Million-Pound Bridge

By: Roads & Bridges

Problem: Hartsfield-Jackson Atlanta International Airport, one of the world’s busiest airports, needed a new runway to accommodate more air traffic. The only available site was bisected by a busy multilane interstate highway. Solution: Build a bridge over the highway strong enough to withstand takeoffs and landings by the latest generation of jumbo jets.

The new runway bridge at Hartsfield-Jackson is one of the most complex structures of its kind in the world and the first runway bridge of this span length in the world. It will be subjected to extremely high loads—the Airbus A380-900 can weigh as much as 1.3 million lb and generate braking forces of approximately 1 million lb.

Heath & Lineback Engineers Inc. considered a number of alternatives before concluding that prestressed concrete beams offered the best solution. Concrete beams were chosen rather than steel beams because of a four-hour fire-rating requirement. To achieve this rating, steel beams would have required false ceiling enclosures. The prestressed beams require no additional fire protection.

The final design employs more than 760 prestressed beams, spanning a total width of approximately 1,100 ft. The beams, fabricated by Standard Concrete Products in Atlanta, were constructed using Lafarge Type III high-early-strength cement with a concrete design strength of 10,000 psi. Lafarge Type III is widely used by precast- and prestressed-concrete producers. Its high early strength increases productivity and accelerates production by allowing forms to be reused more quickly than with conventional cement.