Tama County's Steel Free Bridge Deck

A major bridge problem in the United States is the corrosion of reinforcing steel and the subsequent deterioration of the surrounding concrete due to deicing salts. There have been efforts in the past to alleviate these problems by using reinforcement that will not corrode, including clad steel reinforcement, fiber-reinforced polymer (FRP) reinforcement, and non-corrosive MMFX steel reinforcement. Another innovative concept is the steel-free bridge deck, which has been developed in Canada. These decks are free of internal steel reinforcement and rely on the internal arching action of the concrete slab, when the slab is confined in both the longitudinal and transverse directions. Using shear studs for composite action between the concrete deck and the steel girders provides longitudinal confinement, while steel straps welded to the top flanges of the girders at regular intervals provide the transverse confinement. FRP reinforcement is included transversely and longitudinally in the decks for temperature and shrinkage reinforcement. The most significant potential benefits of steel-free deck bridges are the decks’ durability and the material cost savings due to the significantly reduced amount of deck reinforcing. The favorable durability should provide reduced long-term maintenance costs. To the authors’ knowledge, the first steel-free deck bridge in the United States was constructed in Tama County, Iowa as part of the FHWA Innovative Bridge Research and Construction program. Since the original bridge deck had to be completely removed, Tama County used this opportunity to increase the width of this 41-foot simple span bridge from 24 to 28 feet. Conventional epoxy-coated reinforcement was used in cantilever overhangs. In this bridge, concrete with polypropylene fibers were used to reduce plastic shrinkage cracking and provide post-crack ductility for the slab. The Tama County steel-free bridge deck was designed using the provisions of the Ontario Highway Bridge Design Code. Included in this project are the deck design, construction documentation, periodic load testing, and evaluation. This past summer, the bridge deck was placed with minimal difficulties. Approximately five months after construction, the bridge was load tested using both static and dynamic loadings. Prior to these tests, instrumentation was installed to measure strains and deflections at critical locations. This paper will provide details on the design and construction of the steel free bridge deck, as well as a comparison of the load test performance with the expected design behavior. This bridge is visually inspected periodically and will be tested a second time (approximately a year after the initial test) to determine any changes in its structural behavior.