FDOT Fannie Road Over Dead Lake Bridge

GRAEF was the prime consultant for the replacement of the existing structurally deficient bridge on Fannie Road over Dead Lake in Escambia County, located northeast of Century, Florida. The original bridge was constructed in 1960 and is 121’ long. It had 8 spans ranging from 14’ to 15’ in length and utilized a timber piling substructure to carry a 19” deep superstructure consisting of 12” deep timber stringers at approximately 15” o.c. supporting a 7” thick concrete deck. The original bridge had a posted load limit of 10 tons. The bridge had been rehabilitated multiple times with additional timber piling, steel sheetpile wingwall additions, new approach slabs, and the replacement of the south abutment cap.

GRAEF investigated multiple bridge replacement solutions applicable to the site. Key issues considered included cost, construction duration, constructability relative to site, and minimizing environmental impacts. GRAEF considered both 3-span and 4-span options for this structure and determined that a 3-span option was not only more cost effective, but also provided a larger opening for timber debris to pass during an event and had less impact on the existing environment with one less pile bent needing to be installed. GRAEF used 15” precast slab units with a 6½” composite CIP topping for the superstructure and pile bent foundations utilizing 24” diameter steel pipe piles for the substructure. The use of prefabricated bridge elements for the superstructure decreased the construction duration by an estimated minimum of 2 months when compared to a CIP fl at slab system due to the complexity of falsework required to support the CIP slab during construction and curing. This falsework would have likely required the driving of temporary piling which would have also negatively impacted the existing environment. The precast slab units were prefabricated concurrent with other bridge construction activities and off the construction site in a controlled environment. The controlled environment increased quality control and reduced the dependency on unknowns such as weather. Improving quality of construction improved bridge durability resulting in a longer service life and lower life-cycle costs.