<p>Many theoretical analyses indicated that the circular frequency and damping ratio of flexible rocking structures are increased once they are uplifted, while experiments confirmed the circular frequency increase yet challenged the damping ratio increase. Even though in some studies the uplifted damping ratio is manually revised, this issue has not been truly resolved. To this end, this paper aims to investigate in depth this issue to unveil the damping mechanism. This paper first derives the governing equations of rocking motion of flexible rocking structures in accordance with the existing ways reported in the literature. It is shown that the physically inconsistent increase of damping ratio results from a default Rayleigh dissipation function related to oscillation damping in existing derivations. Then, the governing equations of rocking motion are rederived directly based on damping force, rather than the Rayleigh dissipation function. The new governing equations indicate that the circular frequency and damping ratio of flexible rocking structures are increased and decreased, respectively, which is consistent with the experimental observations. Additionally, new damping mechanism leads to more intense impact events and faster rotation decay. More importantly, the revised analytical model based on new damping mechanism can give better response predictions. Finally, the equivalent rocking damping ratio is defined in terms of the decay of rotation and an equivalent rocking damping coefficient model is proposed by using dimensional analysis. It is shown that the proposed equivalent rocking damping coefficient model is suitable for the simplified spring model of flexible rocking structures.</p>