In order to meet future traffic demands on the AHB, it was determined that the load carrying capacity of the Box Girder Extension Bridges (‘clipons’) had to be increased. This upgrade came in the form of the Box Girder Strengthening Project.
The scope and scale of the strengthening works was unprecedented for this type of bridge. Approximately 600,000 man hours were expended over the duration of the project and nine hundred tonnes of new steel components were distributed along the full length of the bridge. This included:
- 2,300m of deck stiffeners closely fitted to the steel deck during night time traffic closures.
- 14,000m of new and strengthened web stiffeners.
- 190 tonnes of bottom flange stiffeners.
- 300 cantilever cross girders strengthened outside the box girders.
- Internal strengthening of 12 pier brackets
The project brought many associated challenges, including difficult access and logistics, work at height, confined spaces, ventilation issues, the delivery of approximately 10,000 individual components (each weighing up to 500kg), strict road closure conditions and extremely tight design fit-up tolerances of less than 1mm for the components welded in high fatigue areas.
The successful outcome of the project required innovative design work and
construction methods, combined with a collaborative approach from not only project team members but also local residents, stakeholders and the road users.