Research On Reasonable State Of Completion And Construction Of Special-shaped Cable-stayed Bridge

With the development of bridge structure analysis theory and construction technology,special-shaped cable-stayed bridge has become the most competitive bridge type in the selection of Urban Bridge with its beautiful shape,which fully gives expression to the tension of the times and the vitality of the city.The tower of Yongding River Cable-stayed Bridge,west of Beijing,Chang’an Avenue,is the first steel tower in China with "Leaning,arch and twist" shape.The Influence of the special-shaped tower on the inner force and deformation of the bridge under construction is quite different from that of traditional cable-stayed bridges.Based on the monitoring items of the construction of Yongding River special-shaped cable-stayed bridge,problems of simulating special-shaped steel box structure are investigated in this paper.Furthermore,the FEM of the bridge is established,and the reasonable completed state and the reasonable construction state of the bridge under this special tower are thoroughly studied.The main work and achievements are as follows:(1).A fast and accurate method to convert BIM geometric model to FEM is proposed,and the automatic generation of special-shaped cable-tower’s nodes and elements is realized with Matlab;Furthermore,the Plate-Shell Element and Beam Element models of the tower are built by Ansys and Midas;And the reliability of beam element model to express complex steel box tower in static simulation is verified;Finally,3D FEM of the bridge is established by Midas Civil and its analysis is performed subsequently.(2).Reasonable completed state:In the basis of the influence matrix and the minimum bending moment energy method,considering the cable force constraints,the cable force uniformity constraints,the tower-beam displacement constraints and 3D constraints of torsion and transverse deflection,the optimal cable force of the bridge are obtained by solving the quadratic programming function with Matlab.The results show that:The inner force and displacement of the bridge under the optimized cable force are better than those under the original design,which verifies the reliability of the solution of the reasonable cable force under the spatial effect.(3).Reasonable construction state:The traditional Forward and Backward Method is complicated,its calculation efficiency is low for the simulations when structure closure is involved,and Non-Closure problem is usually occured.However,the Non-stress State Method reveals the essence of Non-Closure phenomenon,and the construction process of complex special-shaped structure can be simulated fully with it.Based on the Non-stress State Method,the Non-stress Length is calculated;and the difference between the ideal construction state and the finite element construction simulation under the section Non-stress Curvature is explained and compared;the influence of Non-stress Coupling between the segments of the tower and the girder on the structure under the characteristics of the leaning tower is calculated.Finally,taking the maximum advance and retreat of the nut of the tensioning end under the Non-stress Length into account,the key problems on the construction of the bridge are pointed out and analyzed;and the dismantling scheme of the bracket of the main girder and the tower is optimized,which shows the dismantling work can be completed safely and effectively under the premise of less cable adjustment,and the problems of reasonable construction state can be well solved by the Non-stress State Method.