| Cable-stayed bridge is a combined system of cable, tower and girder. It has become the main type of long-span bridges with its good mechanical performance and economic indicators. It is also widely used in railway bridges. As the link structure between the cable and the girder of the cable-stayed bridge, the cable-girder anchorage structure's problems concentrats on large load transfer, complicated load transfer mechanism and local stress concentration, etc. At present, the steel anchor box is extensively used in cable-girder structure for large-span cable-stayed bridges. The newly built Yongjiang Railway Cable-stayed Bridge on Ningbo Railway Northern Ring, used composite girder with steel box girder and concrete box girder. It was the first application of steel box girder in long-span cable-stayed railway bridge in China. To solve the problems of heavy live load and the volatile stress range on the cable-girder anchorage zone of long-span railway cable-stayed bridge, a new type of cable-girder steel anchor box with double-end fixed was designed and adopted by Yongjiang Railway Cable-stayed Bridge. As the main load bearing members of the double-end fixed cable-girder steel anchor box, the support plate and load bearing plate was respectively welded onto the web and wind fairing plate of the main girder. In this way, the new type of cable-girder anchorage structure was formed, in which the wind fairing plate together with the web plate of the girder bore and transferred cable force. Based on the new type of double-end fixed cable-girder steel anchor box for Yongjiang Railway Bridge, this dissertation developed an in-depth research on the following contents.1. The load transfer mechanism and the stress distribution of the new type of cable girder anchorage structure have been studied by using the method of finite element simulation. The research shows that, after adopting the new type of cable-girder anchorage structure, the anchor box transfers the cable force mainly through the weld seam among the support plates of the anchor box and the web plate and wind fairing plate of the main girder to the main girder in shear mode. The stress distribution is uniform on each component of the anchor box. However, the main bearing components have different degrees of stress concentration. The stress concentrates near the weld seam on the web plate and wind fairing plate of the main girder. This sensitive part of fatigue failure which undertakes bending-tensile stress should be paid serious attention to. Compared with traditional steel anchor box, the new design can effectively solve the problem of the stress concentration induced by eccentric bending moment at top of the weld seam of support plates.2. Train load spectrum has been established through Monte Carlo method according to previous researches and data investigation. The design of the core algorithm and the development of the program interface are completed by using object-oriented method with C# and WPF language. The bridge load effect spectrum is obtained by the subroutine module of influence line loading and rain flow counting method. This program is not only suitable for the fatigue test and fatigue evaluation calculation on Yongjiang Railway Bridge, but also can be applied to the simulation of the train load spectrum of other railway bridges.3. Based on the similarity theory, the model of steel anchor box with double-end fixed has been designed according to the principle of equivalent stress. And the static and fatigue test of the steel anchor box has been carried out. The results of the static test show that, the rationality of the design of the test model is determined by comparing the results of the static test data and the finite element simulation analysis. At the same time, the finite element simulation results are confirmed, and further clarify the stress distribution of the key components of the steel anchor box with double-end fixed. The results of the fatigue test show that, this new type of steel anchor box has excellent fatigue resistance performance and sufficient safety margin.4. In order to provide a basis for the application and development of this new type of cable-girder anchorage structure in the future, the design parameters analysis and optimization design of steel anchor box with double-end fixed have been carried out. The parameters involves the thickness of support plate, the thickness of web and wind fairing plate, the thickness of bearing plate and the length of support plate. The research mainly aims at the influence of the stress distribution of the component and the stress on the weld seam following the change of the parameters. The optimization study of the structure shows that, the proper simplification of some of the plates can reduce the difficulty of the manufacture, reduce the welding workload, and ensure the welding quality, under the condition of stable static strength and fatigue performance of the structure.5. The stress characteristics of 23 different kinds of steel anchor box with double-end fixed on Yongjiang Railway Bridge have been studied by using the finite element simulation method. The fatigue life of these steel anchor boxes is evaluated by using the method of S-N curve. The evaluation results show that, the whole 23 different kinds of steel anchor box with double-end fixed on Yongjiang Railway Bridge have excellent fatigue resistance performance. The No. M20 of steel anchor box with double-end fixed had the maximum damage degree within the design life span, while the No. M03 had the minimum damage degree.Through the research of this new type of steel anchor box, the load bearing capacity and fatigue property can be mastered. The research can ensure the safety of this new structure in the process of bridge construction and operation. The advantages and disadvantages of this kind of structure can be understood, and it can provide the design basis and guidance for the similar structure in the future. |
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