The cracks need urgent repairs to prevent damage to the structure.
Te Matau a Pohe, New Zealand’s only rolling bascule bridge and one of fewer than a dozen of its type in the world, opened in July 2013.
The cracks have been found in welding inside the steel hook beams.
Whangārei ratepayers paid about $17m towards the bridge’s construction, in conjunction with NZTA Waka Kotahi.
The bridge’s two distinctive, giant, white, curved shapes are almost 20m tall and represent Māori fishhooks, reflecting local traditions of fishing, navigation, and the cultural relationship with Whangārei Harbour.
Te Matau a Pohe is one of Whangārei’s most visible landmarks.
There are around 4 million vehicle movements over it each year, or about 11,000 each day, about 40% more than the 8000 it was originally designed for.
Te Matau a Pohe will be closed for 24 hours to do repairs, from 6am on Sunday, May 10. Repair backup dates have been scheduled for May 17 and May 24.
The bridge’s fishhooks are the main structural arms of its rolling bascule (lifting) mechanism. They allow the bridge deck to roll back and lift for boats.
They each weigh 360 tonnes; their moving arms make the rolling motion possible and stable.
A 25m section of the bridge opens to let boats through. The opening road section rolls backward and upward along a curved track while the fishhook-shaped beams roll with it, their 67 tonne counterweights moving in the opposite direction to keep the system balanced.
Whangārei Mayor Ken Couper said the cracks had developed in internal welds over time.
"The need for these repairs was identified during a routine structural inspection and the recommendation was to carry them out promptly to avoid any future damage or disruption," Mr Couper said.
He said the welds had not failed or come apart.
Te Matau a Pohe was designed by United Kingdom bridge specialists Knight Architects, in collaboration with New Zealand engineers Peters & Cheung (now Novare Design), and others, for Whangārei District Council.
The bridge won more than a dozen national and international awards including the transport infrastructure award and the supreme engineering excellence award at the 2014 New Zealand Engineering Excellence Awards.
Te Matau a Pohe means "the fishhook of Pohe", referring to Pohe, the rangatira who welcomed early European settlers to the Whangārei area.
• LDR is local body journalism co-funded by RNZ and NZ On Air.
By Susan Botting
