Study Of Vertical Stiffness Of Triple-tower Double-main-span Railway Cable-stayed Bridge

In recent years, demand to build Triple-tower Double-main-span Railway Cable-stayed Bridge (TDRCB) with extremely large span has been put forward many times in railway construction of our country. Cable-stayed bridge is a flexible structure, while the railway live load is large and the requirement of stiffness of railway bridge is much higher than that of road one. Therefore, in extremely large-span cable-stayed bridges which have been built home and abroad, railway bridges are far fewer than road ones and there is not a TDRCB in real sense. Several retrievable railway cable-stayed bridges with three towers and double main spans or multiple towers and multiple main spans are part cable-stayed bridges in which towers only have stiffening effect and spans are not large. The middle tower of TDRCB is easy to incline to one side because of no anchoring end cables, thus the bridge is more flexible than normal cable-stayed bridge. Funded by planed scientific development project of railway department2011G012-B, the problem of vertical stiffness of TDRCB was studied systematically by taking Dongting lake great bridge on new-built Jinzhou-Yueyang railway as background. Main research work and innovative achievements are listed below.1. According to bridge site, topography, geology, navigation, flood, landscape, environment and economy conditions, several bridge plans were schemed and put forward. After comprehensive comparison and selection, a plan of TDRCB with span arranged as (98+140+406+406+140+98)m was proposed. Static and dynamic analysis, seismic analysis, wind stability analysis and analysis of moving train were done and results demonstrated the feasibility of the TDRCB plan. After several argumentations, the TDRCB plan was approved for implementation.2. Structural parametric research method was proposed, with which the influences of various components of TDRCB on vertical stiffness of bridge were studied. The match range between the ratio of the flexibility of main truss to its span and the ratio of the flexibility of tower to its height and the optimal value ranges of the ratio of the height of tower to the span of main truss and stiffness of cable were proposed.3. The theoretical formulae of the deflection and the ratio of the deflection to the main span of a two-line railway TDRCB under the most negative live load were proposed. Examples of three different main spans showed that the formulae are simple and fast and have a higher accuracy as to two-line railway TDRCB with main span range of378-434m. The formulae can be applied in adjustment and optimization of structural parameters in design.4. The stiffening effects on the vertical rigidity of a two-line railway TDRCB by adding horizontal stiffening cable on the top of towers, stable cable on middle tower,1pair to4pairs cross cables and downward tensile cable were compared and studied. These effects were also compared with the effects by increasing stiffness of main truss, or increasing stiffness's of three towers simultaneously or only increasing stiffness of middle tower. Through comprehensive comparison of many aspects, the stiffening measure of adding stable cables was recommended to Dongting lake TDRCB.5. The adjustment, optimization and refinement of structural parameters of Dongting lake TDRCB were done by applying the results above-mentioned. The strength, stiffness and dynamic characteristics were checked. The results showed that after adjustment and optimization the stiffness of Dongting lake TDRCB is increased by large extent and the strength and stiffness can meet the requirements with great margin.6. A more than30m long model of TDRCB was designed and made. Displacements and stress of bridge model in cases of no stiffening measure, adding horizontal stiffening cable on top of tower, adding stable cable on middle tower and adding1pair,2pairs of cross cables were measured. The correctness of the results of FEA, the theoretical formulae of the deflection and the ratio of the deflection to the main span proposed were inspected and verified. The effects of various stiffening measures were confirmed. The research results have already been used in the design of Dongting lake TDRCB on Jinzhou-Yueyang railway.