Architecture and Structural Security

Architecture and Structural Security


Buildings have always stood under the threat of physical attack, but until the advent of organized terrorism in the latter twentieth century, most structural dangers were limited to fires, natural disasters, and acts of war. Since the early 1970s, however, it has become increasingly apparent to authorities in the West that their physical structures are potential targets for terrorist actions, especially bombings, even during peacetime. Such concerns have given rise to efforts by architects, engineers, and planners, sometimes working closely with government security experts, to create structures designed to meet two differing, almost contradictory, needs: security on the one hand, usability and aesthetics on the other.

Bombings of the 1990s

Among the most notable terrorist bombings of buildings prior to 2001 was the assault on the United States Marine barracks in Beirut, Lebanon, in October 1983, followed a decade later by a string of bombings throughout the 1990s: the first attack on the World Trade Center (WTC) in February 1993; the explosion of the Alfred P. Murrah Federal Building in Oklahoma City in April 1995; the bombing of Khobar Towers in Dharran, Saudi Arabia, in June 1996; and the attack on the U.S. embassies in Kenya and Tanzania in August 1998.

Death tolls differed, from fewer than ten in the case of the first WTC incident to several hundred in the Marine barracks bombing 10 years earlier. And although most of these were perpetrated by Middle Eastern terrorists—albeit from differing groups that collectively represented the breadth of the Islamic fringe—Oklahoma City was an exception, the work of American extremists. Yet, each bombing was alike in terms of basic method: the use of a truck, driven alongside the building or beneath it, to deliver explosives.

The conflict between comfort and safety. In order to create structures that could withstand such an attack, designers must confront a classic dilemma of architecture and structural security articulated by Cheryl Kent in the New York Times. "At heart, the task involves what seems like a contradiction: designing a building that is secure from attack while affording the openness appropriate for a public building."

Prior to the 1970s, security was not the paramount consideration in architecture and therefore, comfort and the human touch remained preeminent considerations. Planners of the 1972 Olympic Village in Munich, Germany—wanting to avoid the appearance of an armed camp, with its potential evocations of Hitler and the 1936 Berlin Games—had created an open, friendly village that proved vulnerable to Palestinian terrorists. The subsequent assault by Black September left 11 Israeli athletes and one German policeman dead. Olympic officials learned from Munich and, thenceforth, greatly intensified the security measures surrounding the Games; likewise the planners of government buildings eventually learned from the terrorist attacks of the 1990s.

The Ronald Reagan building. The learning process was far from instantaneous, as illustrated by a look at the Ronald Reagan Building in Washington, D.C. It was completed in July 1997, a year after the Khobar Towers and a year before the Africa bombings. The first World Trade Center bombing and Oklahoma City were still fresh in memory as evidence that terrorism was no longer a phenomenon from which Americans on U.S. soil were exempt. Yet, a 1999 report by security experts at Sandia National Laboratories found that the building, which had run well over budget to finish at $818 million, was "highly vulnerable" to terrorist attack.

Several factors made the vulnerability of the Reagan Building particularly dismaying. There was its proximity to the White House and Capitol, combined with the large numbers of employees to be housed there. Additionally, it would serve as the headquarters of sensitive agencies such as the U.S. Customs Service, and the venue of high-security events such as the North Atlantic Treaty Organization 50th anniversary celebrations in April, 1999. Yet, the GSA, hoping to defray some of the costs by leasing space to the private sector for restaurants, shops, and convention facilities, had wanted to avoid creating a building that looked like an armed fortress.

The Oklahoma City Federal Campus. By contrast, a Chicago architectural firm managed to create a secure environmental—yet one that did not seem constricting to its inhabitants or visitors—in their design for Oklahoma City's Federal Campus. The new name was chosen to avoid any reference to "Federal Building," a term forever associated in local minds with the structure in Oklahoma City that had been destroyed, along with 168 people.

Design architects planned the site in such a way that, rather than lying hidden behind a protective plaza, the building fills the block on which it sits. This has the added benefit of addressing an aesthetic problem in the Oklahoma City downtown, which, like that of other sunbelt cities such as Atlanta or Houston, is pockmarked with empty lots. By building to the boundaries of the site, the Federal Campus conveys a sense of a populated environment that serves to invite traffic. Welcoming traffic was also apparently in the architects' considerations when they fought off security planners' attempts to close off streets around the building, a measure that might have kept away the public.

One of the few obvious signs of protective considerations in the design is the lack of glass in the outer perimeter of the Federal Campus. The building does have extensive glass areas, but these are inside the protected courtyard, and the glass itself is reinforced—rather like that of a car windshield—so that it would shatter rather than break in the face of concussive force. Walls on either side of the lobby are made to create a powerful aesthetic effect, while protecting office workers in the event of an explosion.

Designing and Protecting the Post-September 11, 2001, World

Ironically, in its September, 2001 issue, which went to press before the bombings, Signal reported that GSA was testing a risk assessment and property analysis software product called RAMPART as a means of determining buildings' vulnerabilities to terrorism. Designed at Sandia, RAMPART made it possible to study a number of threats, both natural and manmade, and allowed users to assess buildings with a point-and-click walk-through assessment tool that took less than two hours.

After the World Trade Center terrorist attack, the idea that such software could get into the wrong hands prompted a joint statement by the American Institute of Architects (AIA) and the GSA to immediately report any suspicious requests to the appropriate local FBI field office. Just as terrorists' strange requests at flight schools—e.g., their desire to learn how to fly a plane, but not how to land—should have, and in some cases did raise red flags, the AIA and GSA warned architects, engineers, and others concerning requests for intricately detailed plans of major buildings.

Months earlier, an AIA member firm had received several e-mail messages from an alleged student in Egypt who requested plans that would show extremely specific information about conduits, duct work, wiring, risers, and other aspects of a particular building. Acting with prescience (given that this was before September 11), the firm turned the requests over to the FBI. The wisdom of such measures became all the more apparent after the March, 2003, capture of Khalid Sheikh Mohammed, a high-ranking al Qaeda figure who revealed that plans were in the works for attacks on structures ranging from the White House and Israeli embassy in Washington, D.C. to bridges in Manhattan and the Sears Tower in Chicago.

In December, 2001, the FBI revealed that the World Trade Center terrorists might have actually used commercially available software to plot the destruction of the towers. Several hundred such programs were on the market at that time, although fewer than half a dozen would have been capable or portraying the effects of a plane crash in any detail.

Studying how the towers fell. During late 2001 and 2002, government and private investigators undertook studies to understand how a jetliner could have caused the collapse of the towers. Quickly, the investigators, including representatives of the American Society of Civil Engineers and the Federal Emergency Management Agency (FEMA), concluded that it was not the impact, but the heat from the burning jet fuel that weakened the steel. The National Institute of Standards and Technology (NIST), which later did its own study, found that the temperatures were not high enough to actually melt the steel, as had been originally assumed. The temperatures were sufficient however, to weaken the steel beams, which crumbled at the impact levels of the towers and, in turn, resulted in weight loads sufficient to crush the floors remaining below, resulting in the total collapse of the structures.

Those involved in the World trade Center site investigation also attributed part of the buildings' vulnerability to what had also been their strength, the use of exterior walls as support. In older skyscrapers such as the Empire State Building, support was at the building's core. This thicket of massive steel girders not only took up rentable interior space, but they had their structural shortcomings, including the fact that they did not prevent a building from swaying in the wind. In the WTC, the exterior columns were linked to the core with steel trusses that had been inadequately fireproofed in the building process. Surrounded only by light foam fireproofing and walled off with sheetrock rather than concrete, the trusses at the impact site were easily exposed by the twin plane crashes, leaving them vulnerable to melting or loss of integrity.

Building for the future. The GSA approved a wide range of designs in December, 2001, that seemed to have already taken into account the World Trade Center tragedy three months before. In fact, these were the result of the same post-Oklahoma City studies that yielded the Federal Campus earlier.

Among the $6 billion worth of projects released in a flurry of GSA approvals was a district courthouse for Miami. Unlike the Federal Campus, this building did sit back from the street, with the intervening space hosting an arboretum. Yet, the arboretum served a security purpose, and not only because it separated the building from the street. "Even if a truck got through the trees," architect Bernardo Fort-Brescia of Arquitectonica, the design firm, told the Wall Street Journal, "they would hit this undulating lawn. We've created an invisible barrier in the sense that it doesn't look like a wall."

Another courthouse, in Springfield, Massachusetts, solved the conflict of security versus aesthetics in a different fashion. Planners wanted local citizens to visit the courthouse frequently for community events, and if attendees had to pass through magnetometers and checkpoints upon entering, this would create a decidedly unfriendly environment. Instead, they separated the entry pavilion from the interior portion, with its security checkpoints hidden from view.

At the new headquarters for the Bureau of Alcohol, Tobacco, and Firearms (ATF) in Washington, designers had dealt with the problem of bollards, the stubby concrete posts that prevent vehicles from driving into buildings at street level. Although useful for security, they are typically far from pleasing visually, yet the architects of the ATF building managed to create bollards that were an exception to the rule. "Instead of looking like dragon's teeth," GSA commissioner for public buildings F. Joseph Moravec told the Journal, "there will be some really cool metal bollards. They'll have an antique, almost Edwardian look."

In at least one spot in Washington, D.C., the GSA's "post-9/11" design criteria had been implemented before the World Trade Center attacks. This was the Pentagon, where architects of a remodeling project had used new techniques and materials intended to ensure that, in the event of a devastating attack, the building section would collapse progressively, rather than in a heap. Architects had also used shatterproof glass and other materials because, as Moravec noted, "One of the terrible lessons of Oklahoma City was that when a bomb goes off near a building, it's not so much the blast that kills people. It's that the explosion creates flying elements, pieces of walls and glass that kill." In the remodeled portion of the Pentagon, "When the blast hit the wall, the wall itself didn't become a weapon. There's no question that the glass panels there saved a lot of lives."



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Dunlap, David W. "Architects Put on the Alert over Requests That Are Rare." New York Times. (October 4, 2001): B8.

Grant, Peter. "Plots and Ploys." Wall Street Journal. (December 26, 2001): B4.

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Watts, John M., Jr. "Our Changing World." Fire Technology 38, no. 2 (April 2002): 99–100.


Computer Modeling
FEMA (United States Federal Emergency Management Agency)
General Services Administration, United States
Kenya, Bombing of United States Embassy
Khobar Towers Bombing Incident
NIST (United States National Institute of Standards and Technology)
Sandia National Laboratories
September 11 Terrorist Attacks on the United States
World Trade Center, 1993 Terrorist Attack

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