As the rescue mission in the Surfside building collapse enters the sixth day, questions over the crashing down of the tower without warning have puzzled authorities and experts.
While there are no clear answers yet, questions point to some failure in the lower reaches of the 13-story building, perhaps in its foundation, columns or underground parking garage.
The notion that the building collapsed due to a failure at or near its base seems to be supported by eyewitness accounts.
Michael Stratton who was on the phone with his wife, Cassondra, who told him their building was shaking just before the collapse. She was looking out from a condo at Champlain Towers South when she told him she saw “a sinkhole where the pool out her window used to be,” he told the Miami Herald.
The phone call then cut off. Stratton is among the scores of people who remain unaccounted for days after the collapse.
BASE OF THE BUILDING
Engineers who have reviewed the available information about the tower’s collapse say the investigation into its cause should focus on potential failures near the base of the building.
The disaster most likely resulted from a combination of foundational and structural problems, said Mehrdad Sasani, a professor of civil and environmental engineering at Northeastern University.
The collapse likely started at lower floors of the condo and could have been influenced by “40 years of exposure to salt, water and salt air and the indication of some level of damage in the garage at the lower floors of the building.”
A range of other factors could have contributed to foundation and structural failures, including vibrations from recent construction work, heavy equipment on its roof and water damage associated with the building’s pool, Sasani said.
Donald Dusenberry, a consulting engineer who has investigated structural collapses, told the newspaper it appeared to be “a foundation-related matter, potentially corrosion or other damage at a lower level,” though he did not rule out design or construction errors.
The building’s proximity to the Atlantic Ocean, with its corrosive seawater, increases the chances for spalling, wherein reinforced steel within the concrete begins to rust.
2018 SURVEY REPORT
A 2018 report, which Surfside has released among other public records, noted problems with the building’s concrete, but an engineer who inspected Champlain Towers South last year said the report mentioned nothing alarming.
“Abundant cracking and spalling of various degrees was observed in the concrete columns, beams and walls,” the survey found. “Several sizeable spalls were noted in both the topside of the entrance drive ramp and underside of the pool/entrance drive/planter slabs, which included instances with exposed, deteriorating rebar. Though some of this damage is minor, most of the concrete deterioration needs to be repaired in a timely fashion.”
The waterproofing below the pool deck and entrance drive was failing and causing “major structural damage,” according to the report by Morabito Consultants.
The report didn’t indicate the structure was at risk of collapse.
Morabito Consultants “provided the condominium association with an estimate of the probable costs to make the extensive and necessary repairs. Among other things, our report detailed significant cracks and breaks in the concrete, which required repairs to ensure the safety of the residents and the public,” it said in a statement.
Condo owners in Champlain Towers South were facing assessments for $15 million worth of repairs, with payments set to begin just days after the building’s deadly collapse.
The building’s association approved a $15 million assessment in April to complete repairs required under the county’s 40-year recertification process.
An itemized list of planned repairs included new pavers, planter landscape and waterproofing — addressing some of the issues noted in the 2018 report.
The most costly project listed was “facade, balcony and railing repairs” for $3.4 million.
A report that emerged last week indicates the condo tower was sinking at a rate of 2 millimeters per year between 1993 and 1999.
It’s unclear if the building continued to sink at that rate following the study.
More information is needed before determining if the sinking played a role in the buildings collapse.
“If everything moves downward at the same level, then not so much,” said Shimon Wdowinski, a coauthor of the study and professor with Florida International University’s Institute of Environment.
“If one part of the building moves with respect to the other, that could cause some tension and cracks.”
Buildings in nearby western Miami Beach, which was built on reclaimed wetlands, were moving at higher rates, “so we didn’t think it was something unusual,” Wdowinski told CNN.
Surfside Mayor Charles Burkett has echoed that assertion, saying, “There’s no reason for this building to go down like that unless someone literally pulls out the supports from underneath, or they get washed out, or there’s a sinkhole or something like that.”
Roof work was ongoing at the now-collapsed tower.
The roof loading, which may have involved a “point load” where equipment wasn’t scattered but was a dead load of equipment in one area that adds forces down through a compromised column.
Barry Cohen, a lawyer who escaped the crippled Champlain Towers building with his wife, said the roof work could be part of a “perfect storm” of causes that combined to bring down the structure.
“They were doing a new roof. And I think, all day long, the building was pounding and pounding and pounding. They’ve been doing it for over a month,” Cohen said.
Surfside building official Jim McGuinness was on the roof 14 hours before the building collapsed and saw nothing unusual, he said. The building’s ongoing roofing permit was going well, he said.