Study On Dynamic Substructure Method For Transient Seismic Responses Of Three-Tower And Two-Main Span Suspension Bridge

By the construction of the tower-cable-hanger system, suspension bridge is designed to transfer successively the load on deck to hanger, cable and tower. The possible lager defection of stiffening girder is transformed into small tensile deformation of the cable and small shortening deformation of the towers. Hence, the suspension bridge can achieve a large-span across. It has become the primary election of the modern large-span bridges. Taizhou Yangtze River Highway Bridge achieved about 3000m-span across with its unique suspension bridge type of three towers-two main spans, to avoid the occupying the main channel like the bridge types of cable-stayed bridge-suspension bridge or a combination of double stitching suspension bridge. The new suspension bridge with three towers-two main spans can save greatly the construction cost and period. It becomes an important developing type of long-span suspension bridge.Long-span suspension bridge has long lifetime. It is possible to encounter seismic hazards during its lifetime. The seismic response analysis is necessary for either design or use. The large volume of structure makes the time-history analysis of seismic response much difficulty in numerical computation and very long computation time. Generally, it had to select the iterative computation time step 0.1s, but the basic characteristics of seismic wave propagation across the bridge and seismic responses of the bridge hard to be gotten and more much important information of dynamic deformation and stress lost. It means that the design and use of large-span suspension bridge has certain blindness. The calculation of the transient seismic responses of long-span suspension bridge needs to select the iterative computation time step millisecond at least. The commercial finite element analysis software is unbearable for the computer resource consumption. Due to too long computation time, the computation can not be achieved in fact. Therefore, it is imminent to develop a high-accurate and high-efficiency calculation method for the transient seismic response analysis of large-span suspension bridgeThis thesis investigated the transient seismic response of the suspension bridge with three towers-two main spans, and the detailed numerical calculations were made for Taizhou Yangtze River Highway Bridge. The dynamic substructural techniques were developed for the transient seismic response analysis of cable, beam and hanger, respectively. By using a combination element method, a dynamic substructural technique was developed for the transient seismic response analysis of large-span suspension bridge. Depending on the seismic data analysis, the seismic wave propagations and long-term seismic response of TaizhouYangtze River Highway Bridge were calculated, so as to obtain the seismic response data and basic characteristics of transient seismic response. The present investigation is significant for the use of Taizhou Yangtze River Highway Bridge and the design of such new type of suspension bridge with three towers-two main spans.The main research work and achievements are shown as follows:(1) Taking into account the horizontal displacement of the cable and tension of the elastic cable, a deflection theory was presented suitably for the static deformation analysis of the suspension bridge with three towers-two main spans. The static deformation and static internal forces were calculated for Taizhou Yangtze River Highway Bridge. A simiplified deflection theory was presented specially for design engineers.(2) New cable element, beam element and hanger element were proposed to consider initial stress and geometric nonlinear effects with the mass matrix, stiffness matrix and internal force matrix derived from the theory of the finite deformation elasticity. Three dynamic substructural techniques were presented, respectively, for the transient seismic response analyses of long-span cable, long-span beam and hanger. The convengency of the techniques were investigated numerically. The numerical results show that the techniques are valid and of high-accurate in numerical simulations.(3) A dynamic substructural technique was developed for the transient seismic response analysis of large-span suspension bridge by the use of cable element, beam element and hanger element together presented in this thesis. The seismic wave propagations and long-term seismic responses of Taizhou Yangtze River Highway Bridge under multi-point seismic excitation were simuilated numerically. The numerical results show that the technique has high-accurate and high-efficiency, can save memory during the calculation and improved more than 16 times the computing speed.(4) Four basic characteristics of seismic responses of Taizhou Yangtze River Highway Bridge have been observed. The first one is that there are many types of deformation waves and internal force waves with different wave speeds. The full-bridge waveform is very complicated. The second one is that the deformations of hangers are much inconsistent. The hangers tilt obviously. The third one is that the long hangers near the side towers and middle tower can be easily thrown violently in the horizontal direction. The throws could reach 0.8m. The resonance phenomenon occurred in individual hangers. The last one is that the large beanding moment generate at the bottom of the side towers and middle tower. The beanding moment at the bottom of the middle tower could reach 2500MNm. It is five times of the ones at the bottom of the side towers. It is also five times of the ones when the left span of the bridge subjected the full static load.