Study On Main Arch Concreting Sequence Method Of The Concrete Filled Steel Tubular Arch Bridge

The main arch of the Concrete Filled Steel Tubular Arch Bridge(hereafter will be abbreviated as CFST)experiences three stages before it is completely moulded:the steel structure(before the concrete within a steel tube reaches the design strength),the encased structures and the stiff skeleton concrete structure(after the cross-section concrete is completed and the design strength is reached).Since the weight of the outer arched concrete and the weight of the stiff skeleton are very different,if too much concrete is poured at a time,the bridge may be unstable.Therefore,how to concrete the outer arch of the main arch has important research significance.This paper studies the character of external force during continuously and orderly concreting the outer wrapped concrete of the main arch by establishing a representative space model of the CFST using the finite element software ANSYS.Subsequently,this paper proposes an optimization scheme for how to segment and concrete the bridge and carries out a numerical analysis and finally discusses the feasibility of different concreting sequences of the main arch of the two 400m class bridges.The main research contents and results are as follows:(1)This paper simulates the construction process of continuously and orderly concreting the main arch,and analyzes the stress of the stiff frame using the influence line.It is concluded that the deflection and stress of each section change periodically with the concreting of the main arch.The 3/8 section deflection,the crown deflection and the stress of the upper chord steel tube and concrete are all reduced first and then increased,while the 1/8 section deflection,the 1/4 section deflection and the stress of the lower chord steel tube and concrete are first increased and then reduced.(2)In order to study the influence factors of the concrete segmentation method of the main arch,this paper designs three kinds of concrete segmentation methods for the representative bridge,namely three,five and seven rings,and analyzes the change of the stress and deformation of its stiff skeleton.It is found that in the three-ring segmentation methods the concrete stress and steel tube stress of the lower chord exceed 5.5%and 11%respectively;in the five-ring segmentation method the concrete stress and steel pipe stress are 2.2%and 8.4%above the limited value respectively;while in the seven-ring segmentation method,the stress of the steel pipe and concrete are within the limits.(3)This paper summarizes and analyzes the general concreting sequence of the main arch,and analyzes the feasibility of different concreting sequences.The results show that for the three-chamber arch bridge,it is feasible to concrete the main arch from the middle chamber to the side chamber and vice versa.For example,for the Wanxian Changjiang River Bridge,the external force of the concrete frame in the former sequence method is superior to that of the later.For the Nanpanjiang Bridge,the stresses of the arching concrete in the two concreting sequences can both reach the standard value of the axial compressive strength.However,when it is concreted from the side chamber to the middle chamber,the stress of the arch rib appears abrupt change,and hence needs close attention during the construction process.