Radial Gate Inspection and Performance Monitoring

The condition and operation of radial gates is crucial to the performance and safety of dams. As the
major moving component on gated spillways, radial gates require special attention. We have found several significant problems on gates as part of a close-up climbing inspection that would not have been discovered from more distant observations, and we have also discovered serious problems by simple visual inspections from the operating deck. While climbing inspections of the gates have proven to be where time is best spent, they may not be a good indicator of changes Figure 1: Steel on steel trunnion pin con-within the trunnion bushing. Many of the gates in nection with no provisions for lubrication service today are more than 50 years old and though these gates are not frequently used, their trunnion bushing can be deteriorating and friction coefficients increasing.
Trunnion pin friction is the issue that sparked the nation to take a closer look at tainter gates. However, it has been our experience that there are other mechanisms that impact the gate’s overall integrity that are just as important as trunnion pin friction. These mechanisms can be simple corrosion, modifications to the original design, distorted members caused by ice or falling debris, and rubbing and jamming.
At this time, most tainter gates at projects regulated by the Federal Energy Regulatory Commission (FERC) have been reviewed to confirm that they can withstand the forces of an assumed value of trunnion friction. Some gate analy-ses used the recommended coefficient of friction of 0.3 if measured values were not available, some used higher values (as prudent for small steel-on-steel trunnions), and some were instrumented to measure friction. As a result of these analyses, some gates have required stiffening modifications to satisfy cur-rent guidelines. However, not much is being done to monitor trunnion friction, which may be an indicator of bushing failure. This could allow for detection of changing conditions and warn operators that more detailed investigations may be advisable.