Nevertheless, in the rocking piers design alternative high stress concentrations at the rotation pole (pier base) are developed, indicating the need for a special design of the pier ends. Both rocking isolation concepts are proven to offer increased levels of seismic resilience, reducing the probability of collapse and the degree of structural damage. The safety margins of the rocking footings design concept are even larger, as it survives in all cases examined. The rocking piers design alternative survives in 8/10 of the cases examined, with negligible residual deformations. The conventional system collapses in 5/10 of the (intentionally severe) examined seismic excitations.

For the latter, an ensemble of 20 records (10 ground motions of 2 perpendicular components each) that exceed the design level are selected. To that end, 3D numerical models of the bridge–foundation–abutment–soil system are developed, and both static pushover and non-linear dynamic time history analyses are performed. The seismic performance of the two rocking-isolated bridges is comparatively assessed to the existing bridge, which is conventionally designed according to current seismic design codes. The examined bridge is an asymmetric 5-span system having a continuous deck and founded on surface foundations on a deep clay layer. The present paper investigates the seismic performance of an actual overpass bridge of the Attiki Odos motorway (Athens, Greece), employing two different concepts of rocking isolation: (a) rocking of the piers on the foundation (rocking piers) and (b) rocking of the pier and foundation assembly (rocking footings) on the soil. Rocking isolation of structures is evolving as an alternative design concept in earthquake engineering. Department of Civil, Environmental and Geomatic Engineering, ETH Zurich, Zurich, Switzerland.Bozidar Stojadinovic and Ioannis Anastasopoulos

Overpass bridge