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FEDERAL GUIDELINES FOR EARTHQUAKE ANALYSES AND DESIGN OF DAMS A. Back!!;round An ad hoc interagency committee on dam safety of the Federal Coordinating Council for Science, Engineering, and Technology prepared "Federal Guidelines for Dam Safety" which was published June 25, 1979. Preparation of these guidelines was directed by a Presidential Memorandum, dated April 23, 1977, to several Federal departments and agencies. A second Presidential Memorandum, dated October 4, 1979, direc ted Federal agencies to adopt and implement the "Federal Guidelines for Dam Safety." Those guidelines were part of a national effort to enhance dam safety, and they ou tlined the technical activities that agency management needs to undertake to ensure safe design of dams. The Interagency Committee on Dam Safety (ICODS) has established the interagency task group on design earthquakes to provide more complete guidelines for earthquake analyses and design of dams. B. Purpose The purpose of these guidelines is to develop some consistency in handling the earthquake analyses and design among the various Federal agencies involved in the planning, design, construction, operation, maintenance, and regulation of dams. They are intended to be used as general guides and are not to be considered as standards. It is recognized that the various agencies have differences in mission and diversified location which make agency independence desirable. It is further recognized that earthquake engineering is in the developmental stage and flexibility is desirable. While the content of these guidelines generally reflects current practices, it will be necessary to make periodic revisions, additions, deletions, etc., to maintain currency with the state of the art in earthquake engineering. The importance, extent, and method of earthquake analysis and design depend on the seismicity of a region or site-specific considerations, the type of structures involved, and the consequences of failure. In some cases, for example, low hazard dams or dams in zones of low seismicity, extensive investigations and seismicity evaluations or detailed analyses may not be required. Previous studies, performance, and experience of existing structures suggest that concrete gravity dams located in regions of low-to-moderate seismicity and adequately designed to withstand the appropriate static forces are competent to also withstand the earthquake forces. The same may be true of certain well-constructed fill-type dams placed on good foundations, for example, well-compacted rolled fill dams on rock foundations. In other cases where the hazard is high or the seismic conditions are severe, extensive investigations and design analyses may be required. The intent of these guidelines is to outline certain appropriate procedures and methods of analyses which can be used; each agency is expected to supplement these general guidelines with detailed procedures, as necessary, to accomplish their specific mission. -5-