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The design of the 19,000 m² Satellite Operations Control Center features two main sections—the mat and the bar. The mat is a disk-shaped concrete structure that slips into the surrounding landscape on two sides. Topped by a gently sloping vegetated roof, the mat houses general office space, support services, and an underground parking garage. Rising above the mat is the three-story-tall bar section, which for the most part is windowless and houses the mission control, launch control, and other facilities for monitoring weather satellites via the rooftop array of rotating dish antennas.
Roland Halbe Fotografie, all |
The design of the Satellite Operations Control Center, a new facility in Suitland, Maryland, for the National Oceanic and Atmospheric Administration (NOAA), visually links the earth and the sky. One portion of the structure lies half buried beneath the ground; the other rises as a platform to support a long array of skyward-looking dish antennas. The design, realized in concrete, steel, and glass, bears testimony to the facility’s role in studying and protecting the earth’s environment by controlling and monitoring the nation’s weather satellites.
Located on a federal office campus approximately 11 km east of Washington, D.C., the Satellite Operations Control Center houses the National Environmental Satellite, Data, and Information Service, the primary mission of which is to provide timely access for its customers—chiefly NOAA’s National Weather Service—to global environmental data from satellites and other sources. The raw data from these satellites stream into the building through the roof-mounted dish antennas, and the numerical and visual information obtained after processing enables the National Weather Service to create the maps seen on television news broadcasts.
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The facility’s 16 antenna dishes are supported on a triangular galvanized space frame truss of tubular steel that extends approximately 25 m beyond the north and south facades of the bar section. A-frame structures—each approximately 20 m tall—provide vertical support for the truss’s gravity loads. Each column in the A-frames is set in its own pad footing foundation. |
The new building—which replaces an aging adjacent facility that originally served as an army hospital—houses equipment for monitoring and controlling NOAA’s satellites 24 hours a day, 365 days a year. It also accommodates the mission control center of the Search and Rescue Satellite-Aided Tracking (SARSAT) system, which detects and locates lost mariners, aviators, and others in distress around the world.
A joint venture of the Los Angeles architecture firm Morphosis—led by the Pritzker Architecture Prize–winning architect Thom Mayne—and the Washington, D.C., office of Einhorn Yaffee Prescott Architecture & Engineering, P.C., designed the $54-million facility. The engineering team included the Los Angeles office of Arup for the concept design and Cagley & Associates, Inc., of Rockville, Maryland, as the structural engineer of record.
The design of the facility began in January 2001. That phase was complicated by the challenges that can arise in federal building projects when the owner—the General Services Administration (GSA)—has a vision for the new structure that differs from that of the announced tenant.
In this case the GSA sought an iconic structure as envisioned under the federal government’s Design Excellence Program, which since 1994 has sought to improve the quality and value of public buildings by, among other measures, “selecting America’s best designers and artists to create facilities that ultimately become respected landmarks,” according to the GSA’s online document “Design Excellence: Policies and Procedures.” The new building has been a success in that regard, garnering a citation for design excellence from the GSA in 2002.
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The GSA also stipulated that the Satellite Operations Control Center should achieve at least silver certification in the U.S. Green Building Council’s Leadership in Energy and Environmental Design (LEED) rating system—a goal that the building appears to be on track toward achieving.
At the same time, NOAA officials expressed interest in a simpler, more utilitarian structure. They also seemed concerned about certain aspects of the planned design, including the fact that much of the structure would be located at least partially underground. The differing viewpoints of the owner and the tenant required a concerted effort on the part of the design team to convince all parties that the proposed design would produce an attractive structure that would meet the occupant’s needs.
Final construction drawings were completed at the end of September 2002. Construction began in May 2003 and was substantially complete by the end of January 2006. NOAA is now in the process of relocating its satellite operations to the new building.
The 19,000 m² facility consists of two main sections—designated by the architects as the mat and the bar. The design of each section depended on whether the functions performed there would be integral to the operation of the satellites or whether the operations would merely provide support.
The mat section is a partially buried disk-shaped concrete structure approximately 126 m in the east–west direction and 100 m in the north–south direction. It slips into the surrounding landscape on two sides, and its gently sloping concrete dome features a vegetated roof. Designed on a
9 m square column grid, the mat houses general office space, support services, and an underground parking garage. The unburied portions of the mat—mostly along its western and southern edges—feature glazed walls and ramps providing vehicular and pedestrian access. Although the central interior portion of the mat section is tall enough for two levels of floors, much of the structure features a single level of double-height space with ceilings that range in height from approximately 4.5 m near the sloping edges to 7 m or more in the central areas.
Cutting across the western half of the mat and rising approximately 20 m higher is the bar section—which houses the mission control, launch control, and computer processing operations in a three-story rectangular structure approximately 90 m long and 20 m wide. The largely windowless bar is aligned north–south to provide unobstructed views of the sky for the rotating satellite dishes that crown the concrete structure. The bar is faced in fiber-cement board and panels of flat and corrugated galvanized steel; its western facade also features galvanized steel letters 5.3 m tall that spell out “NOAA.”
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The building is founded on poor, soft, and wet soils—predominantly nonexpansive clays and sandy silts—in a location where the high water table limits bearing pressures. Heavy rains just before the start of construction only exacerbated these conditions. Although the design team considered using such deep foundation systems as piles or caissons, the best solution turned out to be a concrete mat foundation that varies in thickness from 700 mm under the majority of the mat section to 1,000 mm under the heavier portions that also support the bar section.
The site’s weak soils were stabilized during construction by a combination of techniques, including the use of a perimeter well dewatering system to temporarily draw down the water table; the placement of multiple layers of compacted stone on the soil in numerous locations to provide a stable work platform for construction equipment; and the pouring of a concrete “mud mat” over the stone to provide a dry, stable surface on which to place reinforcing for the foundation. Wherever possible, the advancing mud mat was used as a staging platform. The top of the foundation also serves as the finish surface for a single level of below-grade parking.
The size of the mat section required the use of an expansion joint that runs north–south just east of the bar section. The joint, accommodated by a double row of columns, extends through the mat roof and the office-level slabs. The mat’s foundation slab is monolithic and does not have joints. Another expansion joint runs east–west and is accommodated by a haunch slip joint.
The first level above the foundation, which is located at or below grade at many locations, is the main work floor for the mat section of the facility. Because this section’s domed roof slopes in two directions and the exterior wall curves along its length, this space is curvilinear in both plan and elevation, making concrete a natural framing choice.
The predominant framing system in both the mat and the bar section is a conventional two-way concrete slab system—that is, a system distributing loads in two directions to the supports—measuring 250 mm thick with 150 mm drop panels. But since the plan geometries vary appreciably from floor to floor, several different framing types were used in the structure, including two-way slabs, one-way beam and slab framing, posttensioned beams, and local transfer girder framing. Beam framing in particular was required throughout the building in places where the two-way concrete system was precluded by large openings, large cantilevers, or slab edge locations that could not extend to columns.
The roof of the mat section is supported on round concrete columns that generally are 600 mm in diameter, although larger sizes—710 and 760 mm—are found directly beneath the bar to support the heavier loads of that section.
A two-story space 5.5 m wide surrounds the center of the mat section and is referred to as the ring. It features a cast-in-place concrete slab on a composite deck supported by structural steel framing that fits between the columns. The lower level of the ring contains restrooms, conference rooms, kitchens, and copy rooms. Its upper level houses computer rooms, telephone and data rooms, and rooms for exhaust fans. The upper level also features a pathway that cantilevers 1.6 m over the office space.
The slab over the main work level of the mat section forms the structure’s gently curved roof dome and provides support for the vegetated roof system, which added approximately 195 kg/m² to the roof’s loads. The roof was designed not only to promote drainage but also to emulate the adjacent terrain so that much of the mat section would seem to disappear into the surrounding landscape. The dome shape was created by “bending” two-way concrete panels to the desired shape by placing the top surface of the panel on a slope to create the required shape and then slightly varying the slab thickness. For most of the roof area, this technique was relatively straightforward because the change in the slope of the concrete surface was fairly gradual, being no more than 2 percent over the bay length. But in certain areas the slope gradient was more pronounced—as much as 10 percent over the bay length—and this required a change in conventional slab placement tolerances. Here slabs were allowed to be thicker by as much as 25 mm. This approach enabled the contractor to use conventional flatwork forming along with shoring towers and 1.2 by 2.4 m plywood panels.
Four glass-enclosed courtyards 8 m wide and 24 m long are cut into the roof of the mat section to channel natural daylight into the open office spaces, where most of the employees work. Circular skylights provide additional natural illumination.
The vegetated roof on the concrete dome of the mat section blends this part of the building into the site’s landscape on the northern and eastern edges, minimizing the facility’s visual obtrusiveness. The 12,000 m² roof—one of the largest “green” roof projects on the East Coast—features two layers of a rubberized asphalt waterproofing membrane manufactured by the Henry Company, of El Segundo, California, that help the vegetated roof adhere to the concrete dome, along with a 15 mil (0.38 mm) layer of polyethylene designed to prevent the roots from growing down into the concrete. The roof also includes filter fabric, various layers of primer, and a 102 mm layer of extruded polystyrene insulation that is ribbed at the bottom to promote drainage. Approximately 150 mm of soil low in organic content supports fleshy herbs of the genus Sedum.
The vegetated roof confers many advantages. Besides offering better insulation and protecting the roof membrane, it filters and limits rainwater runoff and reduces the heat island effect.
The lowest level of the bar section is a 1,200 m² room that contains the equipment for processing the raw data received from NOAA’s satellites. The next level is the main launch control center for the facility—an 18 by 54 m column-free, double-height space that gives technicians anywhere within the room an unobstructed view of a large wall of video screens used to track satellite launches and operations. The need for interior columns was eliminated by using five posttensioned beams that span 18 m in crossing the roof. The launch control center also features a small observation area for visitors on the partial third level that overlooks the satellite operations area.
On the roof of the bar section, the facility’s 16 antenna dishes—ranging in diameter from 1 to 9.1 m—are supported on a three-dimensional galvanized space frame truss of tubular steel that extends approximately 25 m beyond the north and south facades of the bar. The truss is triangular in cross section and 8 m in depth. The triangular shape provides resistance to lateral loads—mostly wind—and helps the ends of the truss resist lateral movements and rotation. The steel frames are rigidly connected to the concrete structure at one end by steel plates and reinforcing steel that were embedded into the concrete structure. Truss members were then welded to the steel plates with full penetration welds.
A pair of A-frame structures—one located approximately 10 m back from each end of the truss—provide vertical support for the truss’s gravity loads. Each A-frame is approximately 20 m tall, and its inclined columns are approximately 9 m apart at the bottom. Each column is set in its own pad footing foundation.
Two additional platforms elevated above the main deck at the north end of the truss provide space for antennas with particularly broad sight line requirements.
Placing the antennas on top of the bar section of the building obviated the need for large and costly antenna farms elsewhere at the site, to say nothing of the access roads, power lines, fencing, and other infrastructure that would have been needed for such farms. However, placing the satellite dishes on the roof did impose a strict movement criterion on the building structure in that the antennas would have to be able to track the orbits of various satellites in geosynchronous orbit. The controlling requirement focused on the rotational stiffness of the supporting structures. A system of nine shear walls—each approximately 250 mm thick and for the most part adjacent to stair and elevator cores to avoid loss of usable space—impart the necessary stiffness to the concrete structure. The concrete structure also provides a good deal of stability to the steel space frame, the design of which would have proved very inefficient otherwise.
The roof structure of the bar section was reinforced to sustain the loads of the largest satellite dishes, which are required to resist winds of up to 193 km/h.
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As visual testimony to the role that the new building plays in monitoring the earth’s environment, the mat section links the facility to the ground while the bar section’s dish antennas scan the skies. The bar’s roof structure was reinforced to sustain the loads of the largest satellite dishes, which are required to resist wind loads of up to 193 km/h. |
Another unique aspect of the project is a steel-framed ramp that projects out of the east side of the building at the roof level to provide maintenance access to the antennas. The ramp is a 2.5 m wide steel grate walking surface that cantilevers 7.5 m from the building face before doubling back on itself. Designed to accommodate maintenance equipment, the ramp takes the place of a freight elevator and provides the necessary space on the active roof surface for maintenance work.
The architects’ vision for the building featured exposed concrete throughout the structure. The concrete would be visible in the exposed circular cross sections of the columns, the exposed beam ends, and the undersides of many of the concrete floors, especially the dramatic curve of the mat section’s roof slab. Other predominantly exposed elements include the main access point to the building—a ramp 2 m wide and 40 m long that gives the appearance of a floating walkway because it cantilevers from a beam—and an exposed curvilinear concrete parapet that cantilevers 3 m from the south edge of the mat section’s roof, tapering to a thin edge.
As a final touch, a series of 10 long scrims adorned with satellite images of the earth’s surface and arranged in both north–south and east–west alignments hang from the mat section’s ceiling over the open work spaces, providing a visual reminder of the new facility’s role in environmental stewardship.
Frank S. Malits, P.E., M.ASCE, is a principal of Cagley & Associates, Inc., Rockville, Maryland.
Project Credits
Owner: General Services Administration, Washington, D.C.
Occupant: National Oceanic and Atmospheric Administration
Architecture: Joint venture of Morphosis, Los Angeles, and Einhorn Yaffee Prescott Architecture & Engineering, P.C., Washington, D.C.
Structural engineer of record: Cagley & Associates, Inc., Rockville, Maryland
Structural engineer (concept design): Arup, Los Angeles
Geotechnical engineer: Schnabel Engineering, Gaithersburg, Maryland
General contractor: P.J. Dick, Pittsburgh