Council on Tall Buildings and Urban Habitat
 

CTBUH New York Roundtable Discussion:
The Current State of Slender Buildings in NYC
July 30, 2015
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NEW YORK CITY – On July 30, SHoP Architects welcomed a group of thirty architects and engineers from CTBUH New York in association with the New York Young Professionals Committee (YPC) for a lively discussion and exchange of ideas about slender buildings. The group swapped war stories and exchanged ideas on what worked and what didn’t.

The evening opened with a case study of 111 West 57th Street before the discussion evolved to include other slender skyscrapers, including One57 by Christian de Potzampark, 432 Park and 125 Greenwich Street by Rafael Viñoly Architects, 30 Park Place and 220 Central Park South by Robert A.M. Stern Architects, Central Park Tower by Adrian Smith + Gordon Gill (AS+GG), MoMA Tower by Jean Nouvel Architects, and 1 Park Lane by Herzog & de Meuron.

Many of the largest and most active architecture and engineering firms in New York were represented, including SHoP Architects, Robert A. M. Stern Architects, WSP Group, Rafael Viñoly Architects, SOM, Leslie E. Robertson Associates, Foster + Partners, Arup, Bjarke Ingels Group, McNamara Salvia, and KPF, among others.
Dana Getman, Associate Principal at SHoP Architects, discusses 111 West 57th street
Case Study

111 West 57th Street – with a slenderness ratio of 1:23, the most slender building in the world – was presented by Dana Getman, Associate Principal at SHoP, with interjections by other members of the design team and occasional observations by Sameer Kumar, Director of Enclosure Design at SHoP. The building form was generated by a number of gestures: setting back in the lot to maintain the “reading in the round” of the landmarked Steinway building; straddling two zoning conditions, which generated the feathered setback of the south façade in relation to the precipitous north façade; full floor apartments and small core; and the efficient shear wall construction of the east and west façades, creating in essence a vertically cantilevered wide flange structure.

The building fits beautifully into the genealogy of the New York City skyscraper, both through its use of tapering form and through the use of terra cotta façades with bronze accents. The illumination of the porous, cage-like “spire” sparked a discussion on the vanity heights of buildings, which often comprise up to 30 percent of the overall building height, and in the case of 111 West 57th Street is around 20 to 25 percent.

The group peppered the team with questions, and then the forum opened up to a larger discussion. Jessie Turnbull gave a quick back-story to the history and genesis of superslim projects, and pointed the group to various resources for learning more, including the “Sky High: the Logic of Luxury” exhibition at the Skyscraper Museum (now documented on the skyscraper.org website), and related papers by Carol Willis from various CTBUH conferences; also mainstream media, such as curbed.com and newyorkyimby.com, and other reports like “Accidental Skyline” published by the Municipal Arts Society were mentioned.
An explanation of various lateral load resisting systems of slender buildings was provided by Chris Shirley, Project Manager at WSP Group YPC members Nathan Langdon (WSP) and Jaein Choin (Rafael Vinoly Architects) at SHoP’s office main lobby viewing the towering model of 111 west 57th Street
Zoning & Urban Habitat

Moderated by Jessie, the group discussed the specific zoning issues that made the current crop of slender buildings possible, including merged zoning lots, transfer of unused development rights, bonus floor area ratio for plazas and affordable housing, and the purchase of air rights, most notably evident in Central Park Tower which cantilevers over the Art Students League. Most of the buildings discussed were built as-of-right under NYC zoning laws, which assumes the resulting density can be adequately served by the existing infrastructure. 432 Park and 30 Park Place, among others, take advantage of the plaza zoning incentives. The group discussed the technical difficulties in meeting the requirements for public space, given that it must connect seamlessly to the street, while also conforming to the new elevated flood levels, a conflicting requirement particularly pronounced in KPF’s 111 Murray Street.

The group grappled with the question of a lack of amenities for these new buildings. Although it is generally understood that these buildings function as “safe boxes in the sky” for rich investors – meaning few families will live in them full time – shouldn’t there be some requirements for a holistic planning process that adds amenities alongside residences? David Brown of BIG noted that in fact these buildings, although providing additional living space, have such large apartments that the effective density is actually often lower than what they replace. It was also noted that the Steinway building used to employ over 1000 people on a daily basis, and the occupancy of the new tower will be much lower.
A multidisciplinary group discussion on the current state of slender buildings was led by YPC member, Jessie Turnbull
Structure

Chris Shirley, Project Manager at WSP Group, took the floor for an introduction to the evolution of lateral load resisting frame types used in tall buildings. He explained the basic structural typologies used in various slender New York buildings, and the range of damping mechanisms used in different buildings – from no damper at 30 Park Place, to a column water damper in One Madison (by Cetra Ruddy Architects), to tuned mass dampers in 111 West 57th and 432 Park.

Wind-tunnel testing was also discussed in relation to slim New York buildings. Chris showed an illuminating image of the New York Midtown model produced by RWDI wind tunnel laboratory – where the majority of these buildings are tested – including all the as-yet-unbuilt towers alongside the existing Midtown urban fabric. The group discussed the wind vortex effects on adjacent buildings, with emphasis on the potential negative impact a lack of legislation on the topic could produce.

Architects also chimed in on the subject of allowable acceleration, focusing on how the requirements are fairly subjective and how comfort is very dependent on the perception of the inhabitant. The final design accelerations are often closely held secrets, but the group discussed the idea that these be written into sales contracts so that future residents can’t dispute the comfort level they receive. The great disparity in price between slosh tanks and tuned mass dampers was also discussed, and it was noted that water dampers can also be used as emergency water for sprinkler systems. The cost aside, mass dampers are significantly more effective in reducing a building’s acceleration.

Outcomes

Even with a two-hour timeslot, the discussion was so lively that organizers were unable to cover the short list of anticipated topics. As a result, detailed discussions of concrete, floor plan peculiarities, vertical circulation, and façade materials were put aside for the next discussion. Besides being a great forum for sharing ideas, this meeting served to introduce the emerging leaders in the field of slender buildings to meet one another, fostering future conversations and collaborations. Having opened up this topic, and found some great participants, CTBUH New York and YPC hope to continue the discussion in future round-table sessions, delving into the detail and materiality of some of these towers.

CTBUH New York and YPC would like to extend a special thanks to following committee members for their help in organizing the event: Jennifer Chang (SHoP), Elizabeth Geldres (RVA) and Jessie Turnbull (Formerly of RAMSA). For additional information about the YPC feel free to contact us at ypcnewyork@ctbuh.org.