# The Naked Scientists Forum

### Author Topic: How to measure the natural resonance of concrete?  (Read 8146 times)

#### homebrewer

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##### How to measure the natural resonance of concrete?
« on: 26/11/2013 13:30:36 »
How would you measure the natural resonance of concrete cube ?

Supposing I had a cube of 10 x 10 cm, cast from normal concrete,
suspended in air by two springs, or perhaps laying on a flat surface ?

How would you go about of obtaining the cube's natural resonance
frequency, on a shoe string budget ?

Thanking you

« Last Edit: 27/11/2013 22:52:39 by chris »

#### alancalverd

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##### Re: How to measure the natural resonance of concrete
« Reply #1 on: 26/11/2013 15:35:27 »
The DrDAQ USB data logger includes a microphone, A-to-D converter, and spectrum analysis software, for about £120. It should give you a reasonable response up to 20 kHz.

Load up the software, plug in the ADC, glue it to the concrete block, and tap the block with a hammer.

Or calculate it from the known properties of concrete. Since the elastic modulus of concrete increases with density, you can just weigh the block and look up the answer in any civil engineering handbook.

#### homebrewer

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##### Re: How to measure the natural resonance of concrete
« Reply #2 on: 26/11/2013 19:47:57 »

I have a small sonotrode workstation, and this works in a similar
fashion in the range between 18 kHz to 43 kHz.

If we now stretch our imagination a little further, and instead looking at
something like a big jet engine, could the same technique be applied to
define by experiment the natural resonance of the jet engine ?

A US company is showing a resonance hammer on "youtube" which will
break up concrete at 44 Hz. What a performance .

#### homebrewer

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• Posts: 40
##### Re: How to measure the natural resonance of concrete
« Reply #3 on: 26/11/2013 19:52:19 »
The DrDAQ USB data logger includes a microphone, A-to-D converter, and spectrum analysis software, for about £120. It should give you a reasonable response up to 20 kHz.

Thank you this is a great idea, I will do some research on the DrDAQ USB data logger.

Much appreciated.

#### RD

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##### Re: How to measure the natural resonance of concrete
« Reply #4 on: 26/11/2013 20:03:11 »
Free audio software called Audacity will show frequency-analyses.

Attach a mic to your block, start recording with audacity, hit the block with a hammer, record until block stops ringing , (a few seconds ?), then look at the frequency-analysis/spectrogram of the sound recording using Audacity for resonance peaks.

Here is something similar with resonant frequencies of coins ... http://www.coincommunity.com/forum/topic.asp?TOPIC_ID=112924
« Last Edit: 26/11/2013 20:12:45 by RD »

#### homebrewer

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##### Re: How to measure the natural resonance of concrete
« Reply #5 on: 26/11/2013 22:06:43 »
Free audio software called Audacity [nofollow] will show frequency-analyses.

That is great, nearly real time frequency analysis at a shoe string budget.

It will be my next candidate for evaluation.

Thank you.

#### RD

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##### Re: How to measure the natural resonance of concrete
« Reply #6 on: 26/11/2013 22:27:12 »
How would you measure the natural resonance of concrete cube ?

Supposing I had a cube of 10 x 10 cm, cast from normal concrete,
suspended in air by two springs, or perhaps laying on a flat surface ?

How would you go about of obtaining the cube's natural resonance
frequency, on a shoe string budget ?

dangling on a shoe-string would be better than on springs, otherwise you'll get the resonant frequency of the springs. You may get different resonant frequencies from the block depending on where you hit it due to different modes of vibration.

http://www.thenakedscientists.com/HTML/content/kitchenscience/exp/sounds-from-a-mug/
« Last Edit: 26/11/2013 22:44:27 by RD »

#### alancalverd

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##### Re: How to measure the natural resonance of concrete
« Reply #7 on: 27/11/2013 09:12:54 »
Quote
If we now stretch our imagination a little further, and instead looking at
something like a big jet engine, could the same technique be applied to
define by experiment the natural resonance of the jet engine ?

"The" natural resonance is a joke! Big wobbly things like jet engines and musical instruments have thousands of resonances, but spectrum analysis will reveal them. In the case of a jet engine, the resonant frequencies depend on the density of the air inside, which depends on speed and power, and the air outside, which depends on altitude. I haven't tried playing a double bass at 40,000 ft but I suspect the same applies.

Some resonances are particularly important. High speed x-ray tubes employ dynamic braking so they pass through the critical and potentially destructive resonance as quickly as possible, and some aero engines have a "yellow sector" between cruise and descent power that is best avoided.

Anyway the trick is always the same.  Set up your spectrum analyser, fix a transducer to the critical part, and tap it with a hammer.

#### SimpleEngineer

• Sr. Member
• Posts: 117
##### Re: How to measure the natural resonance of concrete
« Reply #8 on: 27/11/2013 11:16:33 »

Call a vibration monitoring company with a fictional story about having a large concrete structure you want assessing, get them in on a visit to show you what they do to do it, say you have a set up to see the actions (so you can design the structure to be monitored or somesuch) They will come along and test it for you thinking they had a mutlimillion pound deal on the go.. and then phone them up a few months later saying the project had been cancelled.. sorry!

(I dont know how ethical this could be considered...)

#### Bored chemist

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##### Re: How to measure the natural resonance of concrete
« Reply #9 on: 27/11/2013 14:46:30 »
How would you measure the natural resonance of concrete cube ?

Supposing I had a cube of 10 x 10 cm, cast from normal concrete,
suspended in air by two springs, or perhaps laying on a flat surface ?

How would you go about of obtaining the cube's natural resonance
frequency, on a shoe string budget ?

dangling on a shoe-string would be better than on springs, otherwise you'll get the resonant frequency of the springs. You may get different resonant frequencies from the block depending on where you hit it due to different modes of vibration.

http://www.thenakedscientists.com/HTML/content/kitchenscience/exp/sounds-from-a-mug/

A block on a spring in tension has a resonance too.You have just suggested that stringed instruments are impossible.
« Last Edit: 27/11/2013 14:53:39 by Bored chemist »

#### evan_au

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##### Re: How to measure the natural resonance of concrete
« Reply #10 on: 27/11/2013 17:43:09 »
Concrete is strong in compression, but falls apart in tension.
The question suggests finding the resonances of a free-standing block of concrete - but if you cause oscillations in concrete (eg by hitting it with a hammer), the parts that are in tension will tend to fly off, or crack.

Real concrete structures are kept in tension by pre-stressing them with steel cables. So the resonant frequency is actually the resonance of the steel cables, not the concrete itself.

A prestressed concrete bridge is a stringed instrument! It is played by cars, trucks, the wind and occasionally, earthquakes...
« Last Edit: 27/11/2013 17:45:05 by evan_au »

#### Bored chemist

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##### Re: How to measure the natural resonance of concrete
« Reply #11 on: 27/11/2013 22:04:45 »
The mass of concrete stuck to the cables will have a serious effect on the resonant frequencies.
Also, while concrete is pretty weak in tension, it does have some tensile strength- you can pick up a concrete paving slab by one end, and they are not reinforced.
So it would have resonances of its own.
It's easy enough to check- as described above.

Now, all you need to do is drop a concrete block , and hit it while it's falling, record the ringing and do a frequency analysis of that ring.

#### RD

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##### Re: How to measure the natural resonance of concrete
« Reply #12 on: 27/11/2013 22:21:07 »
A block on a spring in tension has a resonance too.You have just suggested that stringed instruments are impossible.

OK how about shoving & dragging the 10cm concrete block across various-sized paving-stones* with various things, sticks, string, hands  ...

[ the parallel horizontal lines on the spectrogram above are the resonant frequencies + their harmonics ]
http://www.freesound.org/people/thanvannispen/sounds/29987/

and only use the frequencies common to both shoving and dragging on all the paving stones as resonant frequencies for the block.

[* maybe add a pinch of fine gravel ]
« Last Edit: 27/11/2013 22:38:26 by RD »

#### homebrewer

• Jr. Member
• Posts: 40
##### Re: How to measure the natural resonance of concrete?
« Reply #13 on: 28/11/2013 01:59:35 »
Thank you for all your kind contributions, you have been a great help with all your ideas, suggestions and links for hardware and software. I will now do some serious work and design my system based on an "electro-rheological fluid shaker" to analyze my sonotrode's  large and small.

I have concluded on this shaker design, as my sonotrodes can weigh from 500 gram to perhaps 20 kg in the future. So thanks again and I will reply with some pictures once I have finished the works.

THANKING YOU ALL.
« Last Edit: 28/11/2013 13:40:20 by homebrewer »

#### evan_au

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##### Re: How to measure the natural resonance of concrete?
« Reply #14 on: 28/11/2013 20:07:11 »
Out of interest, could you clarify the link between the question about concrete resonances and sonotrodes, please?
Were you perhaps thinking of:
• making sonotrodes out of solid concrete?
• using a concrete powder to machine the sonotrodes?
• using sonotrodes to smash concrete?
• They rely on standing waves to concentrate ultrasonic energy
• Standing waves imply both compression and tension in the sonotrode; concrete will fracture when it is in tension.
• A sonotrode must conduct high frequencies efficiently, with low power dissipation.
You can calculate the resonances of a complex mechanical shape by knowing the speed of sound in the material; from this you calculate the wavelength of a given frequency. The sonotrode should be a multiple of half the wavelength at the frequency of operation.

With modern electronics, at is often easier to change the ultrasonic driver frequency than to resize the sonotrode.

Some sonotrode images here.

#### Bored chemist

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##### Re: How to measure the natural resonance of concrete?
« Reply #15 on: 28/11/2013 21:45:21 »
A block on a spring in tension has a resonance too.You have just suggested that stringed instruments are impossible.

OK how about shoving & dragging the 10cm concrete block across various-sized paving-stones* with various things, sticks, string, hands  ...

[ the parallel horizontal lines on the spectrogram above are the resonant frequencies + their harmonics ]
http://www.freesound.org/people/thanvannispen/sounds/29987/

and only use the frequencies common to both shoving and dragging on all the paving stones as resonant frequencies for the block.

[* maybe add a pinch of fine gravel ]

Don't you just love the internet?
Hello, I'd like a frequency analysis of the sound of dragging a rock please.
Certainly- here you are.
Just 20 years ago that sort of idea would be absurd, now it's easy.

#### homebrewer

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• Posts: 40
##### Re: How to measure the natural resonance of concrete?
« Reply #16 on: 14/12/2013 23:56:46 »

In use now sonotrodes + drilling tools made from SS alloys, which weigh app 750 grams.

But when the projected weight of the sonotrodes + drilling tool called for is 20 to 50 times
greater than previously experienced with, I have to acquire new skills as to handle such a
large mass. And here I will start with my experiments with a concrete cube. SS alloys would
be too expensive to begin with.

I see a propability for the application of new fracking techniques employing sonochemistry
to extract all methan gas in a single application, with fewer chemicals and lesser environmental
burdens and higher yields.

With seasonal greetings.

« Last Edit: 15/12/2013 00:16:10 by homebrewer »

#### homebrewer

• Jr. Member
• Posts: 40
##### Re: How to measure the natural resonance of concrete?
« Reply #17 on: 15/12/2013 00:01:15 »
Out of interest, could you clarify the link between the question about concrete resonances and sonotrodes [nofollow], please?

Thanks for your interest, I have replied to the forum a little bit further down.
« Last Edit: 15/12/2013 00:10:21 by homebrewer »

#### homebrewer

• Jr. Member
• Posts: 40
##### Re: How to measure the natural resonance of concrete
« Reply #18 on: 15/12/2013 00:18:57 »

#### RD

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##### Re: How to measure the natural resonance of concrete?
« Reply #19 on: 15/12/2013 02:21:59 »
... And here I will start with my experiments with a concrete cube ...

I see a propability for the application of new fracking techniques employing sonochemistry
to extract all methan gas in a single application, with fewer chemicals and lesser environmental
burdens and higher yields.

The resonant frequencies depend on the dimensions of the cube , ( like bells of the same material but different sizes producing sound at different pitches ). So I don't think the frequency data is transferable to rocks of varying sizes/types which would be encountered in drilling.

« Last Edit: 15/12/2013 02:25:19 by RD »

#### homebrewer

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• Posts: 40
##### Re: How to measure the natural resonance of concrete?
« Reply #20 on: 17/12/2013 00:42:34 »
... And here I will start with my experiments with a concrete cube ...

But I like to study the "Natural Resonance Frequency" of materials
and complex assemblies at random.

A Russian Professor ZP Shulmann inspired me from an article written
in the late 1990 tees, published in the :

"Journal of Non-Newtonian Fluid Mechanics - Elsevier"

in which Prof. Shulmann undertook "Natural Resonance Research", and
postulated research on large structures from "drilling rigs" to "space rockets"
using electro-rheological actuators.

Now in 2013 the ESA, just finished a massive shaker to test "satellites".

Sadly to say, Britain has lost it's role as a space Nation, but the UK government
spends millions of pounds to support Chinese and Indian space research. To
what avail ?

What will the future be for highly skilled UK researchers and technicians ?
Only opportunities to watch the UK stepping into technical oblivion ?

« Last Edit: 17/12/2013 21:19:21 by homebrewer »

#### The Naked Scientists Forum

##### Re: How to measure the natural resonance of concrete?
« Reply #20 on: 17/12/2013 00:42:34 »