In everything from tiny homes to massive skyscrapers, wear and tear can be imperceptible as it happens—a tiny crack here, a slight shift there. Over time, however, all those little changes can compound, adding up to expensive, or even dangerous, problems. Our changing climate and extreme weather events can add strain, accelerating the deterioration of buildings and infrastructure.
Now, University of Wisconsin-Madison engineers will utilize a unique integrated system to monitor damage propagation—particularly in many of the nation’s landmark buildings—while blending structural and geological engineering with mixed reality.
Hannah Blum and Jesse Hampton, both assistant professors of civil and environmental engineering at UW-Madison, are collaborating with the U.S. Army Engineer Research and Development Center’s (ERDC) Construction Engineering Research Laboratory (CERL). ERDC-CERL is supporting the project with a $3.4 million cooperative agreement.
Monitoring and preserving historic buildings is of particular interest to the U.S. Department of Defense, which manages the largest property portfolio in the federal government, with more than 500,000 buildings. Of those, 45 are national historic landmarks, 3,032 are national historic landmark contributing places, 2,370 are individual and contributing historic assets in the National Register of Historic Places, and 16,000 are historic assets determined eligible for inclusion in the National Register of Historic Places.
For its monitoring system, the team will employ fiber-optic sensing networks capable of detecting subtle deformations in a structure. The system works by taking advantage of the physical nature of fiber-optic cables: They are long, narrow strands of glass or plastic that conduct light from one point to another. When light shined along the cable hits an imperfection, it’s reflected. The researchers can use the reflections to interpret where and what type of deformation is occurring in a structure from slow loadings such as temperature changes to fast loadings such as seismic waves.
Engineers are just beginning to use fiber-optic sensing as a tool to monitor earthquakes through what’s known as distributed acoustic sensing. It’s a technique that Hampton, a civil and geological engineer, says is still in its early stages of development; using it to monitor changes in a structure is a cutting-edge application.
“If that cable stretches at any point, those little imperfections that reflect some of that light are going to move further away from each other,” Hampton says. “If they compress, the response changes because those points are moving closer together. With that information, you can understand how a structure is deforming.”
These fiber optic cables are part of the same system that CEE assistant professors Hannah Blum and Jesse Hampton will use to monitor historic structures’ health in a cooperative agreement with the Department of Defense. Photo courtesy of Hannah Blum.
The fiber-optic networks will be particularly useful for noticing new deformation as it occurs, but Hampton says they may also have value for finding preexisting damage in structures. Structures deform slightly when under load—like from the weight of a car passing over a bridge or the force of the wind against the side of a building. Hampton says that because we know how structural materials should perform under load, it may be possible to use initial readings from the fiber-optic network to infer what kind of damage a structure has accumulated. Additionally, the network can remain in place for long-term monitoring of the structures.
The team will create physics-based structural models of the infrastructure and then will feed data from the networks into the models to better estimate the performance of these structures subjected to anticipated future loading conditions. Blum’s team has experience in creating detailed structural models to analyze behavior.
Employing very detailed LIDAR scans to map out the historic structures, the team also will create detailed point cloud models of buildings. Zoomed out, these models look like a 3D representation of whatever structure they scanned; zoomed in, and they’re made of countless, precisely arrayed individual points.
Blum, Hampton, and their partners at ERDC-CERL and the Department of Defense want to make sure the point cloud models are publicly accessible. “These are government sites, for non-classified buildings, everyone should be able to virtually interact with them and see what they’re like,” Blum says.
The 3D point cloud can then be used in mixed- or augmented-reality visualization to improve future site inspections. For example, an inspector could use the visualization tool to overlay the previous inspection information, which will help show damage propagation since the previous inspection. That draws on Blum’s previous expertise; in partnership with UW-Madison’s Web and Mobile Solutions team, she’s been a leader in introducing mixed reality to students in her structural engineering classes. In fact, Blum and Hampton plan to create learning modules for UW-Madison engineering students using the augmented-reality data created from the project.
“Mixed reality is becoming a lot more common for construction site inspections or post-disaster infrastructure inspections,” says Blum, who is the Alain H. Peyrot Fellow in structural engineering. “This is now turning into a mainstream tool and students will benefit from exposure to this technology.”
Though the project’s work is of significant interest to the Department of Defense, with implications for monitoring building health at DOD sites across the United States and abroad, Blum and Hampton will begin their work at sites in Wisconsin. They’re working with the Wisconsin Department of Transportation, the National Park Service and other partners to locate roads, bridges and historic sites they can use to test their new monitoring methods.
The tools they develop could see widespread use for monitoring aging structures. “This is a really timely project, with all of the aging infrastructure we have in the United States,” Hampton says. “It could be extremely impactful. If there’s not enough funding out there to actively monitor and understand the damage evolution of our infrastructure, buildings and bridges, tools like these fiber-optic sensing networks could be invaluable.”
Dawn Morrison, a geographer at ERDC-CERL, said Blum’s and Hampton’s work will support and advance the Construction Engineering Research Laboratory’s programs and tools for monitoring and assessing structural health.
“The work that UW-Madison is pursuing supports the DOD and U.S. Army’s interest in technology for conducting condition assessments, monitoring systems and improving compliance capabilities for historic structures on military installations,” Morrison says. “The DOD and the U.S. Army manage and are responsible for a significant number of our country’s historic structures and having non-destructive methods for assessing the condition of these structures in real or near-real time can be beneficial in the government’s ability to manage its historic structures and buildings.”
Featured image caption: Civil and Environmental Engineering students Gowshikan Arulananthan, Monamy Mustaq and Nate Opperman (from left) set up a fiber optic monitoring system for a test on the SEAhorse vacuum box in the Jun and Sandy Lee Wisconsin Structures and Materials Testing Laboratory. Photo courtesy of Hannah Blum.