Science & Technology - Posted by Neil Tickner-Maryland on Wednesday, August 1, 2012 9:16 - 6 Comments 
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(No Ratings Yet) Loading ...5 years after I-35 collapse, big leap in bridge sensors
"We no longer need to roll the dice when it comes to the structural integrity of the nation's highway bridges," says engineer Mehdi Kalantari. "Technical advances in wireless sensors make real-time monitoring both affordable and practical." (Credit: "bridge repair sign" via Shutterstock)
U. MARYLAND (US) — Five years after the deadly I-35W bridge collapse in Minneapolis, advances in sensors are making warning systems more affordable and practical.
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The text of this article by Futurity is licensed under a Creative Commons Attribution-No Derivatives License.
A new generation of these devices is needed to adequately monitor the nearly 150,000 US highway bridges—about one in four—listed by the federal government as either “structurally deficient” or “obsolete,” say researchers at the University of Maryland.
“We no longer need to roll the dice when it comes to the structural integrity of the nation’s highway bridges,” says engineer Mehdi Kalantari. “Technical advances in wireless sensors make real-time monitoring both affordable and practical.”
Cars rest on the collapsed portion of I-35W Mississippi River bridge after the collapse on August 1, 2007. (Credit: Kevin Rofidal, United States Coast Guard)
Kalantari leads one of two engineering teams at Maryland addressing the need. He is developing a system of tiny, long-lasting, energy-efficient, low-maintenance wireless sensors, along with software that analyzes real-time data collected.
Kalantari’s startup, Rensensys, has manufactured systems for use in the private sector and for testing by Maryland State Highway officials.
Another University of Maryland engineering team is working on a total “smart bridge” package with multiple technology innovations. While the system is not yet available commercially, key elements are being tested by Maryland State Highway officials, the Maryland Transportation Authority, and the North Carolina Department of Transportation.
“Wireless technology definitely makes bridge structural health monitoring more efficient and more effective,” says civil and environmental engineering research professor Chung Fu, director of Maryland’s Bridge Engineering Software and Technology Center and one of the leaders of this second research group.
“If the prices for system hardware and software are further reduced and standardized, we may see more widespread application in the next five to 10 years,” Fu says, adding that he has seen great advancement in this technology in the past decade.
Meanwhile, Kalantari is in the second year of testing his system on a Maryland Interstate bridge along the Capital Beltway in suburban Washington, DC. Over the past 12 months, he has upgraded his system, making it fully operational, and expanded its use to the private sector.
A few US and international firms are using it on transportation projects, as well as for monitoring the safety of building facades and the safety of large construction cranes. Also, he’s adapted the sensors for the purpose of monitoring cracks on bridge piers 120 feet underwater.
A few dozen tiny sensors, strategically placed on small to medium-sized bridges could measure prime factors such as strain, vibration, deformation, pressure, tilt, inclination, displacement, crack activity, humidity and temperature, Kalantari says—and for a much smaller price than current technology.
His team has equipped the system with a wide range of remote sensing functions and data analysis software capable of detecting structural anomalies. Also, the system delivers warnings to bridge maintenance engineers—by email or text messaging, in the case of severe warnings.
New “smart” bridges—including the replacement span in Minneapolis—use wired networks of sensors to detect problems early, when repairs are often cheaper, providing a wide margin of safety.
But these wired systems are generally too expensive to retrofit all the old bridges that need them, Kalantari says. Overall, he estimates that existing wired technologies cost at least 10 to 50 times more than his wireless system.
The latest statistics from the Federal Bureau of Transportation (2010) list nearly 70,000 US bridges as “structurally deficient,” requiring extra surveillance. In addition, more than 77,000 others are categorized as “obsolete”—exceeding their intended lifespan and carrying loads greater than they were designed to handle.
Under federal requirements, structurally deficient bridges must be visually inspected once each year. Others must be inspected once every two to five years.
“Limited, in-person inspections are not sufficient to provide highway maintenance authorities with an adequate margin of safety when compared with real-time monitoring,” Kalantari concludes.
Ultimately, adds Fu, real-time remote sensing will serve as a valuable supplement, but not fully replace human inspections. “You can’t put sensors everywhere,” he says.
In its report on the fatal Minneapolis bridge collapse, the National Transportation Safety Board identified a faulty metal plate as a likely cause of the disaster. It notes an “inadequate use of technologies for accurately assessing the condition of gusset plates on deck truss bridges.”
The new wireless monitoring technology is poised to fill that need, the engineering teams report.
The University of Maryland Integrated Structural Health Monitoring system research is sponsored by the US Department of Transportation, the Maryland Transportation Authority, Maryland State Highway Administration, and the North Carolina Department of Transportation.
More news from the University of Maryland: www.newsdesk.umd.edu
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6 Comments
nerf herder
M. Kalantari
Thanks for the comment and thoughts; however, the system developed by Resensys Team at the University of Maryland is capable would be capable to detect some serious red alerts if it was used on I-35 bridge. I am writing this response with the knowledge of the developed system (as one of the UMD/Resensys researchers contributing the technology). If the system was in place, it would certainly detect both unsafe over-strain and plastic deformation many months (possibly years) before the collapse. It was actually a known fact that the gussets were flawed and over-strained as early as 2003, 4 year before the collapse (according to http://www.startribune.com/newsgraphics/16940646.html); given this fact, the technology would certainly have detected the problem and would generate red alerts if the gussets have been monitored by the UMD/Resensys system.
nerf herder
Thanks for the response! I followed the link, there is visible deformity there. When we see a bridge collapse, we tend to think of it as one catastrophic event, in this case perhaps due to the construction that was going on that week, but not something that was visible years beforehand. There are also some small wires present, I wonder if they already had some type of sensors there, or is that unrelated?
M. Kalantari
I am not sure what kind of instruments were in place, and I could not not much information about the instrumentation in place before its collapse, but from the picture, it looks like they are a kind of acoustic emission sensing sensors (AE).
Kari
As I have done some research about the collapse of the I35-W I’ve noticed how many different things factored into it’s collapse, and I’ve come to understand that there was some deformity a few years prior to this event. These sensors could have detected that deformity when it was initially occurring correct? What are other red alerts that would be detected by the sensors?
Thanks Kari for the comment. Yes your observation is absolutely correct. Our technology would have been able to detect not only the high strain but the deformation in the plates long long time before the collapse. Also, the additional data analysis software and diagnostics tools that we have developed would have been able to provide automated alerts many months before the collapse.
My understanding is that the I-35 collapse was from 1/2″ thick steel plates being used instead of 1″ plates. Not sure how sensors (presumably detecting vibration and such) would catch a problem like that.
Best case, you would have time to evacuate the bridge if deformity was noticed, or if sensors were intentionally placed to detect cracked plates (however that detection is implemented it’s new to me, and that they cracked well before the bridge went down). The latter would imply people knew that the plates were susceptible, but I don’t think it was known. Technology is great, but I’m suspicious Kalantari is putting out a promo piece for his company’s products, masquerading as a science article. It could save some bridges, but I’m unconvinced this technology could have prevented the I-35 bridge collapse in particular.