The upgrade of the New York Avenue Bridge in Washington, D.C., was viewed as a significant improvement project for the District Department of Transportation. The bridge is one of the major transportation corridors into the city from Maryland and is used by more than 87,000 vehicles each day. The upgrade would add redundancy and longevity to the existing two-girder superstructure, but the design team faced many obstacles in meeting the owner's expectations.
"We were confronted with several challenges," says Inmar Badwan, senior bridge engineer with T. Y. Lin International, the engineer of record for the project. "There were site constraints and restrictions imposed by multiple owners of commuter and freight rail lines located beneath the bridge, constructability issues caused by active electrified catenary overhead wires, demolition of existing deck and grillage of floor beams and stringers, and maintenance of vehicular and train traffic."
They also had to meet an extremely tight design-build schedule.
The owners of the bridge originally considered many design options and materials to manage costs and expedite construction time, Badwan says. The design had to be rugged and quick to construct, all while accommodating site constraints and construction complications related to the existing bridge substructure. T. Y. Lin came up with an innovative design that addressed many of these issues using precast, posttensioned concrete deck panels that cantilever 12 ft 10 in. (4 m) over the exterior girders.
"The precast deck panels enhanced the construction acceleration given the impact by the railroads and eliminated long delays associated with formwork construction and concrete curing time," he says. It also facilitated deck replacement and caused less disruption to the train traffic underneath the bridge. "The benefits gained through construction schedule offset the potential cost increase in comparison with the traditional deck-girder system."
The improvements to the superstructure were achieved by replacing the bearings and by erecting a new girder line between existing twin girders to create a multibeam system with structural redundancy. Rehabilitation and repair of the existing substructure to sustain the multibeam superstructure systems was accomplished by constructing posttensioned pier caps that rest on the retrofitted pier columns. The deck replacement was achieved through the innovative erection of longitudinally and transversely posttensioned precast concrete deck panels.
"This required extensive coordination in conjunction with a complicated construction sequence involving multiple stages," Badwan says. "A closely coordinated effort between all members of the project team and stakeholders was instrumental in ensuring the construction flow was resumed despite the complexities involved."
The ungraded bridge opened in October 2013, and the owners are very pleased with the result.
The redesign extended the service life of this major structure, which is vital to the safety and continuing prosperity of the rapidly developing neighborhood. "The completion of this bridge has resparked the improvement of this section of the city by serving as a focal point and entrance into a developing neighborhood," he says. "Moreover, the project satisfies the client's goals to provide multimodal transportation and ensures an ability to accommodate anticipated local and regional vehicular transportation needs over the next 50 years."