Construction World March 2015

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PROJECTS AND CONTRACTS
The wind farm is jointly owned by
Spain’s Acciona Energy and South
Africa’s Aveng Group and when
completed in 2015, will feed up
to 138 MW into the national grid daily. An
agreement between the JV and Eskom will
see ownership of the entire operation being
transferred to the utility giant after 20 years.
Precast towers
The towers are being manufactured by Cape
Town-based precast concrete producer and
Concrete Manufacturers Association NPC
(CMA) member, Concrete Units, in a joint
venture with another Spanish company,
Windtechnix. The latter has extensive experi-
ence in the manufacture of precast concrete
wind towers and is providing engineering
input. Once the project is completed some
16 500 m³ of concrete, 2 800 tons of rein-
forcing steel and 160 000 m² of shuttering
will have been used.
The on-site assembly of the towers and
manufacture and installation of the turbines
is being handled by Acciona Energy’s sister
company, Acciona Wind Power. Another
local company, civil engineering consul-
tancy, Concrete Growth, was appointed by
Acciona Wind Power as an external quality
auditing agency, responsible for the imple-
mentation of quality management in the
manufacturing process.
According to Concrete Units Cape Town
manager, Brian Cook, each completed
tower comprises five 20 m tapered concrete
sections, each section assembled from indi-
vidual precast concrete segments.
How it fits together
The base section, T1, comprises four
segments and is mounted on an in-situ
concrete foundation. T2 which is mounted
on T1, and T3, which is mounted on T2, are
also assembled using four precast concrete
segments each, whereas T4 is constructed
with three parts and T5 requires only two.
T5 sections are assembled at Gouda’s
storage yard where they are made ready
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for supporting the turbines. Turbines
consists of the nacelle and hub which
weigh 140 tons, and three blades each
weighing 10 tons. Sections T1 – T4 are
assembled at the actual tower sites where
individual segments are lifted off the trucks
and then lowered vertically onto circular
concrete bases by a giant mobile crane. They
are then joined to matching segments using
‘bowtie’ connections.
This is achieved by inserting reinforcing
into hollow slots formed by the segments’
two opposing vertical channels. A proprie-
tary high-strength grout is then pumped into
the joint to create a permanent seal.
The 20 m sections are attached to each
other in a horizontal plane using male
starter bars at the bottom end and female
ducting at the top end and these joints are
sealed with grout. The flawless execution
of this process requires extremely accurate
casting and very tight tolerances.
Durability
The Gouda towers have been designed to
bend with the wind and can move up to
700 mm at the top of T5 during strong winds.
This flexibility is facilitated by the use of
steel reinforcing inside the tower walls.
However, this lateral movement is counter-
balanced by the installation of six 90 mm
steel cables, which attach the inner wall of
T5 to the concrete base and provide addi-
tional strength to the overall structure. Once
GOUDA WIND FARM
Forty six precast concrete towers are being deployed for the
construction of one of South Africa’s largest wind farms to date,
situated on farmland in the Gouda district of the Western Cape.
The towers stand at 100 m and support wind-powered turbines,
each with a maximum generating capacity of 3 MW.