Wrecking Corp of America recently completed demolition and excavation work at the Tysons Corner site of Liberty Crossing, the former home of Nextel, a 256,000-square-foot, 10-story post-tensioned building in McLean, Virginia. The building owner was Peterson Companies, and the general contractor was Clark Construction Group of Bethesda, Maryland.

"Post-tensioning is a method of concrete reinforcement using steel cables (tendons) that are tensioned after the concrete hardens," said Terry Anderson, executive vice president of Wrecking Corp. "Since post-tensioning has only been in use since the 1970's, very few post-tensioned buildings have been razed. Wrecking Corp has razed six post-tensioned buildings in the last few years. We feel that we have more experience than most in razing this type of structure, but each one has reacted differently during the razing process, so there is no room for complacency when working with post-tensioning."

"These buildings present a unique challenge to the demolition industry," Anderson said, "because they have the potential for a sequential collapse once some of the tendons are de-tensioned. In addition, the steel cables are dangerous because of their rubber-band-like quality; they also are difficult to process for recycling."

The Liberty Crossing project also included excavation of 100,000 cubic yards of soil and backfill of 20,000 cubic yards on site. The project was completed in six months.