Design change may have led to US bridge collapse

MIAMI: Construction of the pedestrian bridge that collapsed and killed six people in Miami was behind schedule and millions over budget, in part due to a key change in the design and placement of one of its support towers.

Documents obtained by The Associated Press via a public records request showed that in October 2016, the Florida Department of Transportation advised Florida International University and its contractors to move one of the bridge’s main support structures three metres north to the edge of a canal, widening the gap between the crossing’s end supports and requiring some new structural design.

The span’s signature, 33m-tall pylon was to be built atop a base at the span’s northern end.

It was designed for basic support and to contribute to the aesthetics of the bridge, which was touted as an architectural marvel that would connect the rapidly growing university to the nearby community of Sweetwater.

Videos of the collapse last Thursday showed that the concrete, prefabricated segment of the bridge started crumbling on the same end of the span where the tower redesign occurred, two days after an engineer on the project reported cracks in the same location.

The segment that failed had been placed atop the pylon’s footing.

US Transportation Secretary Elaine Chao has ordered her department’s inspector general to conduct an audit of the bridge, according to a news release on Tuesday from the US Department of Transportation.

It is still unclear if the design change contributed to the failure.

But e-mails between the school, contractors, Sweetwater city officials and permitting agencies show a project that was behind schedule and over budget.

When the bridge collapsed, the project was already running about US$2.6mil (RM10mil) over its US$9.4mil (RM36.7mil) initial budget, cost-tracking documents showed. Originally scheduled to be completed in July, the finish date had been pushed back to January 2019.

Multiple engineers who reviewed the documents obtained by AP said moving the tower after the bridge’s initial design invited errors.

Henry Petroski, a Duke University civil engineering professor, said even seemingly minor changes in a bridge’s design could lead to failures.

“Once a design is completed, subsequent modifications tend to be suggested and approved without the full care that went into the original design,” he said.