History and application of seismic isolation to higway bridges in the United States

Seismic isolation is used in buildings to decouple these structures from the damaging components of earthquake ground motion. It is also in bridges where it involves the separation of the superstructure from the substructure, usually at the bent cap level. But unlike a building application the primary intent in a bridge is to protect the structure below the plane of isolation - the superstructure being relatively rigid to in-plane loads and of adequate strength to resist these loads. Bridges are particularly suitable for isolation and literature surveys indicate that more than 90 of the world's isolated structures are, in fact, bridge structures. Applications include both new construction and retrofit work. Implementation within the United States has only occurred within the last few years and then predominantly as a retrofit measure rather than in new construction. This activity is reviewed in this paper along with some potential innovations in the use of isolators for protecting monolithic continuous bridges.(AU)