The 2.9-kilometer Rion-Antirion Bridge in Greece, with its 300 sensors, is a testament to how smart a piece of infrastructure can be. It routinely tells operators when an earthquake, frequent in those parts, or high winds warrant shutting down traffic.
”The bridge tolls are meant to collect thousands of euros per day,” says Alexandre Chaperon, an engineer at the company that designed the system, Advitam, in Vienna, Va. ”Without the monitoring system, the bridge would be closed after every earthquake, more than three days in some cases, instead of 5 minutes.”
Dozens of the largest and most complex bridges in the world are already studded with strain and displacement gauges, three-dimensional accelerometers, tiltmeters, temperature sensors, and other instruments. They are wired to central data-acquisition units—though some newer bridges have wireless systems—which collect and analyze the information and relay it to engineers, in hopes of catching signs of distress before human inspectors could. With the United States injecting US $27.5 billion into revamping the country’s roadways and bridges as part of an $800 billion economic stimulus effort, it might seem like a perfect opportunity to add smarts to more bridges.
But monitoring system costs are too high and the benefits unproven for most of the nearly 600 000 bridges and overpasses in the United States, experts say. Sensor systems seem to make sense only for big, complex bridges and for those that are already known to be in trouble. And it will be many years before these systems can be used on other bridges.
An installation of sensors on an existing bridge that would help save the owners money and mitigate disasters has not been demonstrated yet, says Emin Aktan, director of the Intelligent Infrastructure and Transport Safety Institute at Drexel University, in Philadelphia. ”There is no case where we can say sensors have saved a lot of lives,” he says. For most bridges and overpasses ”it will take 5 to 10 more years before we have sufficient fundamental knowledge to start deploying such systems and expect returns.”
John DeWolf, a civil and environmental engineering professor at the University of Connecticut, in Storrs, who has equipped six bridges with up to 50 sensors each over the past decade, has some of the longest-term data in the country. At today’s costs and level of knowledge, he says, a monitoring system might be of most use on ”an older bridge that is nearing the end of its life cycle or a bridge with known problems.” However, there are potentially an awful lot of those. In 2008, the U.S. Federal Highway Administration listed about 152 000 bridges as structurally deficient or obsolete.
The systems also make sense for bridges with new designs that need to be tested, such as the Rion-Antirion, or for structures like the long suspension and cable-stay bridges that span waterways and cost hundreds of millions of dollars to build. ”With these very complex bridges there is a benefit, and there are enough resources available to apply that level of effort and technology,” says Andrew Foden, a supervising engineer with infrastructure consulting firm Parsons Brinckerhoff.