Aurora Arch Pedestrian Bridge. Aurora, Nebraska

2004 ACI NE Chapter Award of Excellence Project

The 30-m (100-ft) single-span, arch pedestrian bridge in Aurora, Nebraska, is over the Lincoln Creek located approximately 105 km (65 miles) west of Lincoln.  The circular arch has a radius of 22 m (72.5 ft) and a rise of 6.1 m (20 ft).  The bridge measures 5.5 m (18 ft) in height from the walkway to the crown of the arch.  The walking and bicycling deck surface is 3 m (10 ft) wide with 1.4 m (54 in.) timber railings. 

A unique aspect of the bridge design is the use of confined concrete to enhance the strength and ductility of the top and bottom chords of the bridge.  Concrete-filled steel tubes are used for compression chords (i.e., the arches), prestressed concrete-filled steel tubes for the bottom chords.

Arch Bridge Design Using Concrete Confinement
The strength of a concrete member can be significantly increased with transverse or lateral confinement.  A novel application of concrete confinement to tension members has been utilized in the bridge construction.  A high-strength prestressing tendon with a polyethylene (PE) sheath is inserted inside a steel pipe, and positioned at the center by spacers along the length of a bottom chord.  Expansive concrete using Type K cement is pumped into the steel pipe.  After the concrete is hardened, the tendon is post-tensioned to a specified force to exert pre-compression on the concrete inside the pipe.  When the concrete inside is subjected to compressive loading, the steel pipe provides lateral confinement pressure on the concrete very effectively in the form of tensile “hoop stress.”  As a result, the bottom chords can carry much higher tensile forces without causing tensile stresses in the concrete.  The steel pipe is used solely to provide lateral confinement for the concrete, and not intended to carry external loading. 

Project Significance
This project addresses the feasibility of constructing temporary, short-span (less than 100 feet) bridges on existing piers and abutments expediently.  There is an urgent need to construct temporary bridges in natural disaster areas where main bridges are damaged or destroyed.  Erection of deployable and reusable bridges on existing substructure is a cost-effective alternative to retrofitting damaged bridges.  When bridges are damaged by floods and earthquakes, it can take months before the transportation infrastructure is restored.  To replace a damaged bridge, a modular system that is easy to fabricate and build is needed which can be installed within a reasonable timeframe.

The research and development of the arch bridge design were sponsored by the Mid-America Transportation Center (MATC), the Center for Infrastructure Research (CIR) at the University of Nebraska-Lincoln, and the City of Aurora, including the Nature Conservancy, the Prairie Plains Resource Institute, and the Nebraska Vocational Agriculture Foundation.  Kansas Structural Composites, Inc. (KSCI) and the Upper Big Blue Natural Resources District also provided matching funds for the project.