How can I prevent vibration of metal structure in wind?

[Englishman in Adana (Turkey)]

Here's a challenge for you all:

The flat we live in has a wide balcony surrounded by vertical metal bars topped by a larger diameter round rail.

The vertical bars are approx. 1cm diameter and 1m long (didn't measure

- guestimated) and spaced about 10 cm from each other. When the wind blows (which seems to be continuous as we are on the coast) the vertical bars get into rythm and make quite an impressive noise. so much so that some of the residents cannot sleep (their balconies are the same).

Can anyone suggest a method to stop this? We cannot fix them in the middle with a horizontal bar because of safety regulations. I was thinking of something like the dampers used on high-voltage lines to stop the conductors vibrating (see

for details).

Is there anywhere on the 'net that can calculate the weight required?

TIA for any help...

[Stuart]

Can't help with an answer but what safety regs prevent you fitting a horizontal bar and why should that make them any less safe ..?

Stuart

[Chris Bacon]

Can you clamp a bar to the middle as a "temporary measure", or use "U" bolts to clamp something vertically onto some of the bars?

[The Natural Philosopher]

that was my though, also slapping random weights on them (in the middle) will at least mean that the overall resonance of ALL of them will be broken up..

[Chris Bacon]

Presumably it makes it easier for infants to climb them.

[The3rd Earl Of Derby]

they might work in a horizontal plane but how do you know they will work in an Vertical upright plane?

Given the fact we don't know the regulations as to why you can't fit stabiliser bar in center, can you explain what the regs mean? as to why you cant do this.

-- Sir Benjamin Middlethwaite

[John Cartmell]

Climbing up and over?

I assume the problem is that the horizontal bar would need to be fixed solid in order to stop the vertical bars from vibrating at that frequency - and such a bar would be unsafe. All that's left is to change the profile of the vertical bars by adding something to them - at the extreme a piece of panelling along the whole area. Whatever you do you have an aesthetics problem...

Unless you fix a horizontal bar at some distance *outside* the vertical bars but attached to each. Expensive and it may not work. ;-(

[Grumble]

Fitting a horizontal bar would make them easier to climb. You know how kids love to climb stuff.

Grumble

[Donwill]

You could grip the vertical bars and or the horisontal bar in different places (one at a time) to see whether the vibration is damped by contact with your hand, with this method you might find the antinodes of the offending vibrating member(s), you might even be able to feel the vibration? The solution to the problem will probably become obvious to you once you've established the position of the antinodes, However come back to us with more info, it's quite an interesting problem Regards Donwill

[The3rd Earl Of Derby]

Sheet opaque or transparent perspex affixed to the outside of the rails to act as wind barrier.

-- Sir Benjamin Middlethwaite

[tony sayer]

Ah!, thats what their for then!. Won't be going 'an nicking some eh!....

Perhaps some plastic polythene clear tubing split down the side then put over them might damp them without looking a pigs ear?...

[Dave Fawthrop]

|Englishman in Adana (Turkey) wrote: |> The flat we live in has a wide balcony surrounded by vertical metal |> bars topped by a larger diameter round rail.

In the UK it would make the rails "not fit for purpose"

|> The vertical bars are approx. 1cm diameter and 1m long (didn't measure |> - guestimated) and spaced about 10 cm from each other. When the wind |> blows (which seems to be continuous as we are on the coast) the |> vertical bars get into rythm and make quite an impressive noise. so |> much so that some of the residents cannot sleep (their balconies are |> the same). |> |> Can anyone suggest a method to stop this? We cannot fix them in the |> middle with a horizontal bar because of safety regulations. | |Can you clamp a bar to the middle as a "temporary measure", or |use "U" bolts to clamp something vertically onto some of the bars?

This is called resonance, which is quite a problem to get rid of. Do not put things in the middle, that would merely double the frequency,

1/3 of the way down would triple the frequency. Put things in a position which does not involve the numbers 1 to 10.

Have you thought of bungee cord which would be cheap and might damp the resonance.

[Sponix]

It's possible the bars aren't resonating but the noise is due to the wind blowing between the bars.

Presumably, if the wind blows at a certain angle you'd get a similar effect to the hole in an organ pipe?

sponix

[Kate]

Firstly, although I don't know how to crunch the numbers, I'm sure a metal bar 1 cm in diameter will be too 'stiff' to vibrate at audio frequencies, if just driven by air blowing over them at right angles.

What might be happening is that the bars are very slightly different, and athough resonating inaudibly, the slight differences in frequency cause a 'beating' or 'heterodyning' to give an audible note.

Another prospect is that the bars are acting as open-ended organ pipes; these would almost certainly resonate at audio frequencies. The solution is simple: stop the airflow over the openings.

It might be helpful to describe the kind of sound they make in more detail; do they do this with *any* wind, or one that blows from a particular direction? Is there a critical wind-speed?

[Stuart]

Ah right ..Kids ...Grrrr ...Forgot about them pesky critturs ..lol

How about a vertical plate projecting outwards slightly ,one at each end .Would that possibly work by breaking up the wind blowing through the bars .Suppose it would depend on the direction of the wind .

Stuart

[Sponix]

If, as I suspect the rails are acting as organ pipes, I wonder if sticking something to the outside of some/all the bars would be sufficient to break up the airflow?

Self adhesive draught excluder perhaps?

sponix

[Sponix]

How about growing a climbing plant up the bars?

[Dave Fawthrop]

|On Fri, 17 Feb 2006 12:07:56 +0000, The Natural Philosopher |wrote: | |>that was my though, also slapping random weights on them (in the middle) |>will at least mean that the overall resonance of ALL of them will be |>broken up.. | |It's possible the bars aren't resonating but the noise is due to the |wind blowing between the bars.

The wind *causes* them to resonate.

[Dave Fawthrop]

| |Englishman in Adana (Turkey) wrote: | |>

|>Can anyone suggest a method to stop this? We cannot fix them in the |>middle with a horizontal bar because of safety regulations. I was |>thinking of something like the dampers used on high-voltage lines to |>stop the conductors vibrating (see

for |>details). |>

|>Is there anywhere on the 'net that can calculate the weight required? |>

|>TIA for any help... | |Firstly, although I don't know how to crunch the numbers, I'm sure a |metal bar 1 cm in diameter will be too 'stiff' to vibrate at audio |frequencies, if just driven by air blowing over them at right angles.

OP does not say they are *solid* metal, Tubes would resonate.

[Englishman in Adana (Turkey)]

Many thanks for all the replies, (I was AMAZED to get 17 replies in 2 hours!!)

Just to sum up the answers:

Yes, the regulations are to prevent climbing and possible falls. There were horizontal bars there before, they got them all changed at God knows how much expense!!

The wind doesn't have to be very strong to start the vibration, I guess the frequency is around 40-60Hz (compared to mains hum on a radio). I tried holding the bars sometimes, but holding the one making a noise makes another start!! and it's difficult to determine which is the culprit. (I thought that the welding may be vibrating but they all seem firm, therefore resonance is the problem.)

Thought about a bungee cord or similar, plants would be a good solution but not instant. Methinks trying slit PVC pipe would be easiest, maybe on just a few of them would solve it...

I'll let you all know after a few attempts. Thanks again ;)