Out with a Bang

Old Washington Convention Center imploded

By Bruce Buckley

In the first implosion attempted in the District in nearly 30 years, the 800,000-sq.-ft. Washington Convention Center was taken down in a matter of seconds.

After hosting more than 1,500 major conventions during its 20-year existence, the old Washington Convention Center went out with a bang Dec. 18.

In a spectacle that brought down the house, the 800,000-sq.-ft. structure was imploded - the first such demolition attempted in the District in nearly 30 years.

At a project cost of $6.7 million, the implosion not only saved the Washington Convention Center Authority nearly $1 million compared to conventional demolition methods, it also mitigated onsite risks, said Terry Anderson, executive vice president of Wrecking Corp. of America in Alexandria, Va.

"It was safer in terms of not having to put employees up there to do high steel burning," Anderson said. "This way, our guys can do all the work within the safety of an excavator."

Goel Construction Services of Washington, D.C., was the general contractor on the project; Wrecking Corp. served as the demolition contractor; and Demolition Dynamics of Cincinnati, Ohio, was the implosion contractor.

The convention center covers nearly four city blocks, bordered by Ninth St. NW, 11 St. NW, H St. NW and New York Ave. City officials and neighboring business owners watched the implosion from across Mt. Vernon Square inside the new Washington Convention Center, which opened in 2003.

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Tough sell

While the implosion saved the WCCA some money, it didn't save it much time. Getting the proper permits and approvals was no easy task in a city that hadn't allowed an implosion since a 10-story parking garage was brought down in 1974. In addition to working with the city, the team had to allay the concerns of the convention center's neighbors, including the U.S. Secret Service, the U.S. Mint and two major hotels.

"We're in a post Sept. 11 era here, and to take a process that most people aren't familiar with or have only been exposed to via Vegas-style implosions on the Learning Channel, and say that we are going to do this in the city's central business district, that doesn't sit well with some people," Anderson said.

After nearly three months of negotiations, all permits were finalized in mid-November and the team began to prepare the site for implosion. Part of the preparation included gutting as much material from inside the convention center as possible to reduce the levels of dust that could be produced by the implosion.

Schedules were tight because of the extensive coordination required with city agencies. The Dec. 18 date was chosen so the event wouldn't conflict with the holidays or the presidential inauguration ceremonies.

Meanwhile, the team fine-tuned the implosion sequence to figure out how to bring down a large structure packed with heavy steel without damaging neighboring structures. The convention center was built as three two-level structures - Halls A, B and C. The lower level featured concrete framing of about 20 ft. in height, which supported a waffle-pan deck with 250- to 400-lb. loads.

The next level was a steel-truss roof system. Hall A was one of the most daunting challenges because of its veriendeel roof with open spans of 250 to 270 ft. The flanges on that steel were up to 4 in. thick, Anderson said.

"This is some of the heaviest stuff that's ever been shot with shape charges," Anderson said.

The main goal was to drop the steel-truss roof so that it would lie on the concrete slab below and be removed later by excavators, Anderson said.

Ready, aim, fire

The 12-second-long implosion sequence included 400 separate delays set milliseconds apart from each other. During that time, nearly 500 columns set with explosives were shot out, bringing the entire building down like a carefully choreographed domino display.

"You don't want the entire building hitting the ground at once," Anderson said. "The idea is to get one part of the building moving first, then radiate out from there."

The initial blasts began between Hall A and Hall B then moved outward, leaving Hall C as the last to go. Concrete columns, which had been drilled out and filled with a nitroglycerine-based explosive, were shot out first to bring down the floor. By doing so, Anderson said it creates a mattress effect for the upper steel columns to land on.

Milliseconds later, shape charges sliced the steel columns. Shape charges are used specifically for cutting steel in half. They were originally designed by NASA to cut away the metal stages of early rockets during takeoff sequences.

Kicker charges, set on the side of the steel, pushed apart the split columns so they would collapse. As the steel fell, so did the roof, then the walls folded in toward the center of the structure. Anderson said the team attached .75-in. steel cables between the walls and floors at a 45-degree angle to ensure that the walls would fold inward and not out.

Within seconds of the final charge, the last pieces of the old convention center fell to earth. All combined, the rubble included 10,000 tons of steel and 50,000 cu. yd. of concrete and masonry.

Implosion instinct

The process was precise, but Anderson admits that it's not an exact science.

"There are no computer models that can tell you exactly what will happen," he added. "Experience is the only way to anticipate the results you'll get."

Although the vast majority of the structure collapsed, the south wall was intentionally left standing because of its close proximity to neighboring buildings. That wall will be brought down this spring by conventional demolition methods. The project is scheduled for completion in June.

About 90 percent of the structure will be recycled. The steel will be hauled away and the concrete will be crushed onsite to help create a subbase for a parking lot on the site. The site will remain a parking lot until the city determines how the it will be developed in the future.

A few other sections of walls that were intended to fall remained standing after the implosion. The added effort to bring those sections down may weigh on the schedule, but P.K. Goel, president of Goel Construction Services, said it's a small price to pay.

"The trade-off is that the more explosive you use to make sure everything comes down, the more likely you are to damage things," Goel said. "We're a bit disappointed, but by the same token it's better than taking the risk."

Anderson said that approximately two dozen windows of neighboring structures were damaged by the implosion and will be replaced - a small price compared to the overall project savings.

"If we broke a few windows and that's the sum total of the damage, that's not too bad," he added. "Implosion jobs are a wild ride. You get most of what you're looking for, but not necessarily 100 percent. This is a job where the whole is greater than the sum of its parts."

Anatomy of an Implosion