The Stavros Niarchos Foundation Library (SNFL), a branch of the New York Public Library system, has undergone a renovation, preservation, and expansion of its historic NYC building. Originally built in 1914 and first utilized as a department store, the structure’s reuse as a library always felt ad hoc. As such, a multi-million-dollar revamp served to better unify the iconic Main Branch to the rest of the New York Public Library (NYPL) system.
The project included a full gut of SNFL’s 6 stories requiring significant structural modifications to the existing framing throughout the building. Furthermore, a seventh-floor structure flanked by an L-shaped wraparound outdoor terrace was added atop its formerly unused rooftop. The addition’s new geometrical aluminum “wizard hat” roof slopes up to cover the library’s newly configured mechanical equipment. The sculptural, perforated metal rooftop terrace was the Grand Award winner in the 2021 Metal Construction News Project Excellence Awards and winner in the New Metal Roofs category.
McLaren’s construction engineering team provided structural steel framing services that included connection design, temporary bracing, and miscellaneous connections. Although the bulk of this occurred at the new “Wizard Hat” structure, the team also worked on delegated design items for both new and existing steel going up throughout the existing building. Providing stability bracing systems throughout, McLaren helped to ensure the historic landmark remained safe under construction. During the renovation, temporary shoring of the existing steel by way of temporary shoring systems designed to support the dead load and construction live load on each floor allowed for the installation of new additional steel framing. Delegated connection design was performed for shear, moment, bracing, and axial connections.
Constructing an addition on the roof of an existing building in mid-town Manhattan came with its own set of challenges. Logistical constraints required innovative solutions. Working for OCI (Orange County Ironworks), the team realized the best solution to perform the work, save time, and cost was to lift a crane and place it on the roof of the SNFL New York Public Library. Ultimately, a Liebherr mobile crane would lift a smaller Crane onto the top floor to help erect the library’s new structure and “wizard hat” metal roof. This would allow the rooftop crane to be left in place for the bulk of steel erection without having to remobilize multiple times.
At the ground level, the Liebherr mobile crane was positioned along East 40th Street, but its outriggers were situated atop a sidewalk vault. The sidewalk vault did not have the capacity to support the loads imposed by the crane outriggers. As such, McLaren needed to resolve the crane loads by building a custom shoring tower system. The outrigger loading was transferred to the cellar level foundation below via outrigger spreader plates, temporary steel transfer beams, custom shoring tower with adjustable height posts for varying existing conditions, wood cribbing, and multiple levels of steel grillage beams.
Additionally, for the crane placement on the existing roof, McLaren’s construction engineering team designed a temporary platform for the smaller Crane along the north side of the building. At this location, the building’s existing framing received a substantial amount of new steel to support a new heavy green roof planting area. In lieu of providing a temporary new steel platform for the crane support, the team was able to temporarily support the crane placement utilizing the new permanent steel.
But first, the area needed to be reinforced and adjusted for the crane loads imposed. The construction engineering team had to analyze the existing, reinforced, and new steel and design a dunnage system to properly transfer loading to the base building structure. Select members were upsized for the loads imposed by the crane during erection. Custom dunnage mats were designed to ensure the existing roof structure was not being relied on to transfer loads to the base-building steel.