Damping added to floors by seated crowds of people

Floor damping is an essential parameter in the evaluation of the dynamic performance of a floor as the amount of floor damping has a significant impact on floor vibration levels. This paper explores the not well understood relationship between floor damping and seated crowds of people. The paper contributes to the understanding by presenting results of controlled experimental investigations that involved crowds of people sitting on a vibrating test floor. In tests, floor damping and floor frequency are identified for various sizes of the crowd. This in itself throws some light on the not well understood relationship, but it is further investigated whether modelling the human crowd as a single-degree-of-freedom spring-mass-damper system attached to the vibrating floor can explain the recorded floor frequency and damping. Thus, a crowd-floor interaction model describes the combined crowd-floor system, and results show that this model is capable of explaining the overall tendency in recorded floor damping and frequency, and the calibration of the interaction model gives some indications of the frequency and damping of the spring- mass-damper system representing the crowd. The paper describes the tests and the methods used to evaluate the appropriateness of modelling a crowd as a spring-massdamper system. Some implications of the observed crowd-floor interaction are discussed in light of the results.