Miami condo collapse: Engineers’ early theories as to the cause

The search goes on to find survivors under the rubble of the 1981 Champlain South Tower, which suffered a partial ‘pancake collapse’ last week (24 June), resulting in 55 of the building’s 136 flats being entirely destroyed.

At the weekend the City of Surfside published a 2018 structural engineer’s report, which had found widespread problems with the beachside block at 8777 Collins Avenue – including ‘significant cracks’ – requiring extensive repairs ‘in the near future’.

The document, prepared by Morabito Consultants, reported ‘major structural damage’ to the concrete structural slab below the pool deck, caused by waterproofing that was ‘beyond its useful life’ and which needed to be ‘completely removed and replaced’.

The engineer warned that ‘failure to replace the waterproofing in the near future [would] cause the extent of the concrete deterioration to expand exponentially’.

The 2018 report goes on, claiming: ‘The main issue with this building structure is that the entrance drive/pool deck/planter waterproofing is laid on a flat structure.

‘Since the reinforced concrete slab is not sloped to drain, the water sits on the waterproofing until it evaporates. This is a major error in the development of the original contract documents prepared by William M Friedman & Associates Architects Inc. and [now dissolved] Breiterman Jurado & Associates, consulting engineers.’

Morabito Consultants said it had drawn up the document on behalf of the Champlain Towers South Condominium Association ahead of the 40-year recertification of the block.

In a statement released at the weekend, the consultancy added: ‘[The association] engaged our firm again in June 2020 to prepare a 40-year Building Repair and Restoration plan with detailed specifications for completing the necessary repairs and restoration work.

‘At the time of the building collapse, roof repairs were under way, but concrete restoration had not yet begun.’

According to the AJ’s sister title New Civil Engineer, John Pistorino, a Miami structural engineer who evaluated the Florida International University bridge collapse, has now been hired to investigate the cause of the Champlain South Tower disaster.

The remains of the Champlain south Tower at 8777 Collins Avenue, in Surfside, Miami following the building collapse (June 2021)

Surveillance video

He told the Palm Beach Post that he would need to carefully inspect the evidence before making any pronouncements. However, he said he was struck by a surveillance video that showed the collapse started in the centre of the building, which pulled down the entire north section.

‘The video is very tell-tale,’ he said. ‘It shows the centre section collapsing all the way down, and then the tower on the north-east still standing, then it collapsed and pancaked.’

However, Virginia Tech Department of Civil and Environmental Engineering professor Roberto Leon said that it is difficult to come to any real conclusions from this video.

‘What you can see in the video and what a careful analysis of the video might show later on are entirely different things. So, it is useful, but we’re not going to establish the cause of the collapse based on a video alone.’

Leon also added that the way the building collapsed could provide a challenge in the investigation.

‘The kind of remnants that you have in this pancake type collapse unfortunately destroy a lot of the evidence,’ he said.

‘The columns and walls — all the vertical elements that stabilise a structure — appear to have been damaged or destroyed. The lack of intact structural elements will likely affect the pace of the investigation.’

Salt impact

Generally, Pistorino said buildings along the ocean are vulnerable to salt and saltwater intrusion, making regular inspections and maintenance important.

Drexel University engineering professor Abi Aghayere also told news channel 6abc that the structure's location near a body of water raised the question of whether this could have affected its integrity.

Similarly, South Florida construction company National Home Building & Remodeling Corp founder Gary Slossberg told Fox Business that salt in Miami’s coastal air could potentially have assisted the corrosion of steel.

However, he said he was unsure how long it would take for salt to corrode a building’s materials to the point of collapse.

Structural issues

Slossberg emphasised that he hadn’t heard any specific leads on the cause of the collapse but suggested a number of other possibilities. He said that if the building were constructed with a post-tension slab (a concrete slab that has cables running through it) and one of those came loose, this could have contributed.

Another possibility, he said, is that the balconies may have had some construction issues. Many Miami-area buildings built with concrete balconies that are back-pitched and don't allow water to escape properly after it rains.

‘There's a lot of concrete restoration going on, and this is where you see a lot of that rust and rebar coming through the slab between the water sitting there and the salt air — it’s just not a good combination,’ he said. ‘But again, I don't know if that would take down the whole building. We just don't know what happened.’

Foundational failure

West Palm Beach engineering firm WGI specialty structures director Jeffrey Bergmann also cautioned against jumping to conclusions. However, he said that buildings five stories and higher are built using deep pilings in their foundations. The pilings are driven into the limestone, which in Miami-Dade County can just be a few feet below the surface, he said.

Aghayere also suggested that a cause could be a foundation failure.

‘The foundation could fail because there might be a sinkhole, nobody knows, but that needs to be investigated,’ he said.

Source: Felix Mizioznikov/Shutterstock

Rescue teams on scene at the collapse of the Chaplain Towers Surfside on 24 June

Review process

Experts who studied the apartment complex last year warned that it was unstable, with one study from a Florida International University researcher finding that the building had been sinking at a rate of 2mm a year for the past three decades.

‘It was probably designed to the standards of the time,’ Leon said. ‘But our standards have changed quite drastically over the last 40 years or so. With the benefit of modern computer analysis, there could be some design issues that we see today that weren’t clear then.’

Slossberg added: ‘With every hurricane, new construction codes come out. New engineering codes. This is [40] years later [since the building was constructed]. The codes have changed at least a dozen times. I know they have. So, some of these older buildings are not really built to withstand the type of same weather conditions as when they were built originally.’

Leon said it was ‘entirely too early to tell what happened’ to the block, which sits next to Renzo Piano’s recently completed Eighty Seven Park condominium building.

He added: ‘This is going to require quite a bit of investigation, and in the end, we might not come to a complete understanding of what happened here.’