Guy Wires tension

[edanyel]

I don't know if this is the correct forum.
My question is: Does anybody know if there is some international Standard stablishing the correct tension for a guy wire?

I'm talking of a flare stack supported by for guy wires for stability.
I'm looking for something like "...10% of the nominal strengh..." or similar.

Thanks in advance
Daniel

 

[csd72]

I dont think that there is an easy answer to this. I expect that the tension is related to the acceptable deflection in the guys and the tower.

 

[JStephen]

Are you designing from scratch or tightening existing guy wires?

You wouldn't want to exceed the design forces used for the stack or guy anchor designs.

 

[msquared48]

I agree with csd.

When you factor in the lateral loads resisted by the guy wire, which is highly variable, coupled with the size of the wire, grade, connections, plumbing (as in maintaining a vertical attitude) considerations, etc...

It seems to me the pretension force applied needs to be included in the forces seen and the SF applied on the appropriate combination of forces, including that force.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[paddingtongreen]

We used a factor of three for static guys. Divide the manufacturers stated breaking load by the factor. It gets higher for hoists etc.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[edanyel]

It's an existing flare stack, ten meter long over a forty meter high roof.
The four 35 mm diameter and ten meter long guy wires have been there for almost thirty years.

I bought like for like replacement wires. I know the nominal tension for the new ones, but the question is...shall I tension them hard as a guitar string...shall I leave them loose...shall I ask in this forum...

I'm looking for the simplest and most practical answer.

Paddington you talk about 30% how did you get to that figure? Just guess? Did you find it written anywhere?

Thank you very much for your answers
Daniel

 

[JStephen]

If you don't have any information on allowable forces, size or details of the anchorages, etc., I would aim for the slackest setting I thought would work. It would be a lot easier to tighten one up a bit than to have some concrete block come popping out of the ground or to pull your stack down through the building.

 

[paddingtongreen]

edanyel, I'm a Professional Structural Engineer, and even if I was an assistant, I would still be a little offended at the suggestion that I just guessed my safety factors.
That was what we used for transmission and distribution design. However, I did the web search that you should have done in the first place and came up with this:

http://www.usbr.gov/ssle/safety/RSHS/appD.pdf

It has some standards listed (section 3) as well as the "normal" safety factors.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[chicopee]

As far as I am concerned, there is no standard. I have read articles where pre loading is as low as 1/8th of guy cable breaking strength and as high as 1/2 of breaking strength. It all depends where the guy cables are used. For guyed tower, several hundred feet high,such as those used for radio and TV transmitting stations and for tower cranes, you would expect very high preloading forces since you would not want these guy cables to sag on the leeward side of the structures and whip under wind gusts . In your case, 1/3rd of the breaking strength as suggested above sounds reasonable.

Somewhere in your building archives, there could be a set of building plans with the engineering detailing preloading force on the existing guy cables. You could also do your own analysis which is ot that complicated if you do engineering calculations.

 

[edanyel]

Paddintongreen, please accept my apologies I didn't intend to be offensive, sorry if I did.
I'll read carefully this appendice you linked.
JStephen your point is clear, thanks.
The rest of you thanks, you've all been helpful

 

[csd72]

edanyel,

You have indicated by your comments that you are probably not a structural engineer.

It is important that you realise the delicacy of this situation. If you tighten up the guys too much then you may cause a compression failure in the stack, if you tichten them up too little then the stack will deflect too much which could cause fatigue failure.

Best to get an experienced consultant to come in and look at this before you simply replace like for like.

Will it be adequate to current code? It may need to be brought up to current or seismic codes.

What is the condition of the stack?

How will you safely swap over the wires?

This is a far more complex issue than it appears on the surface.

 

[MiketheEngineer]

CSD72 has hit the nail on the head!!

I might add - If you tighten one side more than the others.....bad things can happen

 

[BAretired]

Here are a few links about the subject. You may want to browse through them.

BA

 

[BAretired]

oops, forgot to paste the following:

http://www.google.co.uk/search?hl=&...ff&rlz=1B3GGGL_enCA259CA260&ie=UTF-8&aq=3&oq=

BA

 

[paddingtongreen]

My advice is to hire some experienced transmission/distribution line constructors to set the guys, they have the tools and they have the "feel", guying is not an exact science.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[JStephen]

With a stack, you'd have thermal movement that you wouldn't expect on an antenna or similar guyed structure. I'm not sure it'd be significant, but oughtn't be overlooked at least.