Dynamic Characteristics And Seismic Response Of Cantilever Piers Surrounded By Water

A more facilitating transportation network is urgently needed for the rapidly developing economy and society in China, and bridges crossing large water area are an important part of the system. The complexity of the environment loads will be inevitably considered for a final solution when designing bridges of this kind. Subjected to seismic load,bridges sited in deep water may be seriously damaged and that will lead to great difficulty for reinforcing or reconstruction. Researches show that water surrounding the pier not only changes the dynamic characteristics of the structure but also brings significant hydrodynamic pressure on the pier surface during earthquakes. So how to evaluate the influence of the surrounding water becomes the main issue of this article.The dynamic characteristics and seismic response of cantilever piers surrounded by water without considering incident wave are studied. The main contents and results are simply listed:(1)Based on Potential based method without considering free-surface effect and Morison equation, a systematic study on dynamic characteristic on piers of various heights and changing water depth was carried out, and a discussion for these two methods was simply delivered. Result shows frequencies of the pier-water system decreases as water level goes high, and for higher piers totally immersed in water the effect on frequency becomes significant. The velocity part in Morison equation can be conservatively neglected in evaluating seismic response.(2)A finite element model for an existed high bridge pier surrounded by water which was modeled with Potential Based Fluid Element in ADINA. A concentrated mass and load were applied on the top of the structure to simply consider the bridge deck. A numerical study was carried out on the dynamic characteristics and seismic response for various water depths. A simultaneous work is also done for model based on Morison equation neglecting the velocity part and the result was compared with PB model. It is concluded that the top acceleration of the pier is more sensitive to water depth than displacement, and that also happens to base shear force compared with the moment. Result of seismic response for Morison model is more conservative in contrast with PB model. Seismic response will reduce when including the effect of concentrated mass and load on the top of the pier.(3)Based on Morison equation neglecting the velocity part, a nonlinear dynamic analysis was completed for piers with different water condition under more intense ground motions with peak acceleration of 400 gal. It is found that nonlinearity (for both material and geometry) significantly developing during earthquakes will change the way the water influences the seismic response of pier in elastic state.