Surfside Condo Collapse
Hi and welcome to Failurology; a podcast about engineering failures. I’m your host, Nicole
And I’m Brian. And we’re both from Calgary, AB.
This week in engineering news, fluid based light filtering technology.
● Researchers at the University of Toronto developed a multilayered fluid window system that aims to drive sustainability in the building industry.
● The fluid that flows through the windows is used to control the type and distribution of solar energy that enters a building. It is even able to filter out infrared heat while allowing light to pass through.
● This is often a tricky balance, because light coming in means less overhead lighting and happier people inside, but also means a lot more heat. In the winter more heat is ok, but not in the summer.
● Current systems either let both light and heat in or block them both, but aren't able to block one while the other passes through.
● The savings are said to be very significant, with minimal energy required to pump the fluid through the glass.
● If you want to read more about the fluid window system, check out the link on the web page for this episode at failurology.ca
Now on to this week’s engineering failure; the Surfside Condo Collapse.
● Champlain Towers South was a 12 story beachfront condo in Surfside Florida
● Surfside is roughly 17 km NE of downtown Miami and located on a series of islands between Biscayne Bay and the Atlantic Ocean.
● Champlain Towers South partially collapsed at 1:22am on June 24, 2021, causing the death of 98 people. The two year anniversary is 6 days after this episode comes out.
● Four people were rescued from the collapsed section, although one died shortly after. 35 people were rescued from the uncollapsed portion. 12 days later, it was confirmed that there were 136 survivors.
● The building was demolished 10 days after the collapse.
● The south building was built in 1981 as part of a three building complex, champlain towers north, completed in 1982, and champlain towers east, built between the two and completed in 1994.
● All three buildings were an L-shape, with 12 stories. The south building contained the most units at 136. The penthouse unit design was controversial since an exemption was needed to exceed the building height limits in Surfside. The penthouses were also not on the original building permits. And when it was added last minute, it led to a cease and desist order while the town debated the extra level. In addition, the first general contractor quit and a second was replaced.
● Surfside had a moratorium on new development in the 1970s due to water and sewer infrastructure limitations. Champlain towers was the first new construction allowed after that was lifted. The developers of the complex paid the city $200,000 ($831,000 today) to help replace the sewer system and get approval to build the condos.
● In addition to the 12 stories of condos, the building also contained underground parking and an outdoor pool at the ground level. Due to the L shape building, with a rectangular parkade, the base of the pool made up the roof of the parking below.
● There are a few different ways to construct a building. Usually the structure is some combination of metal and concrete. Best I can tell from all the reading I’ve done on Champlain is the building was constructed using reinforced concrete. After the formwork is installed, which is the mold that the concrete is poured into, rebar or metal rods are placed in a grid like pattern on the formwork to reinforce the concrete. The diameter of the rods, spacing, height within the slab, and other items impact the strength the rebar gives to the slab. In some cases, there may be two or more layers, and there is usually something that resembles a cage around the tops and bottoms of columns to provide extra strength.
● Most of my rebar knowledge comes from years of trying to put holes in slabs for pipes and ducts while avoiding rebar. In new construction, you can either locate the holes away from the rebar or extra rebar can be added around the holes; with the structural engineers approval of course. In older buildings where you are cutting holes, if the hole has to go where it has to go, like under a new toilet for example, reinforcement on the underside of the slab to transfer the load around the hole.
● The collapse started at 1:14am with a partial collapse. From video footage, this appears to have taken place in the parkade.
● Then at 1:22 am the middle section of the building collapsed, followed by the eastern wing. The collapse took 12 seconds and was caught on security cameras nearby.
● It is referred to as a progressive collapse because it started with the failure of a primary structural element, which then led to the failure of adjoining elements.
● An engineering report was completed in 2018 that notes the waterproofing layer around the pool deck was not sloped, meaning water stayed there until it could evaporate. Which in an area as humid as Miami, could take a very long time. Since the water could not evaporate, over time it caused a lot of damage to the pool deck. Some of this was visible in the sizable cracks on the ceiling of the parking deck underneath the pool.
● The report went as far as to say that the pool deck was beyond its useful life and required replacement. It also noted that “failure to replace waterproofing in the near future will cause the extent of the concrete deterioration to expand exponentially” and the repair would be “extremely expensive”. The estimate for repairs at the time of the 2018 report was about $9 million.
● In Oct 2020, engineers noted that repairs around the pool couldn't be completed without destabilizing the area.
● On April 9, 2021, a letter was sent to residents with a $15 million repair program. The roof was part of the repair program and this work was underway at the time of the collapse, but the pool deck had not started.
● In addition to rain and pool water getting into the cracks, due to the location near the ocean, it was highly likely that salwater had also infiltrated the cracks which can cause more aggressive spalling. Spalling is when large fragments of concrete break off the larger mass.
● After the collapse, photos came out from a pool contractor that showed standing water, cracking concrete, and corroded rebar next to the pool. The photos were said to have been taken 36 hours before the collapse.
● A bystander also took a video of water pouring into the parking garage from above and large fragments of concrete lying on the floor. This video was time stamped 7 minutes before the collapse.
● In addition, a report found that the building had less rebar than the construction drawings had shown in the footings and columns. The report notes that this alone would not necessarily cause the collapse. It’s possible that rebar was reduced during construction. It's possible that the design showed more rebar than required. And it's possible that the contractor cut corners and the engineer didn't notice.
● The columns that held up the surviving portion of the tower were almost double those of the sections that collapsed; violating building code requirements at the time. The columns around the pool deck were the smallest. Columns were also placed too far apart in some locations to prioritize parking below. Shear walls were placed in two locations near elevator or stair shafts; shear walls are long columns that look like a concrete wall. But they were also too small and only provided support in one direction. Some beams originally planned for around the pool deck were left out of the final drawings and not constructed. Heavy planters around the pool deck did not drain properly, adding weight to the slab and columns below. The connection between the perimeter wall and the main floor slab was trained and also suffered water damage; requiring repeated maintenance over the years. Punching shear, which is when columns poke through the slab above, was calculated by engineers after the collapse and noted to have always been a risk.
● Due to these factors, which likely led to a number of cracks shortly after construction was completed, hidden by a decorative topping and pavers, the main floor slab sagged under its own weight by up to 40mm or 1.5 inches in some places.
● Corruption during construction has been cited as a potential cause of the collapse. The architect and structural engineer had a number of issues related to cutting corners. The architect had his license suspended for “gross incompetence” after two billboards he designed blew over in a hurricane. And the engineer designed a parking garage that started to fail as soon as it was completed.
● Even though there was some evidence that the engineer did not complete proper inspections, the fact that it stood for 40 years before collapse, through numerous hurricanes, and the excessive deterioration around the pool, and noting that I am completely speculating as a non structural engineer, leads me to believe the water infiltration, which corroded the rebar, was the more likely culprit of the collapse.
● The consensus amongst the structural engineering community, based on the publicly available evidence, was that a column or the slab itself under the pool deck failed, which caused the deck to collapse. This formed a crater under the middle of the tower which then caved in. and we have seen similar examples on other failures we’ve discussed. When any member of a structure fails, its load is transferred to adjacent members. If they are strong enough, they can carry that load. But if they are not, they fail and it creates this domino effect, leading to catastrophic failure.
● One resident on the fourth floor told her husband that a crater had appeared in the pool deck, unfortunately she did not survive the collapse. Another resident who survived later noted that the pool deck and street level parking had collapsed into the parking garage just before the building collapsed.
● To add to all these reasons, the building had been sinking by about 2 mm per year since the 1990s. Miami Beach was relatively stable, but parts of it were still sinking. This phenomenon is called subsidence and it is usually caused by the removal of ground water or other minerals from the ground which causes the pockets between earth materials to get smaller or collapse and the surface to drop. This is what happened to New Orleans; it was built on marshland and as the groundwater is pumped out it causes the surface level to drop. Although I believe New Orleans is sinking at 6-8 mm per year; 3 to 4 times that of Miami.
● The Miami Herald did a really really good investigative series on the collapse that ended up winning them a 2022 Pulitzer Prize. We will include a link to that in the sources for this episode.
Since the Collapse
● The site was bought in May 2022 by a Dubai based developer, with proceeds from the $120 million sale going to the victims and their families.
● In May 2022, a Florida bill was passed to create a statewide inspection program for condo buildings more than 3 stories tall. In 2025, buildings will go through what is called a “milestone inspection” when they reach 30 years of age, or 25 years if located within 3 miles of the coast. They will then be inspected every 10 years afterward. The records of each inspection must be posted online and shared with tenants. In addition, condo boards will no longer be able to waive the requirement to keep a reserve fund large enough to maintain the structural integrity of the building.
So there you have it, the Champlain Tower South collapse on June 24, 2021. A damaged pool deck with a repair plan that was too late led to the catastrophic failure of the 12 story condo building in the middle of the night.
For photos, sources and an episode summary from this week’s episode head to Failurology.ca. If you’re enjoying what you’re hearing, please rate, review and subscribe to Failurology, so more people can find us. If you want to chat with us, our Twitter handle is @failurology, you can email us firstname.lastname@example.org, you can connect with us on Linked In or you can message us on our Patreon page. Check out the show notes for links to all of these. Thanks, everyone for listening. And tune in to the next episode where we;kk talk about lac Megantic, a drastic train derailment in the middle of a tiny Quebec town that happened a decade ago
Bye everyone, talk soon!