Federal Building is Secure and Sustainable
Transparency and security are not necessarily compatible qualities in a government building, but the U.S. General Services Administration says the two have been successfully merged at the new Oklahoma City (Okla.) Federal Office Building. The 181,000-sf facility, dedicated in May, replaces the Alfred P. Murrah Federal Office Building, which was destroyed by a bomb that took 168 lives on April 19, 1995.
Carol Ross Barney, FAIA, president of the building's Chicago-based architects, Ross Barney + Jankowski Architects, says she always considers security as one of a number of important design requirements, adding that this subject is currently in the spotlight because it didn't get much attention until recent years.
Ross Barney is pleased that Oklahoma City's new Federal office building projects what she hoped would be a "strong, but not fortress-like" appearance. Edward Feiner, FAIA, GSA's chief architect, says Ross Barney's design "demonstrated a sensitivity to public architecture and getting the biggest results from a limited budget." He says GSA's goal was a building that is, "to the greatest extent possible, transparent, open and accessible to the public."
GSA wanted a forward-looking building that would address numerous issues — including sustainability and urban design — as part of an overall design program. The building's three-story height was influenced more by compatibility with neighboring structures than by security considerations, Feiner says.
The Oklahoma City Federal Office Building nevertheless incorporates Federal guidelines for blast resistance that were adopted in 1997, according to Robert Smilowitz, a principal with blast consultant Weidlinger Associates, New York. At the time of the 9/11 terrorist attacks, the design was nearly completed, and no security-related modifications were required.
The north side of the new Federal Office Building is its most open elevation. Its 61-foot-high curtain wall (with special security glazing) faces into the courtyard. A colonnade adds a touch of classical Federal architecture.
Smilowitz says the guidelines cover four basic principles: 1) establish a perimeter to create maximum available standoff distance; 2) prevent progressive collapse by providing redundancy that will redistribute structural forces should a perimeter column or wall section fail; 3) limit the amount of injury-producing blast debris; and 4) provide interior partitions that protect occupied spaces from explosive force.
The windows of the Oklahoma City building are fitted with insulated glazing units consisting of an exterior pane of heat-strengthened glass, a ½-inch air space, and an inner pane of laminated glass. Steel angles, bonded with structural silicone adhesive to the interior panes, secure the glazing units to steel tubes of the curtain wall framing and steel window frames. In the event of an explosion, this assembly is designed to allow the glass to push inward and transfer vibrations to the concrete building frame.
"Given the pressure pulse specified by the [GSA] criteria, we selected glass that, if adequately restrained, would provide a low hazard for building occupants," Smilowitz says.
All the building's exterior walls are at least 50 feet away from the four adjacent streets. The building is also more than 100 feet from its designated surface parking lot.
The lobby's concrete walls are designed to compartmentalize blasts produced by an explosive device that might be detonated before it is passed through a screening area just off the lobby.
An adjoining curved thick steel plate, anchored to top and bottom floor slabs to prevent transfer of blast loads to columns and other load-bearing elements, separates the elevator lobby from the screening area.
This combination of features enables visitors and staff to pass directly through the lobby without being subjected to a screening process. A secure lobby on the west side serves as a military entrance processing station. All other building access is via the east elevators or stairway.
When GSA blast-tested a curtain wall mock-up for the Las Vegas Federal office building, completed in 2000, metal sunscreens became projectiles. As a result, the Oklahoma City building has horizontal nylon mesh sunscreens. Vertical sunscreens are fiber-reinforced translucent plastic with an aluminum frame.
Sustainability is another keynote of the Oklahoma City Federal Office Building, which GSA plans to submit to the U.S. Green Building Council for LEED Silver certification.
The building's 61-foot-high, north-facing curtain wall maximizes the entry of natural light. The exterior sunscreens, installed 8 feet above each floor level, act as light shelves that beam natural light to 11-foot-high ceilings. Office workstations are located no further than 59 feet from a window.
Steel-framed corridor bridges that pass across the 40-foot-high lobby at the second-and third-floor levels have laminated glass floor planks and balusters that allow natural light to reach lower levels.
An underfloor air distribution system delivers conditioned air at a low velocity. It creates a tempered air zone extending to six feet above the floor, thereby reducing heating and cooling costs. The system also helps to maximize the comfort of building occupants. Registers in the raised access floor can be relocated; slats in the registers allow airflow to be directed either upward or sideways.
Landscaping utilizes native prairie grasses and drought-resistant plants, such as redbud and honey locust trees, that require minimal maintenance, according to Stuart Dawson, a principal with the project's landscape architect, Sasaki Associates, Watertown, Mass.
Landscape design is often the "frosting on the cake" that gets attention only after construction has begun, Dawson says. But for this project, Sasaki was chosen along with the architect and was able to provide early input to the design. For example, light fixtures and other streetscape items can serve as security barriers if properly integrated into the landscape plan, according to Dawson.
Keeping it simple
The building's simple palette of materials consists essentially of concrete, steel, glass, and rock. "All the finishes are honest and real materials," says James Reynolds, project manager for associate architect The Benham Companies, Oklahoma City. Ross Barney adds: "We decided we could make a beautiful building with exposed concrete." Joint lines of the plywood forms used to construct the foot-thick exterior walls are expressed. Ross Barney says she also finds beauty in the galvanized steel curtain wall framing that is exposed on the interior.
Two colonnades incorporated into the building design recall classical Federal architecture. One is at the southeast corner of the building, where the glass façade angles back to make room for the entrance staircase. The other extends across the courtyard on the north side of the building.
The elliptical shape of the courtyard — a carving out of the building's basic linear plan — was inspired by the ceremonial dance space that is a tradition of Oklahoma's five major Native American tribes.
A landscape sculpture by Dallas artist Brad Goldberg highlights the outdoor courtyard of the new Oklahoma City Federal Office Building, which combines both sustainable and security features. Goldberg calls the rocks a metaphor for the resilience that Oklahomans demonstrated after the Murrah tragedy.
Dallas artist Brad Goldberg created a landscape sculpture for the courtyard by using 1,000 tons of rock. River rock and granite boulders are arranged, in ascending order of size, over an 80×300-foot area. Water flowing over the rocks provides a tranquil setting. Goldberg says the rocks are a metaphor for the resilience that Oklahomans demonstrated after the Murrah tragedy.
Access to the north side of the building is at grade. The south-facing front entrance is accessed from the east by a 17-stair monumental stairway with risers that are only 4½–5 inches high, or from the west by a ramp. The concrete wall bordering the stairway and the ramp provides the additional benefit of making the building more resistant to terrorist attacks. A 15-foot elevation change occurs across the site.
From three buildings to one
A three-block site was initially envisioned for an Oklahoma City Federal complex. The plan was scaled back to two blocks when GSA was unable to purchase property at what it considered a reasonable cost. The original plan called for three 50,000-sf buildings. Citing the difficulty of efficiently planning office buildings of that size, Ross Barney is not disappointed with the revised scheme.
A grassy, tree-lined park occupies the block north of the building, extending the landscaping features adjacent to the building.
GSA's Feiner says the new building was a "commitment" project to demonstrate that terrorism would not deter a Federal presence in the community. Within three months of the attack, Congress appropriated $40 million for the replacement building. Feiner characterized the $34.3 million construction cost as "right in the ball park" for a Federal building of comparable size.
GSA will perform a post-occupancy evaluation after the building has been in service at least 18 months to determine, in particular, the contribution of its environment-related features to worker satisfaction and productivity.
The building's exterior wall is essentially a load-bearing element, meaning that its susceptibility to progressive collapse must be addressed across the entire façade rather than only at column locations. For that reason, GSA would be less inclined to use this type of construction on other projects, Feiner says.
In addition to its built-in security features, a further comfort for those who work in the building is that the FBI and other "at risk" agencies formerly housed in the Murrah Building are now in other locations. The new building does not have a daycare center; 15 of the victims of the Murrah bombing were children in that building's daycare center.
The new building is one block north of the location of the Murrah building. The site is now a grassy area on which 168 unoccupied bronze and glass chairs, representing the blast victims, have been placed. The chairs are arranged in nine rows that correspond to the floor of the Murrah building on which the victims were housed.
On the opposite side of the street from the new building in the next block is the Journal-Record Building, which was extensively damaged by the bomb. It now houses the Oklahoma City Memorial Center Museum, which depicts the horror of the bombing by means of a self-guided tour. One of its most graphic exhibits is the rubble of a men's room left undisturbed as it appeared after the bombing — with jumbled blocks piled on the floor and disconnected pipes hanging randomly. This is a precursor to the admonition displayed for departing visitors: "May all who leave here know the impact of violence."