1. Mick West

    Mick West Administrator Staff Member

    Here a stone tile was suspended between two bricks. A 170lb dynamic weight (me) was applied quickly but gradually. The tile failed with a sharp crack. Analysis shows this was composed of multiple events due to the proximity to the ground.

    Setup:
    Metabunk 2018-02-06 10-53-56.

    First crack:
    Metabunk 2018-02-06 10-54-22.

    2 frames (about 0.01 seconds) later, first crack noise has decayed:
    Metabunk 2018-02-06 10-55-04.

    Second crack, plus other noise.
    Metabunk 2018-02-06 10-56-30.

    Ground impact of wood & tile
    Metabunk 2018-02-06 10-57-22.

    Sound has decayed:
    Metabunk 2018-02-06 10-58-43.

    So the initial snap of the tile was over in less than 0.01 seconds, The entire event took less than 0.04 seconds.

    It seems entirely reasonable that a rapid serious of large scale crackings would be one possible explanation for the faint rapid series of cracks heard at the onset of the Plasco collapse.


    [Minor tech note for completeness, the video was recorded at 240 fps, so each frame is spread somewhere within 0.0042 seconds, with different portions of the frame at different times due to the rolling shutter. So it's impossible to pinpoint an exact time for each frame. However this means, at most, an error of half a frame, or 0.002 second. The waveform and the image sequence still tell the story very well, with the important thing being the initial crack which would be isolated in a larger structure]
     
    Last edited: Feb 6, 2018
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  2. Clouds Givemethewillies

    Clouds Givemethewillies Active Member

    It is largely a waste of time comparing what looks like an anechoic, or time-gated, minimum-phase microphone impulse response (eg. A) with a real-life non-anechoic response from a building. Google things like "reverberation radius" and "RT60"
     
    Last edited: Feb 7, 2018
  3. Mick West

    Mick West Administrator Staff Member

    Indeed, and what Tony was originally comparing was even more removed from reality than that, an "idealized waveform".

    Yesterday someone was shooting a gun a few hundred yards away (I live in the country), so I recorded it. Nothing at all like Plasco, or the idealized wave forms, or the isolated wave forms of the second paper.
    Metabunk 2018-02-07 08-46-22.

    It's hard to even isolate a gunshot out of it, the entire things is echo/reverberation.
    Metabunk 2018-02-07 08-48-48.
    (amplitude scaled)
     
    Last edited: Feb 7, 2018
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  4. Mick West

    Mick West Administrator Staff Member

    The Hansen paper linked was published in 2001, not 1951. The ResearchGate date is incorrect. Note it has references in it going up to 1999.

    Still irrelevant though.
     
  5. benthamitemetric

    benthamitemetric Active Member

    Ah, I relied on the date in the AE911Paper that cited to it. I couldn't figure out exactly where they got that date, but didn't want to spend time trying to sort it out.
     
  6. Seymour

    Seymour New Member

    You wouldn’t say that if you’ve ever been in close proximity of a D-9 ripper shank being snapped off, as I have.

    But perhaps a better objective analysis could be done with examining the “Big Blue” crane collapse in Milwaukee. It’s a well known failure from a 12”pin snapping, and it sounds like an explosion .


    Source: https://youtu.be/ZXr1IeWbP10?t=40
     
    Last edited by a moderator: Feb 10, 2018
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