Study On The Mechnical Behavior & Stochastic Sensitivity Analysis Of Creep Effect Of Half-Through Beam-Arch Combination Bridge On High-Speed Railway

With the strengthening effect of the main arch rib on the girder body, the integral rigidity of the half-through beam-arch combined bridge is improved. The bridge deck system and the main arch rib to form an entirety by the consolidation of the main longitudinal girder and the main arch rib, which makes the bridge meet the high requirements for lateral rigidity, vertical stiffness, torsional rigidity and deck smoothness of the high-speed railway. The flying swallow type of the half-through beam-arch combined bridge shows several advantages such as beautiful shape and can use various construction modes like suspending construction and rotation construction which has little influence on the traffic under bridge. It’s especially suitable for the urban and suburban areas, where expectations and demands for landscape are usually high. At present, there are still few documents in the half-through beam-arch combined bridge. Therefore the research studied systematically the structural system and the mechanical behaviors of the half-through beam-arch combined bridge based on an engineering practice. And the creep stochastic sensitivity of concrete-filled steel tubular (CFST) was investigated. The main research works are as follows:1. Based on the suspender tension membrane forces hypothesis, a simplified mechanical model of the half-through beam-arch combined bridge was constructed. The calculation formulas of the half-through beam-arch combination bridge internal forces and the vertical deformation of the mid-span section of the main arch rib and the main longitudinal girder were deduced on the basis of the deformation compatibility condition and the flexibility method. A calculation program was developed with Matlab software. Despite of the errors caused by suspender tension membrane forces hypothesis, the analytical solutions for project examples showed that the program had high calculation precision. The program has several advantages such as dispensing with modeling, flexible parameter modification and fast calculation, which can be used in scheme design phase as an estimation method.2. Based on the program, the reasonable ranges of the stiffness ratio of the arch to that of the beam, rise-span ratio, the side span to main span ratio and the ratio of floor system height are proposed. And the dissertation also studied influence of three kinds of structure system on the mechincal behaviors of the half-through beam-arch combined bridge based on an engineering practice.3. Based on an engineering practice of the high-speed railway half-through concrete filled steel box (CFSB) beam-arch combined bridge, the beam-arch consolidation region model test was designed and accomplished. The beam-arch consolidation region model test results show that the consolidation region is in elastic state under the design loads, with uniform stress distribution, definite load path, low stress level and local stress concentration of the concrete filled.4. Based on the generalized creep coefficient and the deformation compatibility condition of CFST, it is proved that the freedom creep strain of the core concrete can be regarded as basic variable to calculate the creep of CFST. The equivalent thermal load method is proposed to calculate the creep of CFST. Three typical concrete creep coefficient models are modified to analyze the creep of axially compressed CFST members under long-term loading by equivalent thermal load method and the finite element software. This method simplifies the analysis process of the creep of CFST, which only need to impose the equivalent thermal load on the core concrete of CFST members. The feasibility of the equivalent thermal load method is verified by comparing with the calculated creep values and the measured creep values of CFST models.5. The adaptive hybrid particle swarm optimization is proposed by improving the particle swarm optimization, and the optimization analyses of several multi-dimensional and multi-modal functions show that the adaptive hybrid particle swarm optimization can perform good robustness and accuracy of searching optimization. The adaptive hybrid particle swarm was used to optimize the parameters of the support vector machine. The support vector machine which possesses significant learning capacity at a small amount of information and generalization was used to fit the explicit function of creep for CFST. Based on the explicit function, sensitivity coefficients of random variables were calculated. And combined with the Monte Carlo Simulation, the stochastic analysis of structures was accomplished. Two model test analyses of creep for CFST members were used to verify the feasibility and accuracy of this method on stochastic sensitivity analysis of creep for CFST. The sensitivity of random variables to the creep for CFST members was investigated.6. Based on the equivalent thermal load method, calculation formulas of the thermal gradient load are deduced to calculate the creep effect of the CFST structures under bending moment and compression load. This method was used to analyze the creep effect of a half-through CFSB beam-arch combined bridge on high-speed railway. By the support vector machine and the Monte Carlo Simulation, the stochastic anslysis to the steel box and concrete creep effect on internal force and stress of the dome, the beam-arch consolidation region and the springer for the main rib were accomplished. And the stochastic analysis for the displacement increment creep effect of the mid-span section was also accomplished. The sensitivity of random variables to the creep effect for the half-through CFSB beam-arch combined bridge was investigated.