Bridges

Pot bearings installed in bridges constructed before 1970 are coming to the end of their nominal 50-year design life. In recent years, a new generation of spherical bearings has become available as an alternative to pot bearings. These bearings incorporate new low friction sliding material which has a coefficient of friction similar to Polytetrafluoroethylene (PTFE) but with a higher allowable contact pressure.

On the recently completed Pacific Highway Wyong Road Intersection Upgrade project on the NSW Central Coast, the existing pot bearings on a four-span continuous bridge were replaced. Inspection of the bearings revealed some extrusion of rubber from the pot, slivers of PTFE from the sliding interface and damage to the side guides of the bearings. Also, the vertical loads on the bearings increased due to a cross fall correction overlay applied to the bridge deck.

Sizing new replacement bearings to fit the existing bearing attachment plates proved difficult due to the increase in vertical load. Replacement of the existing attachment plates would also result in a significant increase in the cost of bearing replacement. Consequently, new generation spherical bearings were adopted to accommodate the additional vertical load and re-use the existing attachment plates. Changes to the bridge restraint system were also required to enable the re-use of existing attachment plates. Due to the lack of jacking points, extensive temporary works were required to facilitate the bearing replacement. This project also employed the latest inspection technology using GoPro cameras for bearing inspections and reality capture photogrammetry for confirming existing bearing and attachment plate dimensions.

This paper discusses the bearing replacement project, including the bearing design and selection process and the jacking operations for replacement. The paper also discusses the observed pot bearing defects both in-situ and after removal and disassembly.