An Iconic Bridge Rebuild
After 68 years of serving residents from and surrounding the District of Columbia, the Frederick Douglass Memorial Bridge (FDMB) was declared “structurally deficient and functionally obsolete,” and in need of a rebuild. This would become the largest public infrastructure project in the history of the District.
Some of the design challenges the team faced included working with the arch base connection. Unlike typical steel to concrete connections, which utilize a base plate that is external to the section, all parts of the anchorage for FDMB are internal to the arch section. This layout created several design issues which needed to be considered and overcome including stiffener/anchor rod layout, edge spalling effects, baseplate details and fabrication, and coordination with v-pier post tensioning detailing.
The V-pier substructure allows the arch form to transfer smoothly to the foundations. While the arch induces compression into the V-pier legs, the tangent shape of the legs means that large moments do occur that created several design challenges. The construction of these massive V-piers necessitated large falsework to be built on temporary pile supports. The falsework supported the custom formwork that created the tapering hexagonal shape.
“This project is extra special because it is the first bridge in our Nation’s Capital (a city of arch bridges) with arches that extend above the deck—highly visible by land, water, and air,” Dennis Howland II, P.E., program manager for the District Department of Transportation, told Roads & Bridges. “The FDMB is more than just a beautiful bridge, it is the product of a grand vision, more than a decade of planning and preparation, and years of hard work and dedication. It is an example of what can be done when politicians, professionals, and laborers unite.”
According to engineering firm Systra IBT, which served as the independent checking engineer on the project, “The steel arches are supported on post-tensioned concrete substructures and steel pipe pile foundations. Interior piers have a V shape. The composite deck comprises precast panels on built-up I-shaped edge girders and floor beams. The deck is suspended from the steel arches with vertical hangers.”
Precast Concrete Deck Panels Sustainable Solution
Jersey Precast manufactured custom full-depth precast deck panels for the iconic Frederick Douglass Memorial Bridge. A durable concrete mix was required, replacing part of the cement with fly ash/slag/silica fume to achieve the requirement of 75-year durability. Slag/fly ash/silica fume are recycled products used to replace cement content in the concrete mix helps reduce the carbon footprint. These particles plug between the particles of cement, making the concrete denser and more durable. Year-round indoor fabrication in temperature-controlled environment helped the project meet a demanding schedule.
A total of 480 full-deck deck panels with rebar protruding out on all four sides were staggered for up to four adjacent panels to align precisely in the field. Adding to the complexity, two types of rebar are fabricated into the panels – two sides have epoxy rebar, the other two sides have galvanized rebar.
Jersey Precast’s inhouse trucking made delivering the panels from Hamilton, NJ, to D.C. effortless. |