From structural health monitoring (SHM) to intelligent transportation systems (ITS), intelligent infrastructure is beginning the slow move from purely academic research to practical application. The new, extensively instrumented I-35W Bridge in Minneapolis brought to the forefront some SHM technologies and capabilities that have been developing for at least the last decade. Likewise, the Michigan Department of Transportation began deploying a network of remote bridge load and stress monitoring systems (see “Redecking Michigan’s Cut River Bridge,” RAI, September 2009). And, although still anchored in research mode, the U.S. Department of Transportation’s IntelliDrive initiative promises to push ITS into reality within the next decade (see “Developments in ITS” on page 15).

While experts agree on the potential benefits of SHM, there are differing perspectives on its current status. According to Peter J. Vanderzee, president and CEO of LifeSpan Technologies, SHM has been commercially available for nearly 10 years and provides significant benefits to infrastructure owners, including condition assessment that can support repair and replacement decisions. “Unfortunately,” Vanderzee said, “while public-sector managers continue to acknowledge the technology benefits, far too few project implementations have resulted, slowing what should be a more robust rate of growth for the advanced condition-assessment industry. I contend the lack of aggressive and widespread adoption is more a function of long-standing agency budgeting practices and limited federal funding participation than a lack of owner interest.”

Mark Sereci, president and CEO of Digitexx Data Systems offers a more restrained view. “SHM of bridges is still in its infancy in the United States (and the world) with a lot of continued research taking place to best determine what to measure, how to measure it, and for how long,” he said. “Monitoring bridges isn’t easy. Based on geographic location of the bridge, the structural make-up of the bridge (suspension, cantilever, cable-stayed, truss, or a combination), and the age of the bridge, the requirements vary. The real challenge is developing the algorithms that measure performance and help to immediately detect changes in a bridge’s behavior which are key indicators of permanent structural damage that may not be visible to the naked eye. The good news is there is a lot of new technology available today and a lot of research taking place in sensor technology, bridge materials, and algorithm development.”

Making sense of the data continues to be a challenge, agreed Ryan Woodward, P.E., bridge engineer for HNTB Corporation. “In the past, SHM has been deployed primarily from the perspective of academic research, as opposed to design or maintenance. This research has historically consisted of collecting large amounts of data, followed by a great deal of agonizing over how to interpret the data. By narrowly focusing on stress ranges or comparing events to baseline behavior, we can be lulled into overlooking flawed design assumptions. The recent collapse of the I-35W Bridge tragically demonstrates the difficulty of identifying appropriate SHM strategies. Although the bridge was widely instrumented, the collected data was useful in identifying the bridge failure only after the collapse!”

Clearly, managing the data overload can be as important as collecting the data in the first place. “How do visual inspection data and sensor data combine to provide asset managers with a comprehensive look at what the real structure condition is without simply overloading them with even more data for them to process and account for?” asked Michael Schellhase, CEO, InspectTech Systems, Inc. “InspectTech is focusing on creating advanced software tools to help bridge owners manage and organize this data to comprehensively account for all of the various data sources feeding their planning program, from visual inspection reports to sensor data to other non-destructive testing tools.”

Most condition assessment technologies deployed during the last 10 years have captured variables such as displacement/strain/stress and temperature, Vanderzee said. But more specialized sensing and assessment technologies are available, including geotechnical, acoustic, crack width/propagation, ground penetrating radar, corrosion, vibration, and acceleration.

“Most importantly,” Vanderzee said, “major engineering consultants have learned how to utilize the monitoring data captured to more effectively and precisely evaluate infrastructure condition, allowing them to make technically appropriate recommendations to optimize the limited funding most infrastructure owners continue to experience.”

Woodward concurred: “By installing and experimenting with different SHM systems on some of our built projects, HNTB has developed effective strategies for monitoring our bridges as they mature over time, while remaining responsive to clients’ budgets.”

Woodward recommends that bridge designers take the lead in implementing SHM. “The design team is best suited to interpret the data, as they are most familiar with the design assumptions and the intended behavior of the bridge,” he said. “The designer is intimately acquainted with the load path redundancy and intended redistribution of loads at ultimate state as compared to service level performance.”

Using off-the-shelf components, HNTB developed an economical bridge instrumentation program that is remotely monitored via cellular modem and the Internet. The program was used recently to monitor controlled demolition of a major truss bridge at the New York/Vermont border. Vibration and inclination data allowed the team to monitor the stability of the structure during disassembly, and, according to Woodward, yielded a great deal of information about the behavior and load distribution of the bridge.

This summer, Digitexx is installing a system on a 1,292-meter-long, combination cantilever and steel truss bridge. The system comprises 122 channels containing 100 accelerometers, 18 strain gages, 3 thermistors and one wind speed/direction meter. The system provides both scheduled and event-triggered data recording as well as multi-point channel broadcasting for both remote and local bridge management.

“SHM is coming out of its infancy, and approaching practical applications,” Woodward said. “In the next 10 years, it is hoped that we can overcome the challenges of large-scale data collection and focus on collecting relevant information. As we develop economical SHM strategies that help engineers better understand unusual behavior and improve the owner’s ability to make decisions, SHM will become practical and ubiquitous.”

Vanderzee expresses greater concern about convincing people that SHM systems offer a solution to limited bridge program funding. “When infrastructure owner executives finally accept that these commercially available technologies can be used to optimize limited funding through safe deferring of major capital expenditures for unnecessary repair or replacement projects,” he said, “the growth of this market will be robust for a decade or more.