Involved Companies

Background

This project included the design and construction of a single point urban interchange (SPUI) at US 17-92 and SR 436. The interchange elevated 4 lanes of US 17-92 over SR 436 in Seminole County. The concrete flyover bridge was submitted as an alternative concept, using 96” deep Florida I-Beam (FIB) concrete beams instead of steel girders. The solution led to the unprecedented delivery and installation of the longest single-piece concrete beams ever fabricated and installed not just in Florida but the United States. The flyover bridge was configured in three, simply supported, spans with a main span of 209-feet and two approach spans of 124-feet totaling a length of 457-feet. The approach spans consist of 78-in. deep FIBs and 96-in. deep FIBs (exterior), and the main span consists of 96-in. deep FIBs.

Innovations/Accomplishments

The beams were designed with high-strength concrete (10,000 psi) for increased structural capacity, which allowed us to eliminate a beam line, reducing total beam costs as well as the dead load that must be carried by the substructure. A special technical provision, detailing the concrete properties, was required before the precaster could begin work.

To meet the schedule, two beams were cast in the same bed, but resulted in varying camber between the two beams. After all tendons were stressed, the first beam was formed and the concrete placed. After the concrete cured, the forms were stripped and placed for the second beam. Once the second beam’s concrete reached the strength required for transfer, the strands were detensioned and both beams were removed from the bed.

The difference in concrete strengths at the time of strand release caused variations in camber values when measured at the precast yard. Compounding the issue of camber variation was the construction schedule that was reduced after award to achieve an early completion bonus therefore erecting beams earlier than the design assumption. The beam age at erection varied from 16 to 58 days, when beams are typically erected at 120 days. While all beams had achieved the specified 28-day concrete compressive strength, the large variation in age at erection caused reduced beam cambers and increased variation in cambers. Reduced camber resulted in large beam haunches, at certain locations, larger than 8 inches. To accommodate the additional haunch and determine appropriate camber and deflection, a finite element model was used. To reduce camber and maintain vertical clearance, a multi-staged deck pour, separating the haunch pour from the rest of the deck pour was modeled. The additional composite properties of the haunch allowed the beam to handle the additional loading and maintain the required clearances.

Getting 209-feet concrete beams fabricated, delivered and erected proved to be one of the biggest challenges, as it had never been done in Florida or the United States. Working closely with the precaster, the team addressed the delivery of the 13, 267,000-pound beams. With only two special vehicles, capable of supporting 300,000 pounds, they delivered two beams each night, making the delivery a full week-long process. The entire US 17-92/SR 436 intersection, which carries 100,000 vehicles daily, was closed down and traffic was rerouted between off-peak hours, 11 pm – 6 am each day of that week to accommodate the delivery. Florida Highway Patrol accompanied each truck nightly to help ensure safety and a smooth delivery of the beams.

High Performance

• Precast concrete piles were used for the foundations to expedite construction. They also allowed for high capacities on that aren’t achievable with steel piles.

• Precast MSE walls were used in lieu of CIP walls to improve aesthetics and expedite construction. We also used larger panels, 5’ x 10’, than what is typically used for these panels to reduce the number of joints and expedite construction due to the tight schedule.

• Highway lighting was added to the project to light the corridor for the travelling public. Precast foundations were used for these locations to expedite construction.

• The precast beams met the aesthetic requirements of the project, providing a pleasing beam cross section and allowing for the color scheme the client requested

• The versatility of the precast concrete beams met the structural demands of a large span while allowing the contractor to place beams quickly, meeting the demands of the fast-paced schedule.

• The precast beams were able to be delivered and placed in the same night, reducing the amount of time the intersection was closed, and limited the amount of job site space required to house and store superstructure elements.

• With the ability to place two beams per night, the affects to the project intersection was minimized to one week of nightly lane closures. This was a significant reduction, approximately ¼ of the time, when compared to the construction time for steel girders.

• The use of precast beams reduced the construction schedule, allowing the contractor to receive a bonus by getting the project completed sooner.

• Precast beams have significantly lower maintenance costs and have a long life cycle, reducing overall long term costs for the client and ultimately the public.

• High strength concrete was used which allowed us to eliminate a beam line resulting in savings to the superstructure as well as the substructure and foundations.

• The alternative concept of concrete beams over steel girders was the single largest reason for the successful bid. The change to precast beams saved over $2M when compared to the required steel girder superstructure.

Photo credit: Chris Parmanan - Horizon View Media, LLC; Aerial Innovations, Inc; DRMP, Inc; The Lane Construction Corporation