Transforming Historic St. John’s Terminal into Google’s NYC HQ

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St. John’s Terminal, with three floors of 205,000 square feet each, had the largest floor space in New York City when completed in 1934 (Fig. 1). This freight-focused building, adjacent to the Hudson River, connected to the High Line elevated rail tracks on Manhattan’s West Side at 550 Washington Street and provided storage capacity for 227 train cars (Fig. 2). All floors were designed to withstand a live load of 300 pounds per square foot (psf) in addition to train loads, a specification that would enable innovation nearly nine decades later when the building was transformed into Google New York Headquarters at St. John’s Terminal.

A variety of structural design strategies were instrumental to the successful redevelopment, which added nine stories above the original structure. The most notable involved leveraging structural bridge design principles, typically used for horizontal spans, to enable a vertical expansion, while preserving the character of St. John’s Terminal.

After a steady decline in rail freight following World War II, the High Line ceased service to St. John’s Terminal and was eventually transformed into a public park. Constructed with substantial structural strength and generous open spaces, the Terminal was repurposed in the 1960s for office and warehouse use, accommodating a range of commercial tenants.

In 2016, Cookfox Architects completed an Urban Land Use Review Procedure (ULURP) study that established a framework for redevelopment, including the potential for vertical expansion while preserving the building’s historic character (Fig. 3).

Engaging in discussions with the ownership team, Entuitive was retained in 2017 to better understand the building and inform a future design strategy. What began as preliminary investigations and feasibility studies ultimately evolved into a full structural design for a vertical expansion.
A base design for a commercial office redevelopment was developed, and construction commenced prior to Google’s acquisition of the property in 2021 (Fig. 4). With construction already underway, the design was further refined to meet Google’s programmatic needs while maintaining an aggressive schedule. Through close collaboration between the design and construction teams, the building was completed and occupied in February 2024.

Understanding the existing structure was critical to unlocking its potential for vertical expansion. Original structural drawings were incomplete, requiring a combination of archival research, field investigation, and testing to establish a reliable structural baseline.

The team conducted extensive on-site investigations, including:

Where gaps in information remained, supplemental material testing was performed:

These efforts confirmed that the existing structure, composed of steel framing encased in concrete supporting reinforced concrete slabs, retained significant capacity consistent with its original heavy industrial design.

The original terminal structure consisted of a four-level podium framed with steel columns and steel beams encased in concrete, supporting reinforced concrete slabs approximately 5 to 7 inches thick with beam spacings of 6 to 7 feet.

The structure was supported on caisson foundations socketed into bedrock, typical of early 20th-century heavy construction. Designed for rail loading, the system’s 300 psf capacity far exceeded modern office requirements, providing a strong foundation, both literally and structurally, for redevelopment.

Designs for commercial office spaces typically target live loads of approximately 50 psf. In contrast, the original design of St. John’s Terminal could withstand loads of up to 300 psf. Leveraging this existing capacity eased the challenge of significantly increasing the building height.

The existing structure was able to support the addition of eight new office floors above the original podium. The podium roof was converted into an occupied floor, and a new roof level was introduced above the overbuild, resulting in a nine-story vertical expansion. Structural modifications were localized rather than applied broadly across the building, avoiding the need for extensive strengthening across the entire building. Reinforcement of the existing framing was primarily required in areas with increased demand, including:

Localized strengthening measures included the addition of steel reinforcement plates and welded WT sections to increase the flexural capacity of existing beams. In areas where demands exceeded the capacity of the original framing, particularly at terrace locations, existing members were removed and replaced with new steel girders designed to transfer loads to existing supports with sufficient reserve capacity.

The strength of the original system also enabled selective column removal within the footprint of the overbuild, allowing for open and flexible floor plates aligned with modern office needs (Fig. 7). These removals were achieved through the introduction of transfer elements, including built-up plate girders at the fifth floor, which redistribute loads from the new structure above to align with the existing column grid below.

Gravity loads from the overbuild are supported by the continuous precast core system and a limited number of column lines, enabling clear spans of approximately 34 to 50 feet. At the perimeter, these column loads are transferred through a cantilevered transfer girder system at the fifth floor. These built-up plate girders redistribute loads from the new structure above to align with the existing column locations within the podium below, maintaining compatibility between the new and existing structural systems.

Necessity breeds innovation. A structural retrofit of a nearly century-old building under an accelerated schedule required creative approaches to structural design.

Recognizing that the increased building height would introduce significant lateral load demands, several structural systems were evaluated during preliminary studies, including cast-in-place concrete cores, steel braced frames, and SpeedCore systems (which are prefabricated steel panels filled with concrete). The selection process ultimately centered on how effectively each system addressed the following criteria:

To maximize these benefits, the design team proposed an innovative solution: the use of segmental precast, post-tensioned concrete walls in a vertical building application, a system more commonly associated with bridge construction.

The concept draws from Entuitive’s design of the Manhattan West Platform, where post-tensioned precast box girders span long distances over active rail tracks, minimizing disruption below. At St. John’s Terminal, this concept was reinterpreted by rotating the system 90 degrees.
Instead of spanning horizontally, precast, post-tensioned concrete core walls were introduced within the existing building by cutting openings through the podium floors and extending the cores continuously up from new foundations below, through the existing structure, and into the overbuild above. These elements act as vertical load-bearing and lateral-resisting components within the building (Fig. 8).

These cores serve dual structural roles:

Core sizes were influenced not only by structural demands, but also by elevator requirements needed to service the expanded office floors. Given the size of the floor plates and the additional program, two centrally located cores were introduced to maintain symmetry, minimize disruption to the existing structure, and support large open spans.

The increased height introduced new lateral demands. After selectively demolishing and temporarily supporting the existing framing at the core locations, new mini-caisson foundations were installed beneath the cores (Fig. 11). Cast-in-place starter walls were then constructed to align the precast system with these newly installed foundations.

The existing steel framing was then reconnected to the cores using extended shear tabs bolted to the existing beams and welded to cast-in plates within the precast core walls. Coordination of these embedded plates with the post-tensioning tendons and reinforcement was critical to avoid congestion and ensure constructability.

This approach allowed the new structural system to integrate with the existing structure while establishing a continuous and code-compliant lateral load path through the building as well as leveraging the inherent strength of the existing building. It also enabled parallel construction activities, with steel erection for the new floors progressing simultaneously with restoration work within the existing podium.

Additional efficiencies were realized in construction logistics. The tower cranes used for steel erection also were utilized to lift the precast core segments into place, minimizing the need for additional equipment and reducing on-site storage requirements (Fig. 12). The use of a single trade to install both steel framing and precast core elements further streamlined coordination and communication.

Core wall segments were transported horizontally and erected vertically using custom tilt tables, installed on top of the original podium roof. The crane lifted each segment onto the tilt table, which rotated the wall segment into its vertical position for final placement (Fig. 13).

Coordination was equally critical during design and fabrication. To accommodate transportation constraints, including load limits for crossing the George Washington Bridge (which spans the Hudson River between Manhattan and New Jersey) and dimensional restrictions for truck transport, core segments were designed within allowable shipping limits. As a result, segment heights did not always align with floor-to-floor elevations, requiring careful detailing where floor beams and girders framed into the cores. Temporary steel frames were used during transportation and lifting to prevent temporary load cases from governing reinforcement design and to reduce congestion of embedded components.

Construction analysis was performed to evaluate stresses during transportation and lifting, as well as long-term effects such as creep, elastic shortening, and alignment tolerances. Sequenced erection analysis also was used to monitor deviations from vertical alignment and inform shimming and steel framing installation to ensure proper fit-up between the core system and surrounding structure.

The project team’s prior experience with post-tensioned precast systems on Manhattan West proved instrumental in successfully adapting this approach to a vertical application, enabling the realization of a first-of-its-kind structural solution.

Steel built-up plate girders were strategically introduced at Levels 4 and 5 to facilitate architectural features and structural load transfer.

On the fourth floor along the north side, plate girders support cantilevered areas enabling the creation of skylights and green terrace spaces while maintaining an open floor below (Fig. 14).
On the fifth floor, which functions as a transfer level, plate transfer girders support new column lines of the overbuild (Fig. 15). The perimeter columns from the floors above terminate at this level and bear on the ends of these plate girders. These transfer girders are supported by column lines that align with the existing structural grid below, allowing loads from the new structure to be redistributed and delivered to existing columns within the podium. In this way, the transfer system reconciles the mismatch between the new column layout and the constraints of the original building.

This strategy enables a column-free terrace level on the fourth floor while maintaining compatibility with the existing structural system below.

The existing structure was supported on caisson foundations socketed into bedrock. By maintaining comparable gravity loads, these foundations were largely sufficient for reuse without extensive modification.

However, the original structure lacked a clearly defined lateral force resisting system capable of supporting a taller building. To address this, the newly introduced precast, post-tensioned concrete cores, functioning as reinforced concrete shear walls, provide the primary lateral force-resisting system for the combined structure, extending continuously from the new foundations through the podium and into the overbuild above.

New mini-caisson foundations (small-diameter drilled caissons) were installed beneath the cores to support the new lateral demands.

These mini caisson foundations:

To satisfy updated FEMA map flood requirements and account for the building’s proximity to the Hudson River, a reinforced 1 foot, 6 inch-thick concrete pressure slab was constructed above the existing 1 foot, 6-inch foundation mat slab. This slab resists hydrostatic uplift and integrates the new foundation elements into the overall system.

When St. John’s Terminal was converted from rail use to office occupancy in the 1960s, a large electrical vault, approximately 35 feet by 100 feet and weighing 900 tons, was constructed to support building operations.

For the redevelopment, the vault location conflicted with the new architectural program on the 4th floor, particularly for the green, open spaces. A controlled jacking scheme was developed to lower the vault as a single unit by two floors and shift it horizontally into a new position. This operation required careful planning to maintain the structural integrity of the vault during movement while coordinating with ongoing construction activities. An external support framing system was designed with the jacks placed on top and set to reach an anticipated pressure calculated to be the approximate weight of the vaults. The sequence consisted of lifting the vault using hydraulic jacks, shifting the whole unit horizontally, and lowering the vault to its new location.

This operation resolved spatial constraints, enabled the creation of a new mechanical level, and allowed for early activation of building systems, supporting an accelerated construction schedule.

In a risk-averse industry, opportunities to implement first-of-their-kind structural solutions at this scale are rare. For St. John’s Terminal, the willingness to embrace innovation, supported by the project team and ownership, enabled a unique structural approach.

By leveraging the strength of the existing structure and reinterpreting bridge design principles for vertical application, the project successfully delivered a nine-story expansion while preserving the historic character of the building (Fig. 17).

Nearly a century after its original construction, St. John’s Terminal continues to evolve, demonstrating how thoughtful structural engineering can extend the life and relevance of existing infrastructure for generations to come.■

About the Author

Stephanie Berrios, PE, is a structural engineer committed to strengthening her home city through her work and mentoring the next generation of engineers through SEAoNY. Having grown professionally at Entuitive, she co-founded Adhart to continue blending technical expertise with her passion for New York City.