New York State Thruway Authority (NYSTA)
Tappan Zee Constructors
Location: Tarrytown, NY
Industries Served: Civil-Heavy Construction
Equipment: System Scaffold Stair Towers, System Scaffolding, Tube & Clamp Scaffolding
Services Provided: Drafting & Design, Engineering, Manufacturing & Custom Fabrication, PE Stamp
Scaffold Engineering: Universal Scaffold, DH Charles Engineering
New York State Thruway Authority, New NY Bridge Website:
Fluor Enterprises Project Time-lapse:
Tappan Zee Bridge – Four Years in Two Minutes
Scaffold & Access Magazine, May-Jun. 2017:
Providing Engineered Access To Cross The Hudson River
The primary focal points of the new bridge are the four pairs of outwardly leaning pylon towers located at the two main-span piers. With an overall height of 409-feet, and a consistent outward splay of 5-degrees, these iconic concrete towers presented a number of unique challenges for our team.
In order to achieve the full height requirement of 409-feet, Universal designed and engineered a 290-foot stair tower at the base of the pier, exiting onto a crossover truss connecting the pylon tower with the one next two it, then two additional 120-foot stair towers which were supported on a platform anchored to the pylon's concrete structure at the crossover elevation.
All scaffolding for the main-span piers was designed to follow climbing concrete jump forms. As the forms climbed up the tower facilitating rebar operations and placing concrete, additional scaffold access was barged to the piers and craned into place.
Each bridge consists of 43 concrete piers, 41 approach-span piers and two towering main-span piers. Thirteen piers are less than 45 feet in height and did not require scaffold access. The remaining 30 piers vary in height from 45 to 409-feet, each requiring construction grade stair tower access.
Our engineering team worked with TZC to identify the required specifications of each tower according to the formwork location on each pier cap. Universal provide detailed CAD drawings noting location on the pier base, tie-in locations on each column, and the exit location of each tower.
Limited in area to stage and assemble the scaffold components onsite, each tower was designed and packaged to enable assembly at a secondary location upriver before being loaded onto a barge for transport and delivery to the project site for installation via crane.
The individual towers were lifted into position using a series of custom designed lifting rigs. These lifting rigs are comprised of a steel-beam, single-lift and bridle unit attached to each coupling pin for safe, consistent lifting and results.
Custom engineered scaffold tie-in configurations and components played a critical role in the safety of the team members using the stair towers throughout the duration of the project, with the 290-foot towers presenting the largest challenges.
Due to the outwardly leaning nature of the main-span pylons, combined with a 115 mph wind requirement, the 290-foot stair tower had to be positioned at a diagonal more than 10-feet from the pylon corner with more than 20-foot-long tie configurations at each point.