Study On Mechanical Behavior And Arch Formation Control Of Single-Tower With Double-Anchorages In Two-Span Continuous CFST Arch Bridge

The main arch ribs of continuous Concrete-Filled Steel Tubular(CFST)arch bridges are often constructed using the "single-tower with double-anchorages" cable-stayed anchorage system,which controls the lifting of both sides of the arch ribs with a single anchorage tower.Compared with the traditional "single-tower with single-anchorages" system,the "single-tower with double-anchorages" system has a more complex mechanical behavior during asymmetric construction,with greater difficulties in controlling the arch rib geometry and anchorage tower deviations.This thesis conducts an in-depth study on the mechanical behavior and arch forming control of the "singletower with double-anchorages" system for two-span continuous CFST arch bridges,using the Shuangbao Special Bridge as a background.The main research contents and achievements of this thesis are summarized as follows:(1)Regarding the problem of single-time solution of cable forces during the entire arch formation process of single-span arch bridges and continuous multi-span arch bridges,this paper explores the cable-stayed anchorage systems with both symmetric and asymmetric arrangements based on the stress-free control theory,as well as the cablestayed anchorage system with a "single-tower with double-anchorages" configuration,and proposes an optimization method for cable forces,establishing a model for solving cable forces.Based on the above,a simplified finite element model is proposed for the optimization calculation of cable forces in the construction of continuous arch bridges using the "single-tower with double-anchorages" system,and is validated through a background engineering project.(2)Based on the construction of multiple influential parameters,an optimization model for cable force solution was established.The effects of constraint conditions and objective functions on the optimal cable force solution were analyzed,and the influence of errors in the arch foot hinge sealing and the jointing of the closure segment during arch rib installation on the arch geometry and internal forces was discussed.The research results show that by taking the minimum real cable force of the maximum true cable force as the objective function and strictly constraining the turning angle of the embedded segment,while ensuring that the tower deviation,the arch axis deviation,and the minimum real cable force are within the allowable range,a relatively optimal cable force solution can be obtained.(3)Regarding the control issues of the "single-tower with double-anchorages" cablestayed anchorage system during asymmetric lifting construction,three precise control methods are explored based on anchorage tower deviations,structural internal forces,construction costs,and construction period control.These methods include the rear hanger cable control method,rear hanger cable-cantilever temporary cable control method,and temporary backstay cable control method,and their characteristics are compared and analyzed.(4)Regarding the symmetrical arrangement of arch ribs using the "single-tower with double-anchorages" system on the mid-span tower,this study derived formulas for calculating the arch rib installation deviation caused by segment installation errors and weight errors,and analyzed the impact of these errors on the arch rib installation profile.The study found that the installation and weight errors of one side of the arch ribs can cause deviation in the installation profile of the other side through the tower deviation,especially for the low segments’ installation errors and the high segments’ weight errors,which have a significant effect on the subsequent segments’ elevation and alignment deviation.Therefore,this study explored a real-time and precise control method for the tower deviation based on the influence matrix method and derived the theoretical calculation formula for controlling the arch rib installation error using the shim steel plate method,aiming to reduce the impact of construction errors on the arch rib installation profile and improve the installation accuracy.