An 11-story office tower in Dallas, Texas was set to be brought down in a controlled demolition on Feb. 16, but while implosion dropped the outer shell of the building, it failed to bring down the structure's concrete core. 

Almost two weeks later the slightly tilted core remains standing, and work continues on bringing it down. The demolition contractor, Dallas-based Lloyd D. Nabors Demolition, has said that it has a multistep plan in place to bring the rest of the building down using a combination of an wrecking ball on a crane to demolish the upper structure and a high-reach excavator to knock down the rest of the core.

The former Affiliated Computer Services building consisted of a concrete core and precast concrete elements along the perimeter, with beams spanning in between. The central core, where the elevators and staircases were located, was stronger than the perimeter elements of the building, which came down as planned. The tower is being demolished as part of a $2.5 billion mixed-used redevelopment effort led by Dallas-based De La Vega Development. In the days since the tower's failed implosion, onlookers have gathered to take photos in front of the 'Leaning Tower of Dallas.'

Different types of structural systems often require different demolition approaches to bring them down, but the concrete core of the Dallas tower was not particularly unusual in its design. Yet as various eras of building design age out and are demolished, different techniques will be needed to safely demolish them, says Mark Loizeaux, president of Controlled Demolition, Inc.

Loizeaux’s company was was not involved in this particular Dallas tower demolition, but CDI has demolished structures of a similar design and vintage in the past. “Like in construction, demolition contractors and their clients have to be sensitive to the nature of the structures that are being demolished. As time passes, new and different types of construction are being brought up for demolition, and attention has to be paid to those different systems when designing demolition, by conventional or explosive means,” Loizeaux tells ENR. 

In the case of the ‘Leaning Tower of Dallas,' Loizeaux declined to comment on what might have specifically gone wrong in the demolition of the building’s core. But he does add that “in this case, it may be that the developer or contractor didn’t pay attention to the type of construction, and certainly the developer might have been more thoughtful in considering if the contractor had experience in demolishing this type of structure.”