Auckland Harbour Bridge: Engineers working on permanent fix from detailed scans

Thursday, 24 September 2020

Timelapse video shows temporary repairs on Auckland Harbour Bridge.

Engineers working on permanent repairs to Auckland’s damaged harbour bridge are working off detailed scans, thanks to the world’s fastest laser scanner.

The New Zealand Transport Agency (NZTA) said in a post Envivo Ltd collected millions of data points and created a 3D mesh of the area and its damage.

A freak incident on September 18 blew a truck into a load-bearing steel beam, rendering the middle lanes unusable.

Envivo Ltd were on the harbour bridge hours after it was damaged collecting millions of data points for a scan of it.

The effects of the closure rippled out across Auckland's already congested motorways and continues to cause long delays and gridlock.

* Harbour bridge damage: City on-ramp closure adds to widespread evening delays

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

Two lanes on the bridge reopened on Wednesday morning after the installing of a temporary fix overnight, but a permanent fix will not be complete for another four to five weeks.

Earlier, NZTA transport services general manager Brett Gliddon said about nine structural engineers were working on the problem, which required replacing the entire damaged beam from top to bottom.

Gliddon said the work could be done entirely with materials and expertise already available in New Zealand, and no foreign experts needed to be brought in.

A gust of wind caused a truck to hit one of the beams.

But it is not as simple as finding a new beam and bolting it on.

One has to be manufactured from scratch, taking care that its material and design will work with the six-decade old bridge, Gliddon said.

Fitting the beam will mean using jacks on either side to tension it up and push load back into the support, before tightening the bolts.

What is reportedly the world’s fastest laser scanner scanned the damage on the bridge to help engineers with permanent repairs.

How exactly did this happen?

About 11am on September 18, 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.