Foreword
Perhaps no other field of engineering is subject to so rapidly evolving ongoing research than the field of earthquake engineering. Each new significant earthquake brings revelations to the profession that may be of importance to the project at hand. Applicable technical references are frequently updated, and the methods to select seismic parameters for dam projects need to be updated accordingly.
These Guidelines are intended for the use of engineers familiar with the design of dams, but who may not be intimately knowledgeable about earthquake engineering as applied to dam design and safety evaluation. The less experienced reader may profit by consulting the Appendices, after reading the Introduction. For anyone involved with the design or evaluation of dams for seismic loading, it is essential that the current technical literature on earthquake engineering be consulted. An extensive Bibliography is provided for those who are interested in delving into this subject in detail.
These Guidelines attempt to provide balance between the practice of the profession, as carried out in the Western United States, as opposed to the Eastern U.S. (defined as the area east of the Rocky Mountains). Once the ground motion at a dam site is adequately defined, there are no significant differences in design or evaluation practices. However, the techniques used in defining the ground motion may be quite different when applied to these two geographic areas. This is principally driven by the following factors, applicable to the Eastern U.S.:
- Lack of instrumentally recorded data, especially for large earthquakes
- Lack of association of earthquakes with conspicuous surface faulting
- Relatively longer return periods for significant earthquakes
Over the next few decades, these differences may diminish when new strong motion data are recorded and earthquake-causing mechanisms are better understood.
These Guidelines were prepared by a subcommittee of the USSD Committee on Earthquakes. This subcommittee included Donald H. Babbitt, Gilles Bureau, Patrick J. Creegan, Ronald G. Domer, Joseph L. Ehasz and Faiz I. Makdisi. Review comments were received from other members of the Committee on Earthquakes and, especially, Mohsen Beikae, Yusof Ghanaat and C. Eric Lindvall. Ron Domer coordinated external reviews, and Gilles Bureau was responsible for the final editing of this document.
The subcommittee is indebted to the external reviewers, Russell Green, I. M. Idriss, William F. Marcuson III, Lelio H. Mejia and John D. Smart, for many helpful contributions; and is grateful to URS Greiner Woodward Clyde, Oakland, California, for word processing and graphical support.
Table of Contents
1. INTRODUCTION
1.1. Purpose
1.2. Background
1.3. Scope
2. FACTORS INFLUENCING THE SELECTION OF SEISMIC EVALUATION PARAMETERS
2.1. General
2.2. Influence of Type of Dam
2.2.1. Concrete Dams
2.2.2. Embankment Dams
3. GEOLOGIC AND SEISMOLOGIC CONSIDERATIONS
3.1. Earthquake Potential
3.1.1. Regional Tectonic Framework
3.1.2. Historical Seismicity
3.1.3. Evaluation of Seismic Sources
3.1.4. Maximum Earthquake Magnitude
3.2. Earthquake Recurrence Assessment
4. SELECTION OF EARTHQUAKES FOR ANALYSIS
4.1. General Approach
4.2. Terminology
4.3. Seismic Evaluation Requirements
5. SELECTION OF SEISMIC EVALUATION PARAMETERS
5.1. General
5.2. Peak Ground Motion Parameters
5.3. Duration
5.4. Response Spectra
5.4.1. Generalized Spectral Shapes
5.4.2. Response Spectra Based Upon Attenuation Relationships
5.4.3. Damping
5.5. Acceleration Time Histories
5.5.1. Overview of Spectrum-Compatible Time History Development Procedures
5.5.2. Selection of Starting Time Histories
5.5.3. Guidelines for Generation of Response-Spectrum-Compatible Time Histories
5.5.4. Digitization Interval
5.6. Location of Application of Input Motions
5.7. Probabilistic Seismic Hazard Evaluation
6. BIBLIOGRAPHY
APPENDIX A: SITE AND STRUCTURE HAZARD RATING
APPENDIX B: DEFINITION OF TERMS USED IN GUIDELINES
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