Issue 35

N. Oudni et alii, Frattura ed Integrità Strutturale, 35 (2016) 278-284; DOI: 10.3221/IGF-ESIS.35.32 282 The geometry of a typical non-overflow monolith of the Koyna dam is illustrated in Fig. 4. The monolith is 103 m high and 71 m wide at its base. The upstream wall of the monolith is assumed to be straight and vertical, which is slightly different from the real configuration. The depth of the reservoir at the time of the earthquake is h w = 91.75 m. Following the work of other investigators, we consider a two-dimensional analysis of the non-overflow monolith assuming plane stress conditions. The finite element mesh used for the analysis is shown in Fig. 4. It consists of 760 first-order, reduced- integration, plane stress elements (CPS4R). Nodal definitions are referred to a global rectangular coordinate system centered at the lower left corner of the dam, with the vertical y-axis pointing in the upward direction and the horizontal x- axis pointing in the downstream direction. The transverse and vertical components of the ground accelerations recorded during the Koyna earthquake are shown in Fig. 3. (units of g = 9.81 m sec –2 ). Prior to the earthquake excitation, the dam is subjected to gravity loading due to its self-weight and to the hydrostatic pressure of the reservoir on the upstream wall [8]. Figure 4 : Geometric properties of the KOYNA dam. Parameters used in Mazars’s model for concrete Young modulus E 31027 MPa Poisson’s ratio  0.2 Mass density  2643 kg/m 3 Initial damage threshold 0 D  1.5 10 -4 A t 1.0 B t 30000 A C 1.4 B C 1545 Table1 : Material properties. R ESULTS e note that the displacements are relatively low during the first two seconds because of low the amplitudes of the excitations. The displacements reach their maximum at 3.7 s and 7.5 s, 30 mm was recorded at 3.8 s, the maximum displacement value does not correspond to the maximum amplitude of the excitement that is recorded at 3.65 s. The nodal displacements decrease after 7.5 s. W