Motorists in Chicago can thank precast concrete, in part, for helping improve one of the most congested intersections in the U.S.
The 271-foot Peoria Street pedestrian bridge, completed this summer, spans Interstate 290/Congress Parkway and is adjacent to the rebuilding of the Jane Byrne Interchange in downtown Chicago. Utility Concrete Products (UCP) of Morris, Ill., manufactured the precast panels for the project.
The construction included 15,272 square feet of 8-inch precast deck panels that were set transverse to the main longitudinal I-beams in just four working days. Using precast allowed the underlying deck to be assembled in days, compared to a longer traditional cast-in-place construction project, where forming and curing will increase the onsite duration. By manufacturing the precast at the plant and delivering it to the site, UCP played a crucial role to construct the bridge swiftly and decrease traffic disruption.
“Typically, this would have been a full-depth cast-in-place deck,” says Tom Heraty, UCP’s vice president of sales and engineering. “Utilizing precast, we were able to pour the slabs at our own pace in a controlled environment without the high cost of jobsite delays. It is also much safer to produce these slabs in a plant versus above the high-traffic I-290 expressway.”
Producing the precast concrete deck panels in a controlled setting with high strength, 5,000 psi concrete allowed for a thinner section than typical deck panels with less rebar clearance, but with the same or better durability and structural capacity. The precast panels were produced with a raked finish to create a rough pouring surface for the 2¼-inch overlay.
Tapered pockets were formed into the panels, allowing rebar to pass through. These pockets and the edges of the panel were treated with retarder to create a porous surface for bonding. The edges were formed with shear keys and exposed rebar to help create a continuous structural connection across joints.
Panels were aligned so the pockets were set over vertical headed anchor studs from the top flange of the I-beams below. Rebar extending horizontally out of the edges had to be staggered such that it did not interfere with the overlapping bars from adjacent panels. Panels also included cast-in inserts with leveling bolts for vertical adjustability. Ductal ( Lafarge) ultra-high performance concrete was used to fill the pockets and joints to ultimately create a composite section.
“I hope the success of the Peoria Street pedestrian bridge shows the possibilities that using precast concrete can create,” Heraty says.
The Precast/Prestressed Concrete Institute recently credited the project for its construction technique, which “capitalized on innovative precast concrete accelerated bridge construction techniques that allowed for high strength, thinner bridge sections and reduced delays and lane closures.”