Evaluation Method Of Earthquake Induced Hydrodynamic Effect And Seismic Resilience For Deep-water Bridges In Reservoir

With the rapid development of transportation construction in China,many deep-water bridges in the reservoir have been built or planned in recent years.Different from the bridges on land,the earthquake-induced complex fluid-structure interaction(FSI)and a large amount of cost in the post-earthquake damage detection and repair bring a series of problems and challenges to the seismic design and disaster mitigation for deep-water bridges in the reservoir.Although several achievements have been made towards seismic research of these types of bridges,there are still many scientific problems to be further solved.Based on a thorough literature review,this dissertation aims at several problems regarding the earthquake-induced hydrodynamic effect and the evaluation of seismic performance for deep-water bridges in the reservoir.The following aspects of these problems related to the topic were comprehensively investigated using the analytical derivation,underwater shaking table tests,and numerical simulation:(1)A general estimation method for the hydrodynamic added mass of the immersed column with complex cross-section was proposed based on the FSI numerical simulation.Taking the immersed circular,elliptical,circular tapered columns,and a bridge pier with complex dumbbell cross-section as examples,the accuracy of the proposed method has been verified through the comparison with analytical,experimental,and numerical results.Then,as the application of the proposed method,the characteristics of hydrodynamic added mass of the hollow rectangular pier with variable cross-section were studied.And the calculation equation for hydrodynamic added mass of the submerged rectangular pile cap was proposed based on Bayesian updating,of which the accuracy was validated through the underwater modal tests.(2)The dynamic responses of a typical deep-water rigid-frame bridge in the reservoir were assessed by underwater shaking table tests and numerical simulations.The influences of water depth on the frequency-domain dynamic responses and structural vibration mode of the bridge were investigated.Meanwhile,the effects of the superstructure on the dynamic responses of the main pier was discussed,and the limitations of the traditional method simplifying the superstructures as a tip mass concentrated at pier top were analyzed.In this regard,an improved pier model considering the contribution of the superstructure and a practical procedure for determining the model parameters were proposed.It can be concluded that the change of water depth has a significant impact on the natural frequency and vibration mode of the studied bridge,and the improved pier model can better represent the contribution of the superstructure to dynamic responses of the main pier of the deep-water rigid-frame bridge in the reservoir.(3)The numerical simulations of seismic wave propagation in the bridge sites with different topographies were carried out through the spectral element method.Using the generated seismic records as inputs,the seismic response analyses of a deep-water bridge in the reservoir were performed.The effects of the valley topography on the spatial distribution of ground motions and the seismic responses of the bridge were investigated.The results show that the valley topography can significantly alter the distribution of ground motions in the bridge site and the seismic responses of the bridge,which should be considered in the seismic design of the deep-water bridges in the reservoir.(4)An assessment method of seismic resilience and economic loss of deep-water bridges in the reservoir was proposed,considering the amplification effect of underwater repair work on the economic cost and repair time of the post-earthquake recovery.The fragility,seismic resilience,and economic loss of an example deep-water rigid-frame bridge in the reservoir under the near-fault ground motions and the ground motions considering the effect of valley topography were estimated based on the proposed method.Results indicate that the near-fault ground motions with pulse effect can exaggerate the damage probability,reduce the seismic resilience and increase the economic loss of the deep-water bridges in the reservoir,which is worthy of consideration in the seismic design of these bridges;the valley topography can change the seismic resilience and economic loss of the deep-water bridge in the reservoir,which deserves consideration to reasonably evaluate the seismic performance of these bridges.In this dissertation,the key problems in the seismic analysis and performance evaluation of the deep-water bridges in the reservoir were studied in detail.The research findings and conclusions can provide a foundation for the seismic design and the disaster prevention and mitigation of the deep-water bridges in the reservoir.