Flawed Design, Lax Oversight Led to ‘Astounding’ Miami Bridge Collapse

MIAMI — The pedestrian bridge that collapsed over a busy Miami street last year, killing six people, was doomed by a fatal design flaw, federal authorities concluded in a scathing review on Tuesday. The errors led to unusually severe cracking in the concrete that should have worried engineers and prompted the closure of the roadway below for safety.

Instead, Southwest Eighth Street, an eight-lane thoroughfare adjacent to Florida International University, remained open. The $14 million bridge, which was under construction by the university to connect students to the neighboring city of Sweetwater, fell on top of motorists waiting at a red light, crushing their cars under 950 tons of concrete and metal.

“The bridge was talking to them,” Robert L. Sumwalt, chairman of the National Transportation Safety Board, said with evident exasperation at a board meeting in Washington. “It wasn’t just talking — it was screaming that there was something definitely wrong with this bridge. Yet no one was listening.”

The 174-foot span, which had been prefabricated in a construction yard next to the roadway, was elevated into place five days before its catastrophic collapse on March 15, 2018. During that time, workers documented growing cracks on the north end of the bridge, at a node where a single plane of load-bearing concrete trusses began.

The cracks were 40 times as large as the maximum considered acceptable in a reinforced concrete bridge, Mr. Sumwalt said. Yet none of the many parties involved in building the structure recognized the gravity of the problem. Workers were attempting to stop the cracking by tightening the tension rods of one of the trusses at the time the bridge fell.

“To have a failure like this is astounding,” said Bruce Landsberg, the N.T.S.B. vice chairman.

He called the nearly 19-month review by the agency “one of the most complicated reviews I think we’ve ever done,” in part because of the bridge’s unusual design. Most pedestrian bridges are simple steel structures, but the university, a public commuter school, had planned to build an emblematic bridge that would be a new landmark at the university.

The N.T.S.B. concluded that the chief probable cause for the bridge failure was the design by Figg Bridge Engineers, an experienced Tallahassee firm whose designers, the agency said, underestimated the load on the bridge and overestimated its capacity. But agency officials said that other parties contributed to two more key failures.

The Louis Berger Group had been hired by Figg to conduct an independent peer review of the bridge design. That review should have caught Figg’s critical miscalculations. Yet Louis Berger’s review was inadequate, the N.T.S.B. found.

Finally, Figg and its partners — the builder, Munilla Construction Management; the builder’s engineering consultant, Bolton Perez and Associates; the university; and the Florida Department of Transportation — failed to recognize that the cracking had reached unacceptable levels, and decided to keep the street open while workers tried to fix the problem, worsening the impact of the collapse.

Six people, including an F.I.U. student, died in the collapse, and 10 more were injured, several of them seriously. Earlier this year, Figg, Munilla and most of their subcontractors on the project, excluding Louis Berger, settled an array of civil lawsuits filed by victims and their families.

In a lengthy statement, Figg, which has denied responsibility for the accident, maintained that the bridge would not have collapsed if the concrete truss at the center of the investigation had been built to specifications required by the Florida Department of Transportation. Citing the findings of a forensic engineering firm that Figg hired to investigate what happened, Figg said others were to blame for that failure, but it did not name them.

“The accident was the result of a complex series of events and failings by parties at multiple stages of the project,” Figg’s statement said.

Munilla Construction Management, which is based in Miami, has changed its name to Magnum Construction Management and has filed for Chapter 11 bankruptcy protection.

“This is the first time in our over three decades of operation that we have ever experienced anything like this tragic accident,” the company said in a statement. “We will continue to work closely with all parties to resolve ongoing legal and financial issues in an expeditious manner.”

Mark B. Rosenberg, the university’s president, said in a letter to the community on Tuesday that the university still plans to build a pedestrian bridge over Eighth Street — and that it will include a memorial to the victims of the collapse.

In its findings, the N.T.S.B. faulted the Florida Department of Transportation for failing to provide enough oversight of the university during the bridge construction. The department had delegated responsibility for managing the project to the university, even though F.I.U. had no professional engineers on its staff and relied solely on the expertise of its hired contractors.

Five of the 11 recommendations issued by the N.T.S.B. were aimed at the transportation department. Kevin J. Thibault, the state transportation secretary, said in a statement that the department has already made improvements to its policies and procedures.

In the end, every company, institution and agency involved in the project was partly to blame for the bridge collapse, said Mr. Sumwalt, who has been on the safety board for 13 years and has reviewed many accidents.

“I don’t think I’ve ever seen one where there’s more finger-pointing between the parties,” he said. “Everyone shares a piece of this accident.”

from Hacker News https://ift.tt/32FvxfE