H&H provided design services from feasibility study to final contract documents and post design support for the replacement of the FDOT-designated critical evacuation route bridge for the barrier island community. The new bridge replaces the historic Boca Grande Swing Bridge and was recently named an ENR Southeast Best Project award winner and a 2017 Grand Award from the Florida Institute of Consulting Engineers.
The new swing span bridge, with a 225-foot main swing span, is centered in the navigation channel. The new superstructure consists of “fish belly” steel girders and supports an Exodermic deck. The north approach span structure consists of two 108-foot spans. The south approach span structure consists of two 117-foot spans. The approach superstructure has Florida I-Beam prestressed beams supporting a cast-in-place concrete deck. The total length of the new bridge, including approach spans is 678 feet.
The new substructure is a waterline footing with prestressed piles and hammerhead-type piers. This is the first substructure designed to support a swing bridge using the FDOT navigation vessel collision loads and methodology.
The new bridge profile is higher than the historic bridge’s profile to satisfy Coast Guard requirements, reduce the number of bridge openings, and not be impacted by the storm surge wave crest. The new elevation allowed the new swing span to clear the historic swing span since the older bridge remained in service throughout construction. The new bridge alignment was kept as close as possible to the existing bridge, providing just enough space to tuck the new and existing tender houses between bridges.
The innovative use of Exodermic decking provides a smooth riding surface and protects the supporting steel superstructure and operating machinery from debris and moisture. The pivot bearing, balance wheels, live load rollers, span locks and the end lifts, all provide support and stabilize the swing span superstructure during operation and when vehicular traffic is on the bridge. The systems were designed to be robust, durable elements for the bridge’s extremely corrosive marine environment.