Robert A.M. Stern Architects raises the bar with Philadelphia's Comcast Center
At a 975-foot height, Comcast Center is Philadelphia’s tallest building—a distinction that should last at least as long as the recession. The tower, designed by Robert A.M. Stern Architects of New York (with Kendall/Heaton Associates of Houston as architect of record), brings a trim and tailored presence to a skyline pumped up with spires and tops vying for public attention for 20-odd years.
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As a skyscraper, Comcast’s top—a squared off obelisk—doesn’t announce any new directions in design, nor suggest that it will be as noticeable once taller buildings (such as the projected 1,500-foot-high American Commerce Center by Kohn Pedersen Fox) crowd around it. But like Raymond Hood’s RCA Tower (1933) at Rockefeller Center in New York, what it lacks in jazz at the top, it delivers at the bottom in a multilevel mix of public spaces, rail connections and concourses, shops, and cafés.
Comcast’s abstracted glass-curtain-walled shaft does come as something of a surprise from a firm strongly typecast as a proponent of a historicist approach to architecture. While the Stern office has executed several glass-covered, streamlined buildings in the past decade (notably, in Mexico City and Rio), the Classical Trad look remains entrenched in clients’ minds. The sleek form tapering to a squared-off top is probably Robert A.M. Stern, FAIA, and project partner Graham S. Wyatt, AIA’s most blatantly Modernist design to come to the American public’s attention.
Like the towers of other top-of-the-line corporate-design firms, Comcast’s silhouette harks back to the Late Modern days of the 1960s, only with a more smoothly joined, clearer, and lighter glass curtain wall, and a shaft more articulated with projections and recesses than the shoe-box-on-end of yesteryear.
Liberty Property originally sought out Stern in 2000 to design a mid-rise spec building for which it wanted a “boutique architect,” says John Gattuso, the company’s senior vice president and regional director of urban and national development. “I proposed glass in the beginning,” says Stern, but as Gattuso explains, glass would have been more expensive—especially for what was turning out to be a taller and taller spec tower. After Liberty Properties acquired the 1.8-acre site at 17th and John F. Kennedy Boulevard in 2001 on a still frowsy edge of Center City, the developers announced a scheme for One Pennsylvania Plaza at a 750-foot height. In those days, kasota stone and horizontal bands of glass gave the tower more of an affinity to the shaft—only the shaft—of Howe and Lescaze’s landmark PSFS Building (1932) nearby. Granite cladding next made a brief appearance as a skin concept before glass reentered as the dominant material. By then, a new prime tenant emerged—Comcast, the cable company founded by Philadelphia native Ralph Roberts in 1963, and currently the largest cable operator in the U.S., with Ralph’s son, Brian, at the helm. And with Comcast as the prime tenant, the building grew taller and sleeker, to its height of 58 stories (1,250,000 square feet), accommodating 2,900 employees.
The architects sheathed the winter garden, plus a series of three, three-story atria above it, as well as the corners and crown of the tower, in a clear, low-E, low-iron glass, while using lightly tinted, slightly reflective glass for the rest. As the obelisklike tower rises, the reflective skin does seem to peel away, so that the clear glass emerges in counterpoint.
In spite of the abstractly faceted sheathing, a Classical drift can be detected in the tower’s axial symmetry and its centered elevator and stair core (with its slight asymmetrical displacement on the upper levels). Since the structure is based on a poured-concrete elevator and stair core, steel-and- concrete decks, and steel beams and columns, expansive views can prevail on all sides. And due to typical floor plates of 25,000 square feet, daylight penetrates well into the interior.
Daroff Design and Gensler collaborated on the interiors, which include executive offices and conference rooms at the top, a two-level restaurant on the 43rd and 44th floors, a training center known as Comcast University just below, and the open office floors. Throughout the tower, not only daylight but views of the city are striking, since the ceilings are 11 feet high up to the 43rd floor, and 13 feet high from floors 44 to 56. To emphasize these features, the designers placed circulation at the perimeter walls, and created open workstations with 49-inch-high partitions. On the executive floors, recessed planes of glass, and a four-story atrium linked by a stair with open risers and fritted-glass treads, dramatically enhance the sense of light and space.
Regardless of its record-breaking height and the spacious offices, Comcast’s newly found magnetism comes from the winter garden at the base of the building, and the plaza outside, along with a concourse retail level connecting to the suburban train station. In keeping with its identity, Liberty Property and Comcast commissioned David Niles of Niles Creative Group to create a high-definition video installation, two stories high and 85 feet wide, behind the lobby’s reception desk. Now the media wall and Jonathan Borofsky’s sculptures of people walking, tightrope-style, on steel tubes in the winter garden attracts tour groups and other pedestrians much of the day.
Here, too, there is a Bernini-meets-Busby-Berkeley grand stair taking commuters to and from rail connections below. Stern designed the food-and-retail level there with slightly higher ceilings than are usually found in the subterranean concourses of Center City, by raising the level of the plaza a few steps above grade. Since the tower is in the Penn Center area conceived by planner Edmund Bacon in the 1950s, the design of the winter garden and its connection to the Suburban Station building to the east integrates Comcast extremely well into the urban life of this area. Its activation of this parcel makes it well worth the bonus zoning of a FAR (floor area ratio) of 8 on top of the standard 12 FAR.
In addition, Comcast’s connection at the plaza to the Classical Revival Arch Street Presbyterian Church (1855) to the west adds to the vibrancy of this district. Already the glass tower’s intrusion of high style and public amenities in this location between Rittenhouse Square, Logan Circle, and Benjamin Franklin Parkway has added spark to a moldering area.
Before the recession, liberty property sold 80 percent of its interest in the tower to a subsidiary of commerzbank of düsseldorf. And with comcast occupying about 90 percent of the space, the developers appear to be in a good place. It might be one of those few occasions when the developer, client, and even the city benefit. The top of the tower, however, remains a skyscraper conundrum: how do you crown an abstractly modern high-rise? Spires and pyramids are too old hat, sawed-off tops too blunt, and off-center needles willful. We await the resolution.
Formal name of project: Comcast Center
Location: Philadelphia, Pennsylvania
Gross square footage: 1,250,000 sq.ft.
Total construction cost: $314,000,000
Liberty Property Trust (Malvern, Pennsylvania) and CommerzLeasing & Immobilien AG (Dusseldorf, Germany).
Note: Liberty Property Trust was the developer and our client.
Robert A.M. Stern Architects
460 West 34th Street, 18th floor
New York, New York 10001
Damping — the process of stabilizing a structure against severe motion caused by wind or seismic conditions — is a critical component in many building types, such as long-span and cable-stayed bridges, spires, monuments, and skyscrapers.
Many types of dampers dissipate oscillations by employing springs, fluids, or pendulums. Some, such as the 760-ton gold pendulum for the tuned mass damper (TMD) at Taipei 101 in Taiwan are part of the show. The 1,671-foot-tall tower, designed by C.Y. Lee & Partners (2004), swings in full view of patrons in the restaurants and observation decks.
Most damping devices, however, are part of the structure and not the architecture, so they’re hidden. And yet as buildings get taller and thinner, today’s dampers require and inspire innovation. While extreme oscillations can cause structural damage, more often the challenge is eliminating human discomfort or motion sickness caused by lateral drift, especially in tall buildings with high aspect (slenderness) ratios. Such was the case with the Comcast Center in Philadelphia.
Acceleration is the most common cause of motion effects, and the greater the horizontal force, the more discomfort the human body experiences. An acceleration of one thousandth of gravity is called a milli-g. According to Aine Brazil, managing principal at New York—based Thornton Tomasetti, the structural engineers for Comcast, “The goal was to achieve a range from 20 to 24 milli-g. This is the maximum acceptable for a 10-year return period.” However, with a height of almost a 1,000 feet, the oscillation would have been 30 milli-g.
Thornton Tomasetti worked with Canadian motion-control consultant Motioneering, the designer of Taipei 101’s TMD, the largest of its kind in the world. They sought to find a supplementary damping system (SDS) that would optimize the lateral drift serviceability performance but would be less expensive than the TMD. Motioneering determined that a tuned liquid column damper (TLCD) would be the answer. Since an SDS was only needed along the most slender axis, the consultants decided that rather than installing two perpendicular TLCDs, which is a typical solution, the company would design a large one.
Now, the tallest building in Philadelphia has the world’s largest uni-axial TLCD, with a water mass of 1,300 tons, or 300,000 gallons of water. Its U-shaped tank allows the water to oscillate freely at the frequency that matches a natural one of the structure. Damping is provided by tuning the turbulence levels in the moving water.
Motioneering’s custom design, which included dividing the tank into two parts, maintains efficiency, optimizes the space, and saved the client millions of dollars in structural costs. —
Green strategies for a public space
Liberty Property Trust, proud of its sustainable office buildings, is also seeking LEED certification for Comcast. The architects worked with environmental consultants Atelier 10 on energy-saving strategies — for example, on heating and cooling methods for the six-story winter garden and the atria above. The team specified low-E, low-iron glass on the south facade to reduce solar gain in the warm months, and installed a low-velocity displacement ventilation system. In addition, hydronic tubes embedded in the granite floor of the winter garden extract heat, which is also siphoned out of the top of the atrium by the stack effect.
In the winter, thickened steel mullions serving as sunshades deter downdrafts, deflecting cold air into the 45-foot-high double wall of the winter garden so that it doesn’t enter the indoor areas. Internal radiant fin tubes attached to the steel mullions modulate the temperature on the inside of the glass to prevent condensation. The granite floor stores heat and radiates it back at night, while a low-velocity air system under occupied floors supplements heating. Other measures to save energy include using recycled materials and waterless urinals, which has helped cut the use of all water in the building by 41 percent a year. —
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