Do I need guy wires?

[Snowbear]

I have a supply of steel street light poles to work with. They are all damaged to some degree. Most are the kind that support the big highway lights that connect to a 10' arm that bolts at the top of the pole. I got one of the lights and with the arm weighs about 100-125#.

I took a good lower section and a good upper section and fitted them together for a total length of 52'. My trial genny is a FP w/6' HDPE blades. Since these poles don't normally have guy wires I was thinking I could go without. What do you think should I run guy wires?

[bob g]

the answer to your question depends on at least two very important variables, and possibly
a few less important ones.

1. how big of a mill are you planning on mounting up there?  a 500 watt machine in a moderate wind area, probably no guys needed, a 30 ft machine in a high wing area??

2. what sort of winds do you see around there?  what is the likely maximum wind speed
in your area? doubling wind speed quadruples the power, the "cube" law thing you know
and that means a lot of torque on the tower if you have a big machine up there.

those towers like you have are capable of holding up and arm that is quite heavy, but
the wind action is limited by the area of exposure, and what action there is imparts more torque on the tower section (twist) than it does bending.

you might call the manufacture of the tower and see if one of there engineers can give you some data on what they are capable of standing up to. probably won't get an answer but it never hurts to ask.

me i would probably figure on guys, and at the risk of starting all the bruha again i would use a minimum of 5 guys myself.  i never liked the idea of what happens if one fails...

just an opinion, ymmv and all that

 bob g

[ruddycrazy]

Hi Snowbear,
                   I used to play with those F&P motors as wind gennies and I made a tower out of 3" heavywall gal pipe. I had my guys about 2 metres below the genny and after a huge gale the tower was bent close to 45 degrees above the guy wire point. Now going 52' (close to 16 metres) without guy wires IS asking for a short term wind genny. The first decent wind will see the top of the pole swing quicker and more violent than the Obamanations speach on how good his medicare scheme is. Also there is no mention of a gin pole so how do you expect to raise the tower and lower it for working on from time to time.

Cheers Bryan

[Snowbear]

Thanx Gents. I will continue to think on it. Some concerns I think of... these poles were not meant to be guyed. Moving the fixed point high up the pole reduces the length available for flex and concentrates it at the uppermost guy. This could cause failures like Bryan saw. OTOH these poles weren't designed to have a big sail area either...

We get 1 -2 good blows a year where we see 80 - 100 mph winds. If you watch these poles in those winds they flex and twist a lot but I have never seen one fail because of wind.

I am working on the hinge plate now. It got more complicated when I decided that it needed adjustment bolts to get the tower straight. I have not decided if I'll attach the gin pole to the plate or the tower.

No matter which way I go it'll be erected far enough away that it won't hit anything critical if it makes an uncontrolled descent 

[tanner0441]

Hi

Street lamps have a good ratio of in ground to above ground. how much will you have in the ground, what is your ground like? Street lights don't have to put up with gyroscopic forces, they are like antenna masts, they have a static wind loading and the light boom has a smaller cross sectional area than the swept area of a wind turbine.

I have fitted commercial two way radio antennas on masts and in every case the antenna comes with wind loading which has to be added to the base mast loading.

Most lighting poles I have seen are only 30 or so foot high add another 20 plus feet to that and it is a big lever.  Look at the size of the lighting towers used on big super market car parks they are a foot and a half across at the base and bolted to a big deep block of concrete.

It's OK saying it will be in a safe area if it comes down but can you guarantee you or someone else will NOT be in that area.  For the sake of a bit of metal work or welding I would go down the guyed root.

Brian.

[fabricator]

What is the diameter of the pole at the top and bottom? And what is the thickness of the wall?