Mechanism Of Water-Bridge Pier Dynamic Interaction And Nonlinear Seismic Responses Of Bridges In Deep Water

As for most of the cross-sea and cross-river bridges or the reservoir area bridges in West China, the bridge piers are usually located in deep water. Therefore, with a consideration of the water–bridge pier dynamic interaction, the earthquake induced hydrodynamic pressure on bridge piers is significant. However, there is still a lack of further research about the seismic responses of bridges in deep water both at home and abroad. Theoretical study and shaking table test are developed for earthquake response analysis of bridges in deep water under earthquake excitation, which has great theoretical significance and engineering value to improve theoretical basis for the earthquake hazard refined simulation and performance based seismic design of bridges in deep water. The following innovative work and achievements are include:(1) earthquake induced hydrodynamic pressure formulary of bridge piers in deep water is established based on radiation wave theory and variables separation method, which can consider free surface wave and water compressibility. Meanwhile, the influence of free surface wave and water compressibility on earthquake induced hydrodynamic pressure on bridge piers is studied. The results indicate that: free surface wave will only influence hydrodynamic pressure about the vicinity of water surface under low-frequency load excitation, and this influence can be ignored in seismic analysis of bridge piers. Water compressibility only takes effect on hydrodynamic pressure under high frequency load excitation, and it is found that the primary frequency of earthquake action is smaller than the frequency threshold that water compressibility starts to have obvious effect on hydrodynamic pressure on bridge pier in deep water. In conclusion, the influence of free surface wave and water compressibility can be ignored in the calculation of earthquake induced hydrodynamic pressure on bridge piers in deep water. Added mass concept can be used to analyze seismic responses of bridge piers in deep water, and hydrodynamic added mass will increase with the increase of bridge pier radius and the relative water depth.(2) Earthquake induced hydrodynamic pressure on bridge piers in deep water is usually established based on rigid bottom reflection boundary, and the absorption action of bottom flexible medium on hydrodynamic pressure wave is ignored. Earthquake induced hydrodynamic pressure formulary of bridge piers in deep water is established by introducing bottom reflection coefficient, which can consider the influence of bottom flexible reflection boundary Furthermore, the influence of flexible reflection boundary on hydrodynamic pressure on bridge piers is analyzed. The results indicate that: earthquake induced hydrodynamic pressure on bridge piers will be changed in special load excitation frequency range when bottom flexible reflection boundary is considered, and hydrodynamic pressure on bridge piers will be decreased with the reduction of reflection coefficient. Although earthquake induced hydrodynamic pressure on bridge piers in deep water will be decreased, and this decrease effect on hydrodynamic pressure is not obvious. Therefore, the influence of bottom flexible reflection boundary on earthquake induced hydrodynamic pressure on bridge piers in deep water can be ignored.(3) Water-bridge pier dynamic interaction analysis method is established, and program of applied hydrodynamic pressure on bridge piers is complied based on ABAQUS software platform, which is verified by comparisone with numerical method. Also, the influence of earthquake induced hydrodynamic pressure on seismic responses of bridge pier is analyzed when different earthquake excitations and internal water within the bridge pier with hollow section are considered. The results indicate that: dynamic responses of bridge pier are augmented because of earthquake induced hydrodynamic pressure action, which changes with different earthquake excitations. The effect of hydrodynamic pressure induced by internal water on bridge pier with hollow section seismic responses can't be ignored. Influence of hydrodynamic pressure on dynamic responses of bridge piers in deep water increases with the decrease of the upper structure added mass.(4) Seismic response analysis method of bridges in deep water is established, which can consider spatial variation of ground motion. Nonlinear seismic response analysis of continuous rigid-framed bridge is made by considering the earthquake induced hydrodynamic pressure; meanwhile, earthquake inputs including uniform excitation,traveling wave effect and multi-support excitation are respectively adopted. The results indicate that: dynamic responses of bridge are augmented because of earthquake induced hydrodynamic pressure action, and the influence of hydrodynamic pressure on seismic responses of bridge changes with different earthquake wave excitations and constraint condition about pier-box girder. The effect of hydrodynamic pressure on earthquake responses analysis of bridge is different under traveling waves or multi-support excitation relative to uniform excitation. In conclusion, hydrodynamic pressure action should be necessarily considered in seismic responses analysis of bridges in deep water, and earthquake excitation should employ reasonable earthquake input.(5) Morison equation and radiation wave theory are used to consider wave load for different size of bridge pier, analysis method of bridges in deep water under wave action is established. Dynamic responses analysis of bridges in deep water under wave and earthquake combined action is made. The results indicate that: the effect of wave action on bridge changes with different wave incident directions, meanwhile, the influence about wave action on bridge is smaller than earthquake action. Wave and earthquake action on bridge can't be simplified into a simple linear superimposition when wave and earthquake action are considered at the meantime.(6) Water-bridge pier dynamic interaction is studied with a scaled bridge pier model shaking table test, and the analysis method of water-bridge pier dynamic interaction established is verified. Shaking table test of water-large diameter bridge pier dynamic interaction is carried out. Dynamic similarity ratio design is made using self-made rubber material, and absorbing material is adopted to simulate water area dissipative action on hydrodynamic pressure wave. Experiments for dynamic characteristic and dynamic response of bridge pier in deep water is are performed under the shaking table simulated earthquake excitation. Meanwhile, influence of flexible reflection boundary of bottom on hydrodynamic pressure is analyzed. The results indicate that: natural frequency of bridge pier is decreased and dynamic responses of bridge pier are also augmented because of hydrodynamic pressure effect. Nevertheless, the influence of flexible reflection boundary on earthquake induced hydrodynamic pressure on bridge pier can be ignored. The earthquake induced hydrodynamic pressure action on bridge piers can be well simulated using the analysis method established in this dissertation.