Rocking Isolation of Bridge Piers Using Elastomeric Pads

Abstract eng:
Bridge rocking isolation has attracted the interest of the bridge engineering community, as it minimises damage in the structural system, which conforms to the objectives for resilient and sustainable bridges. Two fundamentally different approaches have emerged in recent years: (a) structural rocking isolation, where the piers (cast-in-situ or precast with/without post-tensioning and/or dissipaters) are allowed to rock and minimise damage and (b) geotechnical rocking isolation, where conventionally designed or deliberately under-designed foundations rock to achieve the same goal. However, both structural rocking and rocking footings are facing challenging design aspects. Structural rocking seems to include post-tensioned partially stressed tendons, dissipators and replaceable, internal or external, rebars. Low dissipation capacity and increased on-site labour seem to be the main acknowledged barriers to the application of structural rocking. On the other hand, bridge piers with rocking footings appear to suffer from excessive settlements and, in some cases, large residual drifts, due to the sinking/tilting effect of footings in yielding foundation soils. Aiming to achieve a simpler rocking mechanism, this paper studies bridge piers isolated by rocking footings, which are deliberately under-designed, yet supported on elastomeric pads. The pier footing rocks on the elastomer and tends to uplift. The pads dissipate energy, whilst exhibit minimal residual drifts. The pier, the footing and the elastomeric pad are supported on an appropriately designed rigid concrete sub-base to achieve minimal settlements. Assessment of the rocking system is based on the response of rocking piers modelled in ABAQUS.

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