On August 14, the nation of Italy was sent into shock after a 200 metre section of the Morandi Bridge collapsed, sending cars and trucks plummeting 45 metres and killing more than 40 people.
This underscored the need for a robust approach toward ensuring the structural integrity of bridges.
In Australia, the historic performance of our bridges has been good. Apart from the collapse of one span of the King Street Bridge crossing Melbourne’s Yarra River in 1962 and that of the West Gate Bridge whilst under construction in 1970, our bridges have held up well.
Nevertheless, a leading academic has raised concerns about a lack of transparency regarding bridge conditions and assessments.
In a recent article on The Conversation, Dr Colin Caprani, a senior lecturer in structural engineering at Monash University and Honorary Secretary of the Australia Group of the International Association for Bridge Maintenance and Safety, argued that it is difficult to give a snapshot of the current state of Australia’s bridges as state road authorities publish scant information about bridge conditions or inspection and maintenance budgets.
None of Tasmania, the ACT or NSW publish data in any form, Caprani said. Queensland provides some data via email and Western Australia does not provide any inspection data. In South Australia, the Department of Transport, Engineering and Infrastructure resisted the release of bridge assessment information under a Freedom of Information request made by MP Martin Hamilton-Smith in 2009 on the basis of national security, although that decision was later reversed by Ombudsman SA.
In a recent interview, Caprani told Sourceable that a good way to think about Australia’s bridges from a safety perspective is to consider being blindfolded and standing near the edge of a cliff. Whilst we are back somewhat from the cliff’s edge, Caprani says we do not know how far back we are or how much further forward we can go before we go too far.
By and large, Caprani says bridges designed in the 1950s, 60s and 70s – around half of all bridges currently in operation – are safe. What we don’t know is how safe they are, as we did not have reliable mathematical models to quantify the margin of safety in respect of each of these assets at the time in which the design standards under which those bridges were constructed were set.
Since then, he says several developments have conspired to bring us closer to the margin of safety.
First, courtesy of corrosion and degradation, the condition of our bridges has likely deteriorated over time.
Second, courtesy of numerous factors, our bridges are being subjected to greater load pressures through heavier vehicles and a greater volume of traffic. Back when many of our bridges were being built, Caprani says legal load limits in respect of heavy vehicles were more restrictive than they are now. There are also more vehicles going over bridges. In the case of the Sydney Harbour Bridge, for example, more than 150,000 vehicles cross each day.
Furthermore, Caprani says describes a tendency to edge progressively closer toward the edge of our safety limits. From a load rating perspective, he says there can be a tendency to increase the number of heavy trucks allowed to cross our bridges. Courtesy of further measurements, there might also be downward adjustments to the dynamic allowance for vibration effects.
To be sure, Caprani acknowledges that maximising bridge use is beneficial. Within reasonable safety limitations, there are legitimate productivity benefits which can be derived from sweating our assets.
Nonetheless, he says that with each incremental step in this direction, we edge closer to the point of working our bridges beyond their capacity to cope.
“You keep taking these small steps toward the cliff face on the basis that nothing has gone wrong so far,” Caprani said.
“This is great, everybody’s happy – until you find out that the next small step is a step too far.
“Right now, we don’t know how far from the edge we are.”
Going forward, Caprani would like action in two areas.
First, he says there must be greater transparency about the state of Australia’s bridges. Toward this end, Caprani would like the introduction of a national inventory of bridges and their condition. This would be based on the model of the National Bridge Inventory in the United States, which is compiled by the Federal Highway Administration and contains information on all bridges and tunnels in the US which have roads passing above. Information available from that includes identification information, bridge types and specifications, operational conditions, bridge data including geometric data and functional description, and inspection data.
At the moment, he says the lack of published data in Australia means it is not possible to assess the current state of our bridges.
Moreover, Caprani is concerned about a lack of accountability and fears that absence of public data creates opportunities to delay budgeting for rectification work. Were data made public, he says pressure for action would intensify and there would be a trail of accountability.
Speaking of the US situation, Caprani says the national inventory has driven accountability.
“It shines a light on the area. It means that decision makers, politicians, senior managers can’t hide,” Caprani said.
“If they make a decision not to fund required maintenance, it’s on their head.
“In Australia, we don’t know who makes the decisions and we don’t know what maintenance has not been done that engineers have recommended be done.”
Beyond that, Caprani would like a quantitative approach to be applied to bridge risk assessment. This would enable quantifiable assessments of bridge safety and condition against levels which are considered acceptable.
He says the mathematical tools to enable this do exist but are not yet widely used.
At all times, Australia must ensure that the risk associated with of our bridges is maintained at acceptable levels.
For this to happen, greater transparency in bridge condition and assessment is needed.