For years, a highway interchange in Jacksonville, Fla., created constant traffic delays. Because the southbound Interstate 95 (I-95) traffic exited to eastbound State Route 202 (SR-202) at a stop light, vehicles would back up for a mile or more during rush hour. City leaders finally decided the problem had to be fixed.
In 2014, the owner awarded a design-build contract for the redesign and construction of the interchange to eliminate the congestion. The winning design featured four bridge structures, new ramp configurations, new highway alignments, and roadway widening of both highways.
The signature piece of the design is a curved post-tensioned, precast concrete U-girder flyover ramp bridge to carry southbound I-95 traffic to eastbound SR-202 lanes, eliminating the traffic backup problem. The seven-span, 1342-ft-long structure is curved on an 1100 ft horizontal radius and features a superstructure composed of curved, spliced precast concrete U-girders that are post-tensioned for continuity.
Falsework Towers Not Required
Because the flyover was constructed over three major traffic crossings, only overnight lane closures were allowed, limiting the construction crew to six 8-hour windows for erection in traffic areas. To accommodate the constant flow of traffic through the jobsite, the designers incorporated several innovative features into the design and construction staging, including precast concrete hammerhead pier caps for interior piers adjacent to traffic. These pier caps also served to support the pier girders during construction, eliminating the need for falsework towers within the traffic zone.
To minimize form changes, both the left and right girders were designed to be cast at the same radius. This casting method did not significantly affect the design, but it allowed for vastly increased efficiency in girder production. Once stripped from the formwork and stored at the precast concrete producer’s yard, the girders were mildly reinforced, and post-tensioning tendons were installed and grouted to control concrete stresses during shipping and erection. These tendons are also part of the final structure design.
Before erecting the drop-in girders, all other girders in the superstructure unit had to be erected with splices cast, lid slabs poured, and partial-length continuity tendons stressed. This required a detailed erection sequence and coordination among the contractor, precast concrete producer, and post-tensioning subcontractor to minimize schedule impacts.
The successful rapid construction of this flyover bridge proves that spliced post-tensioned, precast concrete designs can provide innovative solutions for many bridge design challenges. The new structure will fulfill local traffic needs for years to come.