Here is an example of what happens to old anchor tendons that fail. Images are from an Oklahoma Dam. The sudden tensile stress release from a failed anchor tendon causes an explosive force that "shoots" the rod out of the concrete. This dam used rods that were 50 ft in length. Oroville's Radial Trunnion Gates use 30+ feet length rods.
Oklahoma dam with similar (to Oroville design) post-tension steel anchor tendons. Anchor Tendon rods strengthen the concrete to endure the forces from the pivot anchoring plates of the Trunnion (Radial Trunnion Gate design).
Explosive failure result: Zoom: Oklahoma dam with similar (to Oroville design) post-tension steel anchor tendons.
