Harbour bridge creaking as trucks roll on

NZTA's Steve Mutton says the bridge is in 'fantastic' condition. Photo / Janna Dixon

New engineering work to strengthen the Auckland Harbour Bridge is needed to cope with the supertrucks now allowed on our highways.

The work is detailed in a draft NZ Transport Agency report that documents the constant maintenance needed to keep the country's best-recognised structure in service.

The draft - released under the Official Information Act - is an early version of the first "operating plan" to be developed in the life of the 52-year-old bridge. It says the NZTA needs "certainty" on a new Waitemata Harbour crossing.

Transport minister Steven Joyce said yesterday that a new harbour crossing would be essential within about 15 to 20 years but that meant a decision needed to be made soon.

The draft report also clearly identifies the most urgent work to be done - strengthening the original bridge structure for trucks that are now able to carry loads weighing up to 53 tonnes. The previous maximum was 44 tonnes.

NZTA regional asset manager Steve Mutton said work was under way to work out how much the bridge's centre section needed to be strengthened.

He said the bridge was in "fantastic condition" thanks to steady maintenance.

Mutton said a 100-year plan for the management of the bridge would be created in the next few years to chart the future use of the bridge.

The draft report also details "fatigue cracking" in the clip-on bridge extensions as an "ongoing issue needing active management"and said the rate of fatigue cracking would increase over time.

Engineers have also raised concerns about cracking concrete in the raised approaches to the bridge because of an "alkaline silica reaction", and thin seal on the bridge's centre section.

THE NUMBERS

* 44 tonnes: Previous maximum truck weight

* 53 tonnes: New maximum weight

* 20 years: Potential reduction to bridge lifespan