Spillway radial gate failure at Folsom Dam, California

On the morning of July 17, 1995, spillway radial gate No.3 failed at Folsom Dam, California. It was one of five service gates which had been operated by the Bureau of Reclamation since 1956. There was no warning of structural distress prior to the failure. No one was injured, even though there was a sustained release of 1,132 m(3)/s into the Lower American River. A multi-disciplinary, multi-agency forensic team was formed to investigate the failure. All of the remaining gates were thoroughly inspected for signs of structural degradation, apart from some corrosion, nothing detrimental was found. The failed gate was removed and then thoroughly examined to determine the mode of failure. This examination determined that a diagonal brace joint, adjacent to the trunnion was the initial point of failure. Theoretical finite element models substantiated this study when a trunnion friction coefficient of 0.25 was considered. This value had been confirmed also from friction tests performed on the actual trunnion from the failed gate. Trunnion friction moment was the key factor, and it had been omitted in the original design calculations.