NUMERICAL INVESTIGATION OF SEISMIC ISOLATION FOR SINGLETOWERCABLE STAYED BRIDGES

摘要

Recent earthquakes have demonstrated the vulnerability of cable-stayed bridges to near-fault earthquakeexcitation. The end span connections of the Higashi-Kobe cable-stayed bridge fractured during theHyogoken-Nanbu (Kobe) Earthquake in 1995 causing moderate damage to the overall system [1,2]. Theend spans of the Chi-Lu cable-stayed bridge rose vertically out of their transverse shear keys during the1999 Chi-Chi earthquake in Taiwan resulting in extensive damage to the non-ductile superstructure at thesuperstructure to central pylon connection [3].This paper explores isolation for protecting these structural systems due to large magnitude, near sourceseismic events. Using isolation devices under the central pylon in conjunction with isolation devices atthe end span connections, the complete system can be isolated and the superstructure can be protected.This paper focuses on issues related to isolating the bridge in the transverse direction. This form ofisolation minimizes the demands to both the superstructure and substructure elements. Flexible bearingsare provided connecting the end spans to the substructure and the pylon base to the foundation. Theseisolator groups are tuned such that a vibration mode is created where the superstructure is engagedprimarily in translation.This paper develops the required relationship between the end span and pylon-foundation flexibleconnections to optimize the effectiveness of the isolation system. Furthermore, analytical results for afixed base, fixed end, moderate span, single-tower cable-stayed bridge are compared with results from thepylon isolation system for varying isolation periods using simulations with large magnitude near-faultground motions. Conclusions are drawn on the overall all effectiveness of this method of isolation ascompared with the traditional fixed base system. Results will show that isolation of the entire system is aviable option for the reduction of seismic damage.