Case study · Energy
Two installations of WindCity vertical-axis turbines, on the shore of Lake Garda in 2018 and in England in 2022. No concrete footing was poured in either.
A wind tower does not ask its foundation to carry a weight: it asks it not to let the tower overturn. The dominant load is the moment at the base, with tension on one side and compression on the other, and it changes direction with every gust.
The traditional footing answers with mass: a block of concrete big enough not to be lifted. It works, but it is almost all dead weight — poured on site, and one day to be demolished.
Both machines are vertical-axis turbines by WindCity, with whom we work on the ground anchoring: they build the turbine, we provide the way to hold it in place.
Instead of mass, geometry: several anchors arranged in a ring around the axis of the tower. The overturning moment becomes a pair of forces — tension on the windward anchors, compression on the leeward ones — and each screw works in the direction where it performs best.
Tension is exactly what a screw foundation can take and a footing simply resting in the ground cannot: the helix engages the soil above it instead of just pressing down on it.
The anchors are installed in advance and wait flush with the ground. When the crane arrives the pad is already ready: the structure comes down, is bolted on and the machine is standing the same day.
With a concrete footing there are weeks of waiting between pouring and assembly, and meanwhile the area remains a building site. Here the surrounding area stays a lawn until the very end.
The delicate point of every tower is the joint between base and foundation: if one support is off level, the structure starts out crooked and the error grows over its whole height.
The flange has slotted holes: the bolt positions are adjusted during assembly, and plumb is corrected on the anchors rather than on the ground. With an anchor bolt cast into concrete, that correction is not available.
Small wind turbines, sensor towers, lighting columns and antennas share the same physics: a lot of moment, little weight. It is the family of applications where a concrete footing is almost all useless mass, and where a screwed foundation is sized for what is really needed.
Send us the project, the type of ground and the loads: we reply with the anchoring layout and the right T-Block® models. If your case is like one of these, we will tell you — and if it is not, we will tell you that too.
