Uplift of elastomeric bearings in isolated bridges subjected to longitudinal seismic excitations

Abstract

Bearings are used to isolate bridge substructures from the lateral forces induced by creep, shrinkage and seismic displacements. They are set in one or two support lines parallel to the transverse axis of the pier cap and are typically anchored to the deck and to the pier cap. This detailing makes them susceptible to possible tensile loading. During an earthquake, the longitudinal displacements of the deck induce rotations to the pier caps about a transverse axis, which in turn cause tensile (uplift) and compressive displacements to the bearings. Tensile displacements of bearings, due to the pier rotations, have not been addressed before and questions about the severity of this uplift effect arise, because tensile loading of bearings is strongly related to elastomer cavitation and ruptures. An extended parametric study revealed that bearing uplift may occur in isolated bridges, while uplift effect is more critical for the bearings on shorter piers. Tensile displacements of bearings were found to be significantly increased when the isolators were eccentrically placed with respect to the axis of the pier and when flexible isolators were used for the isolation of the bridge. The results of this study cannot be generalised as bridge response is strongly case-dependent and the approach has limitations, which are related to the modelling approach and to the fact that emphasis was placed on the longitudinal response of bridges.

Keywords::

• bridges
• bearings
• uplift
• longitudinal displacement
• rotation
• pier cap

Disclosure statement

No potential conflict of interest was reported by the author.

Notes

^1. Prior to the final parametric study, different stiffnesses of the continuity slab were tested analytically to define whether the stiffness of the connecting slab allows for different rotations of the bearings. The results of the analyses showed that the discrepancy of the bearings rotations due to the flexibility of the deck slab is negligible.