Construction Analysis And Finite Element Model Modification Of Rigid Construction-continuous Composite Bridge With Low Pier In Closure Jacking Stage

It is an important part for closure jacking construction of the low pier rigid frame-continuous composite bridge.In order to guide the work of bridge closure jacking,the theoretical values of force and displacement in closure jacking are usually calculated by analytic formula method and finite element method before bridge closure jacking.However,there is a difference between the theoretical structure and the actual structure based on the design data,which makes the theoretical value and the measured value often inconsistent.Therefore,this paper takes the closure jacking construction of rigid frame continuous composite bridge with low pier as the research background,and studies the problems in the construction stage of this kind of bridge.The main research contents are as follows:(1)Midas Civil 2020 was used to establish the initial finite element model of the bridge,and then the analytical formula method and finite element method were used to calculate the jacking force respectively.The calculation shows that the final thrust value calculated by the analytical formula method was about 7.8%,larger than that calculated by the finite element method.Then,the actual closing roof thrust was determined according to the field conditions,and the simulation analysis was carried out in the construction stage of the closure jacking to obtain the theoretical value of the pier top horizontal displacement under the progressive pushing force.Finally,the theoretical and measured values of horizontal displacement of pier top were compared,and the difference between the initial finite element model and the actual structure was analyzed.(2)Eight influencing factors were selected from the aspects of structural material properties and load action,and the horizontal displacement of the top of the jacked construction pier,the horizontal displacement of the top of the completed pier and the bending moment of the bottom of the pier were taken as the evaluation criteria.Then,the sensitivity analysis of the parameters of the jacking construction model of the bridge was carried out.It can be determined that the elastic modulus Ea and Eb of the concrete of the main beam and pier are the important parameters affecting the horizontal displacement of the pier roof,and the corresponding sensitivity coefficients are 0.45 and 0.69.The prestressed tension force of the bottom plate and the elastic modulus σb and Eb of the concrete of the pier are the important parameters affecting the horizontal displacement of the pier top of the bridge,and the corresponding sensitivity coefficients are 36 and 16.The prestressed tension force of the bottom plate and the elastic modulus σb and Eb of the concrete of the pier are the important parameters that affect the moment of the pier at the bottom of the bridge,and the corresponding sensitivity coefficients are 19.33 and 8.(3)According to the parameter sensitivity analysis for the influence of jacking construction of pier top horizontal displacement of the important parameters of Ea and Eb and relying on the bridge closure pusher pier top horizontal displacement of the measured results,the horizontal displacement of the pier top are obtained by the response surface method,the response surface function and build the corresponding objective function,and then with the help of the modified particle swarm optimization algorithm and genetic algorithm optimization of target function,and get the parameter modification value.Then,the revised parameter value is substituted into the initial finite element model to calculate the revised horizontal displacement of the jacking,which is compared with the measured displacement value to verify the accuracy and calculation accuracy of the modified bridge model.The correction results show that the relative errors of horizontal displacement of pier tip of GX06 and GX07 are reduced to 4.05%and 5.66%,and the model correction results obtained by the two methods are better,and the model correction efficiency of the improved particle swarm optimization algorithm is higher than that of the genetic algorithm.