The Anna-Maria and Stephen Kellen Tower at the Hospital for Special Surgery (HSS) in New York City is a major expansion to the hospital’s Upper East Side campus. Set to enhance medical care in one of the most densely populated urban areas in the world, this 14-storey tower is an extraordinary example of structural engineering and logistical planning. Walters Group played an important role in the tower’s development, supplying and installing the structural steel and metal decking required for this complex project.
While building over the active Franklin D. Roosevelt East River (FDR) Drive is not new, as other buildings have done so in the past 20 years, our practical approach set this project apart. Walters Group, in collaboration with AECOM Tishman, managed weekend closures of the FDR, which were limited to five hours at a time, allowing us to minimize disruption to traffic beneath the site.
One of the key architectural features of the Kellen Tower is the large, sloping Architecturally Exposed Structural Steel (AESS) columns, spanning Levels 2 through 6. These Y-shaped columns, each weighing around 30 tons, are critical to the building’s design and required a high degree of attention during installation. The complex geometry of the AESS columns required heavy welding to ensure accurate alignment and structural integrity due to the sloping design.
Construction on the Kellen Tower officially began in January 2022 with the foundation work. By November 2022, Walters Group had delivered and installed the first steel columns in preparation for the modules.
Our modular build approach involved constructing two floors using three modules, each two floors high. This method was vital for reducing disruptions to the FDR below, as it minimized the need for road closures during the installation of the modules required for the first two levels. Completing these levels was essential for safely positioning a crane at Level 2, which was necessary for the steel erection above the active roadway.
In August 2023, three large steel modules were pre-assembled on a 400 ft by 100 ft cargo barge in New Jersey and then transported to the site via the Hudson River. Floating the modules down the river was a logistical necessity, as transporting such large structures through Manhattan’s streets would have been impossible. However, pre-assembling the modules on the barge was challenging due to the instability of working on water and the operation of a 200 ft crawler crane moving across the deck. To tackle these challenges, we employed the piano wire method. This technique involves placing piano wire across the top to create a stable plane. This setup helps maintain a constant alignment as the barge moves, ensuring precision during the pre-assembly process.
One of the key architectural features of the Kellen Tower is the large, sloping Architecturally Exposed Structural Steel (AESS) columns, spanning Levels 2 through 6. These Y-shaped columns, each weighing around 30 tons, are critical to the building’s design and required a high degree of attention during installation. The complex geometry of the AESS columns required heavy welding to ensure accurate alignment and structural integrity due to the sloping design.
Construction on the Kellen Tower officially began in January 2022 with the foundation work. By November 2022, Walters Group had delivered and installed the first steel columns in preparation for the modules.
Our modular build approach involved constructing two floors using three modules, each two floors high. This method was vital for reducing disruptions to the FDR below, as it minimized the need for road closures during the installation of the modules required for the first two levels. Completing these levels was essential for safely positioning a crane at Level 2, which was necessary for the steel erection above the active roadway.
In August 2023, three large steel modules were pre-assembled on a 400 ft by 100 ft cargo barge in New Jersey and then transported to the site via the Hudson River. Floating the modules down the river was a logistical necessity, as transporting such large structures through Manhattan’s streets would have been impossible. However, pre-assembling the modules on the barge was challenging due to the instability of working on water and the operation of a 200 ft crawler crane moving across the deck. To tackle these challenges, we employed the piano wire method. This technique involves placing piano wire across the top to create a stable plane. This setup helps maintain a constant alignment as the barge moves, ensuring precision during the pre-assembly process.
Upon arrival, a carefully coordinated weekend closure of the FDR Drive allowed a barge-mounted crane to lift the pre-assembled modules into place. This phase of construction marked a major milestone for the project, as the massive steel components were precisely positioned onto pre-installed columns. The successful coordination of barge movements, crane operations, traffic management, and sequence planning was critical to this phase of construction.
With the modules in place, we moved on to the steel erection phase, which began in November 2023 with the installation of a tower crane at Level 2. This completed level allowed Walters Group to proceed with erecting steel from Level 4 and above while ensuring the safety of both the construction crew and the commuters below.
By February 2024, we topped off the Kellen Tower, completing the steel erection along with the decking and bolting of the final tier. This milestone cleared the way for other trades to begin their work and add the finishing touches to this exciting project.
The next phase of the Kellen Tower project involves the installation of a pedestrian bridge, which will link the new tower to the existing HSS building across East 71st Street. This bridge, fabricated from AESS steel, will be installed during another carefully planned weekend closure of the surrounding streets. The installation of the bridge will enhance connectivity and accessibility in the area, facilitating safer pedestrian movement and promoting increased foot traffic for visitors and staff.
Despite the tight site constraints, logistical challenges, and the complexities of constructing a tower above a major highway, Walters Group took a practical approach to these constraints, ensuring the structural integrity and quality that will serve the community for years to come. Our innovative approach to material transportation, using barges to deliver pre-assembled modules, as well as the detailed planning needed to safely construct over the FDR Drive, set this project apart from other Walters Group projects.
As the final phases start to wrap up, the Kellen Tower is set to become a vital addition to the Hospital for Special Surgery’s medical facilities, expanding its capacity to provide specialized care.
Walters Group is proud to have contributed to this landmark project, and we extend a special thank you to our valued partners:
Learn more: www.waltersgroupinc.com/project/hospital-for-special-surgery-the-anna-maria-and-stephen-kellen-tower/
