Forensic Analysis of Wind Power Generator Tower Cracking

Abstract

Generators that produce electricity for modern wind farms are mounted atop large steel towers. The hollow cylindrical towers, which are typically more than 250 feet in height, are fabricated from mild steel plates (approximately 1-inch-thick and 10 to 12 feet in diameter). Cracks in the steel plates measuring more than 4 feet long were observed in such a tower. The author was retained to determine the cause of the cracking and if that cause was a result of incorrect design (owner) or poor fabrication quality (contractor). Laboratory examination of the crack morphology and finite element analyses techniques were used to characterize the root cause of the failure. Cyclic loading on the tower was developed from wind rose data for the site. It was ultimately shown that the cause of the steel plate cracking was flow-induced vibrations resulting from von Karman street vortex shedding — not the fore-aft loads of the direct wind forces on the blades.