Working with our long-held client, the Orlando-Orange County Expressway Authority (OOCEA), I was met with the challenge of developing an aesthetically pleasing bridge design for a high visibility interchange location just outside of Orlando, Florida. The project was an extension of the John Land Apopka Expressway (State Road 414), a new alignment and limited access toll facility; and the bridge location was a single-point urban interchange that required a clear span of 286-feet.

The geometry of the interchange in question dictated a very long span. Typically such a long single-span bridge requires a very deep beam, but this would have never addressed the client's desire for an aesthetically pleasing structure.

We brainstormed a way to achieve the appearance desired by the OOCEA, and our solution was an innovative bridge design that was being used in the Midwest: the anchored end-span bridge. There were no anchored end-span bridges in the state of Florida at the time, so this would be the first in-state application of its design.

In order to address both the client's vision and the required geometry, we proposed a three-span structure with variable-depth steel plate girders. Our design included spans of 71-feet, 286-feet and 71-feet with "anchored" end spans to offset the significant uplift forces caused by the unbalanced spans.

The superstructure consisted of a cast-in-place concrete deck supported by haunched steel plate I-girders. These girders varied in height from nine feet at the intermediate supports to just six feet at the center of the main span. The girder ends were anchored to the substructure by full length threaded rods. The substructure consisted of multi-column piers for the intermediate bents and a full-height concrete cantilever abutment for the end bents. The short end spans and intermediate piers were bound by textured precast concrete walls that matched the bridge's approach retaining walls. This gave the appearance of a slender single-span bridge, thereby meeting the client's aesthetic vision. The bridge's driven concrete pile foundations could not be in tension, so we sized the abutment footing appropriately where the dead load offset the superstructure uplift forces.

After construction the contractor told me how well everything fit together thanks to our detailed plans. In fact, the bridge went on to win a "Florida's Best in Construction – Major Bridge" award by the Florida Transportation Builders Association.

The anchored end-span is not the answer for every situation. However, by thinking outside the box and accepting new innovations, we helped create an aesthetically pleasing, functional and award-winning bridge.

Don Hammack is an associate vice president in Dewberry's new Orlando office. Earlier this year, Dewberry acquired the highly regarded, Florida-based Bowyer-Singleton, which has become a transportation design leader throughout the state. The addition of Bowyer-Singleton brings Dewberry's Florida presence to a total of eight locations and 115 personnel; and 160 total employees in the southeast and Gulf Coast region. See our official press release for more details.