Vehicles equipped with sensors could revolutionise structural assessments of the condition of thousands of bridges across Australia and around the world, an Australian researcher says.
Dr Makki Alamdari, a senior lecturer with the School of Civil and Environmental Engineering at the University of New South Wales (UNSW), is working with her team and in collaboration with partners at Kyoto University in Japan to develop a vehicle mounting sensor system that whizzes across bridges to build a snapshot of their structural condition and health and safety (see below).
Around the world, the safety of bridges has been impressive over recent decades.
At around one in 100 million per year, the likelihood of fatalities caused by bridge collapses is around one hundred times less than that caused by lightning strikes.
Nevertheless, fatal bridge crashes do occur.
In Italy, 43 people were killed when a highway bridge in Genoa collapsed in 2018.
In Melbourne, 35 people died in the 1971 West Gate Bridge collapse.
Furthermore, Alamdari says the need to make reliable predications about bridge safety has grown as higher traffic volumes and larger and heavier vehicles have increased the load which bridges now have to bear.
This requires more resources and greater funding for their upkeep.
In addition, Alamdari says that many bridges around the world which are approaching the end of their service life and are potentially deteriorating.
Whilst one approach would be simply to demolish and rebuild these, this will not always be viable on account of the cost involved.
The alternative is to extend bridge life through regular assessments for safety and conducting repairs as needed.
In Australia, all of the country’s 53,000 bridges are inspected annually – a task which is shared between state and local governments.
Even here, however, various assessment methods have drawbacks.
For those bridges with low volumes of traffic, simple visual inspections which are conducted annually or more frequently where deemed necessary may be a low-touch method of evaluation which delivers sufficient results.
For brides carrying heavier loads, however, this may not be adequate.
Moving to large-scale bridges (such as the Sydney Harbour Bridge, which is traversed by 58 million vehicles each year), authorities rely on a combination of visual inspections, technology like CCTV and special sensors which are stationed at intervals along the bridge (nowadays, drones are also being deployed).
The sensors provide a continuous stream of data that engineers use to identify any emerging defects or structural weak points. The idea is to watch for changing patterns in the vibrations picked up by the sensors and then act when required.
Indeed, the approach has been deployed on large, iconic infrastructure like the Sydney Harbour Bridge (and more recently, the Gateway Bridge in Brisbane) as well as many bridges in China and around the world.
However, may not be viable for shorter span bridges which in rural areas.
To install a comprehensive sensing system, Alamdari says you are looking at a price tag of around $200,000 per bridge. This includes overheads such as cabling, monitoring, electricity load and analysis systems.
On top of this, there are further costs to replace components every couple of years as exposure to the elements takes its toll.
However, many local councils may have only an annual budget worth around a-tenth of this for each bridge.
According to Alamdari, this matters as many shorter-span bridges in rural areas are being subject to greater loads than what they were designed for.
In some cases, this is happening as bridges are used by overloaded trucks that make detours in order to avoid weighing stations on more direct routes.
To help solve this, the new approach taken by Alamdari involves striking a balance between efficiency and economy.
Rather than loading up bridges with expensive sensors, the idea is to put sensors on vehicles which will measure the state of the bride as they pass over it.
In collaborating with partners at Kyoto University in Japan, Alamdari and her colleagues have developed a custom-built prototype vehicle that travels over bridges.
Taking an appearance resembling a miniature Formula One car, the vehicle is equipped with multiple accelerometer and load cells to measure the dynamic response of the vehicle once it is moving over the bridge.
The cells also measure the interaction force between the vehicle and the bridge.
There is also a data-acquisition system on-board to log data in real-time.
Whilst the vehicle can reach speeds of 10 meters per second, testing thus far has shown that it should be maintained at around two meters per second for optimal results.
The car will move back and forth many times to collect a rich dataset of the bridge.
Collected data can then be analysed off-line in the office to see if there are any anomalies compared to the benchmark state.
At the moment, the vehicle is being tested over a cable-stayed bridge with a span of about 50 meters.
The next step will be to gradually introduce artificial damage into the structure of the bridge and verify that the signals generated as the vehicle rolls over in fact reveals this damage through the processing of vehicle responses.
Whilst she acknowledges that much needs to be done, Alamdari is hopeful that mobile sensor vehicles may become commercially available by the end of the decade.
In her current work, which is being completed as part of her DECRA fellowship – she hopes to bridge the gap between proof of the technology in the lab as opposed to the field.
“In the laboratory we have proven that we can monitor the health status of the bridge using this technology,” she says.
“But in the field, it’s always a different story because from my experience working on the Sydney Harbour Bridge I know there are a lot of unexpected challenges. So that’s something I’m going to explore and see how much we can narrow the gap between our lab testing and in the field.”
“To get it to the required level involves a lot of work in terms of advancing and tuning the parameters of your algorithm and increasing the sensitivity of your sensors. All those things need to be just right to ensure the technology works in the way we intend.”
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