Security cam video of the collapse. (Video courtesy of Fox 13 and YouTube)
UPDATE June 25, 2021. Updated with numbers of dead (4) and missing (159).
In the middle of the night (1:20am, Thursday, June 24) a 12 story beachside building with 136 condominiums in Surfside, Florida (just north of Miami Beach) suffered a total collapse of the northeastern section with about 55 condominiums. 159 residents are feared missing and 4 are known dead at the time of this writing.
A total of 35 people have been rescued from the building, two from the rubble, including a little boy and a man who had been on a balcony.
“We could see his arms sticking out and his fingers wiggling,” said Nicholas Balboa, who was standing outside when he heard a loud rumble. “He was just saying, ‘Please don’t leave me. Please don’t leave me.’” The boy had been with his mother.
Hundreds of emergency vehicles and personnel are on the scene and a massive search and rescue effort is underway. Search dogs were on the scene since 2am but are getting “no hits,” said Surfside mayor Charles Burkett on NBC’s Today Show. “It pancaked. There’s just not a lot of voids that they‘re finding or seeing from the outside.”
The affected structures at 8777 Collins Avenue are known as the Champlain Towers and are composed of three buildings. The South Tower, which suffered the collapse, is the oldest and biggest with 136 units. All three towers are 12 stories tall. The units were sold as luxury residences, recently fetching upward of $700K for a 3 BR, 2 bath unit and $2.9 million for the penthouse. The Towers have been popular with international buyers.
Ironically, the South Tower was undergoing a recertification, required of residential building reaching 40 years of age by Florida law, which would have included a structural evaluation.
What Happened?
In the video, it appears that the central section of the building pancakes, then and the collapse pulls down the Eastern, beach facing section.
That close to the Atlantic, look for long-term corrosion in the steel columns and beams, says an engineer.
The manner of collapse is compared to the manner of the 9/11 World Trade Center collapse, although the cause is almost certainly different.
The collapse is compared to a planned demolition, one engineer saying “You could not get it to pancake like that if you tried to demolish it.”
Observing the video and photos from the scene, the cause of the collapse lacks consensus. A reasonable voice reminds us failures of this type can, and often do have multiple causes. Many qualify their guesses as early conjectures and would like to respectfully wait for results of an official investigation.
One engineer calls the pancake collapse “incredible” and could not the result of the failure of a single column.
A news service points out that repairs were being done on the roof and a local observer mentions heavy equipment on the roof but engineers dispel the notion of anything on the roof causing a local failure, but concede that heavy equipment and supplies on the roof could pass the load to the base of the buildings through columns causing the failure, which from the video, does seem to start at the lower floors.
While the details of the structural construction are not known, there is mention of punching shear failure as a possible cause. Punching shear can cause failure in concrete slabs that rest on columns, creating a concentrated load on the surface that can quickly punch through the slab.
As the collapsed section faces the ocean, structural damage from long term corrosion should be looked at as a possible cause.
The area had suffered a magnitude 3.9 tremor off the coast earlier in the week (June 21), the result of Navy demolition exercise.
Was it Subsidence?
The ground floor has a parking level. An engineer notes the presence of exhaust fans, indicating a underground parking. Building a multi-level below grade parking facility at sea level that close to the ocean would entail building what could be described as a reverse bathtub, a concrete structure to keep the ocean water out. The bathtub for the New York City’s World Trade Center covered 16 acres and was 7 levels deep.
Oh My God
A 2020 study of the area by Shimon Wdowinski, professor at the Department of Earth and Environment at Florida International University, stated satellite radar measurement of the landscape (including buildings) showed lowering at rate the rate of 1.9 mm a year since 1993. In USA Today, Wdowinski mentions that the measurement would detect structural damage, subsidence or a combination of the two. The subsidence could have sped up since his study but cautions it is too early to tell if that was the main cause of failure. The study was done to see which parts of Miami Beach and Norfolk, Virginia were sinking due to rising sea levels and flooding. It found that pockets of the Miami landscape had suffered significant subsidence. Singled out were 4 areas of concern. One of them, a beachfront area described as having “a 12-story high condominium" is clearly (by longitude and latitude readings) the site of the Champlain Towers. Wdowinski says he filed the report and thought nothing of it until surprised by the news of the building collapse and realized, "Oh my God, we did detect that."
While a gradual subsidence, even at a relatively high rate, will cause enough movement to cause cracks, distortion and other detectable signs of impending disaster, it is conceivable that a gradual increasing of forces could at some point lead to a quick and catastrophic failure, such as a punching shear failure.