EFFECTS OF DIFFERENT FREQUENCY CONTENT OF MULTI-SUPPORT EXCITATIONS ON SEISMIC RESPONSE OF A LARGE EMBANKMENT DAM

This paper focuses on examining the combined effects of frequency content and spatial
variability of the ground motion on the response of a large embankment dam. A series of nonuniform
ground motion time histories are generated using spectral representation method. The
influence of frequency content of seismic excitation is taken into account by using three different
types of target response spectra selected from Uniform Building Code (UBC 1994). It is found that
the use of identical ground motions compatible with the Types 1 and 2 response spectra
overestimates the acceleration responses by up to 15% and 30% higher than those of multi-support
excitations, respectively. The above trend is qualitatively valid for Type 3 input motions at lower
elevations of the dam, but not at the crest of the dam where the uniform excitation yields slightly
lower acceleration response. By comparing the displacement responses, it is demonstrated that the
uniform input motions compatible with Types 1, 2 and 3 response spectra result in 10%, 35% and
40% larger crest settlements, respectively, than those predicted under multi-support excitations.