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<br />displacement of the structure. <br />can be made by a simplified or <br />specific procedure. <br /> <br />The deformation analysis <br />a more rigorous site- <br /> <br />(5) Finite Element Strain Potential Analysis <br /> <br />The details of this analysis have undergone many <br />improvements through development and spp1ication of finite <br />element procedures and through the development of improved <br />testing procedures. The basic principles of the method <br />involve: <br /> <br />(a) Determining the cross-section of the dam to be used <br />for ana lysis. <br /> <br />(b) Determining, with the cooperation of geologists and <br />seismologists, the maxinum time-1listory of base <br />excitation to which the dam and its foundation might <br />be subjected. <br /> <br />(c) Determining, as accurately as possible, the stresses <br />existing in the enbankment before the earthquake; <br />this is probably done most effectively at the present <br />time using finite element analysis procedures. <br /> <br />(d) Determining the dynamic properties of the soils <br />comprising the dam, such as shear modulus, damping <br />characteristics, bulk modulus, or Poisson's ratio, <br />which determine its response to dynamic excitation. <br />Since the material characteristics are nonlinear, it <br />is also necessary to determine how the properties <br />vary with strain. <br /> <br />(e) Computing, using an appropriate dynamic finite <br />element analysis procedure, the stresses induced in <br />the enDankment by the selected base excitation. <br /> <br />(f) Subjecting representative samples of the enDankment <br />materials to the conbined effects of the initial <br />stat ic stre sse s and the superimposed dynamic <br />stresses; determining their effects in terms of the <br />generation of pore water pressures and the <br />development of strains; and performing a sufficient <br />nunber of these tests to permit similar evaluations <br />to be made, by interpolation, for all elements <br />co~rising the enbankment. <br /> <br />(g) Evaluating the factor of safety against failure of <br />the enbankment either during or following the <br />earthquake from the knowledge of the pore pressures <br />generated by the earthquake, the soil deformation <br />characteristics, and the strength characteristics. <br /> <br />-26- <br />