Initial Stress Analysis And Ultimate Bearing Capacity Study Of Long-span Concrete-filled Steel Tubular Arch Bridge

In recent years,with the rapid development of concrete-filled steel tubular arch bridge with the advantages of convenient construction,large overall stiffness,strong bearing capacity and good durability,the span is increasing.However,some problems are also encountered in the process of its development:before the composite structure of steel pipe and concrete is formed,the initial stress often exists in the steel pipe,which leads to the advance of the elastic-plastic stage of the CFST,the stiffness of the arch rib is reduced,Eventually,the overall bearing capacity of the bridge is decreased.Taking Tuzha Bridge as the engineering background,this paper studies the change of initial stress of steel pipe during the construction of arch bridge and the influence of initial stress on the ultimate bearing capacity of arch bridge.The main work is as follows:(1)The finite element models of Tuzha Bridge are established by using Midas Civil and BR analysis software,and the key data of the two models are compared to ensure the accuracy of the software simulation.Based on the principle of minimizing the initial stress produced by the steel pipe,the optimal pouring construction sequence of concrete in the pipe is determined.Then,the key section of arch rib is selected to analyze in detail the initial stress change of steel pipe and concrete in the optimal pouring process,so as to guide the actual engineering design and construction.(2)The influence of temperature change on the initial stress of steel pipe is analyzed,and the calculated closure temperature of Tuzha Bridge is determined according to the code.Based on the optimal pouring construction process,the changes of initial stress of steel pipe under three unfavorable working conditions of asymmetric pouring on both sides of the strait,asymmetric pouring of upstream and downstream,and asymmetric pouring of two axes(both sides and upstream and downstream)are analyzed,and the initial stress of steel pipe is less than 10%.Limit the height difference of concrete pouring and improve the pouring technology of concrete.(3)The initial stress model and the non-initial stress model are established respectively.Check whether the initial stress model is still in a safe state during the operation phase of the whole bridge after the completion of the optimal perfusion sequence.At the same time,the influence of steel pipe initial stress on the operation stage of arch bridge is compared and analyzed from the aspects of deformation,stress,internal force and so on.(4)The arch rib composite structure models are established by conversion section method,double element method and unified theory method respectively,and the differences of the three modeling methods are compared and analyzed.The nonlinear constitutive relationship between steel and concrete is expounded and verified.The whole bridge model is established by double element method in ABAQUS software,and the effects of steel content,steel strength,concrete strength and initial geometric defects on the ultimate bearing capacity of arch bridge under different initial stress and different initial stress are analyzed.The curve relationship between the initial stress degree β and the influence coefficient of ultimate bearing capacity Kp is fitted,and the fitting formula is obtained,and then compared with theβ-Kp formula in different codes.The results show that the fitting formula is more accurate in calculating the influence coefficient Kp of ultimate bearing capacity of Tuzha Bridge.Finally,the fitting formula is used to check the ultimate bearing capacity of Tuzha Bridge.