Rocking response of slender, flexible columns under pulse excitation

Abstract

Early studies of the response of rigid blocks allowed to uplift and rock under seismic motion have shown a scale effect that characterizes the response of rocking blocks subjected to a ground motion. Namely; larger objects need a larger ground acceleration to overturn; and longer dominant period earthquakes have a larger overturning capability than shorter period ones. This is why it has been proposed that rocking can be used as an isolation strategy. However, actual structures are not rigid: structural elements where rocking is expected to occur are often slender and flexible. Modeling rocking of flexible bodies is a challenging task. A finite element model of a rocking elastic body that does not involve explicit modeling of impact is presented in this paper. This model was validated by comparing its response to pulse excitation with an analytical solution. It is concluded that the extensively studied rigid rocking block model provides a good approximation of the seismic response of an elastic rocking column for small-size columns and that it provides a conservative response estimate for larger columns. Guidance for development of rocking column models in ordinary finite element software is provided.