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Re: [Phys-L] How loud is a collapsing building?



David,
- Estimating won't work, since it is such a complicated problem probably
with scant collection of data over the decades.
- Hard data is needed.
- You will need remotely "startable" and stoppable recording sound level
meters at all of the distances which interest you. Or you might need
meters that will be triggered by the sound level at the very start of the
building collapse. The triggering would happen at the closest meter, and
that one would trigger the remainder of the meters.
- Up close you should be seeing a 1/distance relationship, and farther out
you should be seeing a 1/distance-squared relationship.
- You will need to determine whether you will use the dBA , dBC, dB or
other meter setting as they variously reflect the sound levels that will be
included in the measurements within the major frequency ranges.
- You will need to set the meters for fast response.
- You will need to account for reflected sound if there are any major
structures opposite the event.
Good Luck! That should be a most interesting set of data.



On Tue, Jun 23, 2015 at 4:07 PM, David Strasburger <
dstrasburger0f@nobles.edu> wrote:

Setup for a Fermi estimate game that kept me amused last night:

There is a building in my neighborhood that has been declared structurally
unsound and the adjacent streets have been closed off. Conversation with
cop at the barrier:

Q: what's up? why is the street closed?

A: that building's about to fall down.

Q: really?

A: yep - any time: could be five seconds, could be a week. But it's coming
down.

Q: wow, that's going to be something

A: oh you'll hear it all right!


After dinner we heard from our house what might have been thunder and
rushed back into the square, cameras ready, but the building was standing.
Walking back to the house my son asked me just how loud we would expect the
sound to be. We worked up an estimate, but I'm quite sure our guess is
catastrophically wrong because we ended up with 100 dB.

I'm curious how folks on the list would approach the problem. How loud do
you think the sound would be if and when the building collapses?

Obviously it requires many assumptions, followed by a number of grotesque
simplifications and a thorough de-subtling. (For instance, my son and I
supposed that the side walls just evaporated and the second floor and roof
just fell en masse.)

Here are some basics to work with:

1) The building has a footprint of roughly 100'x100' and is two stories
tall. It's a mid-to-early twentieth century masonry commercial building.

2) We live about 500 m away.






David Strasburger
Physics Teacher
Noble & Greenough School
(781) 320-7167


________________________

If you really want to go for it, the city's plot plan is here:

http://www.somervillema.gov/sites/default/files/documents/ElmSt240Plans.pdf

The current google satelite pic and streetview of 240 Elm Street Somerville
MA even shows the bright green wrapping around the scaffolding.
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