SHM Research at University of Michigan

Professor Jerry Lynch, in his lab at the University of Michigan Laboratory for Intelligent Structural Technology in Ann Arbor, holds up a sensor that can help detect damage to a bridge before it becomes visible.

"We're aware that bridges are really difficult to maintain over their life, and we're sensitive to that," said Jerry Lynch, U-M professor of engineering and author of a paper on the research.

"But what we'd like to do is give (inspectors) a way to monitor those structures in a better way."

Lynch helped develop a structural coating, made of carbon nanotubes, that uses electrical currents to find damage like strain and corrosion. The idea behind the coating technology is to avoid catastrophes like the August 2007 collapse of the I-35 bridge in Minneapolis, Minn., that killed 13 people. The recent one-year anniversary of the collapse has again drawn attention to bridge safety and monitoring techniques. Faulty design is being investigated as the cause.

"These sorts of failures are very intimidating psychologically. It sort of violates that notion of terra firma," Lynch said. " ... Bridges are not supposed to fail." The breakthrough sensing skin is made of layers of the nanotubes mixed with polymers, and is sprayed as a permanent coating on the structure. A carbon nanotube is microscopic and shaped like a long, hollow strand of spaghetti, said U-M engineering professor Nicholas Kotov, a key developer of the technology. 

It's one of the strongest materials available and, when mixed with the polymers, lends that strength to the coating. When technicians flow electricity through the skin, it produces a two-dimensional image via a central computing device. Electrical resistance shown in the image will indicate structural damage. The hundreds of micro-layers in the coating allow it to sense structural strain, corrosion, pH levels and other indicators of damage. The technology is the first to provide comprehensive data on the entire structure, Lynch said. In traditional bridge monitoring, engineers use data from points of concern, like the structure's joints, to calculate data for the entire bridge. The coating costs about $1 per square inch and is engineered to last decades, Kotov said. "Presumably the carbon nanotube coating won't corrode over the lifetime of the bridge," he said. The sensing skin is set to be tested in Korea or Taiwan next summer. Several Asian countries - particularly those in high seismic areas - are interested in the technology. The technology also is important to U.S. bridges, which are aging. In two or three years, the coating could be ready for commercial use.

In the meantime, Lynch has helped create wireless sensing devices to send bridge monitoring data more cheaply. One of his devices, although only a few inches in diameter, costs $100-$200. Data-sending cables could cost more than $1,000 a piece.

The wireless device, called the Narada wireless sensor, is already installed on 15 bridges worldwide, on a U.S. naval ship and on wind turbines in Germany.

Lynch said he hopes to be able to combine the sensing skin and wireless technologies "for use somewhere down the line." It's important to monitor the country's bridges to prevent disasters like the Minneapolis bridge collapse, Lynch said. And because most bridges fail slowly instead of without warning, sophisticated monitoring techniques are vital. "I think it's critically important, there's no doubt about it," Lynch said. "There's room for improvement when it comes to monitoring bridges. ... it's like medicine. There are always challenges out there."

[Ann Arbor News]

Clarkson University’s Sazonov Performs Bridge Experiments In Malaysia

Edward Sazonov, assistant professor of electrical and computer engineering at Clarkson University, recently collaborated with faculty from the National University of Malaysia (Universiti Kebangsaan Malaysia, UKM) to perform bridge experiments on location in Malasia. UKM sponsored Sazonov’s visit, which focused on wireless bridge monitoring technologies that he has developed at Clarkson with substantial funding from the New York State Energy Research and Development Authority (NYSERDA).

The task of structural health monitoring of highway bridges and overpasses has gained significant attention in recent years. Monitoring the health status of bridges is not only a matter of preventing economic losses from traffic delays and detours, but also an issue of preventing catastrophic failures and loss of human life as occurred in Minneapolis just a year ago. Unfortunately, this has become a worldwide problem as many countries recently have realized a significant increase in the number of aging bridges constructed 50 years ago and more.

Sazonov’s group has developed a wireless system, which provides utility similar to a conventional wired system, but does not need wires. The wireless sensors are capable of time-synchronous data acquisition and 100 percent data delivery in a scalable system that can include hundreds of distributed sensors. Sazonov’s research shows that synchronization on the level of microseconds is required for vibration analysis of highway structures. Sazonov’s system satisfies such stringent requirements and can serve as a platform for applications of structural health monitoring that use vibration.

The experiments in Malaysia followed earlier experiments in New York State in which 44 wireless sensors were deployed on a steel girder bridge. The goal of the joint experiments with UKM was to test the system’s applicability to different construction technologies and different environments. In the experiment, the sensor network was installed on a pre-stressed concrete bridge. Then, the vibration response of the structure, due to passing traffic, was analyzed to provide information useful for damage detection.

The results of the experiments demonstrated that the system can be deployed successfully on structures constructed using different technologies. This was good news to Muhammad Fauzi Mohd Zain, who is deputy dean and co-director, Advanced Engineering Centre, Faculty of Engineering at UKM and Sazonov’s Malasian host. "In Malaysia, commonly we use visual inspection routinely to detect small cracks or defects. It is like finding a needle in a haystack and impossible in areas that are inaccessible or hard to access," said Zain. "Gradually such constraints are being overcome with emerging new technologies... for vibration based monitoring of structures."

[Clarkson University]

Bridges on I-80 monitored for stress, strain during move

Sensors that dotted and crisscrossed the seven bridges that were lifted, driven, launched and lowered into place along I-80 have told officials in charge of the project that the structures responded as they were designed to.

In past bridge projects around the nation, prefabricated decks haven't been lifted and transported to the extent the replacements along I-80 were, so monitoring the integrity of the structures was important, Utah Department of Transportation officials said.

"We had real-time data during the moves that let us monitor the stress and strain on the girders and the bridge deck," said Shana Lindsey, director of research and bridge operation for UDOT. "The sensors allowed us to see if we went beyond the tolerance levels of the materials, and we didn't."

As each bridge moved from the farm to its final location, 28 long-strand fiber optic sensors sent out more than 100 readings per second on the state of the structure. In real-time, a crew of engineers and specialists analyzed the data on-site to gauge the strain on points of stress for each portion of the transport. The readings alerted the observers to potholes or bumps in the route, telling them how the bridge responded.

"If you can pick up the movement of a structure while they're still in their embryonic stages, you can prevent repairs and problems before they happen," said Tom Winant, vice president of technical sales and marketing for Osmos USA.

The bridges were designed to allow for up to three to four inches of deflection on either end and still be able to return to their original state, Lindsey said. According to the sensors and the analysis of engineers, the bridges did not deflect to those levels, but some hairline cracks did appear on the structures.

The cracks were expected, though, because it is concrete's nature to crack even without being transported, Lindsey said. To prevent salt and water from entering into the cracked areas, UDOT has scheduled a polymer overlay to coatthe structures to protect them from early erosion or deterioration.

Lindsey said the massive amount of data compiled from each move will help UDOT refine its techniques and designs for future projects.

The results from the move verified the assumptions designers made when they began fabricating the bridges and planned the launch, said Roy A. Imbsen, an engineer and consultant to the project. With the data, Imbsen said UDOT would be able to implement specifications to the accelerated bridge construction process so other agencies could begin to use it, too.

[Desert News]