Study On The Dynamic Response Characteristics Of Deep-water Bridge Pier Excited By Impulsive Near-fault Earthquake Ground Motions

The vibration mode and dynamic response may be changed obviously because of hydrodynamic pressure acted on the bridge piers under earthquake. And unique spectral characteristics of different types of ground motions will bring effects on the dynamic behavior of bridge. The dynamic response characteristics of bridge excited by impulsive near-fault earthquake ground motions are an important scientific problem to be studied in the seismic design of bridges in deep-water.Taking the equivalent pier of a typical railway bridge in deep-water as an example, the research is carried out based on the potential-based fluid method from fluid-structure interaction theory. The following are the main contents:(1) The dynamic analysis including fluid-structure interaction of pier submerged in water was studied through ADINA programe. The dynamic response characteristics of pier excited by near-fault and far-field ground motions were studied respectively and the hydrodynamic effect on the vibration performance and dynamic response of piers with rectangular and circular cross section were discussed. At the same time, the comparative study of Morison equation was conducted. The result shows that:the vibration characteristic of pier is changed because of the water. With the increase of the depth of water, the natural vibration period of pier gets longer. The dynamic response of pier is changed obviously for the hydrodynamic effect and the dynamic response of near-fault ground motions is greater than that of far field ground motions, so more attetion must be put on the seismic design of bridges built in near-fault zones.(2) The distribution of hydrodynamic pressure and the features of total hydrodynamic pressure acted on piers were studied respectively. The calculation methods of hydrodynamic pressure proposed in Chinese Railway Code, Chinese Highway Code and Japanese Code were examined. In general, the hydrodynamic pressure acted on pier gets greater with the increase of water depth and it increases first and then decreases along the pier, which is parabolic shape. The result shows, total hydrodynamic pressure by Japanese Code is greater than the numerical solution and that of Chinese Highway Code is smaller. The distribution of hydrodynamic pressure under near-fault earthquake, for the rectangle cross-section pier, Chinese Railway Code and Japanese Code are smaller; for the rectangular cross-section pier, Japanese code is conservative, Chinese Railway Code is fit. The distribution of hydrodynamic pressure under far-field earthquake, two kinds of Code are conservative.(3) The influence of three kinds of pulse parameters(velocity pulse peak Vp, pulse period Tp, pulse type)on the dynamic response of piers with rectangular and circular cross section using artificial impulsive ground motions was quantitatively analysised. The results indicate that:the dynamic response of deep-water bridges excited by impulsive ground motions is greater than that of ground motions without pulse. The above three kinds of pulse parameters have great influence on dynamic response of pier. The influence of Vp increase with the rise of Vp. Tp will cause greatest effect when the pulse period is close to the natural vibration period of pier. The C-type pulse has the greatest effect on the dynamic response of the pier, next is the B-type pulse, and the minimal is the A-type pulse.