The K-tower is an innovative, material-saving supporting structure for onshore wind turbines. K-towers are assembled from industrially manufactured components, which results in significant savings potentials.
The decisive drawback of all jacket structures used to date has been and still is their time-consuming manual assembly. To speed up the expansion of wind energy and heighten the competitiveness of jacket structures, cost-reducing production and supply strategies and innovative structures are required.
We offer our customers an innovative design for onshore towers - the K-tower (developed by K-Tower Systems). The K-tower is a three- or four-legged jacket structure in the bottom section of the Towers and either a tubular tower or a lattice structure in the top section.
The design of the tower structures uses mostly series-produced tubes, sections and components, which translates into significant cost savings for our customers. Substantial material savings thanks to the innovative design of the towers and the use of modern foundation methods as well as advanced production strategies can reduce the cost of our tower solutions even further.
In addition, the K-tower can be used for repowering old wind parks. Because the foundations in place can be partially re-used, there is no need to build new, large foundations for the hybrid towers.
The lower section of the K-Tower is a K-Jacket with quadrangular base. Its four legs are made of tubes, with horizontal and diagonal braces for improved stiffness. The braces are made from MSH sections or tubes and fixed to the legs using maintenance-free friction-grip lock bolt joints.
K-Jackets are used as load-bearing structures for tubular towers. The lattice-type load-bearing structure of K-Jackets is significantly lighter than most conventional structures. The design of the load-bearing structure is optimally adapted to the – mostly axial – forces acting on it. This ensures high stability and strength, despite substantial material savings.
As an added advantage, a K-Tower does not require enormously large concrete foundations for the entire tower base. Instead, each of the legs has its own, significantly smaller foundation (footing). This means wind turbines can also be installed in soils with lower bearing capacity, which is why simple soil tests are sufficient when selecting a suitable turbine location.
The series-produced parts and components of the jackets, all made from steel grade S355, can be transported on normal trucks, and facilitate quick onsite assembly of the towers: approximately 23 workdays including the tubular tower.
Dismantling at the end of the tower's service life is just as easy. Even the footings can be completely removed. Since there are no threaded connections, there is no need for extensive testing and maintenance during the operating period.
|K-tower variant||With tubular tower|
|Turbine capacity||2 - 4.5 MW|
|Masse am Turmkopf||100 - 350 t|
|Hub height||90 - 150 m and more|
Height of upper section
(tubular tower/lattice tower)
|Total height of load-bearing structure||Up to 145 m and more|
|Jacket weight||Up to 250 t|
|Legs - tube diameter||610 - 813 mm|
MSH 250 - 350
(or tubes with ∅ 273 - 382 mm)
A major advantage of K-Towers is that they can be installed on material-saving foundations.
Conventional towers need large, round foundation slabs with a complex central anchoring system, as well as extensive steel reinforcement and high-quality concrete.
The footings of a K-Tower only require about 1/8th to 1/10th of the material that goes into a conventional foundation.
The table below provides a survey of foundation methods for specific soil conditions.
|Foundation method||Soil condition||Explanation||Illustration|
|Raft footing||Sufficient bearing capacity right down to the foundation base||For a flat foundation base, the subsoil is excavated to a depth of 2.5 m. Then a reinforced concrete slab (h = 0.6 m) is placed on the ground. This slab is connected with a shaft about 1.2 m in diameter, in which the jacket leg is anchored. Subsequently, the free space is backfilled up to the surface.|
|Soil replacement||Sufficient bearing capacity to a depth of about 1 to 1.5 m below the foundation base.||The subsoil is excavated to the depth of the stable soil layer. From there, it is covered with a sand-gravel mix and compacted layerwise to the level of the planned foundation base. On the last layer, a raft footing can be placed.|
|Vibro-compaction||Sufficient bearing capacity to a depth of about 1.5 to 7 m below the foundation base.||If a location is suitable for this foundation method, a bottom feed vibrator is used to install and compact consecutive layers of coarse gravel from the ground surface to the level of the stable soil layer, until a dense stone column is constructed from there to the ground surface. This column connects the stable soil layer with the foundation base, thus ensuring that the soil has enough load-bearing capacity. Then the process is completed by the installation of a raft foundation.|
|Deep foundations with piles||Soil conditions only allow a deep foundation with piles.||From the ground surface, four piles (e.g. Centrum piles 40x40 cm or 45x45 cm) are driven into the soil at an angle that corresponds to that of the upward brace. At the level of the foundation base, a raft footing is installed which uses a pile cap instead of a reinforced concrete slab.|
Example calculation of a K-Tower with a 4-legged jacket, 3 MW WT, hub height 142.5m, wind zone 2 DIBt, sufficient soil bearing capacity
- by P. Kelemen (K-Tower Systems)
|Depth 2.5 m, average surface area 55 m²||140 m³|
|Slab 6 * 6 * 0.6 m:||21.6 m³|
|Shaft 2.4 * Ø 1.2 m:||2.7 m³|
|Σ||= 24.3 m³|
|Reinforcing steel, incl. anchoring of jacket legs (calculated with 95 kg/m³)|
|Concrete reinforcement 95 * 24.3 kg:||2,300 kg|
|Anchoring, total weight:||300 kg|
|Σ||= 2,600 kg|
|140 m³(spoil) - 24.3 m³(concrete):||approx. 115 m³|
|Spoil||4 * 140 m³||560 m³|
|Concrete||4 * 24.3 m³||97 m³|
|Reinforcing steel||4 * 2.6 t||10.4 t|
|Backfill||4 * 115 m³||460 m³|