The University of Wisconsin will develop and assist in the design of a modified concrete deck and girder system for a major bridge structure. This new technology includes a steel-free deck system. The corrosion of steel reinforcement in conventional deck systems is the main cause of deterioration of deck slabs. Initial construction cost is lower without steel reinforcement and life cycle cost is reduced because of replacement of deteriorated deck is not required. This project is part of a bridge replacement and widening project on Dane County Highway BB over Interstate Highway 39/90 in Madison, WI. The existing two lane, four span slab type bridge will replaced with a four lane, two span bridge using a concrete deck on precast concrete girders. The new bridge will also include two bike lanes and sidewalks. The new spans will be 115 and 125 feet with a bridge width of 82.5 feet. The total deck area will be 19,800 square feet. Construction of the bridge is planned to begin in spring 2006.

The replacement bridge will be built using new deck design technology with innovative materials. This new technology includes a steel-free deck system. Steel reinforcement in conventional deck systems are the main cause of deterioration of deck slabs subjected to deicing salts or exposed to the environment. Steel reinforcement will be totally removed in the new deck system and the girders of the bridge will be tied together to provide lateral constraint, which compensates for the lack of steel reinforcement. New materials such as fiber added to the concrete mix, fiber reinforced polymer (FRP) reinforcing bars or FRP grid will be also used for temperature and shrinkage crack control.

This new technology addresses numerous themes of the Innovative Bridge Research and Construction Program:

• Rapid construction - improving construction speed while reducing construction labor by eliminating placing and tying of two layers of steel reinforcing in the deck; reduced construction time should improve construction safety
• Innovative materials - combining innovative material including new efficient prestressed girders, high performance concrete, a single layer FRP reinforcing grid and FRP stay-in-place formwork will create a new system
• Reduction of maintenance and life cycle costs - eliminating maintenance due to corrosion prone steel reinforcing and reducing initial construction cost will reduce life cycle cost
• Shallow superstructure and longer spans - eliminating the conventional deck forming system and using a thinner deck with membrane action to resist wheel loads will reduce superstructure depth, will substantially reduce the structural dead load and allows higher love load capacity and will allow longer span applications.

A half-scale specimen of the bridge superstructure was constructed and tested in the Wisconsin Structures and Materials Testing Lab (WSMTL) to verify the adequacy of the new deck system. The specimen was inverted, i.e. up-side-down, for the convenience of the test.

The first series of test focused on a deck span with #2 glass fiber reinforced polymer (GFRP) bars as reinforcing to provide flexural crack control. The deck was tested on 54W girders with 8 foot center to center spacing. A single wheel load was applied in the test and the peak deck capacity was approximately 180 kips which provides safety factor of more than 11 against structural failure due to wheel load.

Final failure and peak capacity was reached as a punching shear failure occurred. The UW will continue the specimen testing in WSMTL to finalize the design technology and concept of the new deck system. The completed structure will also be monitored in order to evaluate the in place performance of the structural system.

 

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