Research On The Key Issues Of Cable-stayed Suspension Bridge Design

The construction projects in domestic and abroad to connect island and cross sea put forward higher requirements to bridge span. With the development of new material and construction method, it is also important to design new bridge systems which can provide an even bigger crossing. The cable-suspended composite bridge is a new kind of cable-supported bridges based on the concept of the cable-stayed bridge and the suspension bridge. It combines these two bridge systems into one, and if bridge engineering can take their advantages while ignore their disadvantages, it will be of the ability to compete with other long-span structures. However, there are still some key technical problems that need to be addressed. That is why this kind of bridge is narely built all over the world. This paper selects the scheme of Dongting Lake Second Bridge of as an engineering background, and establishs its full-bridge finite element model. Based on the static and dynamic nonlinear analysis software BNLAS, the concerned problems in this structure are dealt with in detail. The main studies and relevant conclusions are as follows:(1) The longitudinal stiffness, vertical stiffness and torsional stiffness of the cable-suspended composite bridge are analyzed, and the structure parameters which can increase structural stiffness are discussed. The influence line of main components under living load is provided. The interaction between hangers and stayed cables is addressed. The mechanic characteristics of hanger, main cable, main tower, stiffening girder under the temperature loading is presented. Research about several key parameters of the cable-suspended composite bridge are studied and compared, in order to identify reasonable structural layouts.(2) The design criteria, method and steps of reasonable complete stage of the cable-suspended composite bridge are put forward. After multiple optimization and adjustment, the designed stiffening girder configuration, the tensile force in stayed cables, the unstressed length of hanger and the geometric alignment of main cable are presented, leading to a reasonable internal force state of the cable-suspended composite bridge.(3) The bridge under construction is analyzed. The paper discusses the construction practicability of this system, and conducts global structure calculations. Main components' internal force and displacement are calculated and compared with design specifications.(4) Considering the fatigue concerns for stayed cable, hanger and stiffening girder of among the transition zone in the central span, different fatigue loads are employed and checked. The selections and feasibility of fatigue checking loads for long-span bridges are discussed.The research indicates that, the longitudinal stiffness, vertical stiffness and torsional stiffness of the cable-suspended composite bridge are greater than those of conventional single span suspension bridge. The important structural parameters affecting the performance of cable-suspended composite bridge are highlighted, and the reasonable completed stage of the Dongting Lake Second Bridge is estabilished. The construction method for this bridge is safe, reliable, convenient and feasible based the simulation of construction processes. The fatigue stress range of its main components is smaller than the fatigue limits, which demonstrates that the structural design is free of fatigue.The present studies and conclusions may help bridge engineers to understand the structures, and hopefully facilitate the bridge engineering practice in the future.