Inelastic Seismic Response of a 59-span Bridge with Soil-structure Interaction

This paper summarizes the results of a comprehensive study carried out to assess the seismic response of a 59-span bridge, considering Soil-Structure Interaction (SSI). The bridge was built in the early seventies at a distance of about 5 km from a major fault. The methodology adopted to idealize the bridge and its foundation system for elastic and inelastic analysis is briefly described. The SSI analysis is significant in this study due to the length of the bridge, the massive and stiff foundation and the relatively soft deep soil of the site. Detailed three-dimensional dynamic response simulations of the entire bridge are undertaken using several analysis tools to verify the analytical models for the extensive inelastic analysis. 144 site-specific input ground motions are employed to assess the inelastic response of the 2160-meter bridge. The study identifies areas of vulnerability in the investigated bridge and assesses its response at three hazard levels, corresponding to 475, 975 and 2475 years return periods. It is concluded that the seismic response of the bridge at the 500 years ground motions is unacceptable, while the demands under the effect of the 1000 years ground motions almost exceed the capacity of most bridge components. The demands significantly increase under the effect of the 2500 years earthquake scenario and considerably exceed the collapse limit states. The results clearly reflect the pressing need to retrofit different bridge components to mitigate anticipated seismic risk. The presented assessment study exploits the most recent research outcomes to realistically predict the complex seismic response of this major bridge and thus contribute to improve public safety.