Research On Key Problems Of Continuous Rigid Frame Bridge With Double-Leg Thin-Walled Piers In Long-Span Asymmetric Construction

With the development of traffic construction in mountainous areas,continuous rigid frame bridges are developing continuously in mountainous areas because of their mature construction technology and low construction cost.In this paper,based on the project of Liexi Bridge with small side span,the key problems such as closure technology,stability,temperature effect of large volume cap and deflection of main beam in construction stage of long-span asymmetric construction of continuous rigid frame bridge with double-leg thin-walled piers are studied.The main research contents of this paper are as follows:(1)Aiming at the beam section No.27 and No.28 in asymmetric construction,the differences of force and deformation of two asymmetric construction schemes on bridge construction are compared and analyzed by MIDAS/CIVIL.The first scheme is the design scheme,and the second scheme is an asymmetric construction scheme proposed in this paper.Then,on the basis of asymmetric construction scheme,the differences of main beam alignment and stress,pier displacement and internal force of the bridge under three kinds of closure sequence are compared and analyzed,and the difference of variable cross-section spatial stress at the bottom of pier in the ten-year stage of bridge completion is compared by MIDAS/FEA analysis.(2)taking the design closure sequence of Lixi Bridge as an example,the closure top thrust is calculated by using the analytical method and the optimization method based on the sum of the square of the horizontal displacement of the constrained pier top.The push closure reduces the horizontal displacement of the pier top of the bridge by 91.6%in ten years.The local deformation and stress of the adjacent box girder in the closure section are analyzed by using MIDAS/FEA.It is concluded that the main tensile stress of the box girder caused by jacking can be reduced by properly keeping the position of the steel pad away from the bottom plate,increasing the height of the steel pad,decreasing the height of the steel pad and increasing the top thrust of the steel pad.(3)The formulas for calculating the in-plane stability coefficient of bare pier state and symmetrical cantilever pouring state of double-leg thin-walled pier continuous rigid frame bridge are derived,and the variation rules of stability coefficient and pouring beam section of Liexi Bridge during construction are fitted.The effects of pier height,pier spacing,concrete strength and the position of single transverse beam on the stability coefficient of the bridge in the key construction stage are analyzed.(4)The temperature effect in the pouring process of the pier cap is simulated by MIDAS/FEA,and compared with the field monitoring data in the maintenance process,and then the influence on the temperature effect of the cap is analyzed from four aspects:initial temperature,ambient temperature,cooling pipe water temperature and cooling pipe flow rate.(5)Taking the actual project of Liexi Bridge as the background,this paper analyzes the influence of main girder concrete on the deflection of Liexi Bridge in four aspects:shrinkage and creep,prestress loss,construction error and foundation settlement.