The seismic stability of a dam is determined by a set of configurational and constructional measures to preserve the upstream face of the structure (a breakthrough wave is not permitted) against an earthquake of the design intensity, i.e., the condition of the dam corresponds to its main functions in the event of residual deformations and damages [i], which can be eliminated by repairs after the earthquake.

Section 5 "Hydraulic Structures-of SNiP II-A.12-69 "Construction in Seismic Regions. Design Standards" was approved by resolution No. 21 of GosstroiUSSRof February 7, 1972, and put into effect on October I, 1972. The new standard stipulates calculation of hydraulic structures for seismic loads by tlm dynamic (spectral) method, which takes into account the characteristics of the dynamic working of structures and thu~ reflects more correctly their behavior during earthquakes. Within the framework of this standard method it is possible to achieve a considerable economic saving by taking into account the yielding of a foundation, which greatly reduces the seismic loads at the lower vibration tones. The effect of foundation yielding on the dynamic behavior of darns can be determined most completely by the fiulte-element method.The spectral method calls for expanding the external load (seismic action) with respect to the modes of natural vibrations of the structure. For such expansion it is necessary to know the frequency (period) of natural vibrations and the displacements of points of the structure corresponding to a given vibration mode. These parameters are needed for calculating a structure in the case of any form of assignment of the seismic action (seismicity coeffir.tent or analog accelerogram). Their values are decisive when calculating the design dynamic load. Therefore, it is necessary to have at one's disposal modern, effective, and sufficiently accurate methods of determining the frequeaucies (periods) and modes of natural vibrations. In particular, this is important for darns having zones differing in configuration and properties of the materials.A special feature of hydraulic structures which distinguishes them from other types of structures is the large supporting area, which governs the increased effect of foundation yielding on their dynamic characteristics. In addition, these characteristics will be affected also by inhomogeneity of the foundation which is inevitable in view of the considerable length of structures of this type. For example, for the 300-m-high dam of the Nurek hydro development the width at the base exceeds 1.5 kin. It is natural to expect that with such ratios of width to height of the dam the effect of the foundation should be considerable.So far the modes and frequencies of natural vibrations of hydraulic s~uctures have been determined most often according to simplified calculation models in which the structure was divided heightwise into a series of con-cen~ated masses arranged along a vertical Line, each of which had only one degree of freedom-in a direction perpendicular to this line. Here it was usually assumed that during vibrations all points of the dam located at the same level are displaced by the same amount, equal to the deflection of a cantilever, which ignored the difference of displacements of individual points over the width of the structure. In such calculation models the foundation was assumed perfectly rigid, and in individual cases its yielding was taken into acc...

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Reviewed by Ya. I. NatariusTh/s book was prepared on the basis of materiaI presented at a conference organized by the Society for Earthquake and Civil Engineering Dynamics and held on July 7-9, 1970 at the University College of Swansea (USA). This conference was attended by participants from many countries (including the USSP0, who presented papers reflecting the research work in many fields, such as the characteristics (nature) of dynamic processes (seismic motion of the soil foundation mass, wave action of water media, hydrodynamic action under earthquakes, blasting action, etc.); the study of the behavior of dynamic systems: structure-soil, s~ucture-soil-reservoir; the selection and interpretation of the records of vibrations of soils and structures; the organization of seismome~ic services; and full-scale investigations.

There presently is a gap between the specifications for determining seismic loads on dams and those regulating the general calculations of dams in order to check the strength and stability in the case of a special combination of loads. The development of hydraulic const:uction in regions of high seismicky and the associated provision of seismic stability of structures required the development of a number of new methods of calculating structures subject to seismic loads and a critical reexamination of the existing standards.Originally work was done on revising section 6 of SNiP Chap. II-A.12-62, resulting in the creation of a new section 5 "Hydraulic Structures" SNiP (;hap. . The method of calculation used in this section of the construction specifications and regulations (which became effective on October I, 1972) provides for taking into account when determining seismic loads on hydraulic structures the dynamic characteristics of their behavior. However, other standards, particularly the specifications for designing earth dams and concrete gravity dams to be constructed in regions of high seismicity, were left unchanged.