Harbour bridge lane closure: Work starts on Tuesday night to replace damaged strut

Tuesday, 22 September 2020

Waka Kotahi general manager transport services Brett Gliddon on the next steps for Auckland's Harbour Bridge

Work will start on Tuesday night on a temporary fix that could reopen some lanes on the damaged Auckland Harbour bridge, according to the New Zealand Transport Agency.

Auckland commuters have faced extensive delays already this week after damage caused by a freak accident on Friday when two trucks were hit by high winds, resulting in half of the lanes on the bridge being shut down.

The repair involves the removal of the lower half of a damaged 22.7 metre truss to replace it with a new piece of steel.

Only the outside lanes on the bridge are available for traffic, causing big backlogs across the region.

A permanent replacement is still some weeks away, according to Waka Kotaki/NZTA, as teams work to design and peer review replacement parts, source materials, manufacture the parts and plan for installation.

* Harbour bridge closure: Work on temporary fix to reopen lanes to start on Tuesday

If work isn’t completed on Tuesday night, the bridge will also be closed on Wednesday night.

* Auckland Harbour Bridge damage: How it happened and what needs to be done to get it fixed

Waka Kotaki/NZTA general manager transport services Brett Gliddon said the work was a complex undertaking that had never been done before.

“[It] includes mathematical peer review by independent experts, which we are doing in parallel to the construction of the temporary piece.”

Most of the time spent on a permanent solution is in the design, calculation and peer review stage, Gliddon said.

NZTA took media across the Auckland Harbour Bridge on the weekend to see the damage caused by a gust of wind blowing a truck into one of the bridge’s steel struts.

“The new modelling is necessary because the materials of the new structure will not exactly match those that were installed 61 years ago.”

The southbound clip-on lanes will be closed on Tuesday from 9pm to 5am. The closure includes the southbound lanes between the Esmonde Rd off-ramp and Hobson Street on-ramp (including the Auckland Harbour Bridge), the Esmonde Rd southbound on-ramp and the Onewa Rd southbound on-ramp.

Motorists are advised to use the western ring route (SH20/SH16/SH18) while the southbound lanes are closed.

The overnight closures of the bridge would allow NZTA to bring steel in and ensure the safety of workers on the bridge.

Gliddon said steel for the temporary fix was being fabricated in Auckland after coming up from Taranaki overnight.

Once installed, there would be “real-life tests” with heavy trucks going over the bridge to test if it performed to design specifications and requirements.

Auckland Harbour Bridge traffic building up just after 7am on Monday.

While the damaged component of the structure is important, there is no risk to the structural integrity or overall safety of the Harbour Bridge, he said.

Detours and ramp closures will add to the journey times of those wanting to commute at night this week, with a total of 25 on/off ramps having detours in place over the next few days, some happening for just one night, while others stretch across a few.

According to the NZTA, 11,000 vehicles from the North Shore crossed the Auckland Harbour Bridge between 6am and 10am on Monday – 16,000 fewer than at the same time last week.

Meanwhile, Upper Harbour Hwy (SH18) saw 11,600 vehicles travel southbound, 4000 more along the route than the previous week.

Just over 11,000 vehicles travelled north on Upper Harbour Dr, 14 per cent more than last week.

Others have opted to use public transport to avoid the bridge, with passenger numbers for ferries up 85% yesterday compared to last Monday.

Bus passenger numbers from the North Shore were also up 10 to 15% on Tuesday, compared with Monday’s figures.

The middle four lanes of the Harbour Bridge are barren on Monday afternoon.

Prime Minister Jacinda Ardern earlier said there were teams working on both the temporary and permanent solutions to repair the bridge.

She said it was important to remember this was a “one in 50 year event”.

How exactly did this happen?

About 11am on Friday, strong and sudden gusts toppled two trucks as they crossed the bridge, Gliddon said.

One was at the peak of the bridge when it was knocked over by a gust and slammed into a steel beam, twisting the metal and shearing it clean off where it connected to the bridge below the road surface.

Gliddon said the wind was 60kmh before it shot up to a gust of 127kmh before dying down again.

“We were hit by an absolute freak gust of wind which caught a truck as it was right on the top of the bridge.

“That’s really hard to design for.”

The beam did what it was supposed to, shearing off at the bolts, rather than pulling on and damaging other support members, with its load transferred to other supports on the steel truss.

The bridge continues to be able to support itself, but engineers are unwilling to allow traffic over the original inner lanes, which opened in 1959.

The outer two lanes on each side, clipped on 10 years after it opened, have their own support structure and do not rely on the damaged truss.