On March 15, 2018, a pedestrian bridge at Florida International University (FIU) collapsed. The 950-ton structure – which was only partially complete – fell onto a roadway. The debris crushed vehicles and killed 6 people.
One of the first pieces of information reported about the collapse focused on how designers and laborers built the bridge using offsite construction.
So what is offsite construction? And how will the bridge collapse affect the future of this building technique?
How Offsite Construction Works
Offsite construction refers to any building process that takes place away from the ultimate point of installation. The term includes both prefabrication and modular construction.
The ability to work off-site is especially important in cases where construction would slow, or even completely halt, traffic flow. (Traffic disruption was the main reason builders chose to use offsite construction for the FIU bridge.) Workers can build parts of a structure in an unobtrusive area either close to the final installation site, or in a factory many miles away.
Offsite construction has other benefits. Construction workers on a well-supervised factory floor don’t face dangers like falling from scaffolding. (Such falls killed nearly 400 construction workers in 2016 alone.)
In the case of the FIU bridge, workers assembled the main span outside, adjacent to the roadway the finished bridge would have crossed. Workers then lifted the span into place on March 10 – five days before the collapse.
Waiting For Answers
No one knows yet exactly what caused the FIU bridge to collapse. As of May 9, the Miami Herald reported that “worrisome” cracks were spotted in a key concrete support a full 10 days before the structure was lifted into place over the roadway. But no one knows yet whether inadequate design, construction issues, or both caused the collapse.
Because of the high-profile nature of the bridge collapse, the public is giving offsite construction techniques more scrutiny. But engineers and project managers think any public discomfort with such projects is misplaced.
“What really bothers me is with [accelerated bridge construction], the benefits are so substantial that I would hate to see this accident lead to its reduced use,” said Michael Culmo, a bridge engineer in Connecticut. “While this is a tragedy, the process itself is very safe.”