Effect of Supplemental Hysteretic and Viscous Damping on Rocking Response of Free-Standing Columns

Abstract

This paper investigated the nonlinear, rocking seismic response of slender, free-standing columns when equipped along their sides (or at their pivoting points) with vertical energy dissipation devices which offer either hysteretic or viscous (linear or nonlinear) dissipation. The paper derived the nonlinear equations of motion and then revisited the transverse response of the South Rangitikei Rail Bridge. The analysis showed that the 72-m-tall stepping bridge piers exhibit remarkable seismic performance even when excited with recorded ground motions that are much stronger than the known strong motions at the time of the design of the bridge. Subsequently, the paper showed that there are isolated examples of earthquake excitations in which the response of the rocking bridge pier when damped with either hysteretic or viscous dampers is more aggravated than the undamped response. This phenomenon may also manifest when idealized mathematical pulses are used. The paper concluded that the effectiveness of supplemental hysteretic or viscous damping in suppressing rocking response depends strongly on the local kinematic characteristics of the ground motion. Whenever the damped response exceeds the undamped response the exceedance is marginal, and in most cases the damped response is lower than the undamped response.