Super Structures:
Innovative Bridges Spur
Smart Construction Solutions

Bridge construction looms on the horizon in spite of funding challenges and huge projects, like the Tacoma Narrows and the San Francisco Bay bridges, continue to receive widespread attention. However, smaller projects are underway across America, helping to keep bridge construction spending close to last year’s figures.

As of 2000, the Federal Highway Administration reports that 27.5% of the nation’s bridges were structurally deficient or functionally obsolete. While this is an improvement of 1.5% from 1998 studies, it still means that 162,000 bridges are in need of replacement or repair. The ASCE Infrastructure Progress Report estimates that it will cost $9.4 billion a year for 20 years to eliminate all bridge deficiencies. The report also states that “Present funding trends of state DOTs call into question future progress on addressing bridge deficiencies.”

Still, all is not bleak. Many innovative projects are currently underway and typify the quality of work that continues to abound as the industry awaits the reauthorization of federal funds. In addition, international work continues to help designers and suppliers seek new opportunities for creative bridge construction. Here are a few:

American Bridge Company is constructing a 615-ft crossing of the busy Industrial Canal in New Orleans, LA, featuring a 342-ft vertical lift truss span, two roadway lanes, and a single-track railway.

The project includes 30-ft-deep cofferdams, two 220-ft lift span towers, and four 80-ton counterweight rope sheaves (at the top of the towers). Erection of the combined rail/roadway lift span truss is underway on a barge adjacent to the site. For float-in of the 2,200-ton structure, 12 compartments in the barges will be sequentially flooded and sealed to prevent shifting, allowing the big structure to be rested on its abutments. Sailing is scheduled for spring, 2004.

By the fall of 2004, the Millau Viaduct will soar above the Tarn Valley, relieving congestion on the A75 motorway that links Paris and Barcelona. The structure will be supported by two abutments and seven piers. With the center pier exceeding 1,000 ft in height, the viaduct will be about 14% taller than the Eiffel Tower. The 32,000-ton deck will be pushed out from both ends using over 250 Enerpac hydraulic cylinders.

Caltrans’ Rock Creek Bridge is a critical transportation link between Mendocino County and Northern California. Caltrans initially contracted with DMJM+Harris to develop a seismic retrofit solution for the aging structure. However, DMJM+Harris confirmed that a new structure was essential; yet its complexity would prove a formidable challenge for the entire team. The bridge crosses a steep, V-shaped chasm that is completely enclosed by forest and serves as the only north-south highway (U.S. 101) for more than 80 miles.

The steep canyon walls and fractured bedrock made conventional foundations inappropriate. The team instead chose a slantleg structure. Pier shafts were tunneled into the canyon walls at a perpendicular angle, providing both an elegant and stabilizing solution. The steep slopes and distances beneath the bridge approaches prevented the use of large equipment, so mining the shafts by hand proved the most efficient and effective alternative.

The 294-ft-long bridge has a reinforced concrete box girder superstructure. Closing the bridge would have resulted in a minimum detour of 30 miles, so phased construction was used for the superstructure and substructure to keep traffic moving throughout construction.