How did a pool deck break this 13-story building in Miami?
There were many great comments in my previous videos on Champlain Towers South.
I will respond to the main questions posed and demystify this tragedy further.
Was neglect and corrosion the root cause. Perhaps not.
First let's recap the collapse sequence that makes most sense.
This column may have been first to fail because of excessive spans. The column
punched through the slab much like a pencil through paper. Engineers call this punch shear.
This portion of the pool deck collapsed in a quick continuous cascade.
Roughly seven minutes later, half the tower collapsed on June 24 2021.
The signs were there that the pool deck was structurally crippled
and required immediate and drastic action, one year before it failed.
Test holes drilled into the pool slab by engineers revealed ominous structural distress.
The cores indicate how the slab had crumbled and partially disintegrated.
These are bars of steel reinforcement inside the slab also called rebar. But look closer because
there is something curious. The steel does not seem to have significant rust.
Perhaps corrosion was not a central factor after all.
And the cause of the failure more likely due to inadequate structural design and
weak construction. The weak slab had likely been cracking and disintegrating over years.
The lurking danger was hidden from view. The slab had been on the brink of failure for long then
without warning it failed suddenly. The internal crumbling was localized around the columns.
These views show the pool slab intact. The core samples were from these locations.
The official investigators have the broken building pieces. They can evaluate the extent
of corrosion check for dodgy construction and verify if it was built according to the drawings.
Pinpointing the root causes is essential so this doesn't happen again.
Many commented how rickety the columns looked. It is essential tall buildings
have substantial bracing elements to resist the sideways sway from wind or earthquakes.
They are called shear walls shown in red. This building had inadequate shear walling.
All walls of this stair tower should have been solid. But only one was made of concrete. This
is part of a broader pattern of cutting corners on the structure to save money.
The larger columns supported special beams. The tower columns on the west did not extend all the
way to the ground. The lobby driveway columns were in different positions to suit the plan.
These hefty elements in orange called transfer beams redirected the vertical load into the
columns below. This standalone transfer beam here prevented these columns from obstructing
traffic in the parking level. The transfer beams were not a contributor to this collapse.
The columns which failed were continuous from roof to foundation.
Here the smaller H-shape transfer beam is visible in the cleared out site.
These tower columns were still intact. They did not fail from compression load.
The building fell because the slabs were too weakly connected to the columns.
The building ripped loose from the columns and dropped. Champlain South
failed primarily from punch through aggravated by the shock waves generated in the collapse.
Viewers asked why the building didn't have beams.
This building fell because of a lack of punch shear rebar, not because it didn't have beams.
This is called flat slab construction. It is the norm and is safe provided it is done properly.
Beams are disruptive and space hungry. Column heads or drop panels also add strength. But
all of these make the building taller and slow construction which is not feasible.
Eliminating these brings nice clean uninterrupted ceilings and reduces the building height.
The structural drawings indicated this rebar at the slab to column connection.
This is an example of what punch share rebar looks like.
I find no evidence Champlain South had any type of punch share reinforcement. Not in
the engineering drawings or in the photos of the rubble. This was bare bones steel reinforcement.
Under normal conditions including hurricanes the lack of punch reinforcement would not
have mattered. The building would have stayed up for all its useful life. But during this
freak event of losing multiple facade columns the lack of punch rebar proved catastrophic.
Because the pool deck brought down the tower, many viewers asked why they were connected. This is a
good question. However it is standard practice for the ground floor slab to be a key stabilizer.
It braces tower columns against sway. The side walls of the basement will collapse
inwards from the weight of the earth. The slab provides essential bracing.
The perimeter sidewalk is currently barricaded off in case the basement walls cave in.
The pool deck should never have pulled down the tower. The tower fell because of this ill-fated
configuration of beams. i believe they played a crucial role in mortally damaging tower columns.
The critical columns had eight reinforcing bars made from steel embedded inside the concrete.
The rebar carries about half the weight of the tower. The bars joined with overlaps. Kinked
sections allowed the load to carry down in a straight vertical line. This arrangement of
overlaps and kinks is standard construction. Under the immense load the kinks want to bulge outwards.
This outward force is contained by rebar loops and the floor slab. The slabs tore
loose in a clean cut as can be seen here at the lobby. And did not result in wider damage.
But at these beam locations it was a very different story. The beams rotated against
the columns applying a huge lever arm force causing crippling crunching and mangling.
The beams had substantial rebar which applied a large pulling force. It pulled at the weakest
point of the kink. Both forces worked in unison which distorted and bent the rebar like this.
This action pulled down the bars above. Much of the column rebar was mangled and destroyed.
The crippled columns held for about seven minutes but then they failed
and dropped. They dragged down the floors which tore loose bringing down the tower.
The analysis presented here comes from my building knowledge as an architect
and discussion with structural engineers. We need to wait for the official forensic
findings to be certain of the causes. I believe the structure was flawed from day one because
it lacked proper punch through rebar. With the correct structural steel neither the pool deck
nor the tower slabs would have failed and the tragedy averted. This failure sends a loud message
of how ignoring lurking dangers and cutting corners to save money can lead to catastrophe.
We need to look after our buildings and the planet. We ignore the warning signs at our peril.