HUMAN-STRUCTURE INTERACTION IN VERTICAL VIBRATIONS.

■ This paper deals with the subject of human‐structure interaction in vertical vibrations. It presents some results recorded on a cantilevered grandstand at Twickenham which showed that, although the empty structure had a clearly defined fundamental mode, two modes of vibration were apparent when the spectators were seated. The frequency of the empty stand was between the two frequencies of the occupied stand and a significant increase in damping was noted when the crowd was present. This suggests that the crowd should be modelled as a damped sprung mass system rather than as a simple added mass which is sometimes used in analysis. A study of an undamped system with two degrees-of-freedom is then presented which leads to three relationships which are consistent with the observations at Twickenham. The results of tests on a simple beam for a range of activities are given to provide further information on human‐structure interaction and demonstrate that when a person is stationary on the beam the two interact, but when a person is moving he simply acts as a load. Results from tests on low- and highfrequency structures, when both empty and full of spectators, are given which show quite different vibrational characteristics but which are consistent with the basic two-degrees-of-freedom model. The implications of these findings are then considered.