The Theory And Model Test Research On Stability Of Self-anchored Suspension-cable Stayed Bridge Steel Box Girder

Changhong Bridge employed the self-anchored cable-stayed suspension cooperative system with low span ratio of the main cable and small horizontal angle of the stay cable.The steel box girder stability of main bridge becomes the key problem due to the applied high axial pressure all over the bridge.In this thesis,a scaled model test of the steel box girder,a full-scale model test of the stiffened plate and numerical simulation analysis are used to investigate the stability of steel box girder.Take the experimental and numerical results into consideration,the author established a simplified calculation model and calculation method for the stability bearing capacity of U-type stiffened plate.The detailed achievements are shown as follows:(1)Summarized a detailed literature review about the development,application and limitation of the self-anchored cable-stayed suspension cooperative system bridge and orthotropic plate,and illustrated the significance of the stability problem of steel box girder structure.(2)Used the finite element method to analyze the whole bridge stability of Changhong Bridge project,and selected the most risky segment as a reference to design a scaled model test with the scale ratio of 1:4 and the model size of 10.5×3.2×1.1 m.Additionally,a large-tonnage synchronous loading system was designed to support the test.The result shown that the elasticplastic local buckling initiated at the bottom plate of the No.2 chamber and the buckling failure load reached up to 21,600 kN.The test data was analyzed to investigate the structural stress conditions,force transmission and damage characteristics.And the test method and test results could be the data base for the study of the stability problem of steel box girders.(3)Single-rib,double-rib,and three-rib plate was designed to run the full-scale stiffened plate stability test.The digital image correlation(DIC)technology was adopted to observe the structural stress conditions of different loading position.The local buckling at the end of U ribs of stiffening plates was observed in the axial compression test.Then most of the axial force at the buckle position will be transmitted to the sub-plate,and further loading will cause local instability at this position of sub-plate.(4)Based on the tests,the U-type stiffened plates was analyzed,the failure mechanism of the steel box girder and the stiffened plates were illusrated.In the steel box girder segment,the stress eccentricity of the stiffened plate were different.With the eccentricity increases,the compression strength of U rib was weakened.The steel box girder model test and stiffened model test results shown that loading accord to the centroid of the sub-plate matches the site better.Take the material nonlinearity,initial geometric imperfections,residual stress into consideration,the ultimate bearing capacity of the stiffened and steel box girder were investigated by finite element method.And the impact of initial eccentricity on the bearing capacity of stiffened plates were studied by comparing the numerical results and experimental results.(5)Based on the experimental and numerical results,a theoretical analysis were employed to established two calculation models for the stable bearing capacity of U-type stiffened plates.Simplifying the U-rib as the elastic restraint on the non-loaded side,the first model focused on the sub-plate between U-ribs,and developed the critical buckling load calculation formula for the axially compressed plate based on the energy method.This critical load is the lower limit of the load-carrying capacity of the stiffening plate.Considering the stiffened plate geometry centroid as the reference axis and both stiffeners and the sub-plate suffering from the pressure,the second model developed a calculation formula for the upper limit of the load-carrying capacity of the stiffened plate by determining its equivalent thickness.These two models has been verified by the numerical simulation methods.In addition,the parametric analysis of related impact has been carried out.