Fatigue Analysis And Life Assessment For Large Span Prestressed Extradossed Bridge Under The Vehicle Load

Based on the finite element software ANSYS,fatigue analysis and life evaluation of Changshan bridge which is located in Dalian,Liaoning province under the traffic was analyzed in this paper.Changshan bridge is the first prestressed extradossed bridge across the sea in northeast China.Firstly,this thesis contract and summarize the development and progress of fatigue analysis of extradossed cable-stayed bridge domestic and abroad. For the bridge structure, extradossed cable-stayed bridge is different from ordinary cable-stayed bridge. Extradossed cable-stayed bridge is a rigid-flexible bridge,whose stay cables essentially play the role of external prestress cables. The appearance of more and more extradossed cable-stayed bridges domestic and abroad provides a wider space for the development of bridges. In recent years, accidents due to fatigue failure of the bridge emerged in endlessly,so the fatigue of structures also gradually becomes a research focus of scholars domestic and abroad.The determination of fatigue load spectrum is the key to study the fatigue characteristics of bridge under traffic load, the main methods to determine the fatigue load spectrum inclue specification, investigation and field measurement. British BS5400new fatigue design specifications,the U.S. AASHTO highway bridge design specifications and European steel fatigue design specifications all made relevant regulation of standard fatigue vehicle. Due to the Changshan bridge has not been opened to traffic, this thesis will use the U.S. standard fatigue vehicle to load.Determine fatigue "hot spots" based on static analysis of the structure,this thesis mainly analyze the structure fatigue for stay cable, midspan of main beam, tower-pier-beam connected part, midspan of side span and midspan of middle span. The fatigue of structure is determined by the stress amplitude of node under fatigue loading. For the stay cables, we only need to find out the one whose stress amplitude is the highest under the fatigue load,and evaluate its life according to its S-N curve and fatigue damage criterion.The changes of stress of each cable under traffic loads is also analyzed in this paper.For the reinforced concrete beams, drawing the main girder stress influence line to find out the unfavorable loading location of fatigue "hot spot" of main beam,then evaluate its life by using fatigue analysis software FE-SAFE combined with the fatigue properties of reinforced concrete.Based on the analysis results above,fatigue analysis methods for extradossed cable-stayed bridge was summarized,thus providing some basis for the fatigue analysis and life assessment of extradossed cable-stayed bridge.