Size a guyed pipe tower from the storm thrust on the rotor and from mast buckling between guy levels. For a 3 m rotor at 25 m/s the thrust is 2.7 kN, which becomes 5.0 kN of tension in a guy anchored at 65% of the tower height, 57° from horizontal, so use 1/4 inch cable rated 9.0 kN; and keep guy levels no more than about 6 meters apart on a 2-inch pipe, since its buckling load falls from 15 kN over 6 meters to 5.5 kN over 10.
Part of Advanced Wind Turbine
A guyed steel pipe tower is a slender mast held upright by sets of steel cables to ground anchors, the cheapest way to reach 15 to 25 meters.
The Carrier Fixes The Pipe, The Guy Sets And The Height
The carrier asks for 5 to 10 cm steel pipe (schedule 40 or heavier) as the main mast, sections joined by internal sleeves (a smaller pipe inserted inside), and 3 to 4 sets of guy wires anchored at 60 to 70% of tower height from the base, at 3 to 4 heights up the tower, each set of 3 to 4 wires equally spaced. Guy Wire Anchors says three wires at 120° is the structural optimum, and puts the first set at 60 to 70% of the height and the next at the top. The carrier’s height limit for this design without engineering analysis is about 30 meters.
Worked Example: A 12 m Tower In A Storm
Load. The thrust on the 3 m rotor at 25 m/s is 2,706 N, taking a thrust coefficient of 1.0 as a conservative assumption (Tower & Mounting). Wind on the mast adds to it; ignore it here for a first estimate.
Guy tension. Anchors at 65% of 12 m are 7.8 m from the base. A guy from the top at 12 m height to the anchor makes an angle of arctan(12 ÷ 7.8) = 57° with the ground (57.0° to the first decimal), a guy length of 12 ÷ sin 57.0° = 14.3 m. With the wind pushing the top one way, either one guy takes the whole horizontal load, or two guys each take a horizontal tension F between them (their sideways parts cancel), so the worst guy horizontal pull is F = 2,706 N. The cable tension is T = F ÷ cos 57.0° = 2,706 ÷ 0.545 = 4,965 N, with a vertical part of 4,965 × sin 57.0° = 4,163 N pressing down on the mast.
Cable. The Guy Wire Anchors page gives a working load (at a 3:1 safety factor) of 1,230 lb (5,471 N) for 3/16 inch cable and 2,030 lb (9,029 N) for 1/4 inch. The 3/16 inch cable would be at 4,965 ÷ 5,471 = 91% of its working load, too close; 1/4 inch is at 55%. Use 1/4 inch (9.0 kN) for a rotor this size and inspect salvaged cable for kinks and broken strands.
Mast. Pipe dimensions are recalled handbook values: 2-inch schedule 40 is 60.3 mm in outside diameter with a 3.91 mm wall, 3-inch is 88.9 mm with 5.49 mm; steel’s elastic modulus is about 200 GPa. The second moment of area I = (π ÷ 64) × (D⁴ − d⁴) gives, for the 2-inch pipe, I = 2.77 × 10⁻⁷ m⁴ and EI = 55,300 N·m². Euler buckling for a pin-ended length L is P = π² × EI ÷ L²:
| Pipe | EI (N·m²) | L = 4.8 m | L = 6 m | L = 10 m |
|---|---|---|---|---|
| 2 inch | 55,300 | 23.7 kN | 15.2 kN | 5.5 kN |
| 3 inch | 251,000 | 107.6 kN | 68.9 kN | 24.8 kN |
The compression on the mast is the guy’s vertical part, 4.2 kN, plus the weight of the mast (a 12 m length of 2-inch pipe weighs about 5.4 kg/m × 12 × 9.81 = 0.64 kN) and the turbine (an assumed 50 kg, 0.49 kN) and the guy pretension, which the corpus does not give. That totals at least 5.3 kN. A 2-inch mast with guy levels 4.8 m apart has a margin of 23.7 ÷ 5.3 = 4.5. With 10 m between levels it has 5.5 ÷ 5.3 = 1.0, no margin at all. The buckling load falls with the square of the span, so halving the spacing between guy levels quadruples it.
For a 12 m tower, guy sets at the top (12 m), at 65% (7.8 m) and at 40% (4.8 m), the heights from Guy Wire Anchors, leave spans of at most 4.8 m. The pin-ended assumption is conservative for a mast continuous through its guy levels; the margin is a margin against what this estimate cannot see, such as wind on the mast and a crooked pipe.
Method: Build The Mast
Step 1: weld or bolt a base plate and hinge for tilting (Tilt-Up Design for Maintenance). Step 2: join pipe lengths with internal sleeves of smaller pipe, which should fit snugly; weld or pin them so the joint does not rotate. Keep the mast straight within the width of the pipe over its full height; sight along it. Step 3: fit guy rings or lugs at each guy height, with three or four attachments equally spaced. Use thimbles at every cable loop. Step 4: attach the guys to anchors (Foundation & Guy Wire Anchors). Step 5: raise the tower and tension the guys evenly, checking plumb in two directions with a plumb bob.
Common Mistakes
- One guy level at the top only — the mast spans its whole height unsupported and buckles.
- Unequal guy tension — the tower leans and loads one anchor.
- Anchors too close — at 40% of height the angle is 68° and the tension is 2.7 kN ÷ cos 68° = 7.3 kN.
Safety
A tower can fall in any direction
If a guy parts or an anchor pulls, the mast folds toward the failed side in seconds. Keep everyone outside a circle of the tower’s height while raising it, never work on a standing tower in strong wind, and shackle the cables with three clamps per loop or an equivalent splice. Name the person who calls the stop, and agree the signal before raising begins.
What’s Next
- Learn next: Foundation & Guy Wire Anchors to hold the 5.0 kN
- Combine with: Tilt-Up Design for Maintenance