Crossing the River

This bridge replaced a deteriorating, undersized Potomac River crossing with a design selected from seven competing entries that reflects the arch tradition of other river crossings without using a true arch, because true arches create large horizontal forces at foundations in the Potomac's particularly poor soils. Instead, an innovative system of V-shaped piers transfers the load vertically through soft soil to firmer soils 200 feet below. When tall ships approach, staff in the operator's house use motors and machinery to open the drawbridge's movable bascule span, a counterbalanced device that pivots like a seesaw. The bridge is so finely balanced that only small motors are needed to move its 34 million pounds, possibly making it the largest movable span in the world. Its construction used high-performance materials, prefabricated components, and innovative techniques, including steel pipe piles up to six feet in diameter, a cofferdam to create a dry work area for concrete foundations, concrete pile caps and pier pedestals formed atop the piles, V-pier segments brought by barge and lifted by cranes, alternating placement to keep the pier balanced, slender concrete tie beams with tensioned steel cables to connect the V-pier tips, curved steel girders to complete the arch appearance, and a concrete deck slab for the roadway surface.

Maryland · United States