The final layer of concrete was applied by a skilled technician using a hand trowel, an aesthetic treatment that left the final appearance indistin - guishable from traditional methods. This application by the construction team was a genuinely innovative feature of Hudson Commons. Lateral-Load Performance To provide stability to both the existing structure and the new tower, a full upgrade of the Hudson Commons lateral force resisting system was required. WSP collaborated closely with KPF on an architectural design that included a new circulation and mechanical core eccentri - cally placed along the north side of the property that would maximize the building’s rentable area. One notable feature of the building’s core is its prominence in the ar - chitectural expression of Hudson Commons as it rises above the exist - ing building. The new spine of the building uses exposed architectural concrete as a tribute to the historic architecture of the neighborhood. The new reinforced concrete core runs from foundation to the top of the building and is comprised of 10,000-psi concrete shear walls ranging from 12 to 24 inches in thickness. WSP envisioned a box-like configuration wrapping the entire mechanical and circulation program that would counteract the torsional effects associated with an eccentric core. In this closed-box layout, the core is placed along existing col - umn lines, and the existing columns create breaks in the shear walls analyzed by considering individual piers at the base building. One intrinsic benefit of this approach was the absence of link beams in the base building, which allowed maximum flexibility with regards to routing services out of the core. Above the existing roof, the walls were connected through reinforced concrete link beams to provide adequate lateral stiffness. Per industry standards, three-dimensional finite ele - ment analysis software was used to model both the existing and new structure, allowing for an optimized and efficient structural design. WSP’s retrofitting approach for the gravity system included the rein - forcement of existing concrete slabs with steel members around the perimeter of the area to be demolished for the new core. Steel members were installed above and below the slab following the bending mo - ment demand associated with gravity loads. Top steel members were removed after casting the core walls, while steel members below the slab were fitted with studs to trigger composite action and remained as permanent bracket connections between the new core walls and the existing slab. This innovative solution resulted in significant savings in terms of both Another feature included in the project is the potential to turn outdoor open areas on the ninth and 25th floors into green spaces for the tenants. The existing structure has been reinforced and designed to allow for landscaping that could include grass, trees and other green uses. It will be the decision of the tenants on those floors, but the structure cost and schedule. Green Showcase
has been designed to allow for the creation of something quite el - egant on those spaces. WSP worked closely with PMG (Construction Management) to deter - mine the most cost-effective approach to accommodate green spaces on the existing roof. The final structural solution was a secondary support system of steel beams installed under the existing slab to support the significant load of a fully landscaped area on the original building’s roof. The structural solution was detailed in such a way as to not penetrate the existing roof, which would have added significant cost to the project. New steel members were designed as non-composite sections to elimi - nate the need to perforate the roof for stud installation, while clips were installed along the beams to prevent lateral-torsional buckling. Nearly every level of the new building features terraces or balconies providing remarkable views of the city and river. Vertical integration between floors is promoted by the exposed stairway, which also al - lows for an exceptional naturally-illuminated interior. Floor-to-ceiling windows further welcomes daylight coverage on each floor. The green roof, daylighting architecture and plans for efficient energy and water systems are features that lead to Leadership in Energy and Environmental Design (LEED) Platinum certification from the U.S. Green Building Council, and Wired Platinum certification. Vertical Vision Hudson Commons was completed in March of 2020 and tenants are now occupying a building that challenged conventional engineering and construction practice. The building has become one of the most innovative adaptive-reuse projects in New York City. This reimagined commercial building demonstrates the potential for large-scale vertical expansion when innovative solutions are applied. With developers and cities striving towards sustainable solutions, the relevance of projects like Hudson Commons is clearly recognized. One rarely comes across a project like Hudson Commons, mixing steel and concrete in a way that perfectly blends the two, taking advantage of the benefits each material offers economically and in an engineer - ing sense. This project provides developers with a methodology and alternative cost-effective, sustainable solutions that could change the way existing structures are upgraded for future use.
JOSEPH PROVENZA is a senior associate at WSP USA Buildings Inc. and served as the firm’s project manager for Hudson Commons. JEFFREY SMILOW served as the principal-in-charge. YUJIA ZHAI was the project director. MOTAZ ELFAHAL served as the structural analysis manager.
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csengineermag.com
DECEMBER 2021
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