Human-induced swaying forces on flexible structures

This paper addresses the effect of a stationary human subject swaying side to side on a flexible structure that can move perceptibly. Similar tests have not been conducted before, so a unique test rig is described and the test methodology explained. The test rig was developed at The University of Manchester to permit a person to sway on an idealised single-degree-of-freedom system with variable natural frequency and mass. We present a set of results that show the effect of the flexibility of the structure on the levels of force and response that can potentially be generated by swaying humans. The acceleration and displacement responses show significant peaks when the swaying frequency is in the region of half the natural frequency and of the natural frequency itself, which indicates that the first and second harmonics of human-induced forcing functions are exciting resonant response. It has also been found that the force level drops at or near to resonance, which is somewhat analogous to the force ‘drop-out’ encountered near resonance in shaker-based modal testing. This result indicates the potential for significant human–structure interaction in the sway direction when the sway motion of the structure is perceptible.