Precast Concrete Wind Towers
prefabrication and the logistics, transport and erection of large elements. It offers turn-key supply of certified precast concrete towers, using a fully tested and industrially developed tower concept, capable of carrying any turbine to >140m hub heights.
With considerable background experience in delivering very large precast elements for the heavy civil and bridge construction industry, the concept of Inneo Torres uses few large precast elements, in the form of long narrow panels. This compares, for example, with Enercon’s concept, which uses more numerous and smaller ring elements. With the concept of Inneo Torres, the tower is divided into large tubular levels that are typically 20m long. Each level is subdivided into sectors or panels fitting transport weight and size requirements, thus avoiding any transport-related constraints in the tower geometry. On the site, sections are pre-assembled at soil level to form vertical tubular levels. This first phase involves only small cranes. During the second phase, a large crane lifts each level (and the turbine) into position. It thus completes the tower erection in a simple and fast operation.
Despite the fact that concrete tower levels are heavier than the steel tubes of an equivalent steel tower, this does not imply the need for more powerful or expensive cranes. This is because crane requirements are driven by the erection of the nacelle. Obviously, a possible technical limit for the tower hub height and turbine size may lay in crane availability and capacity. The development of new larger cranes will not stop, however, and can be expected to accompany future turbine developments.
Attributes and Advantages of Precast Concrete Wind Towers
The main attributes and advantages of precast concrete towers, as particularised in the Inneo Torres concept, will now be discussed.
Structural Behaviour and Capacity
In order to optimise structural behaviour and capacity, unconstrained election of the most convenient tower geometry and natural frequency is possible. Geometry is not conditioned by transport requirements. Such a choice therefore allows for increased tower diameters and optimisation of structural and dynamic performance. As a result, companies are able to reach hub heights of >140m and support practically unlimited turbine sizes. Using precast concrete towers leads to greater structural damping.2 Prestressed concrete is a fatigue-tolerant structural material.2
The tower
has ductile properties compared with the brittle properties of conventional steel towers with failure modes governed by local buckling. This makes precast concrete more resilient to extreme weather events and ground movement. Ductile behaviour is particularly relevant in seismic areas.
Durability and Maintenance Transportation and Erection Logistics
The logistics of creating precast concrete are significantly simplified by the patented and certified joint system and pre-assembly procedure (see Figures 3 and 4). The number of operations on-site are thus reduced. As a result, erection rates of two towers per week can be reached, which is analogous to steel towers. Simple and cheap transport of tower elements is by means of conventional extensible platforms. Piece dimensions and weights are defined with this purpose in mind. Tower erection can be completed with any desired anticipation of nacelle erection due to the insensitivity to vortex shedding effects. Added to this is the possibility for having temporary manufacturing facilities on site, as described in greater detail below.
MODERN ENERGY REVIEW – VOLUME 2 ISSUE 2
The precast concrete tower is a maintenance-free concept as it includes the joints, in clear contrast with steel towers. Painting of the tower is an option, not a requirement as it is with steel. Another benefit is that concrete structures have greater durability (>50 years) than steel, particularly under marine exposure. Durability is especially favoured by the use of high-strength concrete (>50MPa) and the control/quality achieved through industrial precast manufacturing, as opposed to in situ concrete construction. Precast concrete has greater tolerance than steel to possible damage due to impacts or accidental events. In these circumstances, occasional repairs are simple and economic to make. Concrete also has greatly increased fire resistance compared with steel towers.
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Figure 5: Inneo Torres Precast Concrete Tower for the 100m 3Mw Turbine by Acciona
Figure 3: Transport, Pre-assembly and Erection of Inneo Torres Precast Concrete Towers
Figure 4: Several Pre-assembled and Erected Inneo Torres Precast Towers in a Spanish Wind Farm
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