2021 – Design and construction of large post-tensioned anchors to stabilise spillway pier structures

Jonathon Reid, Mark Sinclair

Large concrete piers supporting gates on spillways can be impacted by earthquake loading and often found deficient in cross-valley loading. However, piers can also be susceptible to damage from upstream-downstream seismic loading and from additional pressures from increased flood loading requirements. This can have detrimental impacts on the connection of the pier with the main dam body. In recent years, a number of projects have required spillway piers to be upgraded by post-tensioning into the dam body with large multistrand anchors, up to 65 strands, to prevent failure mechanisms (bending, shearing, rocking) from forming and causing serious damage. These, often very short anchors, present special design and construction challenges that are explained in this paper. This situation also often requires the anchors to be very closely spaced with bond zones overlapping. Case examples demonstrating potential limitations in the design of spillway pier anchors and the different requirements to the more usual vertical post-tensioning of a dam body are presented.