Miami Beach, Champlain Towers South apartment building collapse, Part 10 79

[SFCharlie]

A continuation of our discussion of this failure. Best to read the other threads first to avoid rehashing things already discussed.
Miami Beach, Champlain Towers South apartment building collapse
Miami Beach, Champlain Towers South apartment building collapse, Part 02
Miami Beach, Champlain Towers South apartment building collapse, Part 03
Miami Beach, Champlain Towers South apartment building collapse, Part 04
Miami Beach, Champlain Towers South apartment building collapse, Part 05
Miami Beach, Champlain Towers South apartment building collapse, Part 06
Miami Beach, Champlain Towers South apartment building collapse, Part 07
Miami Beach, Champlain Towers South apartment building collapse, Part 08
Miami Beach, Champlain Towers South apartment building collapse, Part 09


SF Charlie
Eng-Tips.com Forum Policies

 

[DroppedBits]

Noise data measured by myself with a calibrated Type 1 system out in Wynwood back in May between May 12 and May 21. Wynwood is directly under the flame of MIA and is much closer to MIA than Surfside.

The data was measured both in dBA and dBC averaged over 1-second intervals, so it's a little softened compared to the LAeq_max and LCeq_max. I excluded the max levels from this chart because they are a little disingenuous because usually it's somebody slamming a trunk near the microphone station more than it is broad environmental noise. Max levels didn't exceed 100dBC except once or twice in an 8-day window, and listening to the recorded audio files at those times, it was construction noise of a contractor shooting a nail gun in proximity to the microphone -- not MIA traffic.

About a month earlier I had this measurement system also set up next to the Paramount Miami Worldcenter tower. Lot of MIA noise there, but it generally was in the 80-90dBC range. Obnoxious if it's coming through your window at 3am in the morning, but it's not going to shatter your window or bring your building down. The peak MIA noise was was basically equivalent with the peak waste management truck showing up to empty dumpsters.

Think you've got to find another tree to dig up if you think MIA noise had any tangible impact on the Champlain Towers structure.

 

[Demented]

IMnvHO It is not that Miami-Dade should "compile and present", but what is their justification to prevent the Town of Surfside, the lawyers for the bereaved, the press, from photographing the aftermath? In a normal crime, yes, you want to be able to use the fact that a suspect knew something that had not been made public, but how could that apply here?

The site has been cleaned of remains. As far as I can tell, nothing is happening, why do they need to keep t a crime scene for 3 more weeks?

Of course, they may need to file fill the foundation with water or soil to keep it from collapsing, but that's a safety issue, not a criminal one.

SF Charlie
Eng-Tips.com Forum Policies

Surfside are the only ones being kept out, and they're trying to also keep everyone else out.
Some media is being kept out, but for good reason. Did you guys see the crew who broadcast a body being recovered live on youtube while talking shit with an open mic from a rented vila in view?


This is owned by the Mayor of Surfside. He's freaking out for a reason, and it's not because he cares about Surfside.

http://www.burkettcompanies.com/

The surfside building department is under some heavy scrutiny for many many reasons. With all we've seen so far between files missing, no organization, a whole slew of not caring by officials, the above by the Mayor; even if they hired the best engineer in the world, I don't think we can trust the Town of Surfside here.

 

[SFCharlie]

Thank you for your thoughtful reply! I give it a star. I'll shut my thoughtless mouth...

SF Charlie
Eng-Tips.com Forum Policies

 

[Demented]

Not thoughtless at all. It's not a normal situation by any means.

Precision guess work based on information provided by those of questionable knowledge

 

[SFCharlie]

Surfside Mayor Burkett says Champlain Towers South collapse was inexplicable like an earthquake

"This is one of those things in life that is inexplicable like an earthquake,
like lightning striking,
like uh like a spontaneous huge forest fire that destroys hundreds of homes you know,
nobody knows about,
and you know we were unlucky enough to be the little town where that happened."

Earthquakes are planned for and built for. Lightning strikes are planned for and lightning rod installed. Forest fires are planned for, space is cleared around buildings, fire department are established, and tanker planes are built.


SF Charlie
Eng-Tips.com Forum Policies

 

[SFCharlie]

[URL unfurl="true"]http://www.burkettcompanies.com/[/url]

Thanks for the link.

I know Miami doesn't have earthquakes, but this scares the stuff out of me...

SF Charlie
Eng-Tips.com Forum Policies

 

[zebraso]

data was measured both in dBA and dBC

It may be irrelevant, but aside from the weighting, what do you think you are measuring in the subsonic range of frequency that would coincide with the resonance of a large structure? Are you plotting anything in that range?

 

[DroppedBits]

It may be irrelevant, but aside from the weighting, what do you think you are measuring in the subsonic range of frequency that would coincide with the resonance of a large structure? Are you plotting anything in that range?

This particular measurement system is accurate to within +/- 1dB down to 5Hz. I didn't have spectral logging enabled on this measurement so I can't break down by individual third octave frequency bands, but in terms of the weightings, if there were significant low-frequencies that may contribute to a structural vibration, I would still expect it to present as a peak within the dBC with less prominence in the dBA measurement. Below is an example of aircraft coming or going from MIA.

Red: LCeq_dt
Blue: LAeq_dt
Pink: LCeq_dt minus LAeq_dt

You can see where my cursor is that the aircraft registers in both dBA and dBc, but that as the flight passes over, it is more prominently in the dBC which is where you see the pink line start to trace up. At 65 dBC though, it is still not going to topple a building.

Now I do have an audio recording of this so if I really wanted to be nerdy, I could drop that into a spectrum analyzer but there's not much point and I have other work I need to get out the door tonight.

I will note that structural vibration is a specialty in its own right and not one I can speak to with much confidence, but if there was prominent noise from aircraft in the low frequencies that may subject a building to significant vibration, it would still show up in these SPL measurements. Some of these flyovers may be enough to rattle some windows, but you're not going to rattle an entire building and certainly not generate any resonance that's going to have more impact on the structure than you'd get from an average day of gusty wind.

 

[zebraso]

Now I do have an audio recording of this

Nah, that's ok. Thanks. I think you got it covered. I just did not know the low cut-off of the system. Completeness and all that. No other filters were applied. As far as gusty wind goes. Some seem to think it was a quasi spontaneous event anyway and so all this talk about triggers might not matter. 400 pounder doing jumping jacks. Well that's not happening anyway.

 

[Demented]

"This is one of those things in life that is inexplicable like an earthquake,
like lightning striking,
like uh like a spontaneous huge forest fire that destroys hundreds of homes you know,
nobody knows about,
and you know we were unlucky enough to be the little town where that happened."

Earthquakes are planned for and built for. Lightning strikes are planned for and lightning rod installed. Forest fires are planned for, space is cleared around buildings, fire department are established, and tanker planes are built.

Full segment. Not that there's anything really interesting.

https://www.youtube.com/watch?v=zYqaCg4ZbEQ

Precision guess work based on information provided by those of questionable knowledge

 

[zebraso]

Full segment.

Well what's notable is the thought process that leads to a statement like that doesn't conjure up anything that sounds like accountability is in anyones' interest.

 

[Demented]

@MaudSTL

https://www.local10.com/news/local/...g-through-rubble-to-escape-building-collapse/

Precision guess work based on information provided by those of questionable knowledge

 

[Debirlfan]

The following are the longest body cam videos I've found, around 18 minutes each.

https://www.youtube.com/watch?v=j-yYnuZAPno&t=3s

https://www.youtube.com/watch?v=e8J5YzFreys

https://www.youtube.com/watch?v=1BSHmIQQioQ

 

[AusG]

I expect that the resonant frequencies of RC buildings vary on the design and the firmness of the connections but FWIW this one, a 1980s RC construction in Beijing, China (could Florida be worse?) had a significant resonant frequency between 2 & 3 Hz as seen by the sound of subway trains being filtered in successive floors.

.
These frequencies are within the "G" weighting of industrial sound measurement, which DroppedBits' instrument may not be set up for. Again FWIW the researchers noted what they called effective damping of these frequencies by the structure with time.


Given the pervasive nature of ambient infrasound from wind and from road traffic, etc, and above all the tiny amount of actual energy being imparted, I am 100% in the fuggedaboutit camp vis a vis aircraft noise. All this submitted for general interest only.

Chinese building reference

https://www.iitk.ac.in/nicee/wcee/article/14_07-0066.PDF

general info on infrasound measurement within a doc on wind turbines

https://wind.appstate.edu/sites/wind.appstate.edu/files/040810-SoundLitReviewWTGs.pdf

 

[zebraso]

resonant frequency between 2 & 3 Hz

So would it be fair to say you would have to move the earth before you could excite any modes in a normal structure? I have to keep saying normal though. I mean that's what you would have to expect. And it's why the immediate reaction is "that's preposterous".

 

[MaudSTL]

https://www.local10.com/news/local/...g-through-rubble-to-escape-building-collapse/

Thank you! I was so pleased to see this. I have been going through the long bodycam videos and plan to update the Timeline this weekend, now that we have a better idea of what Shamoka Furman experienced. In one of the long videos, she states strongly that there were three collapses…just as Gabe Nir did. The big difference to me is that she perceives the first collapse as something with the elevator, which would make sense since her desk was so close to it and the sound would have traveled easily through the elevator shaft. Unlike the Nirs, she does not mention thinking that the sound came from above.

I have also watched and logged all the bodycam appearances by the Penthouse 12 Blue Shirt with Badge Guy. One thing I noticed about him is that he mentions his wife and kids to both the cops and Fire. However, I can’t understand what he says about them. I also noticed that he seems more comfortable talking to Fire, which makes me wonder if he’s a firefighter. Unlike Shamoka, who is disheveled and covered in dust, Penthouse 12 Blue Shirt with Badge Guy is tidy and clean. But he does at one point make a statement about looking down and seeing the collapse, which could put him in 1208 or 1209 if he’s from CTS instead of some other building. As BKNJ said, he is likely to be from some other building. I don’t think we have enough info about him to place him, plus he only tells us about hearing the deck and the building collapse, so no new info of value to our inquiries.

 

[AusG]

The audio coupling between soil and foundations is going to be greater than that between air and walls but I don't have any quantitative info.

 

[zebraso]

I guess it's a mechanical pressure wave or impulse at VLF and not audio. But the same principal would apply. No earth is being moved. I doubt that can even be produced at the frequencies in question by aircraft. However in the weeds in terms of multifactorial cause for that deteriorated deck to let go. A different question, different frequencies. It's far out there I know. But in terms of multifactorial and how many factors? At that point does it matter? If you're the mayor, it doesn't, apparently.

 

[Sym P. le]

FWIW I interpret Penthouse 12 as the 12th floor, distinguished from the 13th floor penthouse. He doesn't give a unit number as it was not of foremost importance to him in his stream of conscience, and certainly doesn't disqualify his statement.

And furthermore, using a literal interpretation of these statements, which are desperate attempts by these witnesses to describe events to which none of them would have anything close to lived experience, is pathetic. If it sounded like an airplane crash, the key word is "like" as in what they could only imagine it being similar to.
.

 

[AusG]

Audio of course is still a mechanical pressure wave, but functionally speaking the distinction is meaningful. The difference is one of scale and hence of the potential at high magnitudes for inelastic deformation somewhere in the system. A vibration in the soil, by virtue of its greater mass and hence momentum can impart a greater vibration to the building that air could not - excluding bomb blasts and the like of course. It comes down to availability of energy and the efficiency of transfer. There is not enough energy being imparted to blow the mayor's toupée off.