The Analysis Of Composite Girder Cable-stayed Bridge With Three-tower Based On The Forward-iteration Method

The composite cable-stayed bridge is developing quickly in china recently years which have the advance of fewer steel consumption, lower deadweight and reasonable construction cost. The constructing Wuhan Erqi Yangtze river bridge which girder composed by the steel I beam and concrete deck is the largest composite girder cable-stayed bridge with three towers of the world. To ensure the bridge have a reasonable load distribution in finished bridge state, so grasping the internal force of the constructing is quite necessary. The methods carried out to analyze the bridge construction present have forward-calculation method, taking-away method, forward-iteration method and so on, above all, the forward-iteration method can simulate the construction process and could avoid the question of calculation outcome non-closed.This document takes the Wuhan Erqi Yangtze river bridge as background, firstly to make an whole thought of the way to simulate composite girder bridge construction, to discuss the calculation theory of the composite girder bridge constructing, and then based on the forward-iteration method, a FEM analysis modal of the bridge was built in the Midas/Civil program, after calculation, the reasonable finished bridge state and construction state can be get, and the reasonable final cable force can be calculated. The main conclusion of this document as following:(1)Summarize the basic theory of the construction method and simulation of large-span composite bridge;(1)Based on construction process analysis data of existing cable-stayed bridge, Summary the construction method and calculation of the basic theory of large-span composite cable-stayed bridge. Currently often used methods,such as forward method, backward method, forward-backward iteration method and unstressed state method, More or less exsit a not closed problem, that is the state Calculated by these methods of control parameters loaded into the bridge forward-calculation and the state designed to finished bridge state is inconsistent, however, forward iteration method only needs forward-calculation, and it can minimize the impact of not closed by using the differential method.(2) Based on the forward-iteration method,a FEM modal of Wuhan Erqi Yangtze river bridge considering two-girders of the bridge was built in the Midas/Civil program, Analyzing the internal force of bridge, displacement, and cable tension of the various stages of the construction and completed bridge state.comparative analysis reasonable completed bridge state, Ultimately determine Segment elevation, the internal force of main girder,cable tension of each construction stage. The calculation results show that:compared the cable tension of reasonable construction stage to completed bridge state, errors are within±5%.The maximum high throw of main girder is 40.3cm, tensile stress of concrete Bridge deck does not appear,and the maximum compressive stress is 8.8Mpa,the maximum compressive stress of bottom flange of the main steel girder is 159Mpa,which can illustrate the force in construction stage of the composite cable-stayed bridge with three towers is reasonable, the internal force of main girder, tension and displacement meet the design specifications.(3)In the construction process, due to the accumulation of the deformation, internal forces accumulate, the Maximum cantilever state is the most adverse conditions in the process of assembling cantilever. After completed construction of a segment, the construction of following 5-10 segments have a large influence on each parameter of the stage.So,it should give attention to the construction of following 5-10 segments,which can ensure the safety of the construction process and make completed bridge state meet the design specifications.