Earthquake design of a viaduct with full seismic isolation of bridge deck

The Arachthos Bridge in Greece is about 1 km long and crosses the future Arachthos reservoir. This paper presents the results of the earthquake analysis of the bridge design that won an international design competition. The spans vary from 83 m to 107 m. The Y-shaped piers with heights of up to 80 m are founded on piles. Because of the high seismic stresses in the bridge piers, hydraulic dampers are needed in both the longitudinal and transverse directions. The dampers reduce the seismic stresses in the piers by about 50%. The optimisation of the seismic dampers is discussed in this paper. Two transverse seismic dampers are provided on each pier and one at each abutment. The seismic dampers allow relative movements between the bridge deck and the top of the bridge piers of up to ?500 mm in the transverse direction. The longitudinal stability of the bridge girder under the static and dynamic loads is achieved by the piers, which are connected with the girder in the longitudinal direction, and the seismic dampers at the abutments. In the longitudinal direction, seismic movements of up to ?250 mm are allowed. The longitudinal dampers at the ends of the bridge girder must allow both longitudinal and transverse movements. The dynamic analysis shows that maximum residual transverse movements of up to 200 mm are possible. Therefore, provision for the placement of hydraulic jacks is foreseen on the pier tops for re-centering the bridge deck after a strong earthquake. The stability of the bridge girder under the service loads is provided by shear keys, which are integrated in the pot bearings. Under the design earthquake or an earthquake exceeding the design earthquake, the bridge girder is prevented from falling down from the bearings.