Rachel Carson Bridge (Ninth Street Bridge)

Completed in 1926 by American Bridge, the Rachel Carson Bridge (Ninth Street Bridge) project consisted of one of the ‘Three Sisters’ bridges, which also include the 6th and 7th Street Bridges. These nearly identical, self-anchored, eye-bar suspension bridges are designed so that the horizontal pull of the top chords is resisted by steel girders along each side of the roadway. The suspension system consists of 14″ eye-bars extending from end to end, with two pins at the top of each tower, carrying the roadway by 4″ eye-bar suspenders at the panel points. The stiffening system consists of triple web plate girders placed parallel to the road grade, subjected to bending and direct compression. All three bridges were fabricated and erected by American Bridge. In an innovative approach, AB temporarily turned the eye-bar catenary/deck girder system into a truss by adding a diagonal, enabling erection by balance cantilever and avoiding falsework in the river.