Earthquake Direction Effects on Nonlinear Dynamic Response of Concrete Gravity Dams to Seismic Sequences

In a seismically active region, a concrete dam may be subjected to one or more aftershocks within a relatively short period of time following the occurrence of the mainshock. When the as-recorded mainshock-aftershock sequences are selected as the seismic input to evaluate the seismic performance of dams, the horizontal seismic components are generally applied along the principal structural axes during a time history analysis. It is important to notice that changing the orientation of the seismic input with regard to the principal structural axes will cause a quite different dynamic response to reinforced concrete building structures. The aim of the present study is to examine the effects of earthquake direction on seismic performance of concrete gravity dams subjected to seismic sequences. For this purposes, two seismic incident directions are applied along horizontal axes to assess the maximum structural demands. Nonlinear dynamic analyses of the dam-reservoir-foundation system subjected to as-recorded mainshock-aftershock sequences are conducted to investigate the effects: 1) direction of single earthquake events; 2) direction of seismic sequences; 3) aftershock polarity; and 4) earthquake intensity. The results indicate that earthquake direction can significantly change the damage propagation processes of concrete gravity dams.