550 Washington Redevelopment

New York, US

550 Washington was constructed in the 1930s as St. John’s Terminal, the depot for the tracks that are today’s High Line. The building’s redevelopment will create a new high-performance, health and wellness commercial office building, serving as the new NYC headquarters for a well-known tech company, and described as a “workplace of the future.”

550 Washington Redevelopment

New York, US

550 Washington was constructed in the 1930s as St. John’s Terminal, the depot for the tracks that are today’s High Line. The building’s redevelopment will create a new high-performance, health and wellness commercial office building, serving as the new NYC headquarters for a well-known tech company, and described as a “workplace of the future.”

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Challenge
Though we started with a conventional concrete shear wall system for the two service and elevator cores, our client, Oxford Properties Group, challenged us to develop a system that reduced the onsite construction duration of the structure.
Solution
Precast core construction provides an economical alternative to conventional cast-in-place concrete or structural steel, including composite steel/concrete solutions. The need for large construction tolerances was reduced, the construction schedule was shortened, and worker safety was improved. When used with form liners, the core can be exposed in the final building. In New York City, segments are erected by union ironworkers, who also erect the structural steel for the column and floor framing. This arrangement permits crane operators to switch from erection of the precast to erection of the steel seamlessly, reducing the overall structural construction duration. The offsite fabrication of segments allows stockpiling of the core elements such that their fabrication may begin well ahead of their need on site. The design and shop drawing processes are integrated using compatible design, drafting, and detailing software. All embedded items, reinforcing steel, post-tensioning ducts, and grout tubes are fully modelled for clash detection. The segments are cast on their side with embedded plates and anchors, sleeves, and block-outs for mechanical, electrical, and plumbing, as well embedded elevator rail supports. An enclosed casting yard permits all-weather casting with full access to the casting bed for the installation of reinforcing steel bars and post tensioning ducts. The segments are end-match-cast with the adjacent segments to reduce interfacing tolerance issues. The segments are lifted onto trucks for shipment to the site in this side position. At the site, a hydraulic “tilt table” rotates the pieces to enable their erection. Custom-built spreader beams are used to keep the segments balanced on the crane hook during erection.  The building has 298 precast segments in the two service cores that provide lateral stiffness and gravity support (along with elevators, stairs, and service risers). In the cellar, a conventional cast-in-place concrete “starter core” is supported on new and existing caissons; a new pressure slab also acts as the elevator pit slabs. Site work consists of erection, post-tensioning, and grouting. Segments are placed with a thin layer of epoxy at the horizontal joint. Post-tensioning operations include both vertical bars, present in every segment, as well as horizontal monostrand tendons which are present in some segments. Minor shimming may be required at the horizontal joints to maintain proper alignment, but match casting limits this requirement. The vertical post-tensioning ducts are fully grouted for integrity and corrosion protection, generally in two-level lifts.
Challenge
The construction of 550 Washington includes demolition, building relocation, major renovation, and new construction over a site with a three-block footprint and a bridge over an active roadway. Coordinating all the temporary works to enable construction and protect the public is critical to the safe and successful logistics of the project.
Solution
Turner Construction hired Entuitive to act as a peer reviewer for all temporary works required by the contractor. Entuitive reviewed all the temporary workshop drawings and calculations for errors, omissions, or value engineering possibilities. Entuitive also conducted site reviews to ensure that all temporary works were constructed following the design documents.
Challenge
The existing building supported a 900-ton Con Edison transformer vault on the roof, which had to be maintained in service through construction and into the next life of the building.
Solution
Typically, this problem would be solved by building a new vault, switching over the power, and decommissioning and dismantling the previous vault. Entuitive, Oxford, and Turner Construction devised a construction engineering strategy whereby the existing vault could be supported, de-energized, lowered down by two floors using jacks, horizontally relocated, and re-energized all within a few days. This effort required a lot of “heavy lifting”, but in the end saved months of schedule by minimizing reliance on Con Edison, and produced a building that works much better architecturally.

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