Study On Long-term Deflection And Reasonable Precamber Of Continuous Rigid Frame Bridge

With the rapid development of highway traffic,the continuous rigid frame bridge is favored by many designers for its attractive appearance,economical expenses,driving comfort and large spanning ability.However,varying degrees of the deflection and cracking,which appear after the continuous rigid frame bridge is opened to the traffic,have posed a serious threat to the normal use and structural safety of the bridge.Although setting the precamber is an effective way to avoid the excessive deflection that occurs in the bridge operating stage,this kind of deflection also occupies a quite large proportion of the total deflection value.Therefore,based on the deflection of the existing continuous rigid frame bridge,developing the statistical analysis,studying the cause of this deflection and setting reasonable precamber have a great theoretical significant and engineering application value.This study is conducted based on a project of ‘Studies on the key technology of construction control in the continuous rigid frame bridge’ that is from Shaanxi provincial communication construction group.Extensive investigation,theoretical analysis and numerical simulation are carried out in this project.The sensitive parameters and reasonable precamber of the continuous rigid frame bridge and the prediction of the deflection in the bridge operating stage are studied.First,the real bridge simulation analysis model and the sensitivity equation are established by the finite element(FE)program and changing the parameter respectively,the sensitivity of the parameter can be studied subsequently.second,through the investigation on the status of the continuous rigid frame bridge in Shaanxi Province,the deflection prediction of single and multiple factors can be studied based on the Elman and RBF neural network method respectively.Third,a study on the deflection in the operating stage is performed through the constant load zero moment method.Finally,the least square method is used to study the exiting bridge’s precamber.This method is based on the precamber that acquired in the FE program.The results suggest that the main sensitivity parameters are the concrete bulk density,tension control stress,the elastic modulus of the main girder and the creep coefficient.The relations between the deflection and time,the deflection and the single factor deflection are nonlinear.These two models can predict the deflection well.The long term deflection can be controlled effectively using the constant load zero moment method.The calculated value of the precamber is close to the measured one,so it is reliable to use the optimized method to set the precamber.This study provides a reference to guide the design,construction and operation management of continuous rigid frame bridges.