Analysis Of Mechanical Behavior Of Long-Span Stell Truss Cable-Stayed Bridges Under Ideal Completed State And During Construction

The long-span cable-stayed bridge, a king of indeterminate flexible structure with many redundant degrees, consists of three basic members:the tower, the cable and the girder with variant internal force under ideal completed state, coupling between ideal completed state and ideal state during construction and nonlinear behavior during construction. Based on a large span rail-cum-road truss cable-stayed bridge, this thesis investigates the methods of ascertaining the ideal completed state and the ideal state during construction, and analyses the mechanical behavior characteristics during construction in three different construction schemes with two calculation methods. One is considering linear effects; the other is considering geometric nonlinear effects.1. In this thesis, the basic static analysis theories of cable-stayed bridge are introduced briefly, mainly including the basic principles of the Finite Element Method, the development history of the geometric nonlinear analysis theories in the cable-stayed bridge, the methods of ascertaining the ideal completed state and the ideal state during construction.2. With the rigid bearing beam method and influence matrix method, this thesis comprehensively ascertains the ideal completed state of cable-stayed bridge. Through comparative analysis, the influence matrix method of ascertaining the ideal completed state is better. At the same time, in this thesis, axial force difference between the upper and lower chords of the main truss as a new optimization criterion of the main beam internal forces of steel truss cable-stayed bridge under ideal completed state is presented.3. Through summarizing the problems of traditional backward analysis method, based on the fundamental principles of unstressed state, unstressed state backward analysis method is presented. In the unstressed state backward method, the unstressed state parameters of the bridge as a link between the ideal completed state and the ideal state during construction. With catenary cable elements in simulating the inclined cables, the geometric nonlinearity during construction can be considered precisely.4. In this thesis, two methods are used to analyze mechanical behavior characteristics of three different construction schemes during construction. One is considering linear effects; the other is considering geometric nonlinear effects. According to research, before side span closure, the beam is in symmetrical cantilever state. At this moment, the emergence of asymmetric loads will cause mutations of the tower top deviation, the tower bottom moment as well as the installation elevation of the girder. It should be avoided possible in the construction process. When it is necessary to consider the impact of asymmetric loads, the linear calculation method will produce great error; the geometric nonlinear effects must be taken into account. After side span closure, the main beam is in asymmetric single cantilever state. At this moment, the geometric nonlinear effects can’t be ignored, and the consolidation between tower and girder will reduce the tower top deviation and the tower bottom moment r during construction.