I-74 Bridge over Illinois Central Railroad
I-74, just north of the UIUC campus, is a major east-west thoroughfare with an average traffic load of over 63,000 vehicles per day. The existing bridge passed over 18 total railroad tracks (two for Amtrak trains and 16 for ICRR trains) and was in severe condition. Coordination with IDOT and the railroad was critical throughout the design and construction of this project.
The existing bridge, originally built in 1956, was 725 feet long and 125 ft wide, with EB and WB traffic carried by two separate superstructures sharing the same set of piers and abutments. The bridge was split into two units, with a deck expansion joint over an interior pier. The existing girders were 8’ deep built-up members reinforced by welded cover plates in the midspans and over the piers. The maximum span over the railroad tracks was 225 ft.
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Photo: EXP
Photo: EXP
In Bad Shape
Vinod was Project Manager for Phase I and Phase II, directing a team that inspected the bridge, provided recommendations for repairs, and performed final design under an expedited schedule. The bridge was in extremely bad shape.
An interior deck joint had failed, causing major leakage and deterioration of the pier underneath, with large spalls, exposed rebar and bearing seat loss. IDOT had already installed temporary shoring towers to support the girders on either side. The deck was also in severe condition, with a protective shielding in place over the railroad tracks to protect them from falling spalls. The inspection also revealed advanced deterioration in the beam ends, expansion joints, and bearings.
Fatigue Analysis
The existing steel contained cover plates and lateral gusset plates welded to the girder flanges, details that were susceptible to fatigue cracking with cyclic loading. As a result, the team performed an extensive analysis, as per AASHTO Manual for Bridge Evaluation, to determine the remaining service life of those details. The analysis concluded that the useful life was close to expiring, and that any reuse of the existing girders would require retrofitting of those details.
The labor costs involved in retrofitting more than 100 cover plate ends and more than 300 gusset plates above the railroad tracks, combined with the need for future inspection and maintenance of these repairs, were prohibitive. As a result, the team recommended a complete superstructure replacement.
Photo: EXP
New Bridge
The team recommended making the new structure one long continuous unit, thereby eliminating the interior deck expansion joint. The existing fixed pier was evaluated for the associated increase in tributary length and longitudinal forces. The columns, pile cap and pile foundations were all found to be adequate without the need for extra reinforcing.
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Photo: EXP
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Photo: EXP
The final proposed scope included: replacement the entire steel superstructure with original span configuration but now one continuous unit, reconstruction of abutments backwalls and pier under expansion joint, retrofit the pier caps on remaining piers, installation of modular expansion joints, and replacement of all existing rocker bearings with new HLMR bearings.
The girders were metallized because it provided a service life of 45-50 years and prevented future painting over the railroad tracks. The bolted field splices were placed in the most optimal spots, where shoring towers and cranes could be positioned to minimize disruption to railroad operations.
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Photo: EXP
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Photo: EXP
Proactive coordination with IDOT and the Illinois Central Railroad also helped expedite approvals of the preliminary engineering studies and final construction documents.