Three-dimensional seismic response of earth dams subjected to spatially varying earthquake ground motion

For extended structure, the seismic load has a spatiotemporal variation that simultaneously changes with time and space. The incorporation of the seismic wave spatial random variability effect is especially important when large structures such as long bridges, dams, and large buildings are analyzed. The effect of spatially varying earthquake ground motion (SVEGM) on the seismic response of earth dams is analyzed in this paper. To this end, a parametric study is conducted to investigate the effects of length to height ratio ( ) on the 3D seismic response of the studied dams. Ground motions, consistent with the three-directional lagged coherency model, are generated at different discretized cells at the base of the dam. The dams are assumed to sit on trapezoidal and V-shaped canyons and vibrate in all three directions, upstream-downstream, vertical, and longitudinal. The average coherency of different frequencies is calculated and used for the generation of SVEGM. The time histories are simulated using a spectral representation-based method. The separation distance between the cells is determined in such a way that 90% of correlation between seismic input motions can be captured. For each case of  ratio, a numerical model of the dam and its foundation is constructed using the finite difference numerical method. The 3D seismic behavior of the earth dams is evaluated under the artificially generated three-directional components of SVEGM. Generally, it is concluded that with increasing  ratio, at the midpoint of the dam crest, the difference between maximum of acceleration values obtained by applying uniform and SVEGM excitations decreases. In all cases of analyses, SVEGM has decreasing effect on the vertical displacement of dam crest.