability Problems In Construction Of High Pier Long Span Continuous Rigid Frame Bridge

With the rapid development of highway construction in China,it is necessary to cross rivers and valleys.Long span and high pier continuous rigid frame bridges are highly favored by designers due to their strong crossing ability,reasonable stress,and fast construction.At the same time,with the continuous increase of bridge crossing capacity,issues such as mid span deflection and deformation are becoming increasingly prominent.During the construction process,the stability of bridges is also highly concerned due to various unbalanced construction loads and adverse stages such as maximum cantilever.This article takes the Santan Bridge as the engineering background and uses the large-scale finite element software Midas/Civil to study the deformation and stability issues of the bridge during construction.The main tasks are as follows:(1)The deformation problem of high pier and long span continuous rigid frame bridges is mainly caused by concrete shrinkage and creep.Correct calculation of bridge shrinkage and creep deformation can accurately predict bridge structural deformation.Analyze the theory of concrete shrinkage and creep,compare existing concrete shrinkage and creep prediction models,summarize the influencing factors and applicable conditions of each model,and provide some suggestions for selecting concrete prediction models in practice.(2)Taking the Santan Bridge as the engineering background,it was found that shrinkage and creep have a significant impact on the deformation of the bridge structure,and different concrete shrinkage and creep prediction models have significant differences.As the loading age increases,the deformation of the bridge structure gradually decreases,and each model has different sensitivity to the loading age.Adopting three construction schedule methods,comparing and analyzing reasonable construction processes to reduce bridge structural deformation and improve bridge structural safety.Based on the two construction techniques of the closure section-weight pressing and pushing construction,the analytical solution calculation formula for displacement under the action of weight pressing and pushing force is derived through the force method.Using finite element analysis to analyze the parameters of jacking force and weight,obtain the displacement and deformation values of the bridge structure under various levels of weight and jacking force.The results indicate that the deformation value of the structure varies linearly under the action of pressure and thrust,and the degree of influence on the deformation of various parts of the structure varies.(3)Explain the classification of stability problems,the analysis methods for the stability of compression bars,as well as the judgment of stability and the calculation method for stability coefficients.Combined with the stability theory of bridge structure during construction,the energy method is used to calculate the stability formula of the high pier self,the maximum cantilever stage and the completion stage.Through numerical simulation of the structural stability of the bridge in different stages,the gap between the theoretical calculation and the numerical calculation results is small,and the bridge structure stability in the maximum cantilever stage is the worst.(4)Analyze the overall and local stability issues of the bridge structure under the influence of the wall thickness of hollow thin-walled high piers.Simplify the thin-walled piers into four simply supported plates for stability analysis,and obtain structural measures to avoid local instability of hollow thin-walled high piers,as well as the limit value of the section width thickness ratio.(5)Compare different structural defect simulation methods,use the consistent defect method to simulate the pier offset value of the bridge structure in the longitudinal direction,transverse direction and two-way coupling,analyze the structural stability under different offset values,and take certain measures to avoid pier offset.Combined with local environmental conditions,calculate the wind resistance design wind speed of the bridge,simulate the wind load at the maximum cantilever stage and the completion stage,and compare and analyze the impact of wind load on the structural stability of the bridge.