Study On The Key Techniques Of Four-pylon Single Plane Wide Ridge Low-pylon Cable-stayed Bridge Design

Low-pylon cable bridge has strong competitiveness in the field of 200m span because of its excellent structural performance, good economic indicators and beautiful bridge shape. In recent years, our country's low-pylon cable bridge has developed rapidly, but there is conflict between growing engineering practice and relatively few basic research. At present, most researches are focus on narrow structures of middle-small span. The consensus and analysis theory based on construction can not effectively solve practical problems of large-span, wide-range and continuous girder low-pylon cable bridge. This paper takes Xijiang Bridge of Jiangmen to Zhaoqing Highway as example, and does research on key techniques of multi-pylon wide ridge single plane low-pylon cable bridge design. By summarizing theories and vivificating simulation analysis, the paper generalizes research findings and innovations as follow:(1) Innovatively proposes bridge plans of pier, tower and beam consolidation system multi-tower single plane low-pylon cable-stayed bridge in light of large span and long continuous bridge. It effectively solves core techniques problems of tower top displacement of multi-tower structure and structural stiffness.(2) In order to weaken the dead weight effect of overwide section, innovatively proposes the section of wide ridge section, it effectively improves the shear lag effect by measures of post-cast operation and bridge deck system of long wing panel stiffener. Diversity design is used for mid-web plate to fit non-uniformity of stressed mid-web plate.(3) Innovatively studies the sensitivity of low-pylon cable-stayed bridge's parameters and provides theory for formulating key parameters of tower height, the length of side span and mid span without cable, and ratio optimization between side span and mid span. According to researches, we can see that high-pylon cable-stayed bridge is the trend of cable-stayed bridge's development. When the ratio optimization between side span and mid span is 0.6, the stress state is optimum.(4) Innovatively propses the concept of prestress allocation. Systematically studies sensitivity ratio of stayed cables and internal prestress. And it proposes the optimal allocation of stayed cables and internal prestress on the basis of cost, resistance to vertical load and stabilize the prestress efficiency of main beam.(5) In order to keep pier, tower, and beam consolidation system multi-tower cable-stayed bridge at reasonable stress state, analyzes concrete creep, basical simulated stiffness and sensitivity of concrete dead weight load. The analysis shown that creep has most significant effect on the pier, and its value is 30%. But the other two aslo can not be ignored.(6) According to stress characteristics of wide ridge's tovertical and transverse space, and mechanics of post-cast stiffener bridge deck, the paper innovatively proposes design with due consideration tovertical and transverse space, because there are some limits on original bridge design which is based on tovertical analysis. On the base of it, the paper systematically studies shear lag effect of different stages and different box girders by means of bridge simulation analysis. It provides evidence for reasonable tendon layout and post-cast band. It systematically studies non-uniformity of stressed mid-web plate and points out that the coefficient of non-uniformity is aroud 1.3. According to these, we can determine web plate's thickness of ridge section, mechanics of stiffener bridge deck, coefficient of shear lag and lagging-cast practicability of post-cast band.(7) Through the dynamic characteristics analysis, the dynamic characteristics of low-pylon cable-stayed bridge is closer to continuous bridge's. The stiffness of main mainly controls vibration mode. The stiffness of main tower only affects the vibration of main tower itself. Wind and seismic resistance have less constraints on structural design.(8) Study landscape design of low-pylon cable-stayed bridge and durability design of cables systematically. Effective measures should be taken in the early stage of design to ensure the conservation and raplacement of large tonnage cables. Researches of cable replacement have shown that without interrupting traffic, we can only change a pair of cables each time because of the uncertainty of load.Xiangjiang bridge of Jianmen to Zhaoqing highway makes a number of technique innovations, though there is no mature engineering experience and relevent specification for guidance. The research results of this paper provide reliable guidance for bridge's design and also provide valuable reference for similar projects.