An unconventional restraining system for limiting the seismic movements of isolated bridges

An external restraining system with steel piles is introduced under the main objective of the study, which is the enhancement of the earthquake resistance of seismically isolated bridges. This objective is examined through the possibility of the improved seismic participation of the approach embankments, which are able to dissipate part of the induced seismic energy. The seismic participation of the embankments, which are seismically inactive, according to current conceptual design of bridges, is achieved through the extension of the continuous deck slab of the bridge onto the embankments and its restraint by the backfill through steel piles. The serviceability needs of the deck are accommodated by: (a) the flexibility of the steel piles, (b) the looseness of the backfill soil, (c) the partial replacement of the embankment’s surface layers by expanded polystyrene (EPS) and (d) the in-service allowable cracking of the continuity slab. A parametric study was conducted and showed that the restraining system can effectively reduce the seismic displacements of the bridge. The proposed technique can be utilized in all bridge structures, and is more efficient in those exhibiting large displacements during an earthquake.