Seismic Retrofit of a Historic Pier Using Lead-Rubber Bearings

The San Diego Unified Port District decided to construct a new multi-use building on the historic Broadway Pier. The pier, built in 1913, would require a seismic upgrade to accommodate the new facility. Initial study findings indicated that seismic demand would cause failure of the existing batter pile to deck connections. Preliminary retrofit concepts that involved driving new piles were costly and threatened to delay this important project. An innovative concept was developed that used seismic isolation bearings placed on new pile caps built under the existing deck surface. The new pile caps connected the existing batter piles below the deck and allowed removal of the original pile-to-deck connections. These brittle connections were replaced by the isolation bearings that now serve as both lateral and gravity load paths between the deck and the piles. Detailed construction procedures were developed that allowed the seismic work to proceed concurrently with the building construction, enabling an aggressive construction schedule to be met. This paper describes the seismic vulnerabilities of the existing pier and the retrofit measures taken to improve the pier's seismic performance. The effects of base isolation on the global response of the structure under seismic and non-seismic demands are summarized. Special detailing to maintain an uninterrupted gravity load path during construction and to avoid corrosion of isolation bearings located near the intertidal zone are also described. Lastly, the potential use of the concept in new pier construction is discussed.