Research On Key Problems Of Cantilever Erection Construction Of Long-Span Concrete Arch Bridge

When the reinforced concrete arch bridge needs to cross the complex terrain conditions such as high mountains and deep valleys,the integral prefabricated hoisting construction arch ring is more economical,which has the unique advantages of short working time at high altitude and good overall performance of the structure.With the increase of the span of reinforced concrete arch bridge,the difficulties of construction brought by super-long-span arch ribs can not be ignored.Reasonable buckle and anchor cable force are related to the stress of the arch ring,and the optimization of construction process is helpful to improve the safety of the structure.In this report,taking the Jianniuluhe Bridge as the engineering background,combined with the scientific problems found in the construction process,some problems will be studied in four aspects:reasonable construction cable force calculation,reasonable arch foot sealing time,arch rib joint treatment technology and buckle and anchor cable removal technology.The main contents and achievements are as follows:(1)The stress control principles and stress characteristics in the cantilever assembly construction of long-span concrete arch bridge are expounded.The construction stress control strategy of cable-stayed buckle cantilever assembled arch bridge is clarified.Taking the minimum square sum of the maximum bending moment of the key section of the arch ring during construction as the optimization objective and the stress of the arch rib as the constraint condition,the optimization calculation method of cable force in cable tension construction is deduced based on the balance principle of influence matrix and force,and the reasonable construction cable force is solved with the help of Matlab optimization toolbox,which solves the problem that it is difficult to control the stress of arch ring section in the process of cantilever assembly construction of arch bridge.(2)The finite element model of Niuluhe Bridge in the construction stage is established by using the finite element software Midas/Civil.Based on the two construction schemes of"re-sealing the arch foot after installing the arch section" and "re-sealing the arch foot after the installation of the closure section",through the relationship between the initial tension of the buckle cable and the weight of the arch rib segment,the rationality of the cable force calculation method in this paper is verified.The finite element software Midas/FEA is used to establish the solid simulation model of the arch foot,which is included in the construction stage,and the stress distribution of the arch foot is analyzed.(3)Taking arch ring stress,arch foot steel member stress,cable force change rate,cable force uniformity and arch ring stability coefficient as evaluation indexes,the timing of arch foot sealing and the optimal number of lag segments of arch rib temporary joints are studied.The analysis results show that after the installation of the arch foot of the Niuluhe Bridge and the temporary joint lags behind the pouring of one segment,the maximum tensile stress of the arch section is less than 1.50MPa,and the cable force change rate,cable force uniformity and arch ring stability are relatively good.The stress of arch foot steel members is within the range of safety factor of 2.0,which optimizes the construction process and achieves the goal of construction control.(4)Because the maximum tensile stress of the arch ring section in the construction process of the traditional cable removal scheme is 4.82MPa,through the parameter sensitivity analysis of the concrete stress in the closure state of the key section of the main arch ring,the cable removal sequence is optimized.At the same time,taking the minimum sum of the square of the bending moment of the key section of the main arch ring as the optimization objective,the cable dismantling sequences is determined based on the bending moment influence matrix and cyclic statement in the process of cable dismantling.Finally,the effects of different cable removal sequence on the change rate of cable force,the cable force near the buckle cable and the stress of arch ring are analyzed.