DSI supplies DYWIDAG Tendons for USA’s largest Wind Technology Testing Center
Wind energy is the fastest growing renewable energy industry worldwide. In order to gear the energy mix of the United States more strongly towards the use of wind energy in the future, the Department of Energy decided to build a new testing center in 2007: the Wind Technology Testing Center (WTTC).
WTTC is located in Boston and is the first facility in the United States that can test up to 90m (295ft) long wind turbine blades. The new testing center is of great importance for the research activities of the American wind industry because, until now, turbine blades longer than 50m (164ft) had to be tested in Europe. The facility can accommodate the simultaneous testing of up to three turbine blades according to different criteria such as static loads, fatigue resistance, material properties or quality. Construction work at the WTTC started in October 2009 and was completed in the first quarter of 2011.
The 32 x 12.7m wide and 3.00m (105ft x 41.75ft x 10ft) thick footing was designed to fulfill extremely high requirements. Consequently, 19-0.6" DYWIDAG Strand Tendons were installed longitudinally and transversally and tensioned in addition to the usual mild steel reinforcement. In total, 208 DYWIDAG Strand Tendons were installed in four layers.
DSI USA supplied approx. 74,000m (242,595lf) of Ø 15mm (0.6") strand and 3,800m (12,400lf) of galvanized Ø 100mm (4") duct for this purpose.
Additionally, high strength Ø 46mm DYWIDAG Bars were used to strengthen the massive walls of the test stands. DSI USA supplied approx. 110t of post-tensioning bars, 569 anchorages and approx. 6,924m (22,715lf) of Ø 65mm (2.5") galvanized duct.
In addition, DSI USA produced and supplied 159 Ø 46mm strong floor anchors to serve as future anchor tie-down points in the laboratory during the tests. For a continuous monitoring of the loads during operation, DSI also supplied 25 DYNA Force® Sensors with a readout unit.
Since the bar tendons will be subject to millions of stress cycles during the tests of turbine blades, the DYWIDAG Bar Tendons had to undergo a rigorous dynamic testing program. Nowhere in the United States has this diameter and type of high strength bar been tested to the extent they were tested for the construction of the WTTC. Only after the successful completion of the rigorous testing program could the DYWIDAG Bar Tendons be used for this exceptional project.
Following the owner’s guidelines and working closely with the Engineer of Record, DSI USA Engineering developed the test plans, set-up protocol, QA/QC guidelines and managed the testing program through its successful completion. In summary, nine different tests with differing loads, stress amplitudes and numbers of cycles were carried out. The longest test was 10 million cycles at a 1,000kN (240kip) mean load with a stress amplitude of +/- 20N/mm2 (+/-3.1ksi).