Public Utility Company
The transmission towers were located at various substations and consisted of maximum 90-foot-tall galvanized A-frames. The towers were typically asymmetrically loaded and supported on concrete piers up to 37 feet deep and up to 7 feet in diameter. Typically eight anchor bolts embedded up to 9 feet into the reinforced concrete piers were used to fasten the tower legs to the foundation. The age of the towers and foundations ranged from ten to twenty-five years old.
The cracks, oriented both radially and longitudinally, were commonly 0.100 inches or wider, while some were as wide as 0.625 inches. The cracks initiated primarily at the surface and top corners of the piers and typically passed through or were in close proximity to the anchor bolt locations. WJE completed visual surveys of the exposed pier surfaces and partially excavated select piers to map cracking conditions below grade and to verify the as-built reinforcement using ground penetrating radar. After the reinforcing steel was located, concrete cores were extracted for materials testing to determine the compressive strength of the concrete. Using microscopic techniques, WJE petrographers identified the likely causes of the cracking: volume change of the concrete as a result of drying shrinkage, autogenous shrinkage, temperature change, and internal chemical reactions such as Alkali-Silica Reaction and Delayed Ettringite Formation. Based on these findings, various temporary and long-term repair options were presented to the client to address both immediate safety concerns and to extend the service life of the existing tower foundations.