At the fourth anniversary of the fatal Minneapolis bridge collapse, the University of Maryland announced new technology that could prevent a similar disaster. Mehdi Kalantari, an assistant research scientist in the electrical and computer engineering department, developed wireless sensors that would transmit bridge data in real time. Below are excerpts from our recent interview.
What’s the scope of the bridge problem?
The problem is the aging infrastructure. It’s not just here in the U.S., but around the world. Based on data from the Department of Transportation, something like 70,000 of the 600,000 operational U.S. bridges — about 12 percent — have been rated as structurally deficient. These are operational bridges that are being used daily. Structurally deficient means the structures have signs of problems and if you don’t take better care of these bridges, there will be a problem five or 10 years down the road. Replacement is not an option because of the capital costs needed and, in a lot of cases, shutting down these bridges to replace them would significantly disrupt traffic and have a big impact on the economy. The best choice is to develop technologies to monitor the development of issues that could compromise the integrity of the bridge.
How are bridges monitored now for safety issues?
They are not monitored. They are inspected. The current practice is a visual inspection by an expert once every two years. It’s good practice, but problems can happen much faster than every two years. If you have a bridge that is rated as structurally deficient and it’s 40 to 50 years old, it might look fine. But the next time the bridge is going to be inspected is two years down the road. Problems can develop much faster. They can happen in a matter of a few months. The bi-annual inspections are good, but not sufficient.
Describe the sensors you created that could deal with this problem.
We created easy-to-install, low-cost wireless sensors. Once installed, they’re expected to work for at least 10 years with little maintenance. They measure the bridge’s overall integrity using indicators, such as strain, vibration and flexibility. There are many variables that can be monitored and analyzed and reduced to what we call the overall structural integrity report. That shows if the structure is functioning well or if there are issues that need to be taken care of.
Where is the data transmitted?
Once you have this data transmitted by sensors at different points on the bridge, you collect them on a specific device that is installed at the bridge site. That device aggregates the data and transmits it to a remote center that receives all the data from that bridge and perhaps many other bridges. The data is stored, analyzed and archived. It will be used for generating the regular structural integrity report.
How often is the data collected by sensors?
The data is real time. The delay is minimal. But sometimes in order to produce structural integrity reports with a good confidence level — you could say for certain that there’s an issue — the system gathers data anywhere from a few hours to up to a few days. The data is real time, but detecting issues may take longer than a few minutes.
How much would the system cost?
The cost of our system is minimal compared to two things. 1. The overall cost of a structure. 2. The potential cost of a structural safety issue or the potential cost of an issue being undetected and leading to a more severe problem. We’re talking about something on the order of $10,000 to $15,000 for an average-sized bridge. The whole system I explained — sensors, the data aggregation device, the software — is $10,000 to $15,000. The uncertainty is because a lot of times you can’t say exactly how many sensors you need to cover a bridge. The number of sensors depends on the design and the overall condition. If you compare the cost of a system for an average-sized bridge like the one in Minnesota, the cost of replacing the bridge was $250 million. The cost of a potential failure or a safety issue is much more significant compared to the cost of deploying the system.
Is this a new approach or did you advance previous work?
To a large extent, the sensors and devices we’re working with were developed from scratch. There has been no practice of using technologies like this on bridges. Of course, the area of wireless sensing is vast. There have been uses in other application domains. But on highway bridges, using this technology is fairly new. More importantly, we tailored this technology for bridges and being retrofitted to existing bridges. We’ve done a lot of work to customize the sensors to the application.
What’s the next step?
We have almost finished all the initial lab and field tests. We’re improving the software and hardware. We’re still adding more features. But for us, the real next step is to introduce this to communities that maintain highway bridges. A lot of times the scope of maintenance is different. Some of these bridges are being maintained by states, some by the federal government, some by municipalities. We are trying to introduce this technology and its capabilities and features to these different authorities. Hopefully they start using it. We believe it will make maintenance and operations much easier, and it will save in the cost of maintaining the bridges. More importantly, it’s going to add safety to these bridges.