Photos: Wapello County

“The selection of UHPC for the waffle deck and the girders ensures durability and low maintenance. I would expect we will see more of this usage.”

M. Myint Lwin

 

Bridges: Main Span up to 75 Feet

Little Cedar Creek Waffle Deck Bridge

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The Little Cedar Creek Bridge is the world’s first to be constructed with a full-depth waffle-deck panel system made with ultra-high-performance (UHPC) precast concrete and connected with UHPC field-cast joints. The two-lane replacement bridge in Ottumwa, Iowa, was built as a demonstration project to showcase the benefits of UHPC and waffle-deck panels.

The superstructure on this single-span bridge consists of five standard Iowa Type B precast concrete girders spaced at 7 ft 4 in. (2.33 m). The 8 in. (200 mm) deep waffle slabs, each of which is 8 ft(2.4 m)  long and 16 ft 2.5 in. (4.94 m) wide, was designed to be composite with the girders.

“The selection of UHPC for the waffle deck and the girders ensures durability and low maintenance,” says M. Myint Lwin, a judge on the transportation awards jury. “I would expect we will see more of this usage because it can be useful when elements demand high reinforcement.”

Designed and constructed using federal and state funds, the bridge’s constructability and the structural performance of its critical connections and panels were investigated using large-scale laboratory tests at Iowa State University. These tests applied service, fatigue, and ultimate loads to two test panels produced by the precaster in advance of the work getting under way.

The tests indicated that the waffle deck, including the UHPC joints, performed satisfactorily, with no fatigue damage after 1 million cycles of loading at each location. Displacements of the deck were considerably smaller than the allowable limits of the AASHTO LRFD Bridge Design Specifications.  Measured compressive strength of the UHPC production panels was 33,700 psi (232 MPa).

Following approval from these tests, local Department of Transportation officials designed 14 waffle-deck panels that were installed quickly and easily, despite a delay due to weather. The project was completed in 70% of the time required for a similar design using cast-in-place concrete.

By combining the attributes of UHPC with the efficiency of the waffle-panel design, the bridge deck system creates a durable option that provides longer spans, efficient use of materials, less weight, and faster construction.

The concept can be used for new bridges as well as for rehabilitation of deteriorated bridge decks. It also may provide opportunities for upgrading the load capacity of existing bridges through improved strength and reduced deck weight.

“This project was a good demonstration project for the owner to show accelerated bridge construction techniques with the waffle-slab deck panels as well as the prestressed girders,” says Nancy Daubenberger, a member of the transportation awards jury. “It showed an innovative use of UHPC to achieve durability. It was an extensive use of precast concrete.”

Location: Wapello County, Iowa, over Little Cedar Creek
Owner/engineer: Wapello County, Ottumwa, Iowa, www.wapellocounty.org
Design engineer: Iowa Department of Transportation, Ames, Iowa, www.iowadot.gov
Contractor: Bloomfield Bridge and Culvert Inc., Bloomfield, Iowa
Precaster: Coreslab Structures (Omaha) Inc., LaPlatte, Neb., www.coreslab.com
Bridge length: 63 ft (19 m)
Project cost: $460,000