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Cracks where FIU bridge buckled may have signaled ‘imminent failure’

Rescuers search through the rubble of the FIU pedestrian bridge collapse on Thursday, March 15, 2018, at SW 109th Avenue and 8th Street in Miami. (Roberto Koltun/El Nuevo Herald/TNS)

A key concrete support truss in the doomed Florida International University pedestrian bridge developed worrisome cracks 10 days before the structure was lifted into place over the Tamiami Trail, photographs and an internal email unintentionally released by the school show.

The documents, released in response to public records requests from the Miami Herald, show that FIU’s construction and engineering team discovered potentially problematic cracks in the bridge earlier than officials have previously acknowledged.

The cracks were found in late February at the base of a diagonal support member at the north end of the span. Independent engineers have identified that as the point where the structure shattered on March 15 while under construction, sending the 950-ton bridge crashing onto the roadway below and claiming six lives.

Three independent engineers who examined the photos, records and bridge blueprints at the Herald’s request concurred that the cracks were a red flag signaling potentially critical structural problems. Outside experts have zeroed in on that truss member, identified in plans as No. 11, as being “under-designed” — that is, not strong enough to withstand the pressure from the weight of the bridge it was supposed to hold up.

The location and diagonal shape of the cracks shown in the FIU team’s photos support that theory, the engineers said. They said the cracks should have prompted work on the bridge to stop for an in-depth review that likely would have resulted in the truss connection being re-engineered and significantly reinforced.

“Knowing the stresses that member was under and what happened, that crack was something that in hindsight should have been investigated,” said David Beck, a New Hampshire engineer who helped uncover mistakes in Boston’s $10.8 billion Big Dig project.

Linwood Howell, who runs a Texas engineering firm that specializes in bridge design and inspection, said the cracks were signs of the structure’s “imminent failure.”

“There’s nothing they could have done short of starting over and redesigning the structure,” Howell said.

A third engineer consulted by the Herald concurred with the first two but asked not to be named.

A fourth bridge engineer, Ralph Verrastro of Naples, said the cracks did not appear significant to him.

“The photos don’t clearly provide any clues to me related to ultimate failure,” Verrastro said in an email. “I would assume these cracks would have been repaired by epoxy injection before the bridge was moved.”

Because FIU and state transportation officials continue to withhold other critical records under instructions from the National Transportation Safety Board, it’s hard to say what the FIU team’s response to the cracks was.

In a Feb. 28 memo, Jose Morales, a consulting engineer for FIU, notes one crack in particular “merits special attention.” Morales urges that the bridge engineer of record be consulted “to provide a response.” That engineer of record is W. Denney Pate of FIGG Bridge Group, which designed the bridge. The memo was sent to a project manager at Munilla Construction Management, the bridge project’s builder, and copied to Alberto Delgado, a construction project manager at FIU.

NTSB, which is investigating the bridge collapse, has told FIU and the Florida Department of Transportation not to release records dated after Feb. 19, so there are no available public records to document any response from FIGG or other team members to Morales’ memo. The Herald has sued to obtain subsequent records related to the bridge collapse. The bridge collapse is also the subject of a Miami-Dade police homicide investigation. Families of some of the victims have filed lawsuits.

The Feb. 28 memo and the attached photos of cracking were released in error, an FIU attorney, Eric Isicoff, said Monday. After the Herald contacted FIU for comment on the cracks, Isicoff demanded reporters delete any copies of the documents from their computers.

“Any hard copies that have been made also should be destroyed,” Isicoff wrote.

Mark Caramanica, an attorney at Thomas & LoCicero representing the Herald in its public records requests to FIU, said the Herald has no obligation to comply.

“The Herald has a First Amendment right to publish this information, and the public has a right to know what may have led to this terrible event,” he said.

The cracks documented in the Feb. 28 memo were discovered while the span was still resting on the ground, after the removal of temporary shoring that provided support while it was built by the side of the Trail.

Beck and Howell said that’s potentially telling because the span at that point was resting only on a support on either end, mimicking the way it would stand once installed over the roadway. The cracks thus could have been a sign of shearing pressure — a sideways stress — that the No. 11 truss could not handle once under the full load it was meant to carry.

Both Beck and Howell, echoing other outside engineers who have analyzed publicly available blueprints, records, photos and videos, believe the connection between the No. 11 truss and the bridge deck — the place where the cracking occurred — was poorly designed, lacking sufficient steel and concrete to bear the enormous load placed on it. All the engineers emphasize that a clear-cut cause for the collapse may not be established until the NTSB publishes its conclusions, and that their analysis could change based on new information.

Ten days after the Feb. 28 memo, the bridge’s main span, fabricated by the side of the road, was lifted into place by two special transporters. That means FIU’s engineers and contractors had either done something to address the cracks or concluded they were not an issue, the outside engineers said.

Concrete cracking in construction is common, and records show FIU bridge team members were expecting some cracking as they prepared the bridge span and moved it into place.

In fact, some minor cracking was discovered even earlier, other released records show, but dismissed as inconsequential — a conclusion the two independent engineers agree with.

But five days after the bridge was lifted into place, Pate called an FDOT official to report that cracking had been found at the north end of the bridge, records released by the agency immediately after the collapse show. In a recorded phone message, Pate said the cracks did not represent a safety hazard but should be repaired. It’s quite possible that the cracks Pate reported were the same ones in the photos and memo from Feb. 28, Howell said.

The cracks might have become worse after the bridge was moved and set in place, resting atop a pylon at either end. That would especially be the case if the No. 11 truss, the last diagonal piece at the north end, was beginning to fail under the full load of the bridge, he said.

The cracks were discussed at a meeting of project team members the morning of the collapse, though no safety concerns were raised, FDOT said. The bridge collapsed while crews were atop the walkway’s canopy, adjusting the tension on steel support rods inside the No. 11 truss member as traffic continued to flow on the open road below.

Whether the crews were tightening or loosening the rods has not been disclosed, but could be critical in explaining the cause of the collapse. Because the truss-type design of the bridge means there is no redundant support, the failure of a single structural piece can bring the entire overpass down under its own weight, experts say.

One early report, by U.S. Sen. Marco Rubio, had the crews tightening the rods in an effort to close the cracks, leading to speculation that over-tightening could have caused the truss to shatter.

But other experts, citing released bridge plans, say they were more likely loosening the rods. The rods were apparently a modification to the plans, added to the bridge design after FDOT asked FIU to move the entire bridge 11 feet north to accommodate a future lane for transit.

The move forced a change in the carefully calibrated plan for moving the bridge into place. It put the north end of the main span well off the edge of the roadway on a canal bank. Because a transport machine could not traverse that roadway edge, the point where it would lift the structure was moved toward the center of the bridge. That means the end would sag when lifted. To prevent that, the rods were added to provide extra compressive support.

The rods were tightened before the bridge was lifted off the ground. The plans called for them to be loosened after the bridge was in place because that extra compression was no longer needed. That’s the operation some experts believe was under way when the bridge plummeted to the ground.

The cracks in the Feb. 28 document were discovered after the rods were tightened, or stressed, in preparation for the lift. In the accompanying memo, Morales, an engineer with FIU consultant Bolton Perez & Associates, asked MCM and Pate to “determine if these were expected during the bridge stressing,” and singled out one crack that “due to the size” needed “special attention.”

Citing the cracks and his own calculations showing that the No. 11 truss was crushingly overstressed, Howell speculated that either operation — tightening or loosening — could have been enough to shatter the connection.

“Since it was right on the brink of failure, anytime you disturb it — boom — it goes,” Howell said. “It just needed a little push to go over the edge.”

A sufficiently attentive engineer, knowing what kind of load the No. 11 member was supposed to carry, should have exercised great caution and ordered a thorough review, preferably by an independent engineer not involved in the project to ensure objectivity, Howell said.

Given the bridge was moved into place soon after and subsequently fell, he assumes that did not happen.

“The cracks are telling them that the connection is failing, but they’re not seeing it,” Howell said. “When it’s your design, you rationalize your way around it. “


© 2018 Miami Herald

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