Evaluating Post-Tensioned Trunnion Girders: A Comparative Study of Scale Model Tests and Numerical Analyses

Abstract

Water flow in dams is commonly regulated using Tainter or miter gates, which are extensively employed in the navigation network of locks and dams managed by the United States Army Corps of Engineers (USACE). Tainter gates are well known for their effectiveness in managing the flow of water through dam spillways. Post-tensioned Tainter gate anchorages are widely utilized in numerous dams across the nation, particularly within the Mississippi Valley Division (MVD), the Great Lakes and Rivers Division (LRD), the Southwestern Division (SWD), and the Northwestern Division (NWD). Between 2010 and 2017, ten dams underwent testing, revealing that eight of them had failed rods. Out of the 5,371 greased trunnion anchor rods tested, 22 were found to be broken, and 6 had slipped gripping hardware. While the overall failure rate might appear low, a detailed analysis shows that individual anchorage failure rates ranged from 2 percent to 29 percent, potentially affecting anchorage capacity and performance. Apart from the trunnion rods that failed due to breaking or slipped connections, 278 rods (202 on Markland Dam and 76 on Greenup Dam) exhibited significant cantilever bending or corrosion, conditions that can contribute to anchor rod failure. This study aims to establish experimental and numerical methods for posttensioned anchorages with different rod configurations. Laboratory tests on scaled anchorages, featuring a concrete trunnion girder with nine high-strength post-tensioning rods, were conducted. Finite element (FE) analyses were validated using experimental data, replicating various trunnion rod failure scenarios. The FE results accurately predicted load changes on each rod under different loads and de-tensioning configurations. The findings from this research provide valuable insights into anchor rod failure rates, which can assist district engineers in assessing the current condition of anchor rods and planning proactive maintenance and remediation strategies.