Research On Structure System And Mechanical Characteristics Of Long-Span Rail-Cum-Road Suspension Bridge

With the progress of science and the advancement of new materials and technology, the span of the suspension bridges is becoming longer and longer, and it has been used in the construction of railway. With the appearance of the longer span suspension bridges, in order to meet the high standards of operational requirement of the railway suspension bridges, some new solutions need to be seeked to improve the serious problems of single-cable suspension bridge stiffness, the limitations of a ultra-large span and widely used in the railway construction.The global stiffness of the suspension bridges mainly come from the cable system. The new cable system, because of the difference of the structure with the single-cable suspension bridges, leads to its different mechanical characteristics. In this thesis, the two kinds of cable system of the suspension bridge were studied, which were double-layer-cable system and double-stranded system. Hoping the conclusions can be used for the reference of the ultra-large span suspension bridges and rail-cum-road suspension bridge during scheme selection and preliminary design.1) By taking a strait-crossing rail-cum-road suspension bridge as an example, the full-bridge finite element model of the single-span and three-span single-cable suspension bridge, the double-layer-cable suspension bridge and double-stranded suspension bridge were established with the bridge nonlinear anlysis system BNLAS. the double-layer-cable suspension bridge and double-stranded suspension bridge dead load state, internal force and deformation under live load, deformation under the action of the horizontal wind, analysis of train bridge static effect, vibration characteristics to compare to single-cable suspension bridge, the analysis of the stress state of the two kinds of cable system, vertical stiffness, lateral stiffness, driving and dynamic characteristics, finally the results show that the advantages of double-layer-cable suspension bridge and double-stranded suspension bridge to improve the vertical stiffness of the bridge structure and improve driving stability, but the cable system has little effect on the lateral stiffness.2) Refer to the deflection theory of the single-cable suspension bridge, through detailed derivation, balance differential equationes of single-span double-layer-cable suspension bridge and double-stranded suspension bridge were established, by solving the differential equation, the analytic formulas for the main cable horizontal component of incremental, the stiffening girder internal forces and deflection under live load could been received; the preparation of dynamic programming in FORTRAN software is based on analytical method for calculation program; with the apply of BNLAS finite element model, analytical calculation results with the finite element results were compared to verify the correctness of the analytical analysis methodology and programming; The results show that the influence lines of the double-layer-cable suspension bridge and double-stranded suspension bridge analytic calculation program is consistent with the results of finite element analysis, also the stiffening beam bending moment and deflection envelope figure are closer, analytical formula of the double-layer-cable suspension bridge and double-stranded suspension bridge is correct, and the calculation program is available.3) By the calculation program,the influence of rise-span ratio and distribution ratio of dead load in the two layer main cables on the static characteristic of the double-layer-cable suspension bridge was studied, also the influence of sag-span ratio and ratio of side span to main span on the static characteristics of the double-stranded suspension bridge. Through discussion about the amount of material and structural stiffness in the different parameters, center on the consideration the height of tower, the stiffening girder internal forces, the main cable area and structural stiffness, so as to offer reasonable range of rise-span ratio and dead load distribution ratio of double-layer-cable suspension bridge, and the rise-span ratio of the double-stranded suspension bridge.