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Wireless sensor to monitor structural integrity of bridges


July 29, 2011

Kalantari hopes his sensors can prevent disasters like the I-35W bridge collapse in 2007 (Image: Pete Markham via Flickr)

Kalantari hopes his sensors can prevent disasters like the I-35W bridge collapse in 2007 (Image: Pete Markham via Flickr)

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According to a 2009 estimate by the U.S. Society of Civil Engineers, more than one in four U.S. bridges are either structurally deficient or functionally obsolete. While newer "smart" bridges have embedded wired networks of sensors to monitor their structural integrity, the high cost of installing such systems on existing bridges is simply unaffordable for strained city, state and federal budgets. Now University of Maryland electrical engineering researcher Mehdi Kalantari has developed a tiny wireless sensor that monitors and transmits minute-by-minute data on a bridge's structural integrity that he estimates is one-hundredth the cost of a wired network approach.

The wireless sensors, which Kalantari is marketing under the name SenSpot, measure all the variables reflecting the structural integrity of bridges that conventional wired systems do, such as strain, vibration, tilt, acceleration, deformation and cracking. The sensors themselves are less than five millimeters thick and are comprised of four thin, flexible layers. The first senses and measures structural parameters; the second stores energy; the third transmits data to central computer for analysis; and the outer layer harvests energy from ambient light and radio waves.

While serious problems would quickly trigger an alarm, more subtle early-stage problems may take up to a few days until the system is confident enough to report a structural integrity issue.

Kalantari says the sensors are rugged and, because they are self-adhesive, require no potentially damaging drilling into the bridge structure. He says they should last at least a decade with practically no maintenance required. As they harvest energy from ambient light and radio waves, they don't require any wires, batteries or dedicated external power source. With each unit costing about US$20, the total cost for an average-sized highway bridge needing about 500 sensors would be about $10,000.

"If this kind of technology had been available in Minnesota four years ago, there's a good chance the fatal bridge collapse could have been avoided," Kalantari says, referring to the August 1, 2007 bridge collapse along Minneapolis I-35W that killed 13 and injured 145. "This new approach makes preventive maintenance affordable - even at a time when budgets are tight. Officials will be able to catch problems early and will have weeks or month to fix a problem."

In conjunction with the Maryland Department of Transportation, Kalantari has been testing the sensors by measuring the structural parameters of highway bridges in a real setting for almost a year. He says this has allowed him to optimize the device's performance and energy consumption with the updated model smaller and 10 times more energy efficient than its predecessor. The field testing has also allowed him to track the bridges' response to changes in weather conditions and traffic.

To commercialize his technology, Kalantari founded Resensys LLC through the University of Maryland's Technology Advancement Program incubator. He expects to scale up production of the sensors in September this year.

About the Author
Darren Quick Darren's love of technology started in primary school with a Nintendo Game & Watch Donkey Kong (still functioning) and a Commodore VIC 20 computer (not still functioning). In high school he upgraded to a 286 PC, and he's been following Moore's law ever since. This love of technology continued through a number of university courses and crappy jobs until 2008, when his interests found a home at Gizmag. All articles by Darren Quick

\"If this kind of technology had been available in Minnesota four years ago, there\'s a good chance the fatal bridge collapse could have been avoided,\"

Bhoomika Joshi

What is actually "functionally obsolete" is the insistence of US governments to rely 100% on motor vehicles and roadways to move people from point A to point B in this country. In every other industrialized nation there is government funded creation of mass transit systems across the country. People do not need a car to go to work or to school or to go shopping. It is time to stop subsidizing the auto industry, the concrete industry, the trucking industry, and the coal industry but spending public funds on the roadways but instead spending public funds on systems that economically and efficiently transport people during the daily course of their lives.

And the manufacturing should rely 100% on US based companies who use 100% US made parts by 100% US labor force. We need to stop using taxes collected from workers to subsidize companies that are busy exporting capital, technology, and jobs overseas.


Vibration is the culprit. Earthquakes are the result of to surfaces rubbing as one slides. They can cause a mountain of granite to crumble. Here are few things that did not exist when most bridges were built: boom boxes, exhaust pipes designed to make more noise, bigger diesels and a lot more traffic. Most bridges were built to handle weight and wind and not abuse.


The Minnesota bridge collapse was 100% avoidable. First by spending money on maintenance and upgrading the structure, which the government responsible for the bridge chose NOT to do several times because it was too expensive. Second by NOT overloading the structure with too many layers of paving.

The bridge wouldn\'t have collapsed if they\'d stripped all the old paving off and laid down an all new surface. By doing that the loading on the bridge would have been reduced to what it had been when originally built, or possibly even less if they used newer concrete technology.

Instead they went the cheap route, putting off critical maintenance and reinforcement upgrades. Pounding around on it with heavy equipment on top of more paving than it was designed for was the cause of the failure.

There was nothing wrong with the bridge\'s design. It met the criteria for when it was originally built. The government agencies who routed more and more traffic over it and all the other neglect and abuse heaped onto the bridge are responsible for its collapse.

Truly a case of penny-wise and pound-foolish! Saving a couple of million not fixing up the bridge properly cost them many millions and killed several people. Had they \"wasted\" that couple of million on an \"old\" bridge, it would still be standing and stronger than it was when built.

Gregg Eshelman
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