Mechanics Analysis And Optimization Research On The High-speed Railway U-shaped Continuous Beam Bridge

With the process of the high-speed railway "going out" is accelerating, high-speed railway bridges require new ideas on the design and construction. As a new type of improved channel beam, the U-shaped beam is of many advantages, such as steel saving, noise reducing, maintenance convenience and strong anti-seismic performance. However, researches were mostly limited to study the structural characteristics, application advantage of the U-shaped beam, and bending, torsion, crack and other static effect, the study of its bearing capacity status and optimize performance was rare. Now few engineering example of U-shaped beam has been used in the high-speed railway bridge. Therefore this article focused on the high-speed railway bridge of U-shaped continuous beam to study its performance and optimization, the main ideas are as follows:Firstly, this paper systematically reviewed the domestic and foreign projects and the development status of U-shaped beam in terms of a 40m+64m+40m prestressed concrete U-shaped continuous beam bridge, and summarized the finite element analysis theory,the stability theory,the ultimate bearing capacity theory,optimization theory and time history analysis theory, thus provided the foundation for better promoting U-shaped beam to be used in high-speed railway bridge projects.Secondly, in order to study the influence of material property on the structural characteristics for the high-speed railway U-shaped continuous beam bridge, a dynamic performance analysis Midas model was established, the research of 7 different strength grades of concrete from C40 to C100 was achieved. According to the displacement amplitude and frequency change range, the strength grade of concrete at C50 was determined for the high-speed railway U-shaped continuous beam bridge.Thirdly, in order to study the influence of section property on the structural characteristics for the high-speed railway U-shaped continuous beam bridge, the elastic stability analysis model and geometric nonlinear limit state analysis model were established respectively, this paper selected 6 kinds of solutions for the girder slab thickness, the girder slab width, the web thickness, the web height and the flange plate thickness separately and obtained the laws of buckling safety factor, and analyzed the ultimate bearing capacity of axial forces and bending moments for the high-speed railway U-shaped continuous beam bridge.Fourthly, in order to study the reasonable section property under certain span conditions for the high-speed railway U-shaped continuous beam bridge, on the premise of safety and economy to optimize the model, relative maximum principal stress and relative quality were selected as the two objective functions. Under the design variables of the girder slab thickness, the girder slab width, the web thickness, the web height, the flange plate thickness, and the constraints of tensile stress, compressive stress, shear stress and displacement, the optimization model of high-speed railway U-shaped continuous beam bridge was established and the reasonable parameters of the U-shaped beam cross section was determined.Fifthly, to investigate the reasonable span under certain properties of material and section for the high-speed railway U-shaped continuous beam bridge, according to the optimized result for materials and profiles, this paper established a dynamic performance analysis model, by way of two program types as "keep the middle span constant, vary the ratio of side span to middle span " and "keep the ratio of side span to middle span constant, vary the middle span " to conduct the reasonable span comparison. In this paper, the influence of the ratio of side span to the middle span on maximum bending moments of side span and middle span was explored, the reasonable ratio of side span to middle span for high-speed railway U-shaped beam bridge was selected to be 0.6 to 0.7. Using time-history analysis, based on the concept of hysteresis curve, the impact of span to energy dissipation capacity was determined and the reasonable middle span for high-speed railway U-shaped continuous beam bridge was defined to be 50 to 70m.