Emporis Skyscraper Award 2015

The completion of One World Trade Center marks a major milestone in the history of New York City. More than 13 years in the making, the 104-story, 3.5-million-square-foot, 1,776-foot tower – the tallest in the Western Hemisphere – recaptures the New York skyline, reasserts Lower Manhattan’s preeminence as a global business center, and establishes a new civic icon for the country.

One World Trade Center was designed as an memorable architectural landmark – a symbol of the American spirit, whose simplicity and clarity of form will remain fresh and timeless. Equally important, it sets a new international standard for supertall-building performance. In terms of structure, life-safety innovations, and sustainability, the tower at One World Trade Center stands unsurpassed.

The basic numbers are staggering: 46,000 tons of steel, more than 200,000 cubic feet of high-strength concrete, thousands of square feet of exterior glazing. But the numbers reveal little about the tower’s unique qualities and the unprecedented challenges Skidmore, Owings & Merrill LLP (SOM) and its collaborators overcame to complete a building of this magnitude on such a difficult site. The building features numerous innovations designed to exceed standard building code requirements. After more than a decade of tireless effort by thousands of people, One World Trade Center stands as a marvel of urban modernism and advanced technology.

One World Trade Center is a bold icon filling the skyline void left by the fallen towers. While the adjacent World Trade Center Memorial speaks of the past and of remembrance, One World Trade Center speaks about the future and hope as it rises upward in a faceted form. Depending on the viewer’s perspective and angle of light, One World Trade Center appears to shape-shift from a platonic solid reminiscent of the original twin towers to an obelisk recalling the Washington Monument.

A publicly owned commercial building with approximately 3.5 million square feet of office and retail space, observatory, and broadcast and antenna facilities, One World Trade Center replaces almost one quarter of the office space lost on September 11, 2001. (Overall, downtown lost approximately 11 million square feet of office space on September 11th, with ten million square feet lost at the World Trade Center proper.) Below-grade concourses comprise approximately 55,000 square feet of retail space and connect to an extensive transportation and retail hub that includes 11 subway lines, PATH commuter trains to New Jersey, and entry to the Observatory.

The program is organized as follows: Rising from the plaza level, a 50-foot-tall public lobby is topped by a series of mechanical floors; together these form a 186-foot-tall building podium. Seventy-one office stories (floors 20 – 90) rise above the base to an elevation of 1,131 feet. Above that are mechanical floors and a three-level observatory at elevations of 1,238, 1,248, and 1,265 feet, which culminates in a parapet, marking 1,362 feet and 1,368 feet – the heights of the original Twin Towers. Communication platform rings rise above the parapet. The 441-foot, cable-stayed spire rises from the 105th level, 25 feet below the parapet. An innovative LED beacon crowns the project.

The height of the beacon is 1,776 feet, a symbolic reference to the year of American independence.

Site

One World Trade Center fits seamlessly into the northwest corner of the World Trade Center site, on land claimed from the Hudson River over centuries of development in Manhattan. The site, several blocks east of the river and in the heart of the financial district, will ultimately house more than ten million square feet of commercial development in five towers, a performing arts center, 500,000 square feet of retail, a transportation hub, and, at its center, the National September 11 Memorial & Museum.

The master plan restores Fulton and Greenwich Streets, formerly blocked by the World Trade Tower plaza and the original 7 World Trade Center building, breathing new vitality into the area. The new 7 World Trade Center, which opened in 2006, reopens Greenwich Street, easing the flow of commerce and sending a message of accessibility to the approximately five million annual visitors to the memorial and museum. The 2013 opening of 4 World Trade Center, the second tower to rise on Greenwich Street, signaled an important step towards completing the spiraling master plan, wherein each new tower stands progressively taller, culminating in the symbolic 1,776-foot One World Trade Center.

Podium

The tower rises from a podium whose square plan measures approximately 204 feet by 204 feet, the same footprint as the original towers. The podium is 186 feet tall and is clad in triple-laminated, low-iron glass fins and horizontal, embossed stainless steel slats. The more than 4,000 glass fins, each measuring approximately 13 feet by two feet, are fixed and positioned at varying angles along the vertical axis to form a regular pattern over the height of the podium. This pattern both accommodates ventilation for the mechanical levels behind the podium wall and, in combination with a reflective coating, refracts and transmits light to create a dynamic, shimmering surface. The podium’s heavily reinforced concrete walls serve as a well-disguised security barrier.

Tower

Above the podium, the tower’s square edges are chamfered back, transforming the square into eight tall isosceles triangles. At its middle, the tower forms an equilateral octagon in plan and then culminates in a stainless steel parapet whose plan is a 150-foot by 150-foot square, rotated 45 degrees from the base. The resulting crystalline form captures an everevolving display of refracted light: the surfaces change throughout the day as light and weather conditions shift and as the viewer moves around the tower. Careful thought was also given to the design of the tower’s corners. Made of embossed stainless steel, the eight edges recall the reflective corners of the original twin towers.

Structure

One World Trade Center features a hybrid structure comprised of a high-strength concrete core surrounded by a perimeter moment frame of steel. Paired with the massive concrete shear walls of the core, the steel frame adds rigidity and structural redundancy. Both bolted and welded together for maximum connection strength, the steel members were hoisted into place by two Manitowoc cranes – the largest ever used in New York City. The tower’s tapered, aerodynamic form reduces exposure to wind loads while simultaneously reducing the amount of structural steel needed. Rising a quarter mile into the sky, the tower is brute strength veiled in glass.

High-Strength Concrete

Standard concrete has a compressive strength of 3,000-5,000 psi. All 200,000-plus cubic yards of concrete used during the construction of One World Trade Center exceed that strength, with slabs ranging from 4,000 to 8,600 psi and walls ranging from 8,000 to 14,000 psi, the strongest mix ever used in New York.

To meet the stringent curing demands of the high-strength concrete in order to avoid thermal cracking, crews substituted ice for mix water and shifted pour schedules to cooler times of the day. They imbedded Radio Frequency Identification Devices (RFID) data-loggers in the concrete to measure internal temperatures, heat of hydration, and maturity of the newly constructed walls.

Spire and Broadcast Rings

Three communication rings and a 441-foot spire top the tower. The spire consists of eight vertically stacked digital-broadcasting sections, each decreasing in width. At the top, a stainless-steel capsule houses the LED beacon.

To support against wind, transparent Kevlar guy cables, designed by structural engineer Schlaich Bergermann und Partner, are connected from the mast to the rings. Window-washing equipment is incorporated into the spire ring structure. Because of its circular shape, this design makes it possible to service the building with only three building maintenance units.

Beacon

The spire is illuminated by a beacon housing 264 50-watt LED modules. These cutting-edge, full-color lights emit a horizontal light beam that can be seen across the metropolitan region.

The three communication rings and beacon reference the nearby Statue of Liberty and her messages of welcome and international solidarity.

Curtain Wall

A glass curtain wall sheaths the tower on all sides from the 20th floor to the observation deck. For the curtain wall, architects worked with industry experts to develop glass of a new monumental scale that is capable of withstanding the wind loads of a supertall building as well as stringent security requirements. The 5-foot by 13-foot-4-inch insulated glass panels span the full floor-to-floor height with no intermediate mullion – a first in skyscraper construction. These glass units, the largest ever mass-produced for a building of this scale, help give the massive tower its crystalline elegance. Coupled with a maximized soffit height, the tower’s glazing system provides 90 percent daylight autonomy. The tower’s triangular facades that align with the four cardinal points stand perpendicular to the ground while the other four have a 1:16 slope.

To fulfill its design vision, SOM architects pushed for thicker glass to avoid the wavy appearance known as “oil-canning.” To avoid the greenish tint of most architectural glass, thereby maximizing daylighting, they sourced a low-iron product. From the outside, the glass appears to have a slight blue tint, but it is crystal clear when viewed from inside. Windows have twice-laminated outer lites and were treated with a low-E coating for maximum energy efficiency.

Pushing the Glass Envelope

To achieve its vision for a seamless crystal tower, SOM challenged the conventions of the day by designing a glass curtain wall with a minimum number of mullions, the metal bars that typically hold and divide windows. The biggest threat of failure was from condensation on the inside faces of the windows. Needing a higher level of research to make condensation predictions for this new concept, SOM’s engineers developed a fluiddynamic model of the facade.

Though the modeling proved the design was sound, the firm discovered that none of the world’s glass manufacturers produced panels large enough to meet SOM’s specifications. The design called for 13-foot, 4-inchtall panels at a time when the largest available measured only 12 feet, 8 inches tall. SOM worked closely with Minnesota-based fabricator Viracon, which developed an entirely new production line to meet the project’s needs—and to do it cost-effectively. Not only do the larger glass panels contribute to the building aesthetics, but they improve views and let in more sunlight, reducing the need for electric lights.

Floor Plan

In designing an exceptionally secure skyscraper, SOM did not sacrifice workspace quality. On the contrary, the tower’s robust structure allows for unprecedented office flexibility, natural light, and breathtaking views in all directions. On every office floor, tenants occupy the column-free perimeter space surrounding the central core. All bathrooms, elevators, stairways, and utility closets are contained within the core, and they are all accessible from within the core via a 13-footwide corridor, an arrangement that improves efficiency, enhances security, and keeps the perimeter office space free of doors and other obstructions. This people-centered, sunlight-flooded floor plan encourages collaboration and transparency and constant inspiration through its panoramic views.

Plaza

The design allows the building to flow out into the plazas to create areas for people to gather, sit, relax, and reflect. Generous open spaces are filled with trees and places of respite for the tenants and the estimated three million annual visitors. These areas connect the tower with the adjacent neighborhoods and allow views and access into the memorial.

Lobbies

Entrances on all four sides of the building, each 60 feet tall and ranging in width from 30 feet on the east and west sides to 50 feet on the north side and 70 feet on the south, activate the building at street level. Glass canopies and large cable-net walls framed by metal portals define the entrances. The west portal provides entrance to both the Observatory lobby on the concourse level as well as the transportation systems. The east portal provides access for office tenants who will ascend to the top of the building. The wider north and south entrances provide access for commercial office tenants and are marked by an array of dichroic glass panels. These panels, composed of multiple layers of clear, etched, and dichroic glass, draw on the spectral qualities of light to create vibrant color patterns across the surfaces of the lobby. The design draws on the results of a yearlong research project into the optical effects of dichroic glass in transmission and reflection. Dichroic glass fins are also recessed into the marble wall behind the north and south lobby desks.

The grand lobby encircles the central core and is filled with natural light that enters the space through the east and west entrances as well as through apertures in the north and south walls. Carrera marble clads the lobby walls. The floor is composed of black granite and stainless steel.

The material palette and the 50-foot height echo the lobbies of the original twin towers.

Cable-Net Walls

Tall, highly transparent cable-net walls define each of the four building entrances. While they set a welcoming tone, flooding the lobby with natural light, the innovative entry walls are highly secure without appearing fortress-like. As opposed to the brute strength of the podium walls, the glazed entry walls were engineered as an energy-dampening system. They feature a first-of-its-kind interlayer, mechanically fastened in place by pins, that remained stable throughout extensive testing.

Elevators/Observation Deck

High-tech elevators sweep Observatory visitors skyward at a rate of 2,000 feet per minute. The record-breaking speed is imperceptible because of the ultrasmooth ride.

Life-Safety

The building incorporates advanced life-safety systems that far exceed the requirements of the New York City Building Code and lead the way to a future filled with safer high-rise buildings. In addition to structural redundancy and cementitious fireproofing that is dense and highly adhesive, the building includes particulate and chemical filters in the air supply system. All of the building’s life-safety systems – egress stairs, communication antennae, exhaust and ventilation shafts, critical risers, standpipes and elevators – are encased in a high-strength concrete core that is, at its minimum, two feet thick. Within this core a range of major improvements optimize egress:

• Extra-wide, pressurized exit stairs
• 30-inch by 48-inch rescue assistance area in the corner of every stair landing
• Photoluminescent paint striping to improve visibility
• Emergency lighting with battery backup
• Door located at “down” side of stair to optimize flow
• Exit stairs that interconnect at the 2nd floor, providing multiple, redundant egress points
• Tower stairs exit directly to the street

In addition, the design includes other innovations that facilitate emergency responders:

• Enhanced communication systems
• Pressurized, two-hour-rated vestibule with CCTV coverage
• Dedicated, pressurized stair for use by firefighters
• Water resistant emergency-responder elevator housed in its own shaft, which protects against smoke and fire but also water from hoses, a common cause of elevator failure (due to electrical shorts)
• Protected tenant collection points on each floor

SUSTAINABILITY

One World Trade Center uses new technologies to maximize efficiency, minimize waste and pollution, and reduce the impact of its development. The building’s sustainable design strategies, including water and energy efficiencies, go beyond the criteria established for LEED CS Gold certification.

The tower’s seamless skin incorporates a visually subtle insulated spandrel, while allowing natural light to reach over 90 percent of the office areas, reducing the electrical lighting requirements and associated cooling loads, while improving the quality of the office space. The enclosure also features a high-performance, low-E glass coating technology to minimize unnecessary heat gain from ultra-violet, infrared, and excess visual light, conserving energy needed to cool the building. Low-energy equipment, such as variable-speed fans and pumps, adaptable to varying occupancy levels further maximize efficiency. The tower features a high-tech building management system (BMS), which optimizes energy use and indoor air quality, based on data collected by thousands of sensors located throughout the building.

Along with energy savings, the building will generate power through elevators with Variable Voltage Variable Frequency (VVVF) drives and hoist motors that produce energy through regenerative braking. Under certain conditions, the elevator motors turn into small generators supplementing power in the building’s power distribution grid, thus reducing demand for electrical utility power.

A grey water system, utilizing harvested rainwater from the main roof areas, plaza, cooling coil condensate, and steam condensate, provides makeup water to the building’s cooling towers and site irrigation. 100 percent of stormwater runoff is captured on-site and stored in one of three retention tanks, which have a total storage capacity of 165,790 gallons. As part of the overall water use reduction strategy, high-efficiency plumbing fixtures were also specified. In all, the building uses 41 percent less water than the LEED 2.0 baseline.

Over 40 percent of the materials used in the construction of the tower were made from post-industrial recycled content, including gypsum boards, ceiling tiles, and glass. The structural steel was produced from 95 percent recycled materials, and the building features “green concrete,” made from waste fly ash collected from coal plants. Combining the benefits of material performance and reduced environmental impact, the team sourced recycled steel and concrete that are superior in strength to standard products. The majority of wood used during construction was certified as responsibly harvested by the Forest Stewardship Council. Over 87 percent of construction waste was diverted from landfill, and materials containing potentially harmful volatile organic compounds (VOCs) were restricted. Additionally, 34 percent of construction materials were regionally sourced (extracted, harvested, or recovered as well as manufactured within 500 miles of the project site).




Owner/Client: 1 World Trade Center LLC, The Port Authority of New York and New Jersey, The Durst Organization

Architect
Skidmore, Owings & Merrill LLP

David M. Childs, FAIA Design Partner
T.J. Gottesdiener, FAIA Managing Partner
Kenneth A. Lewis, AIA Managing Director
Nicholas Holt, AIA Technical Director
Nicole Dosso, AIA Senior Technical Designer
Julie Hiromoto, AIA Project Manager
Frank E. Mahan, AIA Senior Design Architect

Construction Manager: Tishman Construction Corporation
MEP Engineer/ Vertical Transportation: Jaros Baum & Bolles, Inc.
Structural Engineers: WSP Cantor Seinuk Group
Spire/cable net wall: Schlaich Bergermann und Partner GbR
Civil & Transportation Engineer: Philip Habib and Associates
Acoustics: Cerami & Associates
Broadcasting: Metropolitan Television Alliance
Code Consultants: Code Consultants, Inc.
Program Manager: STV Inc.
Counsel: Wachtell, Lipton, Rosen & Katz
Digital Animations: Screampoint
Environmental Counsel Arnold & Porter
Exhibition: Ralph Applebaum Associates
Cladding Supplier: C/S Construction Specialties Company
Façade Maintenance: Citadel Consulting/ Lerch Bates Consulting
Geotechnical Engineer: Mueser Rutledge Consulting Engineers
Landscape Architects: Mathews Nielsen Landscape Architects; Peter Walker Landscape Architecture
Lighting
Lighting Consultant: Claude R. Engle
Podium Lighting Designer: Brandston Partnership, Inc.
Model Making: Radii
Parking/Traffic: Philip Habib and Associates
Pedestrian Traffic Modeling: Booz Allen Hamilton
Protective Design Engineer: Weidlinger Associates
Renderings: dbox Studio
Security: Ducibella, Venter & Santore
Signage: Pentagram
Sustainability Consultants: Viridian, Steven Keppler & Associates
Wind Analysis: Rowan Williams Davies and Irwin Inc. (RWDI)
Outside Agencies/Researchers: Lawrence Berkley National Laboratories, NESCAF, New York City Department of Transportation, New York Department of City Planning, New York State Department of Transportation, NYSERDA, U.S. Department of Energy, University of Illinois at Urbana-Champaign, Clean Air Communities
Other Stakeholders: Community Board No. 1, Lower Manhattan Development Corporation