11/2/2026 McCall Macomber
Written by McCall Macomber
When Gov. JB Pritzker signed the Rebuild Illinois bill in 2019, investing $25.3 billion in Illinois’ roads and bridges, the Illinois Department of Transportation saw an additional opportunity: the chance to study in detail how load distribution occurs in a bridge and evolves over its lifespan.
An Illinois Center for Transportation team studied two newly constructed skewed steel I-girder bridges on Mattis Avenue over Interstate 57 and Interstate 74 in Champaign, Illinois, in an IDOT-sponsored research project. Larry Fahnestock and James LaFave, University of Illinois Urbana-Champaign professors, led the project with Mark Shaffer, IDOT’s engineer of bridges and structures.
Skewed steel I-girder bridges — which cross a roadway at an angle — are common in the U.S. Their structure, however, makes it challenging to estimate how they may respond to various loads, such as shorter-term effects, like day-to-day traffic, as well as longer-term effects, like seasonal temperature changes.
As a bridge ages, its distribution of these loads may shift although the loading conditions remain similar. Better understanding load distributions will allow IDOT to determine areas where bridge design may be improved for long-term effects, leading to longer-lasting, more cost-effective bridges that require fewer replacements.
Fahnestock and LaFave’s team equipped the Mattis Avenue bridges with sensors that measure strain, displacement and tilt, and used these measurements to monitor movements and stresses that developed during construction and after opening the bridges to traffic.
“This was a unique opportunity to collect multiple years of field data for full-scale bridges subjected to realistic loading conditions,” Fahnestock said. “We appreciate the partnership with IDOT to expand fundamental understanding of bridge behavior so that stresses can be determined more accurately for bridge design.”
They processed and synthesized the sensors’ data, collected from September 2021 through December 2025, and developed models for finite element analysis, a computer simulation technique used to predict real-world performance. These companion models allowed them to simulate a wider range of parameters beyond those covered in the field monitoring campaign. The extensive parametric study was designed to evaluate effects of varying bridge geometry, abutment type, traffic loads and thermal loads on bridge response.
Substantial stress developed from thermal loads in skewed steel I-girder bridges, particularly ones with integral abutments — where girders are encased in concrete at the ends. Stresses from thermal loads also increased substantially with skew angle and integral support restraint, with the largest stresses concentrated near abutments and piers.
“Being able to have a record of all bridge movements, stresses and strains helps IDOT understand the true behavior of many standard bridge details,” Shaffer said.
“The project resulted in vast amounts of data that will lead to many different implementation paths for different bridge elements,” he added. “The applicability of the results is well beyond the initial scope of the project. IDOT will be using this data to improve our standards for years to come.”
Read the reports for the IDOT-sponsored research project, R27-194: Spatial and Temporal Load Distribution in Steel Bridge Superstructures: Vol. I, Vol. II, and Vol. III