Seismic Response Analysis of the Planar Rocking Frame

Abstract

Unlike conventional seismic design, the columns of a rocking frame are designed to uplift and pivot during earthquake excitation. This paper investigates, analytically and numerically, the seismic response of a rocking frame with columns unequal in height (asymmetric), which are either freestanding or hybrid, i.e., enhanced with supplemental damping and recentering capacity. The paper establishes the equations of motion following the principles of analytical dynamics. Throughout the study, the deformation of the structural members is considered negligible. The analysis considers both pulse-type and non-pulse-type (historic) ground motions. It shows that the effect of asymmetry on the seismic stability of the rocking frame is marginal compared with the symmetric configuration, despite the very different kinematics of the corresponding rocking mechanisms. In contrast, the seismic stability of the hybrid rocking frame is very sensitive to fracture elongation of the supplemental restoring (tendons) and damping devices. The results confirm the high-performance seismic behavior of the planar rocking frame, thus illustrating its potential as an alternative seismic design paradigm.