Miami bridge that collapsed lifted into place without suspension cables, support tower
Miami bridge that collapsed lifted into place without suspension cables, support tower
March 16, 2018
The pedestrian bridge that collapsed in Miami was designed as a suspension bridge, but the central tower typical of such a structure wasn’t in place when the main span was lifted into place Saturday.
Florida International University posted pictures of the bridge as envisioned, with a tall central column and cables stretching down to hold the bridge, shaped like a sailboat. The design is called a cable-stayed bridge, which is a type of suspension bridge.
Cable-stayed bridges have cables attached directly from the column to the span, while suspension bridges string cables between towers and have other cables descend to the span.
#DidYouKnow the new pedestrian bridge that will connect our FIU and the @CitySweetwater is the first in the world to be constructed entirely of self-cleaning concrete? #WorldsAheadpic.twitter.com/lQVJh09Pv2
— FIU News (@FIUnews) March 10, 2018
Amjad Aref, a professor at University of Buffalo’s Department of Civil, Structural and Environmental Engineering, said a suspended bridge is typically built gradually, with the center tower or towers erected early.
Pictures from the scene of the collapse don’t show a central tower.
“Whoever is going to investigate, they will ask the fundamental question: shouldn’t the tower be there, and the cables ready to connect to the structure, when you lift it?” Aref said. “That’s a question for them to answer.”
Andrew Hermann, past president of the American Society of Civil Engineers, said cable-stayed bridges are built in stages, with pieces of roadbed placed on piers before the cables are attached. At each phase in the project, the supports such as piers are designed to hold the entire weight placed on them, he said.
“When you’re doing staged construction like this, what you have to make sure is that at each stage that the structure is strong enough for the loads that are on the bridge,” Hermann said. “The engineering, both design and the construction engineering, should have taken that into account with the bridge in that condition.”
National Transportation Safety Board chairman Robert Sumwalt led a team of investigators Thursday to determine what went wrong and what could prevent similar collapses in the future.
“That’s part of our investigation,” Sumwalt said of the lack of central column.
Suspension bridges are popular across the country — from the George Washington Bridge in New York to the Golden Gate Bridge in San Francisco— because the way they are built allows for construction across rivers.
The Kosciuszko Bridge, which carries Interstate 278 called the Brooklyn-Queens Expressway over Newtown Creek in New York City is a cable-stayed bridge. So is the John James Audubon Bridge across the Mississippi River in Louisiana and the Sunshine Skyway Bridge in Tampa.
Those bridges are much longer and heavier than the bridge at Florida International University, which was built to only handle pedestrians, not cars and trucks.
“I wish I would be on that kind of investigation, to be honest with you, because in this country we build so many cable-stay bridges for carrying trucks, not pedestrians, and all of them work fine,” Aref said. “The spans, from one end to the other, is much larger than that.”
Typically on such bridges, the central tower or towers are erected first, Aref said. Then slabs of pavement are lifted into place, alternated from each end and connected to the shortest cables closest to the span connected to the main tower, he said.
“When they cross rivers, you don’t have the luxury of having a big bridge in one piece and moving it in place like this,” Aref said.
Robert Bea, a professor of engineering and construction management at the University of California, Berkeley, told the Associated Press that without knowing precisely what happened, the “innovative installation” was risky because the bridge spanned a heavily traveled thoroughfare.
“Innovations take a design firm into an area where they don’t have applicable experience, and then we have another unexpected failure on our hands,” Bea said after reviewing the bridge’s design and photos of the collapse.
The $14.2 million FIU bridge was designed under a process called “accelerated bridge construction” that allowed for larger sections to be built and then lifted into place. A 174-foot section weighing 950 tons was hoisted and rotated into place across the six-lane road Saturday. When finished, the bridge would have been 289 feet long and 109 feet tall.
Aref said he was unaware of such a large section of bridge being put in place without supporting cables.
“I don’t want to speculate. From a structural-engineering point of view, the forensic engineers won’t take long to figure out what happened,” Aref said. “I think it is not a long investigation. There are glaring things.”
Munilla Construction Management, a Miami-based construction management firm, won the bridge contract with FIGG Bridge Engineers of Tallahassee. Munilla said it would cooperate with the investigation. FIGG said in a statement “in our 40-year history, nothing like this has ever happened before.”
But FIGG was fined in 2012 after a 90-ton section of bridge collapsed on railroad tracks in Virginia. Munilla was accused of substandard work in a lawsuit filed this month after a makeshift bridge collapsed at Fort Lauderdale International Airport.
Occupational Safety Health Administration records show fines totaling more than $50,000 against Munilla for 11 safety violations in the past five years for complaints about unsafe trenches, cement dust and other problems.
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