Dynamic Characteristics and Models

Vibration levels of flooring-systems are generally difficult to predict. Nevertheless an estimate may be needed for flooring-systems that are prone to vibrate to actions of humans in motion (e.g. grandstands, footbridges or long-span office floors). One reason for the difficulties is that the dynamic characteristics of a flooring-system do not only depend on material characteristics, floor dimensions and boundary conditions. They are also influenced by the presence of stationary persons on the floor, and these persons may or may not be present. Stationary persons are humans in, for example, sitting or standing posture, and that these persons influence the dynamic characteristics of the floor (floor frequency and floor damping) is demonstrated in the paper. The mechanism of the dynamic interaction between the floor mass and the mass of stationary persons is generally not well understood and the paper therefore looks into this mechanism which is done by carrying out controlled modal identification tests on a test floor. The paper describes the experimental investigations and the basic principles adopted for modal identification. Since there is an interest in being able to model the scenario, attempts are made to calibrate a dynamic model (human-floor system) to experimental findings.