In the days before an under-construction bridge collapsed in Miami and killed six people, workers identified cracks in its structure but failed to report them or close the road under the bridge to traffic, a federal report commissioned after the collapse found.

The bridge commissioned by Florida International University, immediately after its collapse March 15, 2018.

When the span of the $14.2M, 174-foot, 950-ton bridge commissioned by Florida International University collapsed over a major road in Miami in March 2018, it was because of deficient structural design, according to a report released last week by the Occupational Safety and Health Administration's Directorate of Construction.

During a window of time as the bridge was being pieced together, its load was unsupported.

OSHA's investigation uncovered text messages and photos showing that cracking in the concrete was known about and discussed for days before the collapse. OSHA found that much of the responsibility laid with the engineering firm, but that multiple other experts involved failed to exercise their own professional judgment, which could have prevented the tragedy.

The concrete bridge was supposed to connect FIU's campus with the adjacent city of Sweetwater, letting students and pedestrians cross over a busy road, Southwest Eighth Street, that runs alongside campus. FIU's design criteria emphasized that the bridge should be aesthetically impressive, a landmark project for the city.

Munilla Construction Management Inc. was chosen as the design-build contractor, and teamed with FIGG Bridge Engineers, a Tallahassee company that touts "creating bridges as art," as a subcontractor. FIGG served as the engineer of record.

FIGG's unique design was made to look like a cable-stayed bridge, but its strength would really come from a traditional truss structure — in this case, two trusses that would connect and create one contiguous bridge. Because of the focus on aesthetics, it was designed without redundancies; if one part failed, the whole thing could.

Using a technique called Accelerated Bridge Construction, components were built just off-site, then transported into place, where work could be finalized while traffic flowed below the bridge.

A screenshot shows that a worker texted images of cracked concrete to his supervisor on March 10, 2018 — five days before the FIU bridge collapsed.

The concrete passed strength tests, but cracks first appeared in late February 2018, as construction teams prepared to move the precast sections into their final location.

"When the shores under the bridge were removed and the truss was self-supported over the mega shores, a loud popping sound was heard by at least three employees ... one of the employees from the MCM walked over the bridge and noticed cracks," the OSHA report says.

Photos were taken by employees from BPA Networking Engineering Services Inc., an affiliate of Bolton Perez and Associates Inc., the project's construction engineer and inspector, and sent to MCM, then forwarded to FIGG, whose reps said the cracks would be sealed.

On March 10, the bridge's major components were moved into place over the road. A company called Structural Technologies LLC had been hired to perform post-tensioning on parts of the bridge. Seeing significant cracks, a supervisor named Kevin Hanson "became visibly disturbed," took pictures, and sent them to his supervisor, stating that “it cracked like hell.”

Hanson also alerted an MCM employee, who in turn sought guidance from FIGG, saying that “some of these cracks are rather large and/or of concern.”

The university said that the bridge's 950 tons equaled the weight of 271 elephants.

FIGG asked MCM to put an additional plastic shim “right away” to replicate conditions casting yard, where the truss had been self-supporting from February 28 until March 10 without significant cracking.

On March 14, 2018, as cracks were getting larger, FIGG analyzed photos and prepared for a meeting the following day. In the meantime, VSL asked MCM if the cracks would be fixed before more re-tensioning work, but was told to proceed "because of FIGG’s assurance that the cracks did not present any safety issues."

On the morning of March 15, as VSL worked, a meeting was held in MCM’s trailer with attendees from FIGG, FIU, MCM, the Florida Department of Transportation and BPA.

"FIGG did not know the reason for the cracks, but still expressed no safety concerns," the OSHA report states. "However, FIGG in its presentation alluded to a lingering concern about the structural inadequacy of the 11/12 node until the intermediate pylon and back truss were completed."

While FIGG presented remedial measures to capture the loads, it did not recommend the shoring of the bridge at intermediate locations of the span or closure of Eighth Street.

"That was an error on FIGG’s part," OSHA's report found.

OSHA also pointed out that FIGG had failed to comply with an FDOT requirement for an independent peer review at 30%, 60% and 90% of completion of the construction documents. A company called the Louis Berger Group had been retained to conduct the required peer review — but only the final check, not the design check at intermediate stages.

"[Louis Berger] did not examine the structural design of the main truss during intermediate stages of construction when the main span truss would be placed on the piers without the advantage of the back span and intermediate pylon, a condition that existed from March 10 through March 15," OSHA's report says.

Louis Berger's entire review was conducted by one engineer without any assistance.

OSHA placed much of the blame at FIGG's feet. At the March 15 meeting, "[FIGG] acknowledged that his computations could not replicate the cracks and therefore, he did not know why the cracks were occurring," according to the report. "Despite knowledge that the cracks were growing in size, [FIGG] stated more than once that the cracks did not present any safety concerns."

OSHA's report found that FIGG "should have known" that the nonredundant nature of the structure meant that one failure of a diagonal in the bridge could cause the entire truss to collapse. With that knowledge, FIGG should have instructed the bridge be reinforced and the road below closed.

OSHA also concluded that officials at FIU, FDOT and MCM should have insisted that all computations performed by FIGG, including FIGG’s recommendation to re-tension the PT bars, be peer reviewed. But "they deferred to FIGG’s conclusions, and failed to apply their own judgement and judiciousness, even though FDOT, BPA and MCM have extensive experience in bridge and concrete construction."

As a licensed professional engineer, the rep from FDOT should have recommended pausing all work.

Five motorists were crushed when their cars were stopped at the traffic light at the time of the collapse. One VSL employee was fatally injured, and another VSL employee was critically injured.

Separately, the Miami Herald has also asked experts to opine on the bridge's design; they found that "to carry through the cable-stayed look, the struts had to line up with the pipes from the mast, resulting in a highly irregular arrangement that the experts say may have made the critical defect harder to detect than it might have been in a conventional truss design."

The National Transportation Safety Board is also investigating and is expected to release a final report later this year.