Photo: AP

On March 15, 2018, a pedestrian bridge at Florida International University collapsed, crushed the cars underneath, killing six people and injuring 10 others. The tragedy was the result of a litany of errors by the contractors designing the bridge, an independent reviewer supposed to catch those errors, and the contractors’ dismissal of obvious structural defects prior to the bridge being put over the roadway, the National Transportation Safety Board concluded in their their report.

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Here in the United States of America, many of our roads and bridges are very old and poorly maintained, but this was not one of those bridges. It was in the process of being built, and the span was put up less than a week prior to the collapse.

The $14.2 million project was supposed to be architecturally unique and visually striking. Instead, the designers appear to have put an awful lot of effort into designing a cool-looking bridge and very little into making sure it would stay up.

From the report:

The National Transportation Safety Board (NTSB) determines that the probable cause of the Florida International University (FIU) pedestrian bridge collapse was the load and capacity calculation errors made by FIGG Bridge Engineers, Inc., (FIGG) in its design of the main span truss member 11/12 nodal region and connection to the bridge deck.

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In other words, the contractors did crappy math.

To be sure, mistakes happen. That is precisely why independent reviewers are hired to check the math.

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Unfortunately, the independent reviewer, Louis Berger, was “not qualified” by the Florida Department of Transportation, according to the NTSB, and “failed to perform an adequate review” of the plans. Specifically, NTSB said:

Contributing to the collapse was the inadequate peer review performed by Louis Berger, which failed to detect the calculation errors in the bridge design.

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The report went on to say that Berger knew he should have checked the math on the calculations that resulted in the bridge collapsing, but “he indicated that there was not enough budget or time to evaluate those factors.”

Name-checking budget and time constraints on the independent review is an indirect reference to the technique being used to build the bridge in the first place, a technique FIU has an entire center to promote.

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This approach to bridge-building, accelerated bridge construction (ABC), is where precast parts are made offsite then put together quickly over the roadway. It is more expensive and architecturally difficult but is increasingly popular because it allows the work to be done without closing the road below. ABC is supposed to be fast and convenient but expensive, so the independent contractor name-checking aggressive timelines and lack of budget is particularly noteworthy.

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That being said, while ABC is mentioned a bunch in the 152-page report, the NTSB didn’t seem overly concerned with the ABC approach in itself, but more how the contractors actually implemented it.

Perhaps the most galling findings, though, were related to the cracks.

For more than a month, workers warned the contractors they saw giant cracks in the parts of the bridge being precast offsite. The contractors didn’t think it was a problem.

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As early as February 13, more than a month before the collapse, construction personnel reported cracks in precast parts of the bridge. Workers reported more cracked parts in early March. Over the weeks, dozens of photographs were sent to the contractor. Here’s a photo included in the NTSB report taken on March 13, two days before the collapse:

Screenshot: NTSB

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That is a three-to-four-inch deep crack in a main structural support for the bridge.

These warnings didn’t bother FIGG, who repeatedly told workers in the days before the collapse that they did not see the cracks as a safety issue. The NTSB quotes seven separate statements from FIGG managers in writing, voicemail, and as reported by others, in the two days prior to the collapse that the cracks were not a safety issue.

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The morning of the collapse, workers took these photos and sent them to FIGG management:

Screenshot: NTSB

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Screenshot: NTSB

Still, there was “no concern with safety of the span,” according to FIGG managers.

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In a bitterly ironic twist, the morning of the collapse, FIGG project managers had a meeting with the Florida Department of Transportation and FIU, among others, and a slide in their presentation declared “And, therefore, there is no safety concern relative to the observed cracks and minor spalls.”

Four hours later, the bridge collapsed.