AP Area beneath partial slab collapse in convention center.

Investigators, including members of the original design and construction team, are trying to determine why a 60 x 20-ft section of a 6-in-thick concrete floor slab collapsed at the nearly five-year-old David L. Lawrence Convention Center, in Pittsburgh. Although the cause is not yet known, investigators are focusing on how rapidly falling temperatures may have affected an expansion joint. No injuries were reported as a result of the Feb. 5 incident.

The break in the slab occurred in the second-floor loading dock, outside the footprint of the exhibit halls and above an underpass and the main entry thoroughfare—where the building straddles Tenth Street. The collapsed section of slab held a trailer-truck, which was unloading for a now-cancelled auto show.

The project’s construction manager—a joint venture of Turner/P.J. Dick/Advanced Technology Systems Inc.—is actively working with the public owner, the local Sports & Exhibition Authority and others to investigate and determine the cause of the collapse, says a spokeswoman for Turner Construction Co. According to the engineer-of-record, Joe Goldreich of New York City-based Goldreich Engineering, Tim Macfarlane of the job’s New York City-based structural consultant, Dewhurst Macfarlane and Partners Inc., was on site investigating on Feb. 8. Shortly after Monday’s collapse, said Mary Conturo, executive director of Pittsburgh’s Sports and Exhibition Authority, the team also includes representatives of Viñoly’s office and steel contractor ADF Group. Their early efforts are focusing on an expansion joint in the area above where caissons shifted in 2001.

Allegheny County chief executive Dan Onorato attributed the failure to “a major mistake that was made somewhere.” Joining with Pittsburgh’s mayor, Luke Ravenstahl, he insisted on an outside review.

In response, the sports authority hired structural consultant, Wiss, Janney, Elstner Associates Inc., Cleveland, to help in the investigation. The New York City-based structural firm Leslie E. Robertson Associates will also be reviewing the work of the convention center’s designers and construction team. The building will be closed for at least a week pending their findings and recommendations.

Designed by Rafael Viñoly Architects, New York City, following a 1998 competition, the center opened in phases between 2002 and 2003. Its central masts and suspended roof took inspiration from nearby bridges to create open, day-lit convention halls offering city and river views.

The slab collapse is only the latest mishap in the building’s troubled history. In addition to shifting caissons that required unexpected repairs in November 2001, a 90-ton truss collapsed on Feb. 12, 2002, killing ironworker Paul Corsi Jr. and injuring two other workers . The fatal collapse occurred just before the first section of the convention center was slated to open. The following November, cracks appeared in the slab. They were eventually deemed cosmetic.

The fatal truss collapse was eventually pinned on improper bolts used to fasten truss pieces. “The failures at every level of this project were so blatant and overwhelming that…errors and omissions on the part of Dick Corp. more than rise to the level of recklessness and grossly negligent conduct” under state law, said the report by Allegheny County Coroner Cyril H. Wecht and Michael C. George, presiding inquest attorney. A year after the Wecht had recommended that local prosecutors lodge a homicide charge against the employer most directly connected the fatal accident, Pittsburgh-based Dick Corp., District Attorney Stephen Zappala announced there wasn't enough evidence to charge the firm. Zappala also publicly criticized jobsite ironworkers, in addition to project firms.

This is the second major Viñoly building to experience difficulties in the last few years. After Philadelphia’s Kimmel Center for the Performing Arts opened late and over budget in 2001, Philadelphia sued, alleging negligence. The architect reached an out-of-court settlement last winter; neither it nor the city admitted liability or fault.