Study On Wind Stability Of Long-Span Cable-Stayed Bridge Under Construction

Recently, the span of cable-stayed bridge have been greatly enlarged with the emergences of new materials and new construction technologies and refreshments of the bridge design theoies. Cable-stayed bridges with spans longer than1000m are becoming more and more. However, the increases of span length of cable-stayed bridges have caused a series of new problems, such as the increase of bridge construction time, the decrease of structural stiffness and of structural stability. Meantime, during the construction period, when different construction methods of are chosen,the bridge structural system is constantly changing which might eventually affect the final state of the bridge in completion. Thus some factors that will affect the design and construction of the cable-stayed bridge are becoming increasingly important, especially the wind stability of cable-stayed bridge.The wind stability of constructing cable-stayed bridge is a quite complex subject, including aerostatic stability, flutter, buffeting and galloping. And each one of them can cause the decrease of structural stiffness and overall stability of cable-stayed bridge in completion, increase of structural deformation and wind-induced vibration response. In order to ensure the security of the construction process of cable-stayed bridge, further researches need to be done on the wind stability of cable-stayed bridge under construction. Based on a Yangtze River bridge and using large scale finite numerical simulation software MIDAS/Civil and BSNAA(BRIDGE STRUCTURE NONLINEAR AEROSTATIC ANASYSIS) and BSFA(BRIDGE STRUCTURE FLUTTER ANASYSIS) written by FORTRAN Language, this thesis has analysed aerostatic characteristics, dynamic characteristics and aerodynamic stability of the critical stages in the construction process of the bridge.And by comparing with the results calculated through methods that are used in realistic construction processes,this thesis reveals the dynamic characteristics and the variation and mechanism of the wind stability of constructing cable-stayed bridges.The results show:as the construction progress continues,(1)the critical wind speed of aerostatic instability is becoming smaller and smaller with the lowest one at the maximum single cantilever stage;(2)the natural frequencies decrease slower in the later stages than the early stages.After the temporary piers are set,the vertical bending frequency increases remarkably. Many lateral-torsional coupled modes show up in the later stages;(3)the flutter critical wind speed is becoming lower and lower gradually with the lowest one in completion of the bridge. By completing the side spans and setting the temporary piers in side spans,the aerodynamic stability of the bridge under construction can be greatly improved;(4)compared with the results of wind tunnel test,the results calculated by the calculation method in Specification are much smaller which makes the calculation in Specification conservative.