Did construction technique lead to FIU pedestrian bridge collapse?
MIAMI – The unfinished pedestrian overpass that toppled onto the Tamiami Trail on Thursday was being built under a relatively novel approach called accelerated bridge construction – a fast, tested method that carries some risks if not rigorously carried out.
Until it’s fully secured, a quickbuild structure is unstable and requires the utmost precision as construction continues. Properly shoring up the bridge can take weeks, a period during which even small mistakes can compound and cause a partial or total collapse, said Amjad Aref, a researcher at University at Buffalo’s Institute of Bridge Engineering.
Just before the bridge’s concrete main span abruptly gave way Thursday, crushing at least six people in cars to death and injuring others, a contractor’s crews were conducting stress tests on the incomplete structure, Miamidade Mayor Carlos Gimenez said. The 950-ton span, assembled by the side of the road over a period of months, was hoisted into place in a matter of hours on March 10.
That stress testing typically involves placing carefully calibrated weights on the span and measuring how the structure responds to ensure it’s within safe parameters, Aref said. Crews may also have been adjusting tension cables that provide structural strength for the span’s concrete slabs.
“The loads have to be calculated precisely in the analysis to make sure the partial bridge would be able to carry them safely,” Aref said.
That doesn’t mean that testing or tension adjustments caused the structure to fail, he said. Other factors, from heavy wind to design flaws to a crane hitting the structure, can also come into play in a failure. It’s still too early to even guess at a cause, engineers say.
“It might not be one factor,” Aref said. “It could be a combination of things.”
In almost all bridge or building collapses, though, construction errors are to blame, not design, said Ralph Verrastro, a Cornell-trained engineer and principal of Naplesbased Bridging Solutions, which is not involved in the FIU project.
Determining what exactly went wrong will likely take months. The National Transportation Safety Board has opened an investigation.
Over the coming weeks, forensic engineers will try to unravel what happened in a complicated analysis that involves picking through debris, looking at designs, and piecing together inspections, said A view of the main span of the Fiu-sweetwater University City Bridge after collapsing on Thursday in Miami.
Princeton University civil engineering professor Maria Moreyra Garlock. The construction phase, she noted, is often the most dangerous point in the life of the bridge.
Engineers could sample material at the site to test for strength, she said, and look at the sequence of inspections to determine what happened when. Site inspections might also reveal what caused the sudden collapse.
“Maybe there’s some sign that a support got unseated,” she said.
Thursday’s tragic accident is sure to raise questions over the decision by Florida International University to take the quick-build approach, adopted in large part to minimize the need to interrupt traffic on the busy highway. The decision by its contractors to undertake testing while traffic flowed along the busy roadway below will also be scrutinzed. FIU was running the project under an agreement with the state.
Accelerated bridge construction, ABC, has become more common in the past decade, especially in urban areas with heavy traffic, Verrastro said.
“That’s the driver and why ABC is so popular, because it allows you to keep the road open,” he said. “It’s more expensive to do, but it gains the advantage of keeping traffic moving, and that’s what makes the phone ring at the mayor’s office.”
FIU’S engineering school has become a hub for accelerated bridge construction training and research in recent years.
In 2010, after recognizing the need for more engineers trained in the method, FIU started a center focused on the approach. It has drawn 4,000 people to its webinars since launching in 2011, according
to a center website, and in 2016 became one of just 20 programs nationwide to receive federal funding amounting to $10 million over five years.
The center’s director, Atorod Azizinamini, recognized by the White House in 2016 as one of the world’s leading bridge engineers, said the method is safer and more efficient than conventional construction.
“We are able to replace or retrofit bridges without affecting traffic, while providing safety for motorists and workers who are on site,” he said in a 2016 press release about the program. “The result is more durable bridges.”
The FIU center, however, was not formally involved in the pedestrian bridge project, a university spokeswoman said last week when the span was laid lifted into place.
But FIU administered the $12 million bridge project, which was funded by the federal government. Because it has its own building department, the school was also in charge of approving plans, permits and inspections for the bridge. Although the structure spans a state highway, the Florida Department of Transportation was only tangentially involved, the agency said in statement issued Thursday.
FDOT did raise one potential red flag: Under its agreement with the state, FIU was supposed to hire a “pre-qualified” engineering firm to conduct an independent design check – meaning a firm previously approved by the state. FIU used a large international firm, Louis Berger, that was not preapproved, according to FDOT. The agency also emphasized that FIU is responsible for overseeing all aspects of design and construction for the project.
A 155-year-old legend about buried federal gold appears to have caught the attention of the FBI.
Dozens of FBI agents, along with Pennsylvania state officials and members of a treasure-hunting group, trekked this week to a remote site where local lore has it that a Civil War gold shipment was lost or hidden during the 1863 Battle of Gettysburg.
The treasure-hunting group Finders Keepers has long insisted it found the gold buried in a state forest at Dents Run, about 135 miles northeast of Pittsburgh, but said the state wouldn’t allow it to dig.
The FBI has refused to say why it was at the site Tuesday, revealing only that it was conducting court-authorized law enforcement activity.
A Republican Maine House candidate who called a Florida high school shooting survivor a “skinhead lesbian” and called another a “baldfaced liar” is quitting the race.
Leslie Gibson was widely criticized for insulting the survivors of last month’s shooting, which killed 17 people. The Portland Press Herald reported Gibson said Friday he’s walking away with his “head held high.”
One of the teenage students Gibson attacked online was Emma Gonzalez, a leader in student efforts to combat gun violence. He said there was “nothing about this skinhead lesbian” that impressed him.
Gibson had been unopposed in the 57th District contest.
– Appeal-democrat news services