Researchers assess tech-based methods for structural evaluation

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One of the iPods used in the OIT project to monitor structural movements

We drive on infrastructure from the last century, never knowing when its shaking in the wind might herald a collapse, while in our hands are devices that can communicate with satellites, capture high-definition video and sense the motion of a fly. To C.J. Riley, it seemed like the one should be able to help with the other.

Riley, an associate professor of civil engineering at the Oregon Institute of Technology, is working on NITC research aimed at using low-cost, ubiquitous technology—like third-generation iPods—to evaluate the soundness of bridges and other transportation structures.

The goal of his just-published NITC education project, Dynamic Evaluation of Transportation Structures with iPod-Based Data Acquisition, was to expand Oregon Tech’s research lab while simultaneously figuring out two things: how can widely available technology be leveraged to assess structural integrity, and what is the best way to teach students this process?

To address both questions, Riley established the Structural Health and Kinetic Evaluation (SHAKE) Laboratory at Oregon Tech. While exploring options for structural assessment, Riley put some new lab tools in the hands of his graduate students: twelve third-generation iPod touch mobile devices with on-board accelerometers, Texas Instruments SensorTags, virtual visual sensors, and a benchtop shake table capable of scale-model dynamic structural response demonstrations and accelerometer testing.

In another NITC research project currently underway, Riley will focus on putting together a Rapid Transportation Structure Evaluation Toolkit for practitioners to use. Later this month he will give a webinar on that topic.

The initial vision was to zip-tie the iPods to different parts of a bridge and let them provide data about the bridge’s movements, shedding light on its stability and potential weak areas. The system would be suitable for smaller, single-span bridge structures, where permanent and more expensive structural health monitoring systems are cost prohibitive.

Riley and his students tested the iPods using the shake table, and found that the sensitivity of their accelerometers was a match for that of the SensorTags, with some advantages such as battery life making them a superior alternative.

They also explored a method known as vision sensing.

“The idea is that you have a video and you can track moving objects within a video in order to get information about that movement,” Riley said.

Using virtual visual sensors, variations in the intensity of pixels in a video, especially those located at the edges of vibrating elements, can be used to determine the frequency of vibrations. The researchers determined toward the end of this project that of all the methods evaluated, virtual visual sensors can provide the simplest and most easily implemented means for evaluating the dynamic parameters of a structure.

As for determining the best method of teaching students, Riley took advantage of his class structure to do a small controlled experiment.

“I had basically three groups. There were three students who were off on a trip and they weren’t going to be in the lab. I used that fact to treat them like online students,” Riley said.

Of the remaining in-class students, one group did all the data collection and all the hands-on work, while the other group just received the data and an explanation of the experiment. Learning gains as a result of the module were assessed via a survey of students’ perceived learning, as well as an evaluation of submitted lab reports.

“The results do show that the learning gains looks better for the students who experienced the hands-on process,” Riley said.

Because of the small sample size, these results were not statistically significant. Students, however, indicated that they preferred using the iPods and doing data collection in the laboratory over simply working with the data.

The more comprehensive experience seemed to enhance students' engagement with and understanding of the material. In the video below, graduate student Sam Lozano monitors bridge movement under live traffic conditions.

For more information on the learning outcomes and methods evaluated in this project, download the final report.

Riley will give a NITC webinar May 25 with more details about his current efforts to develop a structure evaluation toolkit for practitioners.

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