Guided Wave Testing of Trunnion Rods at West Point Dam, Georgia

This Coastal and Hydraulics Engineering Technical Note CHETN describes trunnion rod crack detection testing using the portable guided wave test system on a sample of the trunnion rods located at West Point Dam, Georgia, in January 2016. It is also intended to be used as a guide for test efforts at other sites. INTRODUCTION During the 1960s, Headquarters, U.S. Army Corps of Engineers USACE, mandated the use of post-tensioned trunnion anchor rods in the design of spillway tainter gates. The majority of the USACE projects used a trunnion anchor design that required the rods to be anchored to a metal plate embedded deep within the concrete spillway pier, with the free end extending through the downstream face of the pier Figure 1. The rods extend through the concrete and attach the trunnion girder to the pier. Trunnion rods are now failing at dam sites. Several of these broken rods project through the trunnion anchor cover boxes, as highlighted in Figure 2. The appearance of the cracks in the rods examined indicates that the trunnion rods had been cracked for some time prior to breaking. Stress corrosion cracking may have caused the final loss of the trunnion rod shown in Figure 3. As of 2012, 10 USACE dams contained broken trunnion rods Table 1. Due to continuing trunnion rod breakages, engineers from the U. S . Army Engineer Research and Development Center ERDC, Information Technology Laboratory, were tasked by the Navigation Systems Research Program NavSys with developing a system for evaluating the condition of trunnion rods utilizing non-destructive testing techniques. A portable system to inspect the rods using Guided Wave Ultrasonics was developed and is now available for deployment to sites wishing to test rod condition.