Liang Pier Top Isolation With Isolation Damping Effects In The Pier End Of A Comparative Study

On a beam bridge that assumes seismic isolated system, the bearing of seismic isolation is generally set on the top of piers.This is so-called pier-top seismic isolation. But under some conditions , for example, if piers are so high and weighty that their design is based on their own inertia force,it shoud be considered to set the bearing of seismic isolation at the bottom of piers,such isolation type is so-called pier-bottom seismic isolation. So far, a few bridges which adopt pier-bottom seismic isolation have been built in the world.When the bearing of seismic isolation is set on the top of piers and at the bottom of piers respectively, the basic period and the seismic response are bound to be different. This paper first makes an analysis of the characteristics of structure type of the bridge that adopts pier-bottom seismic isolated system and then carry out another analysis to seek general changing law of the basic period and the seismic response of a regular beam bridge when the bridge seismic isolation type is changed from pier-top seismic isolation into pier-bottom seismic isolation .At last,this paper makes response spectra analysis and time analysis of a concrete beam bridge using the NBA program.The results of all the analysis show that pier-bottom seismic isolated system is generally more efficient in extending basic period and reducing seismic response than pier-top seismic isolated system , but the bridge which adopts pier-bottom seismic isolated system is also difficult to be popularized for some disadvantages of its own, for example, it is limited by the type of structure to a more large extent, and it is comparative difficult to be constructed.