Seismic Response Analysis And Performance Study Of Isolated Bridge In Deep-water

In recent decades, a large number of deep-water bridges have been constructed in China,included cross-river bridge, coastal bridge and the bridge in western reservoir. Underearthquake excitation, the interaction between the bridge piers in deep water and thesurrounding water bodies (hydrodynamic pressure) will affect the dynamic characteristics andthe dynamic response of the bridge structure.In the earthquake, and wave actions is one ofconstant load in deepwater bridge substructure design. Currently, there is still a lack of fuetherresearch about seismic response and seismic performance of deep-water.The isolation bridgeis main study object in this paper, the characteristics of isolated bridge seismic response andthe seismic performance of isolated bridge under combined hydrodynamic pressure and waveactions have been researched, which has great theoretical significance and engineering valueto performance-based seismic design and select seismic strengthening program.The followingmain work and achievements are described as follows:1. Based on a large number of domestic and foreign literatures, the research status abouthydrodynamic pressure, wave actions, seismic performance evaluation and seismic fragilityanalysis of bridge are summarized, and then this article research framework and thinking areformed.2. Based on the radiation wave theory and the Morison equation, a dynamic equilibriumequation of bridge taking the hydrodynamic pressure and the wave action into account isestablished. The effect of the hydrodynamic pressure on the natural frequencies and seismicresponse of non-isolated and isolated bridges have been analyzed and compared by the finiteelement analysis. The sensitivity of these two bridge systems to the wave action wereinvestigated under considering the hydrodynamic pressure, and the seismic damping effect ofthe isolated bridge was analyzed. The study showed that the hydrodynamic pressure willchange the dynamic characteristics of the bridge and increase its seismic response. Waveeffects may increase or decrease the seismic response of the bridge, but its effect was less thanhydrodynamic pressure. The non-isolated bridge was far more sensitive to hydrodynamicpressure and wave action than the isolated bridge on either the natural frequencies or theseismic responses. It follows that the seismic performance of isolated bridge structure is betterthan the non-isolated bridge in offshore areas.3. The elastic-plastic finite element analysis model of isolated bridge structures undercombined hydrodynamic pressure and wave actions was established. The17natural groundmotion records were selected from the database of the Pacific Earthquake Research Center(PEER) to perform the incremental dynamic analysis (IDA), the seismic performance of thebridge was assessed based on forming IDA-based seismic performance evaluation curves. Theresults indicate that IDA-based seismic performance evaluation curves not only reflect clearlydamage status of isolated bridge under different earthquake intensity, but also assess the levelof structure resistant earthquake with defined limits state; The IDA curves of bridge pier andLRB under theearthquake of17natural ground motion records show that the degree ofdispersion of each curve is more obvious with the increase of the peak ground acceleration (PGA); An assessment of the seismic performance of bridge pier and LRB show LRB enteredthe yield stage at about0.1g PGA, LRB is the weak link in the design process, it is moreeasily damaged in the earthquake.4. Based on the IDA data of deep-water isolated bridge, the seismic fragility curves of thebridge system and major components using IDA methods were formed. And the probability ofexceedance was assessed at various different levels of damage based on the fragility curves ofthe piers abutment and bridge system. The results show that the pier showed good ductilityfrom minor damage to collapse, and the probability of collapse has reduced significantly, thepier has a good seismic performance; Due to the model and location in the structure of LRBwtre different, the seismic performance of side pier abutment (LRB800) is worse than the pierabutment (LRB1600); And the bridge system is more vulnerable to damage than the piermembers in earthquake.