When a concrete slab in Pittsburgh's David L. Lawrence Convention Center collapsed on Feb. 5, the results were alarming, but not serious or lasting. A break in a support beam for the second floor loading dock caused a 6-inch-thick, 30-foot-by-60-foot section to fall into the road and walkway at Tenth Street, which cuts through the Rafael Viñoly building and provides access at ground level. No injuries were reported.

The convention center was the result of a 1998 competition. It opened in phases in 2002 and 2003. A civic showcase for the city, it has had prior structural troubles. In 2002, a truss collapsed during construction, killing one worker. The collapse was attributed to incorrect bolts that were insufficiently tightened.

The Sports & Exhibition Authority (SEA), the city-county joint authority that owns the building, hired the Cleveland office of engineers Wiss, Janney, Elstner Associates to investigate the slab collapse and Leslie E. Robertson Associates of New York to review design and construction. Studies determined that the failure occurred in cold temperatures when an expansion joint seized. A contracting beam then pulled its L-shaped connectors away from the adjoining girder, causing a weld to fail, resulting in the collapse.

Illustrations show (left to right) the X-9 expansion joint, where the failure occurred; the movement of the beam, which caused the slab to collapse; and the repair solution.

Illustrations show (left to right) the X-9 expansion joint, where the failure occurred; the movement of the beam, which caused the slab to collapse; and the repair solution.

Credit: Rafael Vinoly Architects

As a fix, contractors welded 1-foot-square steel seats with Teflon pads underneath the joints of the replacement beam and 25 others, a structural design element indicated in early drawings but never executed. At a March 6 Allegheny County Council meeting, SEA executive director Mary Conturo said a further investigation would determine why the seats were not installed originally.

The repairs were completed in time for the March 9 opening of the popular annual Home & Garden Show. County Executive Dan Onorato and Pittsburgh Mayor Luke Ravenstahl appeared at the convention center in person and in a local blitz of TV commercials to assure the public of the building's safety.