Cities thrive on a dynamic interplay of economics, politics, and design. They host a rich blend of uses and serve as magnets for talent and tourism. Great cities are engines of innovation; they are never static and always full of surprises—part of their allure for world-class companies and institutions.

“Maintaining a city’s vitality depends, in part, on how well it preserves the past while adapting to and accommodating the future,” says Nick Leahy, co-CEO and executive director of Perkins Eastman. “Promoting the intelligent reuse of existing fabric through sensitive adaptations is central to the firm’s approach to our work with the Simons Foundation in the Ladies’ Mile Historic District [aka the Flatiron District] of Manhattan.”

The Simons Foundation is a philanthropic organization founded in 1994 by the late Jim Simons, a renowned mathematician, and Marilyn Simons, an accomplished economist with expertise in the nonprofit sector. It works to advance frontiers of research in mathematics and the basic sciences through the support of computational scientists and makes grants in several areas, including education and health. In 2016, the foundation, which is headquartered at 160 Fifth Avenue, established the Flatiron Institute at 162 Fifth Avenue. The historic buildings, both constructed at the turn of the 20th century, face one another across West 21st Street.

The foundation and the institute employ a total staff of 500 and host more than 5,000 visiting academics and researchers from around the globe each year. In addition to conducting critical research, the institute serves as an important economic driver and vital nerve center for both the Flatiron District and the city at large.

Perkins Eastman master planned, designed, and executed the gut renovation of 162 Fifth Avenue to create a collaborative research facility for the institute, one of several projects the firm has completed for the Simons since the early 1990s. Essential to the client’s research philosophy is the idea that insights and innovations happen when people convene in person. The institute renovation, for example, includes a variety of formal and informal convening spaces, and it is equipped throughout with chalkboard walls for scribbled formulations and discussions.

View of the Simon’s Foundation Skybridge looking west on West 21st Street. Photo | © Perkins Eastman

In 2019, with robust activity occurring on both sides of West 21st Street, Jim Simons proposed a skybridge to improve access and increase interaction between the two buildings, while enabling development of the 160 Fifth Avenue rooftop as another convening amenity. Perkins Eastman set about developing concepts to span the street.

The challenges were apparent from the outset: the city’s planning commission rarely approved skybridges (believing they take pedestrians off the sidewalks), and historic district restrictions increased the level of scrutiny. The firm’s solution needed to be unique, contextually appropriate, and able to navigate the revocable consent process, the Uniform Land Use Review Procedure (ULURP), and regulatory approvals.

After studying the architectural character of the two buildings, which have very different expressions, and assessing the best place to connect them, the firm proposed a structural glass enclosure—formally precise and visually light. Two options for the bridge deck were explored: folded steel plate and carbon fiber. The latter was selected for its structural and visual lightness, ability to accommodate integrated services within the deck’s depth, and reduced structural impact on the existing buildings.

The next step was to build a team that could make the skybridge concept a reality. Engineer Michael Ludvik is a long-time collaborator with a keen sense of design. The creative thinkers at Derive Engineers were brought on as the mechanical consultant due to their ability to “think outside the catalog.” Façade consultancy Walter P. Moore, TM Light, and fire and life-safety specialist AKF rounded out the group.

Together, the team set out to gauge the city’s appetite for the project. At an initial meeting with the Landmarks Preservation Commission, the skybridge was viewed with bewildered enthusiasm—a positive sign, but the project stalled during the pandemic. By 2022, however, efforts to revive the city also sparked renewed interest in the bridge.

The Center for Computational Neuroscience is within the Simons Foundation building at 160 Fifth Avenue.
Photograph by Andrew Rugge | © Perkins Eastman
Diagram showing the web of interactions between 160 and 162 Fifth Avenue and demonstrating the need for a physical connection between the two buildings. Diagram © Perkins Eastman

1 When Jim Simons suggested a skybridge to link 160 and 162 Fifth Avenue and address safety and efficiency concerns, he also inspired the vision: a modern, cutting-edge design to reflect the advanced research happening inside these buildings. The result is a sleek glass and carbon fiber structure 135 feet above ground level. The 63-foot-long skybridge will link the shared program and convening spaces currently separated by the noncontiguous nature of the Simons‑Flatiron campus.

After studying the differences in architectural styles and structural systems of the two existing edifices, the design team concluded that “the most respectful and elegant connection between the buildings should contrast with their massiveness and be as technologically advanced as construction has progressed today,” says Project Architect Andrés Pastoriza of the Neo-Renaissance 160 Fifth Avenue (1892) and Beaux- Arts 162 Fifth Avenue (1903) buildings. “We’re trying to dematerialize the bridge as much as possible and to maintain the integrity of the two existing historic buildings.”

Watercolor illustrating the client’s “light of knowledge” concept. Watercolor by Andrés Pastoriza | © Perkins Eastman
Sketches illustrate the legacy of the architectural expression of structure in and around New York City (left to right): load-bearing masonry and vaults at the Cathedral of St. John the Divine; ribbed stone vaults at St. Patrick’s Cathedral; cast-iron and glass vaults at the New York Botanical Garden Enid A. Haupt Conservatory; and cast-in-place concrete at the TWA Flight Center terminal. Sketches by Nick Leahy | © Perkins Eastman
Detroit Publishing Co., Copyright Claimant, and Publisher Detroit Publishing Co. Flatiron Building, New York, N.Y. Photograph. Retrieved from the Library of Congress,

2 The team began a journey to prove the design would be an appropriate connection both between the client’s buildings and within the historic district. Working with historic consultants Higgins Quasebarth & Partners (HQ) and planning and development attorneys Kramer Levin, the team crafted an argument for the skybridge, the appropriateness of the design approach, and the reasons why it would not set a precedent for future bridges. HQ noted that the Ladies’ Mile Historic District designation cited the area’s rich mix of architectural styles and technologies, reflecting the latest structural systems of the day. The 22-story Flatiron Building (1902)—the namesake of the institute, one of the city’s earliest steel-framed structures, and one of its first skyscrapers—was a case in point. Also noted was the history of businesses’s growth in the area, which involved connections between buildings, including bridges. Using these findings as a framework, the team studied the district and developed a visual lexicon of the city’s pedestrian bridges.

“By proposing a minimal connection using advanced materials, we created a complementary design that continued the district’s history of embracing advanced technologies,” Leahy says. The proposal also demonstrated that the architectural expression of a structure was a function of the materials it employed, illustrating this with local landmarks such as St. Patrick’s Cathedral in Manhattan and the TWA Flight Center at JFK International Airport in Queens.

In consultation with Kramer Levin and the advocacy group Kasirer, the team worked with various city agencies to build support for the project, emphasizing the Simons Foundation as an important asset for the city. Perkins Eastman’s previous work with the client to increase the presence of ground floor retail and activate sidewalk interactions, which involved designing an entrance to 162 Fifth Avenue on West 21st Street, was also conveyed to alleviate the city’s concerns about losing foot traffic to the skybridge.

A series of sketches shows the progression of architectural technology as part of the argument supporting the design approach to the skybridge. Sketches by Andrés Pastoriza | © Perkins Eastman
Diagram by Pablo Cabrera Jauregui | © Perkins Eastman

3 The skybridge is a unique advanced solution; it pushes the boundaries of materials. The team selected structural glass and carbon fiber, which is lighter than a conventional glass and steel assembly. This decision reduced the need for reinforcement within the existing buildings and eased construction challenges. “Both glass and carbon fiber lend themselves to a prefabricated strategy, which is what is needed to span a busy street in Manhattan and avoid unnecessary delays during installation. The structure can be lifted into place and installed in one day,” Leahy says.

While the design of the skybridge is complex, it radiates simplicity. Advances in the use and size of structural glass enable the specification of 63-foot-long single sheets of triple-laminated glass, thereby increasing the visual lightness of the bridge. Glass is an extremely strong material, but it’s brittle too. However, when laminated using high-performance interlayers, it is an efficient combined structural and enclosure element. The structural glass offers multiple benefits: the roof’s ceramic frit will help with glare, heat gain, and other energy issues; and a pattern on the laminated interlayers of the wall glazing will alert birds to the skybridge’s presence. Glass will also reduce the skybridge’s impact on sight lines from the street, within the buildings, and from neighboring structures.

4 Carbon fiber is extremely strong. It’s also lightweight and easily shaped. It has long been used in transportation and nautical sectors, and more recently in architecture. The carbon fibers and resin are cast in a mold, a process that reflects the use of cast terra-cotta on 162 Fifth Avenue and in the district. Just as the two institutions use computational methods, the latest technology is being used to create the skybridge design. The team developed an optimized structural shape for the carbon fiber deck to address the forces that will be acting on the bridge. Using Rhino and Grasshopper software, the team customized the geometry of the deck to support the exact load for maximum efficiency. Energy performance was also an important consideration, and the project was modeled and designed to meet local energy codes. The high‑efficiency mechanical systems for the fully conditioned bridge interior will be housed in the deck. Aware that the underside of the skybridge would be the most visible element of the project from the street, the team designed soft illumination for the deck to highlight its sculptural contours at night.

Point cloud image of 160 Fifth Avenue. Point cloud reconstruction and postprocessing by Pablo Cabrera Jauregui | © Perkins Eastman
Point cloud image of 162 Fifth Avenue.

5 Precision is fundamental to the design of this project: structural glass and carbon fiber require it, as does the architectural sensitivity of the historic buildings. A thorough understanding of the geometry of their façades and ornament is necessary to determine how to make precise connections.

The design team used the data from a Lidar survey (light detection and ranging), a remote sensing method that employs lasers to survey an object or surface in three dimensions, to map the façades. The resulting point clouds (collection of data points) helped the team detail the structural connections and architectural intersections between the skybridge and each building.

To accommodate movement of the two buildings, the skybridge is fixed at 160 Fifth Avenue and features a flexible connection at 162 Fifth Avenue. Throughout the design process, careful consideration has been given to the installation and construction sequence, which impacts detailing decisions.

6 At 162 Fifth Avenue, with only inches to spare between the finished floor and the bridge, “We had to make a structural connection that was minimal, so we hung it from the floor above,” Pastoriza explains. “We can then reinforce it from the roof without impacting a lot of the existing structural elements or the façade elements around the opening.” Steel rods hung from brackets on the underside of beams will support the bridge. “It’s a swing that’s receiving the bridge, and it allows for four inches of movement between the two buildings [in case of seismic activity],” he adds.

Sketch diagram shows how movement is accommodated: fixed anchor at southwest corner of 160 Fifth Avenue and hung with swing at 162 Fifth Avenue. Sketch by Nick Leahy | © Perkins Eastman
The view of 160 Fifth Avenue. Renderings by Yujin Lee | © Perkins Eastman
Interface between 162 Fifth Avenue and the skybridge.

7 Last December, the city’s Landmarks Preservation Commission approved the design, marking an especially important milestone in a long engagement with multiple agencies and community organizations that started in 2019. It is the first of many important steps, and the team continues to work together to shepherd the project through the regulatory process in addition to refining the document packages for bid. Next steps include the revocable consent approval process and ULURP, which typically takes up to a year to complete. While there is much to be done before the skybridge is installed, including completion of a rooftop amenity on 160 Fifth Avenue by TPG Architecture, Leahy notes, “The momentum toward bringing this design to fruition and connecting the scientists and researchers of the Simons Foundation and Flatiron Institute is very exciting.” N

Simons Foundation Skybridge
West 21st Street, New York, NY

Client: Simons Foundation
Owners Rep: Cushman & Wakefield
Program: Pedestrian skybridge
Size: 500 square feet; 63 feet long, 10 feet high, 8 feet, 4 inches wide
Site: 135 feet above West 21st Street (The skybridge will connect at the 11th floor of 162 Fifth Avenue and a proposed 10th floor addition of 160 Fifth Avenue.)
Completion: Expected 2026

Design Team: Nick Leahy, principal in charge; Andrés Pastoriza, project architect; Amra Kulenovic, job captain; Giaa Park, senior designer; Pablo Cabrera Jauregui, Yujin Lee, Maggie Zou; Coco Mong (intern)
Model Builder: Kazimierz Rzezniak
Renderings: Michael Kane
Design Consultants: M. Ludvik Engineering (bridge structure); Derive Engineers (MEP); Walter P. Moore (façade and building maintenance); AKF (fire and life safety); Severud Associates (existing building structure); TM Light (lighting)
Agency and Advisory Consultants: Metropolis Group Inc. (code and expediting); Higgins Quasebarth & Partners, LLC (historic preservation); Kramer Levin (zoning attorney); Kasirer (lobbyist)

Sadly, Jim Simons passed away on May 10, 2024, but his philosophy lives on in this project: “Do something new; don’t run with the pack. Surround yourself with the smartest people you can find. Be guided by beauty. Don’t give up easily. Hope for good luck!”