Experimental Investigation For The Mechanical Behavior Of Steel And Steel-concrete Composite Bridge Towers

Steel bridge towers have the advantages of light weight, high strength, good durability and reliability, rapid construction speed and good seismic performance, but compared with concrete bridge towers, steel towers' slenderness ratio is large and the component plates are thin, thus the whole buckling and local buckling are liable to happen. Steel bridge towers have been used in many bridges in foreign countries for years, and receive more and more attention in China recently, but little research has been practiced until now. Steel-concrete composite bridge tower is a new type of bridge tower developed from the composite structures, which combines the advantages of steel tower and concrete tower, and will has wide application in bridge engineering, while the application and study are not reported yet in China. Therefore, this dissertation has a further study on the mechanical behaviors of steel bridge towers and composite bridge towers. Firstly, carried out two types of experiments, in the first type, the specimens were all steel tower segments, in the second type, the specimens were all composite tower segments, and in each type, the cross sections of the specimens were different. Then, based on the experiments, the finite element analysis and theoretic calculations were practised, in order to have an overall and systematical research on the steel bridge towers and composite bridge towers. At last, some practical suggestions were proposed to the design and analysis of steel and composite bridge towers which have been adopted by the new edition of highway steel bridge design code under revising. In details, the following aspects were investigated:1. The constitutions and cross sections of steel bridge towers in cable-stayed bridges and suspension bridges were studied, and a steel bridge tower segment specimen which has the typical constitution and typical rectangle cross section was designed. The specimen was tested under axial compression with a 20000kN compression testing machine, the local buckling mode and mechanical behaviors of the specimen were obtained from the test, and the failure mechanism of local buckling was also presented.2. Against the project background of a practical steel bridge tower, another bridge tower segment specimen of rectangle section with chamfers was designed and fabricated, an axial compression test was practiced, the local buckling mode, deformation and strain rules were acquired from the test. Through the comparison of the mechanical behaviors of the two steel bridge tower specimens with different cross sections, the influence to the stability of steel bridge towers caused by the two types of cross section was analyzed.3. According to the first type test, the finite element models of the specimens were established which using shell elements in software ANSYS, the linear and nonlinear stability analysis were both practised, in the nonlinear analysis, both material and geometric nonlinearities, as well as the initial local deformation were including. The calculation results show that the nonlinear stability analysis was in good agreement with the test results, which can be used in the stability design of steel bridge towers.4. In the second type test, the specimens were steel-high performance concrete composite bridge tower segments of rectangle section and rectangle section with chamfers as in the first type test, the specimens were also taken an axial compression test. The mechanical behaviors of composite bridge towers with the two different types of section were investigated, the contrast to the steel bridge towers were also practiced. The contrast results indicate that compared with steel bridge towers, composite bridge towers have much more bearing capacity, and the local buckling of the panels can be delayed, the composite bridge towers have obvious advantages in structure performance.5. According to the bearing capacity calculation methods of square and rectangle concrete filled steel tubular structures in relate codes in China and abroad, the bearing capacity of the composite bridge tower specimens was calculated after some corrections; furthermore, on the basis of the steel bridge tower tests, other calculation methods were put forward. The calculation results were compared with the test results, and the application scope of each method was determined.6. The static and stability behaviors of steel bridge towers adopting different tower styles were analysized using finite element method, the influence of tower style and location of the crossbeam to the static and stability characters, as well as the bearing load capacity of the steel bridge towers were also investigated.7. The appropriate constitution type of steel bridge towers was investigated, the influence of dfferent constitutions to the stability of towers was analysed. Furthermore, a design method of stiffeners was put forward, which can be referred to the design of the constitution in steel bridge towers.8. The connecting methods between steel bridge towers and foundation were studied, and the mechanical characteristics and the load transfer path of typical connecting methods were compared together, so the application principle of each method was obtained and presented.