Client: Swalling Construction Co.
Owner: Fort Richardson Non-Appropriated Funds (NAF) Office
Cost of Work: $500,000

This project involved a pair of post-tensioned cable bridges, for pedestrian and golf cart traffic. A 140-foot bridge crosses upper Ship Creek and a 250-foot bridge crosses Ship Creek and a wetland area further downstream. The ability to span the wetland area without construction impact was an important aspect of the design.

“Strand bridges” are a PND development. (In November 2002, the U.S. Patent Office notified PND President Dennis Nottingham that he had been awarded a patent for the “strand bridge.”) They are designed to support maintenance vehicles weighing up to 10,000 pounds, with vertical deflection limited to 1/300. Other load conditions include typical uniform pedestrian or snow loads without deflection limitations. Overload capacities for emergency vehicles are inherent in the design with increased deflection. Higher loads for special circum-stances are possible.

The primary structural elements are epoxy-coated or galvanized post-tensioning cables, similar to that used as barrier strand in parking garages. Superstructure elements comprise draped post-tensioned strands to control the bridge shape; horizontal post-tensioned strands to provide local stiffness to the bridge; and a timber deck. These elements are attached to light intermediate steel frames. The horizontal strands double as barrier strand. The substructure is composed of steel towers that bear on cast-in-place footings. Back-stays attach to grouted soil anchors that are embedded into gravelly outwash deposits in the area.