Human Jumping and Bobbing Forces on Flexible Structures: Effect of Structural Properties

Abstract

The behavior of humans jumping and bobbing on flexible structures has become a matter of some concern for both structural integrity and human tolerance. The issue is of great importance for a number of structure types including stadia terraces. A unique test rig has been developed for exploring the forces, accelerations, and displacements that occur when a human subject jumps or bobs on a flexible structure where motion can be perceived. In tests reported earlier, it was found that the subject is able to generate near resonant structural response but it is extremely difficult, if not impossible, to jump or bob at or very near to the natural frequency of the structure when its vertical motion is significant. Also, under such near-resonant conditions, the force developed by the subject was found to drop significantly. In this paper, the effect of altering the subject-to-structure mass ratio and the damping ratio of the structure on these phenomena is presented. As would be expected, it is shown that as the structure becomes more massive and more highly damped it moves less for nominally the same excitation. In this situation, it becomes easier to jump and bob near to resonance and the degree of force dropout reduces, although it is still significant for even the most massive and highly damped case considered. A method for including these effects of human-structure interaction in a load model for dynamic response calculations is then proposed.