Bridges

Steel bearings, including pinned, roller, and rocker types, are commonly found on older bridges globally, although they are rarely used in modern bridge construction. Pinned bearings allow for rotations without longitudinal or transverse displacement capacity. Rocker bearings enable rotations and small longitudinal displacements but no transverse displacements. Roller bearings allow for greater longitudinal displacements and can accommodate rotations if combined with a pinned connection. If the rotational or movement capacity of these bearings is exceeded, instability failures can occur, compromising the bridge superstructure's support. Such failures have been observed in numerous bridges worldwide.

Bearing failures generally result from unforeseen loads and movement effects not accounted for in the original design, such as inadequate braking load allowances and unexpected superstructure or substructure movements. Failures of steel bearings are typically non-ductile, unlike the more ductile failures of modern elastomeric or pot bearings. Mitigating the risks associated with steel bearing failures requires regular inspection, monitoring, and timely intervention.

This paper presents a case study of a heritage bridge that experienced excessive movements, risking the failure of its steel pinned and rocker bearings. Field investigations and comprehensive geotechnical and structural assessments using complex finite element models were undertaken to determine causation of the excessive movements and impacts on the bridge's performance.

An innovative engineering solution was implemented to restore the bridge’s performance. The remediation design involved stabilising the bridge substructure from further ground movements with a post-tensioned concrete base slab integrating the existing narrow strip footings and a composite concrete block to strengthen the abutment. Additionally, the bridge's longitudinal movement capacity was restored by jacking the superstructure to reinstate rocker bearing verticality and original expansion joint gaps. Design and construction challenges, particularly those related to the constrained site and minimising traffic impacts on a major road network, are also discussed in this paper.