Te Matau a Pohe, NZ’s only rolling bascule bridge and one of fewer than a dozen in the world, opened in July 2013. Photo / NZME
Whangārei’s $32 million Te Matau a Pohe bascule bridge will close for repairs after cracks were found inside its distinctive fishhook-shaped structures.
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 in the world, opened in July 2013.
Since then it has lifted more than 25,000 times for boats making their way along the lower Hātea River, upstream from where it meets Whangārei Harbour.
About 50,000 boats have crossed underneath heading between the Whangārei Town Basin and the harbour.
Cracks have been found in welding inside the steel hook beams.
Whangārei ratepayers paid about $17m towards the bridge’s construction, in conjunction with NZ Transport Agency (NZTA) Waka Kotahi.
The bridge’s two distinctive giant 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 four million vehicle movements over it each year. That’s about 11,000 daily, around 40% more than the 8000 it was originally designed for.
Te Matau a Pohe will be closed for 24 hours for repairs from 6am Sunday, May 10, to Monday, May 11.
The bridge and Dave Culham Drive will be closed to vehicles from Port Rd to Riverside Drive – with detours via Riverside Drive and Dent St.
Pedestrians will be able to walk the bridge’s footpaths unless there is an emergency.
Repair backup dates have been scheduled for May 17 and 24.
Its fishhooks are the main structural arms of the bridge’s rolling bascule (lifting) mechanism. They allow the bridge deck to roll back and lift for boats.
They each weigh 360 tonnes, their moving arms making the rolling motion possible and stable.
A 25m section of the bridge opens to let boats through. The opening road section rolls backwards 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,” Couper said.
Repairs to the welds were being done to ensure the structure’s long-term durability.
He said the welds had not failed or come apart.
In a Whangārei District Council communication forwarded to boaties, the weld repairs were described as urgent.
Whangārei Marina has advised boaties who might want to cross under the bridge during its closure to make alternative arrangements.
Those who needed access under the bridge during that time could possibly be accommodated at the new Okara Marina, downstream of Te Matau a Pohe.
The bridge was designed by British bridge specialists Knight Architects, in collaboration with New Zealand engineers Peters & Cheung (now Novare Design) and others, for the district council.
It has 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 ā Pohe means “the fishhook of Pohe”, referring to Pohe, the rangatira who welcomed early European settlers to the Whangārei area.
Cracks in internal welds are taken seriously because they occur in high-stress areas, a known fatigue issue in large steel bridges, and can usually be monitored and repaired long before safety is compromised.
The way cracks in bridge steel are dealt with depends on crack size and length, whether they are growing and whether they affect primary load-carrying parts of the bridge such as its main beams, supports, and connecting pieces.
In large steel bridges, weld cracks are typically repaired once they reach a few centimetres in length, show signs of growth, or occur in critical load-bearing locations.
Repairs are usually triggered by crack growth or location, rather than waiting for large visible damage.
■ LDR is local body journalism co-funded by RNZ and NZ On Air.