Damping and frequency of human-structure interaction system

Human presence can change the dynamic characteristics of human-structure interaction systems, i.e. particularly their damping and frequency. In many design codes, the pedestrian is regarded as a moving force (MF) while a more complete model, referred to as moving spring-mass-damper (MSMD) has received attention recently. Unlike the MF model, the MSMD model is able to take into account the human damping and stiffness effects. This paper is devoted to determining the instantaneous damping and frequency of the human-structure interaction (HSI) system subjected to a single and multiple pedestrians. Each pedestrian is modelled as a MSMD, and a methodology for determining the system damping and frequency properties is described. A simply supported beam structure is considered and modelled in modal space. The imparted pedestrian vertical force is modelled adopting the first four harmonics of Fourier representation using Young's dynamic load factors. It is concluded that human presence can significantly increase and decrease damping and frequency of the structure, respectively and it is so important to consider human effect on the system's damping and frequency in serviceability assessment of footbridges.