Bridge Monitoring Helping "Rebuild Illinois"

By McCall Macomber

In 2019, Gov. J.B. Pritzker signed the Rebuild Illinois bill, committing $45 billion to improving the state’s infrastructure — including bridges.

One such endeavor is the recent Illinois Center for Transportation (ICT) and Illinois Department of Transportation (IDOT) joint project, “R27-194: Evaluation of Spatial and Temporal Load Distribution in Steel Bridge Superstructures.”

Larry Fahnestock and James LaFave, professors in the University of Illinois Department of Civil and Environmental Engineering, lead the project along with Mark Shaffer, IDOT’s bridge design policy engineer.

The research team is studying skewed bridges — which cross a roadway at a non-perpendicular angle — under construction on Mattis Avenue in Champaign, Illinois, over I-57 and I-74.

A skewed bridge presents extra challenges for engineers, as its structure can complicate how they estimate the bridge’s response to loads.

Here researchers are working together to examine shorter-term effects, like day-to-day traffic, as well as longer-term effects, like seasonal temperature changes, on load distribution in skewed steel bridges.

With construction of the bridges in full swing since August 2020, the research team is hard at work placing strain gauges on the installed girders as well as between the girders on cross frames, which control twisting and lateral bending.

The gauges will help to detect localized contraction or elongation in the steel, which is then used to calculate changes in stress as they occur.

“One of the major objectives of this project is to obtain a clearer understanding of the stresses that develop in skewed steel bridges so that skew effects can be more accurately considered in the design process,” Fahnestock said.

“Right now, for skewed bridges, fairly rough approximations are made in the design phase, and so we’re hoping that this project can provide better understanding and knowledge about the real stresses in these bridges,” he added.

The next steps?

The team is aiming to get two years of good data collection related to both temperature and traffic effects, and it plans to perform some shorter-term, live-load tests focused on traffic.

“After construction is complete and the bridges are in service, we will close a lane of the bridge and bring a truck of a known weight and drive the truck across the bridge and place the truck in certain locations,” Fahnestock said. “This type of live load testing provides the best opportunity for direct comparison between a real bridge and an analysis model.”

“We’re going to combine the field data with results from analysis models that we develop, so we will also have complementary simulations that cover a much wider range of parameters — like virtual field monitoring of many different bridges,” he added.

Fahnestock credits the success of the field work thus far to the “excellent” partnership with IDOT and the construction team as well as the hard work of the UIUC students.

“We have some very bright, motivated and committed students who are doing really fantastic work on this project,” he said. “It’s definitely been great to see their initiative and their dedication.”

“In particular, Sunny Zhou, the primary graduate student on this project, is to be commended for her leadership in the complex field monitoring operation,” he added.

Thanks to the researchers’ efforts, Illinoisans can expect to see more cost-effective and efficient bridge design as well as safer bridges.

“The project will result in more resilient bridge details, resulting in longer-lasting structures with less required repairs,” Shaffer said. “There is a cost savings to the public in that there are less bridge replacements, and a time savings in that there are less required construction zones.”