Design of the New NY (Tappan Zee) Bridge Cable-Stayed Main Span

The existing Tappan Zee Bridge crosses the Hudson River approximately 25 miles (40 km) upstream of New York City, connecting the communities of South Nyack and Tarrytown, and was constructed in 1955. The bridge is functionally obsolete, carrying far more traffic than it was designed for, the timber pile foundations are deteriorating and maintenance and rehabilitation costs were estimated at $3 to $4 billion over the next 20 years, with $750 million having already been spent over the past 10 years. The New NY (Tappan Zee) Bridge Project includes the demolition of the existing bridge and replacement with separated east and west bound structures. The New NY Bridge is an important investment and critical asset for the New York State Thruway Authority (NYSTA) and all of the bridge’s daily users. The bridge is designed for a 100-year service life before major maintenance for non-replaceable components using a limit states design approach that is new to North America. Components that can be replaced without significant disruptions to bridge use are designed for lower service lives. The new main span comprises parallel east and west bound cable-stayed bridges with 1,200’ (366 m) main spans and 515’ (157 m) side spans. The main span bridges comprise composite steel and concrete decks, parallel strand stay cables, iconic V-shaped reinforced concrete towers, reinforced concrete anchor piers and pile caps, and reinforced concrete-filled steel pipe pile foundations. The foundations and pile caps are designed to support the future installation of a cable-stayed commuter rail bridge between the adjacent east and west bound road bridges. The road bridge towers are designed to be expanded and strengthened in the future to support the rail bridge superstructure. Similar to the importance placed on service life design, the provision of redundancy in the New NY Bridge was a strong guiding principle. The bridge includes several features that address operational and structural redundancy. Operational redundancy refers to the flexibility available to the bridge operator to adjust how traffic is conveyed across the bridge. Structural redundancy refers to the ability of the bridge to sustain localized damage/failure without it leading to progressive collapse. This paper describes the design of the main span bridges and the features of the design that will allow the bridge to achieve the stringent service life requirements and remain safe and serviceable for all required loading and operational scenarios.