“The photos are hauntingly similar,’’ said Steven J. Smith, the Washington, D.C.-area based vice president of CTLGroup, an engineering firm hired to review the Tropicana collapse as well as the 2007 collapse of the I-35W Mississippi River Bridge in Minneapolis, Minn.
OSHA investigators eventually blamed contractors’ failure to provide adequate temporary shoring support while the concrete dried. They also concluded that steel reinforcements in the concrete were not properly attached to supporting columns, and said a last-minute design change might also have helped undermine the structural system. OSHA fined contractors and engineering inspectors on the job a total of $119,500.
The courts found the project contractor to be largely at fault. The case produced one of the largest awards in U.S. construction industry, topping $100 million.
In the Miami Dade building, Smith noted, a south-side wall consisting of columns and horizontal girders remained standing “and looks reasonably intact,’’ but the garage floors appear to have separated from the wall and dropped away.
“That is what you would expect if there is a connection failure. In all structures where there is a failure, one of the first places we look to are the connections, the joints. That’s going to get scrutinized first.’’
Miami-Dade County’s veteran building director, Charles Danger, concurred. Speaking conjecturally, Danger said a garage floor at or near the top of the building could have fallen, striking and taking down the rest of the structure beneath it. Another possibility, he said, is that a crane operator could have hit a portion of the structure while installing a floor slab.
“The whole section went like a domino,’’ said Danger.
It could not be determined how much of the section that collapsed had been permanently tied together. Typically, the structure is held in place by its own weight, though temporarily braced or shored up with wires or cables, as it is assembled. Completed floors or sections are welded or bolted together, with the joints often also covered with concrete, but the bracing is supposed to stay in place until inspections are concluded, Santos said.
The still-standing but separated south wall from which the floor slabs fell away was wrapped in cables suspended from the arm of a large crane on Thursday. Byrne, the contractor, said that was the same position it was in when the collapse occurred.
Another question, Danger said, is how good the checks and balances on the job were. To ensure a building project’s integrity, an independent “threshold’’ engineering inspector is hired — typically not by the contractor but by the design team or the building owner — to verify that proper procedures are being followed. Investigators may look at whether the permitting and inspection process carried out by the college was adequate, Smith said.
Byrne, the contractor, said Thursday he did not know what work was going on at the time of the collapse, nor whether the threshold inspector was on site.
Another potential source of trouble could be the plans for the garage, Smith said. Even when the design is solid, plans can sometimes be unclear or incomplete. It’s the contractor’s responsibility to get designers to clarify the plans. But in the Tropicana garage incident in New Jersey, Smith said, the contractor failed to do so, another contributing element to the collapse.
Smith said having the college essentially regulate its own building system is unusual, though Santos said other public institutions across the country do so.
“If there is something in the system here that is not functioning as it should, it will come to light as part of the investigation,’’ Smith said.