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Collapsed Florida bridge unique, none like it in Michigan

The bridge in Florida is unlike any Michigan bridge. It was a post-tensioned concrete structures with cable-stayed bridge pylons.
Credit: (Photo by Joe Raedle/Getty Images)
Vehicles are seen trapped under the collapsed pedestrian bridge that was newly built over southwest 8th street allowing people to bypass the busy street to reach Florida International University on March 15, 2018.

The Florida pedestrian bridge that collapsed Thursday was an example of what bridge engineers call "accelerated bridge construction."

It's a technique used to reduce traffic delays associated with road construction projects.

Bridges are built off site and moved into place. That technique has been used to replace bridges in West Michigan. However MDOT's Chief Bridge Engineer Matthew Chynoweth says not all accelerated bridge construction projects are the same.

The bridge in Florida is unlike any Michigan bridge. It was a post-tensioned concrete structures with cable-stayed bridge pylons.

Less than one week ago, workers move the Miami bridge from a construction site and hoisted it into place. The bridge was on temporary supports that were to hold until it was connected permanently to the structure's columns and foundation.

Related: Miami bridge collapse rescuers recall chaotic first minutes: 'We need help!'

Engineers conducted a "stress test" on the bridge before it collapsed. It's cables were also tightened. The entire structure weighed more than 950 tons. The National Transportation Safety Board opened an investigation into the cause of the collapse.

MDOT used accelerated bridge construction at Alden Nash and I-96. A new bridge was built adjacent to an existing bridge. The new bridge was built using standard bridge construction practices and slid into place after the old bridge was removed.

The project cost MDOT about $2 million more, but that extra expense saved drivers months of lane closures.

The Michigan bridge most similar to the Miami bridge is the Bagley Pedestrian Bridge near Detroit.

The $5 million project was built to provide easy access between the east and west sides of Detroit's Mexicantown. The Bagley bridge was the first cable-stayed pedestrian bride in Michigan. Unlike the one in Florida, it has a steel super structure and was built in place.

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