Abstract:
A series of free vibration tests were conducted on a free standing single degree of freedom structure with a range of elastic natural frequencies. The tests were conducted over a rigid concrete strong floor and on Auckland soil. A typical response was obtained when the structure was displaced from its original alignment, held still, then released and allowed to rock. The response as tested over the concrete strong floor fitted Housner’s simple rocking model, however it required an empirical manipulation of the damping factors. Interestingly, the experimental result showed that the amount of radiation damping, measured as the apparent co-efficient of restitution, is relatively constant irrespective of the structure’s geometry, which contradicts the traditional rocking models. The results showed that when the structure rocked on insitu ground, the dynamic behaviour was greatly modified. The time history response demonstrated a change of principle damping scheme from radiation to viscous. The response over the continuous medium failed to correlate with Housner’s model due to the increased viscous damping, which is attributed to the soil absorbing energy through deformation. An elongation in the rocking period for a given amplitude was observed.
