Can We Trust Bridges? - Hope 103.2

Can We Trust Bridges?

Can We Trust Bridges? We take for granted the large infrastructure projects being built around us but can it all come tumbling down like the bridge in Florida?

By Anne RinaudoTuesday 27 Mar 2018Open House InterviewsNewsReading Time: 2 minutes

Listen: Dr Nadarajah Gowripalan in conversation with Stephen O’Doherty

Recently a massive, 950 ton concrete pedestrian bridge collapsed on to an eight lane highway in Florida killing six people and injuring others.

We are used to  large scale infrastructure going up all around us, but how confident can we be that new construction techniques, like that used in the Florida bridge, are safe.  

The technique used in the case of the bridge in Florida is called Accelerated Bridge Construction or ABC.

Like many other big engineering projects some parts are created off-site or at ground level and moved in to place.

Concerns were expressed about cracks in the Florida bridge several days before the collapse, which occurred without warning as workers were adjusting the tension of the cable-stayed bridge.

In Australia there have been a couple of terrible bridge collapses, the West Gate bridge in Melbourne which failed during construction and the Tasman Bridge in Tasmania which was hit by an ore carrier.

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Famous in engineering circles is the is the collapse in November 1940 of the Tacoma Narrows bridge, located in Washington State.

The bridge had been closed justshortly before the dramatic collapse which came just four months after the bridge opened.

It had earned the nickname “Galloping Gertie” because of the vibrations and bouncing it displayed.

There were attempts to fix the problems and by November 7th the bridge was closed as the bouncing movement had given way to an alarming twisting.

Just half an hour after the closure the bridge twisted for a final time and collapsed into Puget Sound.

When it was designed in the 1930’s aerodynamic forces were not well understood.

The spectacular failure of the Tacoma Narrows Bridge was driven by wind-generated vortices that reinforced the twisting motion of the bridge deck until it broke.

In other words,  twisting created more twisting, then greater and greater twisting. This increased beyond the structural strength of the bridge and it failed.

The replacement bridge was of a different design and earned the nickname “Sturdy Gertie”

Dr Nadarajah Gowripalan is an engineer with very specialised knowledge of concrete as well as a serious love of all aspects of engineering.

He is a Senior Research Fellow, School of Civil and Environmental Engineering at the University of Technology Sydney.

The US National Transportation Safety Board is investigating the exact cause of the Florida bridge collapse.

However, Dr Gowripalan says it seems odd there was not more concern about the cracking and that in Australia the traffic would not have been moving under the bridge while stays were being tensioned.

In general, he says bridges are designed to last 100 years and the FLorida University City Bridge was designed to hold up in a category 5 hurricane.

Dr Gowripalan explains that the public need not be overly concerned about the chance of infrastructure failing.

He indicates that catastrophic failures like this are actually rare and that engineers are highly skilled and very careful in their work.