Iowa State
doctoral student Robert Peggar, right, helps prepare a Hexcrete cross section
for load tests at
the University of Minnesota's MAST Laboratory. Photo courtesy of Sri Sritharan.
(November 11, 2015) Hydraulic
equipment in two civil engineering labs recently pushed and pulled at test
sections of a new kind of wind turbine tower, simulating the heavy, twisting
loads that towers have to withstand.
In Iowa State University’s Structural Engineering Research
Laboratory, an actuator rocked a 12-foot-high and 6.5-foot-wide test section
with 100,000 pounds of force every 1.25 seconds. The test section’s two panels
and two columns only moved a tenth of an inch, but the movement was visible –
especially the swaying of the long wires attached to 65 strain and displacement
sensors.
Those sensors collected data 50 times every second over
weeks of fatigue testing. Meanwhile, Hartanto Wibowo, an Iowa State
postdoctoral research associate, was on the lookout for tiny cracks or any
other signs of wear in the test section, particularly around the prestressing
cables connecting the panels and columns.
An experiment at the University of Minnesota’s MAST
Laboratory tested operational and extreme wind turbine tower loads on a full-scale
cross section of a tower – an assembly that was 16 feet 7 inches high, 8 feet
in diameter and included six panels and six columns tied together with
prestressing cables. Engineers took data to see if the assembled tower pieces
would hold up under the loads and whether they’d transfer the load from piece
to piece and act as a single unit.
Sri Sritharan, Iowa State University’s Wilson Engineering
Professor in Civil, Construction and Environmental Engineering and a member of
the College of Engineering’s Wind Energy Initiative, said the tower cross
section had no trouble resisting the loads and preliminary data analysis
confirms that observation.