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'[EE] Tuned mass dampers'
2007\11\01@122245 by Alan B. Pearce

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The link below leads into an interesting set of pages about vibration modes
and mass dampers. One of the pages has a heap of movies looking at various
experiments with motion and damping.

How to stop a wine glass ringing ...
http://www2.eng.cam.ac.uk/~hemh/tmd.htm

or http://www.tinyurl.com/czvkt

Link found while browsing a science magazine in our library, where a reader
had sent in a question about strange objects attached to the suspension
wires on the Severn Estuary road suspension bridge - which turn out to be
Stockbridge Dampers, or a variation thereof (see link at bottom of page to
go to interesting 6 to 8 page discussion of these and variations).

No I am not attempting to outdo Russell, just figured these would be
interesting to people here.

2007\11\01@211249 by M. Adam Davis

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This is great!  Every time I saw something like that on the powerline
I would wonder what electrical purpose it served.  I need to broaden
my thoughts!

The second link appears to be classical music, and a 30 second clip of
Die Walküre (Ride of the Valkyries) is just not as inspiring as the
whole thing.

Now I'm gloing to have to find it amongst my other music.

-Adam

On 11/1/07, Alan B. Pearce <spam_OUTA.B.PearceTakeThisOuTspamrl.ac.uk> wrote:
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>

2007\11\01@213606 by Carl Denk

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The subject has an application, on tall structures in seismic active
buildings, a damper is installed on an upper floor. It is usually a
heavy weight with hydraulic or elastomeric (rubber) shock absorbers to
snub the buildings sway. Sometimes also used for wind loads.

M. Adam Davis wrote:
{Quote hidden}

>> -

2007\11\02@011152 by Russell McMahon

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The subject has an application, on tall structures in
seismic active
buildings, a damper is installed on an upper floor. It is
usually a
heavy weight with hydraulic or elastomeric (rubber) shock
absorbers to
snub the buildings sway. Sometimes also used for wind loads.

Indeed.
Taipei 101, the world's tallest building by N-1 of the N
measures used for such things (comm tower didn't reach as
high as ?) when I visited a few years ago has an immense and
immensely impressive $4 million very dense, 660 ton (!)
beehive looking structure hanging in a multi storey well on
its top floor for this purpose.

First building over half a kilometre (!) high.
Didn't feel THAT impressive from the top considering.

Photo here of the damper plus much more interesting stuff.

       http://en.wikipedia.org/wiki/Taipei_101

http://images.google.co.nz/images?hl=en&q=taipei%20101%20damper%20wind&oe=UTF-8&um=1&ie=UTF-8&sa=N&tab=wi

   Thornton-Tomasetti Engineers along with Evergreen
Consulting Engineering designed a 662[14] metric ton steel
pendulum that serves as a tuned mass damper. Suspended from
the 92nd to the 88th floor, the pendulum sways to offset
movements in the building caused by strong gusts. Its
sphere, the largest damper sphere in the world, consists of
41 layered steel plates, each with a height of 125 mm being
welded together to form a 5.5-meter diameter sphere.[15]
Another two tuned mass dampers, each weighing 4.5 tons, sit
at the tip of the spire. These prevent cumulative damage to
the structure due to strong wind loads..

2007\11\02@050930 by Alan B. Pearce

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>The second link appears to be classical music,

Ah, that is because I copied the link wrong ;))

Should be http://www.tinyurl.com/3czvkt

which should then take you to the first link.

Glad you enjoyed it.

>The subject has an application, on tall structures in seismic
>active buildings, a damper is installed on an upper floor. It
>is usually a heavy weight with hydraulic or elastomeric (rubber)
>shock absorbers to snub the buildings sway. Sometimes also used
>for wind loads.

Yes I have seen descriptions of these for earthquake proofing tall buildings
in Japan.

There are also some bridges in New Zealand where the bridge structure is
used as the mass, and the damper portion is a lead/rubber mount. I used to
work at the DSIR where one of about 3 people who were paid more than
department director tested such mounts using a D8 Caterpillar tractor with
the track removed and a big eccentric mounted on the driving shaft, to get
enough energy to test the damper unit.

Picture of the railway bridge I am thinking of here
trains.wellington.net.nz/misc2/south_rangitikei_1985.jpg
(I don't think I would want to be on this in an earthquake). Also appeared
on a stamp
http://stamps.nzpost.co.nz/Cultures/en-NZ/Stamps/StampsHistoricalIssues/1989+-+1985/Bridges.htm
which gives a description of how it can move in an earthquake (see the third
description).

For some interesting looking theory (which also discusses this bridge) see
http://www.eng.buffalo.edu/~bruneau/4NSBC%20Pollino%20Bruneau.pdf

Guess I better do some real work now ... ;((

2007\11\02@063603 by Russell McMahon

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> Picture of the railway bridge I am thinking of here
> http://trains.wellington.net.nz/misc2/south_rangitikei_1985.jpg

Is that the one that fell down fatally during construction
the first time ?

Maybe that was Mangaweka.

AFAIR from long ago, the one mentioned has a maximum design
side sway of 5 metres at the top during a quake. Now THAT
would be an interesting train ride.


       Russell


2007\11\02@070131 by Alan B. Pearce

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>> Picture of the railway bridge I am thinking of here
>> http://trains.wellington.net.nz/misc2/south_rangitikei_1985.jpg
>
>Is that the one that fell down fatally during construction
>the first time ?
>
>Maybe that was Mangaweka.

Hmm, don't remember that.

>AFAIR from long ago, the one mentioned has a maximum design
>side sway of 5 metres at the top during a quake. Now THAT
>would be an interesting train ride.

I don't think one would not be worrying about how interesting it would be -
one would probably require a change of trousers ... Guess that makes it 10
metres wide at the top, so 5 metres would still (just) allow the CoG to
still be between the feet.

The other bridge I remember is the Symonds St vehicle bridge in Auckland,
over the south motorway. It is flexibly mounted in such a manner that it
resonates with a bus engine at idle. With a set of traffic lights at both
ends, it can be un-nerving to be sitting at a red light and have a bus pull
up beside you in the bus lane, and suddenly have the car bouncing vertically
with the combined movement of the bridge and car suspension giving the car
body an oscillation that feels like about 3" of vertical movement.



2007\11\02@083221 by Carl Denk

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The Tacoma Narrows bridge "Galloping Gertie"
http://www.ketchum.org/bridgecollapse.html is probably the most famous,
the traffic loading or strong winds had nothing to do with it. Just a
moderate wind in right direction, the right shape, and harmonics. This
was 1940

1964 Univ. of Mich. as part of a senior level structural engineering
class I reported on the Quebec bridge, started  3 times before it
lasted, and still in use today. The 2nd collapse - the cantilever end
amplitude was 6 feet after the center span load came loose. Bridge
opened 1917.
www.google.com/search?q=quebec+bridge&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a
(address might get wrapped, should be one line)

Alan B. Pearce wrote:
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