Effects of coordinated crowd motion on dynamic responses of composite floors in buildings

This paper explores the vibration behaviour of composite floors in an existing building using a comprehensive study of the modal dynamic responses. Different panels are subjected to loads induced by human motion. The computed fundamental natural frequency and vibration modes are first verified against experimental and numerical results from previous studies. Departing from close correlation established by comparisons, this study investigates the effects of coordinated passive live loads as additional stationary mass due to crowds jumping. In another case, the effects of different intensities and the loads created by different jumping crowd sizes are investigated. Thirty modes of vibrations are selected to obtain all the possible excitations and to make a third harmonic load frequency available to excite the critical modes. In addition, the presence of different coordinated passive live loads on the composite floor results in different behaviours for each particular panel that is associated with location of load and passive live load intensities. This study shows that an increase in crowd size and the intensity of the active load are not directly proportional to the dynamic responses especially for displacement. It is also found that the synchronisation of active load plays a part in reducing structural dynamic responses, an observation that has not been highlighted before in previous studies.