Assessment of Washington Avenue Bridge across the Mississippi River in Minneapolis, Minnesota, for Central Corridor Light Rail Transit

Retrofit of the iconic Washington Avenue Bridge is proposed for the incorporation of light rail over the Mississippi River, a critical link in the 11-mi Central Corridor Light Rail Transit (CCLRT) Project connecting St. Paul and Minneapolis, Minnesota. The structure is a unique double-decker bridge carrying an upper-level pedestrian deck with an enclosed walkway and a lower-level vehicular deck with two roadway lanes in each direction. The CCLRT Project proposes to replace one roadway lane in each direction to accommodate the light rail transit. Considered nonredundant and fracture-critical, the existing superstructure consists of dual girder-floorbeam-stringer-type framing with two noncomposite and independent reinforced concrete decks. The retrofit proposes the installation of four new longitudinal trusses constructed within the existing superstructure cross section and a new full-width composite deck. Designed to match the stiffness of the existing girders, the new trusses effectively convert the existing dual two-girder system into an eight “girder” composite superstructure. Built in 1965, the bridge incorporated innovations new to the bridge industry at the time of original construction, namely, the use of high-strength quenched and tempered steel. Advanced analysis of the structure was performed to meet the following project goals: (a) provide a functional structure for its proposed usage including light rail, (b) provide a redundant superstructure, (c) provide a structural system reliable against fatigue and fracture, and (d) provide a structure that meets load and resistance factor design criteria for a 75-year design life.