A variable mass model for describing load impulses due to periodic jumping

This paper reviews the current philosophy for describing the effects of jumping humans on the vibration behaviour of structures. Focusing on the Semi-sinusoidal pulse force model, which is included in the BS 6399-96 code of practice for the description of jumping human loads, it was found that this model is unable to predict the correct shape of the load impulse or its dominant harmonic for jumping frequencies that are significantly less than 2 Hz. This paper presents a new general model, which incorporates impulse shape factors and is based on the treatment of the structure–jumper system as a pseudo-variable mass system. By considering recent findings in the technical literature, it is shown that the proposed model can be used to describe load impulses for all attainable jumping frequencies, by choosing appropriate impulse shape factors. In the experimental verification, the acceleration response of a structure with a fundamental frequency of 7.1 was found to be dominated by the second harmonic of the jumping frequency (ignoring the resonant frequencies) when a human subject jumped at 1 Hz, confirming that the load impulse is dominated by the second harmonic for this jumping frequency, as reported in the literature. The simulation of the jumping load impulse using the proposed model also predicted the same pattern in the acceleration response, verifying that the model is accurate.