Bearing replacement and strengthening of Forth Road Bridge approach viaducts, UK

The existing Forth Road Bridge spans the Firth of Forth in Scotland. The steel girders of the approach viaducts are supported on steel roller and rocker bearings. An initial study of the bearings identified that the rollers had locked up due to corrosion and distortion, and the concrete beneath the bearings and elsewhere on the pier tops had deteriorated due to chloride contamination. Assessment showed that structural deficiencies in the pier were exacerbated by both the concrete deterioration and change in articulation. These factors lead to the decision to replace all the bearings on the viaducts. The original structure was not designed to facilitate replacement of the bearings so the structure had to be strengthened and modified by the addition of jacking stiffeners and corbels to the pier tops. This paper outlines the design of the strengthening and modifications to the bridge to facilitate bearing replacement, together with a detailed description of the design of the temporary works needed to maintain the bridge’s articulation during jacking. Lessons learnt during construction are discussed and the structural benefits of design to Eurocodes are emphasised.