Environmental Engineering Reference
In-Depth Information
adhesive, and the approx. 800 connections between the ducts for the prestressing
tendons with their tubes to protect the couplers must match up exactly. The pockets at
the connections, into which the steel U-bars project, are filled with a rapid-hardening
grout.
In the meantime, towers with a hub height even higher than 100m have been built using
precast concrete segments. This development, too, can be attributed to Enercon.
The ENERCON E-126/6 MW is the most powerful wind turbine in the world
(Figure 5.4); it generates enough electricity to supply more than 5000 four-person
households. The hub height is 135m, the total height 198m and the rotor diameter
126m. Each rotor blade is made in two pieces so that it can be easily transported to the
site by road.
The precast concrete towers consist of a total of 35 segments with walls up to 45 cm
thick. With a base diameter of 14.5m, each of the first eight segments has to be split
into three parts so that transport by road is still feasible (Figure 5.5). Each of the next
22 segments is divided into two parts and only the top five are complete rings. The final
segment, on which the nacelle is mounted, is of steel.
All the tower segments are cast at the precasting works. The high accuracy of the precast
concrete segments is guaranteed by the steel moulds specially built for this work.
The individual tower segments and the foundation are connected by internal prestress-
ing tendons which are fed through ducts located on the centre-line of the shaft wall.
Although the tendons are fed in from the top, they are prestressed and grouted from a
space within the foundation.
The vertical faces between the subdivided segments are in the form of pockets, profiled
to handle the shear forces due to transverse loads and torsion and also provided with
loop-type starter bars for connecting to the other segments.
The erection procedure involves first positioning and aligning the individual elements.
After the structural vertical reinforcement has been installed, the joints are filled with a
high-strength grout.
Fig. 5.5 One-third segment
