Behavior And Calculation Method Of Self-anchored Suspension Bridge With Steel-Concrete Mixed Girder

In recent years self-anchored suspension bridges are developed rapidly. The spans are increasing and forms are various. There are a lot of self-anchored suspension bridges were just finished and under construction. Combined with the Pingsheng bridge, the self-anchored suspension bridge with mixed girder was studied in this paper. The main research achievements are as following:1. The limit span of self-anchored suspension bridge with mixed girder was studied. According to the material limit intensity condition of main cable and stiffening girder of self-anchored suspension bridge with mixed girder, the formula of the limit span of self-anchored suspension bridge was deduced. Both axial force and bending moment on the stiffening girder were considered. It is shown in the results that the limit span of self-anchored suspension bridge with mixed girder considering the action of the bending moment is less 3%～21% than that without considering the action of the bending moment. The influence factors, such as ratio of side span to main span, sag-span ratio, stiffness of hangers were studied, and the influence of sag-span ratio for the limit span of self-anchored suspension bridge with mixed girder is greatest.2. Based on energy principles, a method named two isolating bodies approaching method for calculating the behavior of self-anchored suspension bridge with mixed girder was proposed. The basic formulas for calculating the forces and deformation of stiffening girder and the horizontal component of forces of main cable of the twin-tower three span self-anchored suspension bridges with mixed girder and the single-tower two span self-anchored suspension bridges with mixed girder were deduced. The main cable and hangers of self-anchored suspension bridge were truncated and replaced by unknown forces in this method. The main cable and continuous stiffening girder were respectively taken as isolating body and analyzed by approaching method. The deformations of the main cable both under the dead load and under the live load were considered. The actions of both axial force and bending moment on the stiffening girder and beam-column effect were considered. The results of the examples show that the results got from this method coincide with those got from geometry-nonlinear FEM method and its convergence rate is fast.3. On the background of Pingsheng bridge in Foshan, the behavior of self-anchored suspension bridge with steel-concrete mixed girder was studied by the two isolating bodies approaching method. The results show that structure stiffness is increased by increasing the sag-span ratio of main cable and the upward camber of stiffening girder. Though the deformation of the main span girder can be reduced by increasing the flexural stiffness of stiffening girder, but the moment of stiffening girder will be greater. Compared with the earth-anchored suspension bridge with mixed girder, the self-anchored suspension bridge with mixed girder has great axial force. Because of the beam-column effect, it makes the moment and deformation of the self-anchored suspension bridge to be greater than that of the earth-anchored suspension bridge. But it is beneficial to the steel-concrete joint of mixed girder. The results of self-anchored suspension bridge with mixed girder coincide with those of self-anchored suspension bridge with steel girder under the same parameters, and the different is less 5%.4. The steel-concrete joint is one of the key of self-anchored suspension bridge with mixed girder. Contrast experiment on structural forms of steel-concrete joint of self-anchored suspension bridge with mixed girder was studied. Three steel-concrete joint models with different structural forms were designed and made. The FEM analysis, bending test, shear test, compression test, simulating actual bridge test and failure test were done. The results show that the failures of three models are not controlled with joints and their structures are reasonable. It is necessary for making the stiffness of steel girder be closed to the concrete girder by partly strengthening the steel box-girder near the joint and varying the stiffness of concrete box-girder. The connections of both two types shear connector—PBL shear connector and stud are reliable.5. Shear connector is an important force transformation element in steel-concrete joint. PBL shear connector is a new type shear connector. The push-out test of 59 PBL test samples composed of 20 different groups were designed and made. The mechanical behavior, ultimate bearing-capacity, and failure of PBL shear connector were studied. The influence factors for the ultimate bearing-capacity of PBL shear connector were discussed. They are compared with stud shear connector. The formula for calculating the ultimate bearing-capacity of PBL shear connector was put forward.The research achievements in this paper have been applied in Pingsheng bridge. All those can provide reference for the design of other self-anchored suspension bridges with mixed girder.