Field Test and Analytical Methods for Safety Assessment of Radial Spillway Gates

摘要

A forensic investigation by the US Bureau of Reclamation into the 1995 failure of the Folsom Dam spillway gate concluded that excessive trunnion friction, which was not considered in the design, overstressed the gate struts. Following the release of the report, the Federal Energy Regulatory Commission required an analysis of all Tainter gates, using a friction coefficient of 0.3 in the absence of a measured value. The U.S. Army Corps of Engineers (USACE) requires that the trunnion pin friction moment be calculated with a coefficient of friction of 0.3 in ETL 1110-2-584, "Design of Hydraulic Steel Structures." While this is a reasonable analysis assumption, it does not accurately determine the reliability of an existing gate. An in-service evaluation requires the actual pin friction and other measures of gate performance. For several years, strain gage tests have been used to obtain stress levels on radial gate arms in an effort to estimate trunnion friction. Due to the time and expense associated with this work, field tests have generally been done only in cases where there was a significant concern. The lack of standardized test procedures and standardized interpretation of the strain gage instrumentation data has also resulted in some inconsistent and inaccurate results. This paper introduces efficient field and analytical procedures for obtaining measured trunnion friction values and other Tainter gate performance measures such as lift loads, total friction and lift symmetry. Methods for validating the strain gage measurements and the corresponding calculated trunnion friction, using a 3-D finite element model, will be discussed along with the effects of trunnion friction on gate performance. General procedures and results will be illustrated with the evaluation of spillway gates at two dams in Washington: the Chief Joseph Dam on the Columbia River; owned and operated by USACE, and the Upper Baker Dam on the Baker River; owned and operated by Puget Sound Energy.