MIAMI, Florida – As the investigation into what caused a pedestrian bridge to collapse onto traffic in Florida gets underway, a local engineer offered insight on the process used to build the bridge. The bridge was pre-constructed before being mounted into place, a process called accelerated bridge construction.
WHAT IS ACCELERATED BRIDGE CONSTRUCTION?
It’s a time-saving measure, according to Mina Dawood, an associate professor at the University of Houston.
“[Accelerated Bridge Construction] could range from building components of the structure off site and then putting the final components in place, all the way to constructing the entire structure off to the side of the roadway and then in a very short closure picking up the structure and putting it on the abutments or the piers,” Dawood said.
WHY IS THE PROCESS USED?
That’s simple, Dawood says.
“The whole objective is to minimize delays in the amount of time that the structure or roadway has to be closed in order to achieve construction,” Dawood said.
DOES THE PROCESS TYPICALLY COMPROMISE THE INTEGRITY OF THE STRUCTURE?
No. In fact, it’s commonly used, according to Dawood, who added that a pedestrian bridge like the one that collapsed Thursday needs a lot of engineering to construct.
“If you think of a pedestrian structure, a structure designed to carry the weight of people, you have to consider, for example, there could be an event on the roadway underneath and you could have people standing shoulder-to-shoulder on the entire structure. While that may not seem like a lot of load, that is a substantial amount of load,” Dawood said.
BRIDGE COLLAPSES ARE RARE
Dawood told KPRC2 events such as this take the engineering community by surprise.
“I was stunned. I was extremely stunned,” Dawood said. “Bridge engineers, in particular, are very conservative and are very mindful of the fact that they are responsible for public safety,” he said.