Building’s Facade Hides a Bomb-Resistant Design

In a town that boasts the country’s most eclectic urban architecture, the newest monument comes not from a creative casino but from the button-down federal government: a building designed to stand up to a terrorist bombing.

It’s the new federal courthouse--an eight-story building that officials say would have survived an attack like the 1995 bombing that destroyed the Alfred P. Murrah Federal Building in Oklahoma City, killing 168 people.

Determined to avoid an inhospitable concrete design that would project fear and hostility to the public, builders instead created a $97-million courthouse that looks nothing like a fortress. In fact, it appears almost vulnerable, with extensive use of glass and a skylight-topped rotunda entry.

Looks, the builders say, are deceiving.

Set to open July 15, the courthouse is the first to be designed and constructed by the federal government incorporating architectural guidelines on blast resistance adopted after the Oklahoma City bombing.

Most of the safety features are all but invisible to passersby.

The floor slabs, for instance, are fastened to support beams so they won’t fall down--or be blown upward--in a blast. That design feature reflects what structural engineers learned after the 1994 Northridge earthquake, in which buildings were suddenly thrust upward.

Interior support columns are constructed so that if one collapses in an explosion, others will not follow like dominoes, as in the Oklahoma City tragedy.

Landscaping elements and exterior design treatments--including concrete planter boxes, stairs and other concrete barriers--will prevent explosives-laden vehicles from parking near the building, which sits on Las Vegas Boulevard between Bridger and Clark avenues.

But the most important feature of the new-generation structure, engineers say, is its exterior shell.

Because modern high-rise buildings are supported by their interior steel frameworks, rather than by exterior walls, those outside facades are actually little more than sidings of aluminum and window glass attached to the floor slabs.

These so-called curtain walls are designed to protect the building’s occupants from the outside elements: wind, rain and extreme temperatures. The curtain walls of high-rises in some areas, such as the Florida coast, are stronger to better withstand hurricane-force winds.

But until now, curtain walls have not been designed to absorb the concussion, wind and flying debris caused by a bomb blast.

That changed when the General Services Administration examined what happened in Oklahoma City and drafted new construction criteria on blast resistance. Overseas embassy buildings are constructed to different security standards developed by the State Department.

The Las Vegas courthouse, approved by Congress in 1996, is the first to incorporate the GSA’s new anti-blast design standards. Nearly $5 million of the construction cost reflects the new security measures.

The government did not tell prospective contractors how to build the structure, but simply required that it be able to protect occupants from a terrorist’s bomb. Just how large a blast the building can withstand is secret, said Mary Filippini, a GSA spokeswoman in San Francisco.

To meet the new requirements, contractor J.A. Jones Construction of Charlotte, N.C., hired Harmon Ltd., a Minneapolis-based company specializing in curtain wall design and construction.

Working with the GSA’s blast consultants and others, Harmon engineers improved upon existing designs to construct a curtain wall so effective that it surprised doubters, officials said.

The curtain wall is anchored to the building’s framework more effectively than in other structures. It also is thicker--12 inches, instead of the more common 6 or 8 inches--because of extra aluminum reinforcement.

Part of the curtain wall is what appear to be ordinary glass windows. But they are made of multiple layers of glass attached to a clear laminate membrane, designed so that the glass will shatter but not fly off in an explosion. The windows are held in aluminum framing backed by channels and tubes designed to bend in a blast, but not to be blown away altogether.

Some of the courthouse facade features conventional precast concrete panels, which also are blast resistant but allow the use of smaller windows only. The government shied away from an entirely concrete exterior to avoid a forbidding appearance.

“Normally, people contemplate a bunker-type fortress--a lot of concrete with small windows--when they want to protect occupants” from blasts, said Bob Smilowitz, a structural engineer hired by the GSA. The use of a relatively lightweight curtain wall may seem counterintuitive, he said, but it is designed to absorb a blast and protect the structure--and people--within.

Prototypes of the new curtain wall were subjected to blasts at the government’s White Sands Missile Range in New Mexico, and they survived beyond expectations, said Smilowitz and the GSA’s Filippini.

“It was pretty phenomenal,” she said. “The computer told us it would work, but when we tested full-size panels by actually trying to blow them up, they came through very well.

“I won’t say how large the blast was, but it was at least as large as the Oklahoma City blast,” Filippini said. “We feel very comfortable in saying that if this curtain wall was used in Oklahoma City, it wouldn’t have been damaged the way it was.”

Engineers say they were pleased that they were able to incorporate blast resistance in the building without compromising its aesthetics.

“Large expanses of concrete are very successful from a protective standpoint, but obviously they say a few things about the perception of threat--that we’re building bunkers and kowtowing to potential terroristic threats,” said Kevin Cole, manager of design at Harmon Ltd.

The building will house 10 courtrooms, as well as offices for the U.S. attorney, Nevada’s congressional delegation and other federal officials.

Some tenants said they were upset that the GSA was touting the new building as blast-resistant, for fear it would draw attention to the facility.

Terrorism aside, others said the courthouse is a welcome addition to downtown Las Vegas. “It’s a beautiful structure that will enhance and revitalize the downtown community,” said Chief U.S. District Judge Howard McKibben. “We’re looking forward to occupying it.”