Closure Analysis And Optimization Design Of Five-span Continuous Beam Bridge

With the vigorous development of China’s transportation industry,prestressed concrete continuous beam bridge has been widely used,but such bridges often appear mid-span deflection and beam cracking and other diseases.In order to solve these two kinds of diseases,this paper takes Sitan Xiangjiang Bridge as the engineering background,based on the optimization of closure construction technology,puts forward the design optimization scheme of UHPC-NC hybrid girder bridge from the perspective of material and design.The specific research of this paper is as follows:(1)Based on the actual project,two types of six closure schemes are proposed,and the finite element models are established by Midas/Civil software.The influence of different schemes on the alignment and stress of the bridge during the closure completion stage,the completion stage and the creep stage is analyzed.The results show that the second scheme can cause a deflection mutation of up to 250 mm at the closure section,and the stress near the midspan may exceed 1.6 times of the first scheme,and the creep deflection of the second scheme changes more.Finally,combined with the engineering practice,scheme one is determined as the best closure scheme.(2)Aim at the calculation of the additional pressure weight needed to eliminate the closing deviation,the error of the calculation result is reduced by 2.5%considering the influence of shear deformation of the beam.The influence of single closing deviation on the stress in different construction stages of the bridge is analyzed.The results show that the secondary middle span deviation is more sensitive to the closing deviation than the middle span deviation,and the influence of the secondary middle span deviation on the stress of the beam body is about 10%more than the middle span deviation.At the same time,through the analysis of the existence of multiple closure deviations,the results show that the effect of multiple closure deviations can be regarded as the superposition of single deviation effect.(3)Based on the response surface method,the response surface model between the optimization parameters and the objective function is established to optimize the design parameters of the UHPC-NC hybrid girder bridge.The optimal combination of parameters is obtained,that is,the thickness of the roof of the mid-span section is 22 cm,the thickness of the web is 25 cm,the thickness of the bottom plate is 32 cm,the replacement length ratio of UHPC is 0.63,the number of beam bottom curves is 1.8 and the height of the mid-span beam is 3.35 m.The optimal parameter combination is used to establish the model and the original scheme for comparison in bending moment,deflection and stress.The comparison results show that the pier top bending moment of the new scheme is significantly reduced compared with the original design,the overall bending strain energy is reduced by more than 30%,the beam element stress is reduced to varying degrees,and the mid-span deflection is reduced by more than 20%.