Construction World March 2015

PROJECTS AND CONTRACTS

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.

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

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

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- 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 vidual precast concrete segments. How it fits together

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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

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CONSTRUCTION WORLD MARCH 2015