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.