It’s easy for a forensic engineer to identify the probable cause of a failure in the built environment based on preliminary data – to give an initial hypothesis. (Ref. 1) Collapse of the 12-story Miami condo on June 24, 2021 is no exception.
We do this based on:
- A briefing by the client
- Reading the documents
- Our experience and observation over time
The briefing and documents in this case were news reports and photographs, an engineering report and a research report.
The collapse was not a disaster waiting to happen. It was a disaster unfolding over 40 years since construction of the condo in 1981. Slowly at first then real fast – the collapse. (Refs 2, 3 and 4)
What’s the evidence?
- The condo was a reinforced concrete structure. Columns, beams and floors were made of concrete reinforced with steel for greater strength. Steel rusts in water and loses strength. (Ref. 5) You can see this type of construction underway in our towns and cities where ever there is a tall crane – for example, today on Prince Albert Road in Dartmouth, Nova Scotia.
- An engineering study in 2018 found the concrete spalling – exposing the steel to water. (Ref. 3) The study reported major structural damage and ‘abundant’ cracking. Example locations included the concrete slab below the pool deck and in the parking garage. Cracking could be expected in the concrete columns, beams and balcony floor slabs.
- The condo foundations were supported on limestone, reportedly soft and porous. (Ref. 2) Limestone is soluble in water – it dissolves in water. Think sinkholes in Nova Scotia and elsewhere.
- The source of the water? The condo site was a former wetland on a barrier reef an estimated couple hundred feet inland from the ocean and a couple metres above. (Ref. 2) This means the groundwater – for certain, salt water – was in the limestone supporting the foundations and not far below. This is like the water level that you see in a dug well. This is a harsh (marine) environment for exposed steel and soluble limestone.
- Another source of water? There were reports that the deck of the swimming pool and the floor of the parking garage were poorly drained. (Ref. 3) These wet surfaces would be near the level of the foundations that are supported on limestone.
- A study by a professor at Florida International University found that the condo was sinking steadily since the 1990s. (Ref. 4) That’s what happens to condo foundations supported on limestone that is softening over time.
So, where’re we at with respect to cause?
The condo foundations were subsiding (sinking) on the soft limestone for years causing the columns above to settle – move downwards. Excessive foundation settlement is a failure in itself and certain to have contributed to the collapse, and possibly been the main cause.
This vertical movement of the columns stresses the steel reinforcing the concrete and the steel connecting the beams and floors above to the columns. This is the steel weakened by water over time – the structural distress reported in 2018.
In time, this movement over-stresses the steel causing the connections to break and the condo to fall down – collapse.
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That’s an initial hypothesis as to cause based on press reports and photographs – preliminary data for sure but still something. And better than nothing when seeking comfort at such a loss of life.
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(It’s interesting that the engineering study in 2018 did not comment on the foundations and the underlying porous limestone nor on the fact that the condo was sinking since the 1990s. Possibly because it appears to have been a visual structural assessment of exposed surfaces. Still, red lights if ever there were any – porous limestone and a sinking condo)
References
- Where does an expert’s initial hypothesis come from? Posted February 25, 2019
- Various news reports, pictures and video after the collapse on June 24, 2021
- Report of a structural assessment by Morabito Consultants, Inc., Miami on October 8, 2018
- Study of building subsidence by a professor at Florida International University, Miami
- Why did the bridge collapse in Italy and how might Advocates have known this could happen? Posted October 5, 2018
(Posted by Eric E. Jorden, M.Sc., P.Eng. Consulting Professional Engineer, Forensic Engineer, Geotechnology Ltd., Halifax, Nova Scotia, Canada July 14, 2021 and updated July 18, 2021 ejorden@eastlink.ca)
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