Dynamics of Rhythmic Jumping on Vertically Vibrating Platforms

Abstract

Contemporary sustainable structures including grandstands, footbridges, and floors, are susceptible to vibration serviceability issues caused by human-induced loads. This thesis investigates the dynamics of rhythmic jumping subjected to vertical vibrations. The description of jumping on vibrating surfaces encompasses not only the frequency of jumping but also its timing relative to the platform’s vibration cycle, which was overlooked in the literature. Whole body kinematic and kinetic data were collected as ten test subjects jumped on a non-vibrating platform and a sinusoidally vibrating platform of 2m/s2 and 2.0, 2.4 and 2.8 Hz. The frequencies of jumping were 2.0, 2.4 and 2.8 Hz, with cues to time landing at specific positions of the platform. For jumping synchronised with platform vibrations, despite being cued, test subjects tended towards efficiency by employing jump timings related to lower energy input, appropriate contact ratio and lower forces. Analysis of the human body centre of mass kinematics and kinetics revealed timing-dependent displacement, force, contact ratio, leg stiffness and energy flow. A model has been developed to predict the loads due to rhythmic jumping on vibrating platforms. The generated forces on the vibrating platform differed from the non-vibrating platform indicating self-excited force due to the effect of vibrations. For jumping on a lively structure, positive self-excited forces, indicating energy supply, can result in a reduction in mass and damping of the system, potentially leading to larger vibrations. Negative self-excited forces imply energy removal that can potentially result in an increase in mass and damping of the system, leading to vibration attenuation. Results indicate that there is always a net energy supply in the case of non-synchronised jumping, underscoring its importance on lively structures. The outcomes of this thesis will help in improving the knowledge of human-structure interaction to help reduce conservatism, uncertainty and risk in structural design and as a means of reducing the amount of construction material.