Seismic Retrofit of Piers Supported on Battered Piles Using Lead-Rubber Bearings

The use of battered piles in the design of new piers located in areas of seismic risk is discouraged based on the poor performance of battered piles observed in previous earthquakes. However, there are a significant number of existing piers with battered piles in service that may require seismic retrofitting. Typical retrofit schemes involve driving additional plumb or batter piles that are integrated into the existing deck with new pile caps or other means but permitting restrictions, pile installation difficulties, and interruptions to facility operations may preclude this approach. In this paper, the use of lead-rubber bearings (LRB) is proposed as an alternative seismic retrofit concept for batter pile-supported piers. The paper summarizes the basic principles of base isolation and presents a case study of an example pier retrofitted using two concepts, one withnew driven piles and the other with LRBs mounted on new subcaps supported by the existing battered piles. The seismic performance of the example pier and the two retrofitted structures was evaluated using displacement-based analysis method. Budget cost estimates developed for both retrofit concepts indicate that the LRB retrofit may be more economical than the driven pile concept for the configurations studied.