When we think of a building like this failing,
there can be kind of two different failures.
And of course there are many, many different failure possibilities.
But you have the failure of the concrete itself, or and or
the failure of the rebar within the concrete.
And that's why we're talking about sounds today.
What would it sound like when the concrete begins to crumble?
When you have that concrete falling from the ceiling versus what would
people have heard if it were reinforcing steel within the concrete
structure beginning to fail in different ways?
And of course that changes what we understand about how quickly the building
could fail the patterns of the failure.
>> I'm gonna go back against to the laboratory, which I think is really where
we learn a lot about these sounds and what these sounds are telling us.
So in my career, I've broken a lot of reinforced concrete on purpose to
better understand how it behaves.
And when you're in the lab,
you do use these sounds as a forensic tool as you're mentioning.
And so when a reinforcing bar fractures, it's a very loud noise.
And of course, as the bar size increases, the noise increases.
So here the bars in the slab tended to be number five bars,
maybe a little bit larger.
So, some are probably between a half inch and an inch in diameter.
So those bars are going to have a pretty loud sound, but
not, it's not the same as large steel beams failing.
And the other thing to know is that because that reinforcing
steel is buried in the concrete,
that sound can be more muted than if the reinforcing bar was just out in air.
As we always like to say it in the lab, a reinforcing bar and
air is going to have a louder sound, but
it does sound like you would expect metal fracturing to sound.
But it's also very distinct and when it fractures it short, so
the one barbell fracture, and then if it progresses,
maybe another bubble fractures.
So you could hear these individual sort of popping sounds or
other sorts of loud sounds from the reinforcing fracturing.
So that is one of the first things we can think about in the lab one week because
a lot of times when that bar fractures, we actually can't see it.
Because it's still underneath and covered up by the concrete.
That's the first important sound that we
really identify if we can't observe what's happening.
>> So jumping in here, you did provide a video from a colleague of yours who
is breaking a steel bar in a lab.
And I just want to pause and let our audience look at and listen
to what that sounds like before we go on to other sounds of potential failures.
[BLANK_AUDIO]
That was steel reinforcement of about the size that we would have
expected in Champlain towers in that area that we
are looking at as the potential area where the first failure happened.
What about concrete? The actual coarse aggregate and the cement. What does that
sound like?
And when would you expect it?
That someone at Champlain south would have heard concrete rather than rebar.
>> Right, so if we think about what we've seen in the photographs before the tower
collapse. We've seen a lot of photographs of
structural components, especially within
the garage that have exposed reinforcement so
clear to the concrete cover has fallen off.
And so obviously a small piece of concrete falling off of a bar that's corroded.
And because as the bar corrodes it expands and pushes out and crafts of concrete.
We expect to see that in these buildings that sustain corrosion.
Probably a resident wouldn't be able to hear it unless they were right next to it.
So the sound of the concrete makes depends on the volume of concrete that's failing.
So, one of the things that's very striking to me when I saw
the video that was taken of the garage is that there is a lot of
concrete that had fallen from the ceiling of the garage.
Which is also the pool deck. And so that sound would have been like that piece of
marble that you drop on your floor. That sound would have
been heard most likely
by a lot of residents