Bridges

Replacement of bearings is typically done by jacking to raise all beams at a headstock sufficiently to free the bearings for replacement or resetting. To avoid damage to the structure and to restore the initial bearing reactions, it is necessary to exercise tight control over jacking displacements and the final levels of the new bearings. The process may be complicated by the presence of epoxy of variable thickness above or below the bearings. Traffic delay due to the road closure is a significant impact and may be extreme if problems extend the night works into the morning peak.

An alternative approach is to replace bearings individually using flat jacks as well as hydraulic jacks. The method is to support the bridge on hydraulic jacks adjacent to the bearing to be replaced, with a very small (sub-millimetre) upward displacement. As the bearing is removed by demolishing the pedestal or mortar pad under it, its load is transferred to the locked-off hydraulic jacks. A new bearing is installed on a permanent flat jack which is inflated with epoxy to restore the previous load on the bearing and hydraulic jacks, which are removed once the epoxy has gained strength. Displacements and loads are monitored throughout the process. Only brief road closures are required.

The method was used successfully to replace bearings at two bridges on Ipswich Motorway in Brisbane.

The method may be appropriate for situations involving major roads, a structure sensitive to relative displacements, bearings with variable epoxy depths, very wide bridges, or where only isolated bearings require replacement.