THE MAGAZINE

Building Designs Cope with Threats

By Robert Elliott

Architectural design changes to high-rise buildings sparked by the 9-11 attack on the Twin Towers and the 1995 Oklahoma City bombing of the Murrah Federal Building are slowly finding their way into commercial buildings and government facilities.

Public and private buildings will have no choice but to comply with building modifications in locations where municipal governments adapt federal codes, as has already occurred in New York City. But improvements are still voluntary in most cities.

Today, commercial building tenants and owners are especially concerned about underground garages being open to the public, says Eve Hinman, president and cofounder of Hinman Consulting Engineers. “In the event of an explosion in an underground garage, the whole building could come down.” Hinman says building owners are beefing up the columns in their garages and instituting various levels of perimeter protection, such as access control.

Some low-cost changes that don’t quite rise to the level of design changes also help to minimize the potential for damage in the case of an explosion. One practice that is being widely adopted is covering windows with antishatter film that holds the glass together, preventing shards from exploding and harming occupants. Another “defensive architecture” method is the use of antiram barriers around buildings, but these must have a sufficient setback zone, which isn’t always possible in cities.

High-risk buildings—such as courthouses, FBI field offices, and security operations centers that are mobilized during emergencies—are undergoing more extensive upgrades to their structures. Slab and wall systems are being overhauled with fiber-reinforced polymers, a film that prevents shrapnel from raining down after an explosion. Also, columns are being fortified.

Federal requirements for blast resistance have created an incentive for businesses to develop new options, and the result is a rash of groundbreaking materials. “There is a tremendous amount of innovation occurring, where new blast-resistant materials and products are coming onto the market,” says Hinman.

Whereas a decade ago pour-in-place reinforced concrete of bunker-like design was de rigueur, the commercial sector is now being catered to with lightweight building envelopes that can also withstand explosions, she notes.

New federal structures also feature lobby pavilions that are segregated so that screening occurs away from the main building. Parking is restricted around the buildings, with only authorized personnel allowed to park in lots beneath the structures. Parking areas around these buildings have minimum setback requirements.

Another modification that arises from the lessons of 9-11 is fireproofing, which has been improved so that it adheres to the structure longer, says Jeffrey Garrett, a senior engineer at the Chicago-based CTL Group. The fireproofing used on the World Trade Center’s structural surfaces peeled off under the heat sooner than expected when the fires erupted, according to the forensic evidence. Another change is the move to wider stairwells to facilitate mass evacuation. Additionally, the structure around stairways and entranceways have been strengthened.

An all-hazards approach encompassing terrorist attacks and natural disasters is on the horizon for building designers. Currently there are teams made up of nonengineers who walk around buildings and assess the likelihood of damage during an earthquake. This “rapid visual screening” approach is being adopted by FEMA and the American Society of Civil Engineers for antiterrorist design as well, says Hinman. “They are taking the model for sustainability requirements and applying it to antiterrorism,” she says.

Buildings in the future will be rated for security, with the three categories being gold, bronze, and platinum. “These things aren’t out in the street yet, but next year they are going to start to appear,” says Hinman.

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