Foundation Retrofit of the Third Avenue Bridge in New York

The Third Avenue Bridge over the Harlem River links Manhattan to the Bronx. The rim bearing swing span bridge was constructed in 1898 and is in need of complete reconstruction to eliminate structural deficiencies and meet current traffic requirements as well as satisfy the seismic safety guidelines set forth by the NYCDOT. The new center bearing swing bridge, when reconstructed, will have a swing span of about 108 meters. Most of the piers and their foundations will be replaced. The critical center pier will be retrofitted using ten 6-ft diameter drilled shafts socketed into bedrock. Several major challenges regarding the design and construction of the replacement bridge were encountered. The existing center pier is founded on a hollow cylindrical caisson, which is partially embedded in the soil profile and does not rest on bedrock. This pier was found to be inadequate to carry the design seismic loads. The swing span mechanical system has minimal tolerance for permanent settlement and tilt of the foundation. This paper presents the details of the new bridge and its site conditions, followed by the seismic geotechnical engineering analyses performed to develop the foundation retrofit design for the center pier.