HUMAN-STRUCTURE INTERACTION IN VERTICAL VIBRATIONS

This paper deals with the subject of human-structure interaction in ve rtical vibrations. It presents some results recorded on a cantilevered grandstand at Twickenham which showed that, although the empty struct ure had a clearly defined fundamental mode, two modes of vibration wer e apparent when the spectators were seated. The frequency of the empty stand was between the two frequencies of the occupied stand and a sig nificant increase in damping was noted when the crowd was present. Thi s suggests that the crowd should be modelled as a damped sprung mass s ystem rather than as a simple added mass which is sometimes used in an alysis, A study of an undamped system with two degrees-of-freedom is t hen 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 informatio n 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 high-frequenc y structures, when both empty and full of spectators, are given which show quite different vibrational characteristics but which are consist ent with the basic two-degrees-of-freedom model. The implications of t hese findings are then considered.