Engineers: Probable Champlain Towers Collapse Sequence
Thanks to a surveillance video, photos, a 2018 building-system survey and the original 1979 plans, structural engineers have pieced together the probable sequence of the fatal progressive collapse of part of the 12.5-story Champlain Towers South residential condominium, north of Miami Beach in Surfside, Fla.
But the initiating event on June 24 that brought down a wing, about 150 ft long, of the 40-year-old reinforced concrete structure remains a mystery.
“I’m trying to find the trigger,” says Allyn Kilsheimer, founder of KCE Structural Engineers, who is investigating the collapse for the city.
The start of the deadly event, which killed at least 11 people and left 150 still missing, “seems to be near the base … but there are lots of questions,” Kilsheimer adds.
The surveillance video from a nearby building that has been widely studied starts a few seconds into the collapse. Kilsheimer, at the site since June 25, says he hopes other videos will surface, including one that shows the very beginning of the collapse. “That one video [we have] doesn’t give you a 3D view of the building,” he says.
The wing of the residential building still left standing, looking from the east. The shear wall of the elevator-stair tower is in the center of the photo.
Photo by: Jeff Greenberg/Universal Images Group via Getty Images
Reinforced Concrete with Flat Plate Slabs
The reinforced concrete building has flat-plate floor slabs. Flat plates are relatively thin concrete slabs supported directly on columns. The building is lightly braced by shear walls.
The video shows that the failure occurred lower down in the central south-facing perimeter of the building, which is a fat L in plan. The failed long leg of the L extended east to west on the north side of the footprint. “It is possible the failure started higher up in the building on the interior and cascaded downward but it is not visible in the video,” says Jack Moehle, a professor of structural engineering at the University of California, Berkeley.
The video also shows a “very rapid vertical collapse of the interior portion of the building, with relatively little apparent side sway,” says Moehle.
The north side of the long leg followed the south side collapse, almost immediately. “That is apparent from the video,” says Glenn Bell, a forensic structural engineer and director of Collaborative Reporting for Safer Structures (CROSS-US), a division of the American Society of Civil Engineers’ Structural Engineering Institute.
Next, the east end of the building, nearest the Atlantic Ocean, got pulled toward the midsection to its west.
The video shows the east end standing for a short while after the midsection collapsed, gradually leaning toward the midsection. Likely there was an imbalanced load due to loss of support from the portion of the building that collapsed, which dragged the remaining portion sideways until its gravity load-carrying capacity was exhausted and it also collapsed, says Bell. In the second part of the collapse, the floors are a little offset from one another because of this effect, he adds.
Champlain Towers South was finished in 1981. One failure theory is that there may have been a problem with the elevated pool deck slab near the crook of the L-in-plan building.
Imagery © 2021 Data SIO, NOAA, U.S. Navy, NGA, GEBCO, IBCAO, Landsat / Copernicus, Google, Imagery © 2021 Maxar Technologies, Map data © 2021
Shorter Wing Left Standing
The failure stopped at the west end of the midsection, near where the two legs of the L join, leaving the shorter leg of the L standing. The break was cleaner along the elevator and stair core on the southwest edge of the collapsed section, where there is a shear wall, says Bell.
“There are lots of theories circulating about the trigger,” adds Bell.
Some observers, who have studied the collapse video and photos, the 2018 field survey report by structural engineer Frank P. Morabito and the original 1979 plans by William M. Friedman and Associates Architects Inc. have pointed to distress in the pool deck at the base of the area on the south side of the midsection.
The deck sits over the one-level-basement parking garage, which fills the entire site, including and beyond the building’s footprint. The structural engineer for the development was Breiterman Jurado & Associates.
The theory is that the pool deck’s concrete slab may have failed, possibly because of deteriorated waterproofing, says Bell.
The failed north wing, the longer leg of the L building plan, is shown at the top of the site plan. The section remaining runs north-south, on the west side of the building.
Courtesy of Town of Surfside
Repair Estimate
In his report to the Champlain Towers condo association, Morabito estimated the price of needed repairs at $9.1 million. The estimate for remediating the garage, the entrance and pool deck was the most expensive line item, with a cost of roughly $3.8 million. Remediation of the building’s façade would require an additional $3.2 million, according to Morabito. The repairs, which were planned for 2021 back in 2018, had just begun when the collapse occurred.
There are at least three theories about the trigger of the progressive collapse, beyond the pool deck slab: column failure, slab failure due to punching shear or failure of the pile foundation system, perhaps under the pool deck. Kilsheimer, Bell and others speculate there may have been more than one contributing factor, as in a perfect storm.
Progressive failure is caused either by columns that fail axially due to axial over-stress or shear damage that progresses to axial failure or punching shear failure, says Moehle.
In punching shear, one or more of the building’s flat slabs develops a shear failure around the column and drops relative to the column.
If there is no continuous bottom reinforcement in the slab passing over the columns—a detail not required in 1981—then the slab can move downward relative to the column, redistributing load to adjacent slab-column connections, which in turn can fail. A slab that eventually lands on the floor below it overloads that floor system, and there is more punching shear, says Moehle, who has done extensive testing of concrete structures.
If the columns were the trigger, then it is likely but not certain that the collapse started at the bottom of the building where the axial loads are largest, adds Moehle. If it was the slab-column connection, then the failure could have started just about anywhere in the building and progressed downward in a vertical collapse that extended across the floor and down to the base.
Circled area in photo shows a column with rebar hanging out like hair strands, missing its slab after the slab crashed down, vehicles and all, to the floor below it due to punching shear. The view of the debris pile is from the south looking north.
Original photo courtesy of Miami-Dade Fire Rescue
Some photos of the debris suggest that the collapse involved, at least as a secondary mechanism, punching shear failures. “This could have been a secondary aspect of the collapse, with the primary cause of the collapse being something else,” says Moehle, who adds that his observations are “very preliminary speculation.”
Other possible contributing factors: It is “plausible” that sea spray over 40 years increased the chloride content of the concrete, which, after reaching a critical point, starts corrosion of the rebar, adds Moehle. There could have been a more recent acceleration of corrosion, which accelerated the loss of column strength.
One area of the pool deck simply ended up a level down, columns and all, with no sign of punching shear. It is possible that the pile foundations under that area sank because of the opening up of sinkhole or some other factor. The lowered deck could then have pulled down the rest of the structure.
Another theory is that differential settlement across the footprint of the building can cause the redistribution of internal forces and can over-stress some members.
“It will be a long time before this has been thoroughly studied and thoughtfully considered” to give engineers the confidence to draw lessons about what happened, says Moehle.
See more here: enr.com
Header image: CHANDAN KHANNA/AFP via Getty Images.
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Peter F Gill
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Roy Spencer opined that it may be a sink hole. He said that he had heard a that the swimming pool drained before the collapse.
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Joseph Olson
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Grenfell Tower in London burned uncontrolled for 24 hours on 14 June 2017 and the abandoned reinforced concrete, 24 story frame is to be demolished in 2022. On Sept 11, 2001 two 110 story skyscrapers burned for a hour and fell in 14 seconds each. Today Dr James Fetzer and I will discuss alternate, non group think methods of non explosive demolition.
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Lloyd Slezak
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From the article:
“One area of the pool deck simply ended up a level down, columns and all, with no sign of punching shear. It is possible that the pile foundations under that area sank because of the opening up of sinkhole or some other factor. The lowered deck could then have pulled down the rest of the structure.”
The photo shown just above this quote refutes the statement. Several columns in the collapsed pool deck area can be seen “punched through”. A corollary of this observation is that, if the pool deck failed first, it clearly did not take columns with it.
My view is that the pool deck collapse was secondary. Need to see the columns beneath the tower in the garage (after debris removal).
Regarding Roy Spencer opinion, the pool itself appears fully intact after the failure.
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Heretic Jones
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Um, no.
For a good summary of this Jupiter and Twin Pillars ritual please check out this link.
https://gematriaeffect.news/the-florida-champlain-towers-south-collapse-destruction-of-the-twin-pillars-the-full-moon-part-1/
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Tom O
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I watched that video over and over – most everyone that put it up played it multiple times. The speed with which the central part collapsed, and yes, even the fall of the late falling wing, just doesn’t look like cascading failure. Let’s face it, if it is falling because of a structure failure, it is going to fall sequentially, floor to floor. That first part of the the collapse lust looks like the whole section collapsed nearly simultaneously, and dropped nearly straight down. Seems suspicious. And a 9 page report on structural issues sure doesn’t suggest, to me, that there were any real issues there at all. And the TV presentations of that report with 3 highlighted pairs of words and with no way to see what the content of the report was, looked like they were trying really hard to hype this as a failure.
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D. Boss
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C’mon people – enough of this conspiracy, nut job speculation about something deliberate or an even more ludicrous suggestion of it being explosive demolition….
Here is a real structural building engineer assessing the FACTS:
There is a new video shot 7 minutes before collapse, showing the pool deck collapsed first (a portion is seen as debris on the garage floor) And I might add these people were a mere 75 feet from the north side of the building and adjacent to the parking garage opening on the North side, and if there were some explosive demolition charges – they would be deaf, and likely dead or severely injured from shrapnel and the blast over-pressure. So enough about explosive nonsense!
And if you go back and watch 3 or 4 more videos from this real engineer, you see that the 3 columns addressed in the 2018 report, are the most likely points of failure to have brought down the first of 3 parts of the building seen collapsing in the surveillance video.
https://www.youtube.com/watch?v=dSQq2FimiXY
https://www.youtube.com/watch?v=e3xrUkRtHQE
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Carbon Bigfoot
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“you see that the 3 columns addressed in the 2018 report, are the most likely points of failure to have brought down the first of 3 parts of the building”
The column failure was the result of the sinkhole collapse.
A real professional engineer and concrete builder.
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D. Boss
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I don’t dispute the sinkhole postulate. What I am tired of is idiotic theories like controlled demolition….
And if you watch all the videos at this “Building Integrity” site linked to above, he presents some reasonable ideas the forensic engineers would explore. Failure of the key columns he identifies due to corrosion of the rebar – is also highly plausible. (more so now that the video of 7 minutes before collapse has emerged)
And a wake up call is seen in this video:
“On Point – Episode 4, How Concrete Damage Can Hide”
And finally, I defer if you are in fact a real professional engineer and concrete builder – and wholly concur that no structure anywhere in South Florida should be built below grade. That could in fact be the ultimate cause or fault in the system. (it never should have been built or designed that way)
Aside, I reside in S. E. Florida – where water table is in fact only feet or inches below grade so you are preaching to the converted here….
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T.C. Clark
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Hemingways’s house in Key West was built by first excavating limestone from the ground….and then building a 2 story limestone walled house over the hole. A Miami Municipal building was built from locally quarried limestone that has some visible ancient animal or plant outlines in the limestone.
Carbon bigfoot
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My observation is that many of the comments here are not by concrete builders. Or for that matter, someone that has direct experience with the perils of actual high-rise construction. As someone who has physically controlled the hose end of a concrete pumper discharge and built structures, I think I can assess the qualifications of those that offer an opinion on this collapse. How many of you have actually engineered or designed a high-rise and further, actually been involved in the hands-on construction of a high-rise? Or for that matter, live in a Florida Condominium and serve on the Board of the POA??
Over the last fifty (50) I have been privileged to work with such an individual, engineering at times or partnering in the actual physical construction of projects too numerous to mention. Many of the projects were in soil conditions and water table, i.e., New Jersey Shore (beach) and Philadelphia PA which is built on a marsh land fed by underground streams.
My colleague is still involved in his own General Contracting business at the age 76 trying to groom his youngest so he can retire. I forwarded numerous information to him, indicating he might want to consider selling his condo before it is worthless.
He sent this response from his phone and unedited for your perusal. He was out in the field working and his first response did not come through—this is his second.
I have been working outside and all day so I don’t remember what I said but whatever it was it was profound. Our condominium is a flat slab normally reinforced structure . WE aren’t subject to the salt air problems that places near the ocean. Anyone who builds a basement in Florida is crazy. Almost anywhere in the state the water table is just below the ground. Every time they dig a hole for a retention basin they create a lake . The normal water table is then diverted and thus they get sink holes. Sink holes are a problem in a place like the Villages (central Florida) but since they are all single story buildings the ground doesn’t open up and swallow whole buildings. This building was built by a builder–developer which might be the worst combination prior to Obama–Biden.
Bonding Companies don’t allow developers to be their own builders and smart banks won’t finance builder–developers . A guy like Trump calls himself a builder but he never builds anything with his own company. He always hires a builder or construction manager to build his buildings. This same developer built a bunch of buildings so there are probably a bunch of buildings that need serious review. The only thing worse than a builder, developer is an Architect-Builder-Developer.
That’s what Bill Rouse (Philadelphia Company) was trying to do with his own Architectural Firm, Building Company and Development. He even tried to have his own subcontracting company. When he went to the banks they demanded a Bond and of course the bonding companies were smart enough to say no way. Who do you sue ? There is an old argument that has never really been settled. If a designer has E & O and the builder has liability insurance and there is a latent defect -is the insurance company liable 40 years later if the latent defect occurred when the insurance was in effect ?
In my view the basement ( ten feet +/- ) below grade was a latent design defect and a potential ticking time bomb.
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