Grant Schmitz, an Iowa State graduate student of civil, construction and environmental engineering, and Sri Sritharan, Iowa State’s Wilson Engineering Professor and leader of the College of Engineering’s Wind Energy Initiative have found a solution using concrete panels and columns to build wind turbine towers using prefabricated, easily transportable components. Sritharan and Schmitz designed the concrete towers to be built in hexagon-shaped segments, with six panels connected to six columns.
They tested three methods to connect the panels and columns: bolted connections; horizontal, prestressed connections with cables running through the tower pieces; and a grout connection using ultra-high performance concrete poured into the joints between panels and columns. In addition, the concrete columns were attached to a foundation using pre-stressing methods. The goal was to test three column-and-panel segments for the expected loads at the top of a turbine tower. The engineers wanted to see if the segments could handle 150,000 pounds of load, 20 percent over the extreme load at that height.
All three versions of the test segments withstood 150,000 pounds of lateral load. The researchers also tested the segment with the grout connections under 170,000 pounds of load, 36 percent beyond extreme load. In each test, the segments performed well with no sign of distress at the operational load of 100,000 pounds. Some distress to the test segments was visible at the extreme load and beyond. The project has been supported, in part, by a $109,000 grant from the Grow Iowa Values Fund, a state economic-development program. The concrete tower design offers more life compared to steel tower. It is easier to transport precast material. The concrete is less reliance on imported steel for turbine towers. The towers can be tailored for any turbine size or even a height beyond 100 meters for a 2.5 to 3 megawatt system.