Project Overview
Building a new highway overpass is never easy, especially in a dense and congested urban setting. So when designers began planning the new flyover bridge at US 17-92 and SR 436 near Orlando, Fla.—which handles 100,000 travelers every day—they knew they needed a design that would be as minimally disruptive as possible.
The new interchange would elevate four lanes of the two highways in Seminole County. The original plan called for a continuous steel superstructure with staggered posttensioned pier caps, but DRMP, the engineers on the project, submitted an alternative concept, using 96-in.-deep precast concrete Florida I-beam (FIB) instead. “The 96-inch-deep FIB allowed us to span lengths that previously weren’t achievable with prestressed concrete beams,” says TJ Lallathin, PE, senior project manager for DRMP. “It allowed us to construct the bridge in one phase and without the use of posttensioning.”
Precast Solution
The structure was configured in three simply supported spans with a main span of 209 ft and two approach spans of 124 ft totaling a length of 457 ft. The beams were designed with high-strength concrete (10,000 psi) for increased structural capacity, which allowed the team to eliminate a beam line, reducing total beam costs as well as the dead load carried by the substructure. Lallathin reports that his team had to get special approval from the Florida Department of Transportation (FDOT) for the concrete.
The design offered benefits to the schedule, budget, and durability of the project, but erecting it wasn’t easy, Lallathin says. Along with addressing a short schedule and a constant stream of traffic, the team had to figure out how to cast, deliver, and erect thirteen 209-ft, 267,000-lb beams to the jobsite within the tight timeline.
Working closely with the precaster, the team addressed the delivery of the beams with only two special vehicles, capable of supporting 340,000 lb each. They delivered two beams each night, closing the intersection during off-peak hours to accommodate the delivery and erection. Florida Highway Patrol accompanied each truck nightly to ensure a safe and smooth delivery of the beams.
The result: the interchange was only closed to traffic for 7 nights—rather than the 4 weeks that were required to build the steel superstructure. “By using precast for this project, we were able to reduce beam fabrication and erection time, which ultimately helped us deliver the project 33 days ahead of schedule,” he says. “It also improved the aesthetics and lowered maintenance costs giving our client, FDOT District Five, a great cost savings measure.” |