It is March 1981 and construction workers are preparing to pour the concrete for the
roof of a new apartment block.
Most of the concrete framework has already been completed, during the pour, the newly
built structure would fail catastrophically killing 11 and Injuring 10s more.
Today’s video we are back in Florida to what seems to be a state tradition: the collapse
of a concerete structure.
My name is John. Welcome to plainly Difficult and this is my video on Harbor Cay Condominium
collapse.
Background
Our story starts in the land of the Florida man, officially known as the US state of Florida,
but today more specifically cocoa beach.
A small coastal town around here on a map.
The area's economy was closely linked to NASA’s operation from nearby Kennedy Space Center,
in which many locals were employed either directly or via 3rd part companies.
as such when the Apollo program was shelved in 1975, the local economy crashed.
Unemployment went to 14%, but the local jobs market would improve after the announcement
of the space shuttle program a few years later, this would bring new people to cocoa beach
and as such new housing was needed.
Cocoa Beach was had been undergoing a building boom with new condos being built along State
Road A1A.
Part of this demand would be plugged with Plans to build a new 5 story concrete framed
set of apartment blocks.
The developer was Milwaukee-based Towne Realty, they had built other buildings in the area,
and to help they contracted out construction work to Univel Inc.
The building plan
The cocoa beach apartment blocks were planned to be made up of 5 stories and were to be
242ft 74m long and 58ft 18m wide.
The structure would rely on reinforced concrete, and framed with multiple columns 10 x 18 in
(254 x 457 mm) wide with narrower ones of 10 x 12 in (254 x 305 mm) at the ends of the
building, and those at stairwells were 8 x 12 in (203 x 305 mm).
The floor slabs were to be 8 in (203mm) thick although slightly thinner for the balcony
sections.
But state regulatons had actually required 11 inches.
Both the slabs and coloms were reinforced with atsm 60 grade steel.
To hold the steels in place during concrete pouring things called chairs were used, these
insured that the vital reinforcement is at the correct depth.
You see if it’s not in the right place the concrete section can bend as the load is spread
unevenly.
The facade walls were to be non structuralmasonry.
Construction works began in 1980 with preparation of the site and building the blocks foundations.
The structure itself would begin to be built in February 1981,when the ground floor form
work was begun.
The schedule for frame construction was to add a floor a week this would involve:
Starting at The south half of each particular floor slab cast on Tuesday.
The placement of steel bars in the north half of the slab and casting of the columns over
the south half were carried out the next day.
On Thursday, the columns in the south half were stripped, then. the north half of the
slab was cast and the forms below the south half of the slab were lowered.
On Friday, the forms in the south half were replaced by reshores and flown to the same
location in the story directly above, and the columns over the north half were cast.
The following Monday, the columns in the north half were stripped, the steel bars in the
south half of the slab above were placed, and the flying forms below the north half
were lowered, replaced by reshores, and flown to the story directly above.
But although quick soon after the first floors were added workers noticed some worrying indicators
of disaster ahead.
Several workers raised concerns that cracks had started to show on some of the concrete
work.
After each levels flying form were removed, cracks could be seen on the slab at the mid
span and where the Columns met the floor.
A foreman circled the cracks with a crayon and called out the structural engineer, on
March 10, 1981.
By now the 2nd and 3rd floors were in place, the suggestion was to place more reinforcing
bars in the mid spans.
Joints between the columns and the floor slabs were described by some workers as honeycomb
or spiders web cracked.
Slabs around the north and sound end 2nd floor apartments had deflected almost immediately
after their forms were removed.
Deflection is the bending or sagging of a slab.
A worrying little quirk was found during the construction of the 4th floor, workers discovered
on the east side near the lift tower, a puddle of water.
What does a puddle have to do with anything you might ask?
Well This was hinting at the building becoming uneven; the depression was refinished with
a concrete skim, but bizarrely the water reappeared.
Multiple issues were highlighted by workers on almost every part of the construction,
parts of the structure had its rebar exposed after form removal.
Which needless to say exposes the structure to corrosion and poorly poured concerete.
Concrete quality was also poor with low water content, meaning it dried out too quick for
it to be properly finished.
The project received its concrete from two sources the first was from a ready made supplier,
this account rated for ⅓ of the total requirement.
The other was from an on-site batch plant, this was the source of the dodgy concrete.
Although issues were raised, construction continued all the way to the top floor, nothing
had failed so fair well until it did.
The disaster
The time had come to start preparing the Cocoa Beach Condominiums roof, workers began their
shift on March 27, 1981, and I'm sure no one expected how the day would end.
The building at this point had In the south end, the exterior walls for the first two
stories were in place, and In the north end, construction of masonry walls was completed
in the first three stories. Each floor has some level of activity on it
with various stages of the project being undertaken, on the roof concrete was being placed around
column line H. Two flying forms at the north end of the building
did not have concrete on them. As the pour had continued throughout the day
some workers noticed some trembling throughout the building, at 2:45 pm a worker on the 5th
floor heard a popping sound. At roughly 3pm, around the center of the building
at the 5th floor suddenly gave way, in what would be described as a "one long slide with
one thump." Within seconds the entire structure plummeted
into the ground, with a massive pile of concrete and rebar, anyone who could nearby swamped
what was the building trying to find and save any workers who were just a few minutes before
having just a normal day at the office. Due to the area undergoing a building boom,
many workers on other projects helped with the rescue works, some turning up with heavy
equipment. Emergency responders and airforce members
reached the site and helped with the rescue efforts.
Floor slabs were cut into approximately 20 ft (6 m) square pieces by air hammers and
removed by mobile cranes, during the rescue operations.
The work continued over the weekend as heavy equipment removed the concrete and other debris,
finding dead bodies as they went. It would only be Sunday that rescuers got
down to the foundation where the final two bodies were recovered.
In total 11 were killed in the collapse with 27 more being injured.
Now as with all of these types of incidents, the question of how and why must be asked,
and this would lead to an investigation. The investigation
The NATIONAL BUREAU OF STANDARDS would head up the investigation into the collapse, investigators
would visit the site on March 28-30, 1981, one day after the collapse, and the second
visit was made on April 7-8, 1981. Investigators found The slabs broke away from
the columns at the slab-column interface, as well as a number of vertical reinforcements
bent severely hinting it had been damaged during fabrication.
A number of conflicting witness statements from the workers onsite raised questions over
how the building was reshored. You see reshoring is a vital part of concrete
building construction, after the forms are removed when the newly poured concrete is
set enough, reshores are added to support the structure as the concrete hardens.
This is because even though it looks solid concrete gets fully set over a period of time,
in which it needs extra support. This is where the reshores are vital as if
they are removed too early then the concrete hasn't gotten strong enough to support itself
and more importantly the weight put on top of it.
This issue can be even more dramatic if the concrete is of poor quality.
The investigation would involve not just the onsite visits but also forensic examination
of the whole project from design to concrete mix.
They found the concrete was of poor quality especially around the samples taken from the
5th floor, which was discovered to be less than 85% of the required 4000 psi of compressive
strength. After all was said and done the investigators
released its report, and it was really damming of the whole project.
They found that the placement of the reinforcing bars in the concrete slabs were inconsistently
placed which violated the ACI Code requirement for clear spacing.a congestion prevented flow
of concrete into the space between reinforcing bars.
This inconsistency created a congestion that prevented flow of concrete into the space
between reinforcing bars, which inturn caused issues with bonding the concrete to the rebar.
The concrete slabs were only 8 inches (200 mm) thick instead of the required 11 inches
(280 mm) to satisfy the American Concrete Institute's Building Code minimum.
During construction lower individual chairs for supporting the top layer reinforcing bars
were used, reducing the effective sheer capabilities of the slabs.
This caused the structural integrity of the building to be severely reduced, and the addition
of extra weight during the roof pour was the straw that broke the weakened concrete camels
back. The damning report helped with charging Two
engineers, an architect, and two contractors with negligence, misconduct and failing to
conform to state and local building laws. Both of the engineers gave up their license
to practice engineering in the state of Florida, were charged fines, and had to promise to
never practice in Florida again. Unival, one of the contractors, folded almost
immediately, under the financial strain and The developer, contractor Towne Realty out
of Milwaukee, agreed to a settlement out of court to avoid litigation. They have continued
to develop properties to this day, including several more in cocoa beach.
The disaster helped the state shore up its enforcement of construction projects, but
it wouldn't fix it completely as well. We know from a number of recent collapses that
nothing is foolproof Strangely enough one of which also involved
a construction project started in the 1980s, this came to light very recently called the
Champlain Towers. Now a number of you have noticed I haven’t
been doing disaster scales at the end anymore, well this is because the ratings were getting
a little bit erratic. So I’m launching a new scale the phone balls
rating, it will have 5 set ratings. The first is not great- after all the story
found it’s way on to the plainly difficult channel
Second is bad day at the office The next is oh balls people will remember
this Fourth is outright negligent
And the final and 5th rating is dumpster fire This weeks video is outright negligent
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Plainly difficult videos are produced by me John, in a wet and windy suburban Southeast
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https://www.govinfo.gov/content/pkg/GOVPUB-C13-c3d64fd6d7663600a6e3a147919af0a1/pdf/GOVPUB-C13-c3d64fd6d7663600a6e3a147919af0a1.pdf
https://digital.library.unt.edu/ark:/67531/metadc38326/m2/1/high_res_d/metadc38326.pdf