A mixed finite element method is used to simulate a building structure-acoustic volume interaction system subject to multiple human footfall impacts. The pressure in the acoustic volume and the displacement of the structure are chosen as the fundamental variables to describe air-structure interaction dynamics. The governing equations and the corresponding variational formulation for generalised air-structure interaction systems are presented. From the variational formulation, the finite element and substructure-subdomain equations are derived. The available experimental results of footfall impact load histories are described and discussed. Based on an experimental result, an approximate footfall load time function is proposed to model the footfall loads in two successive human foot-steps. This approximate footfall load is applied at each structure point at which a left or right foot contacts at the corresponding time instant. Therefore, this footfall load is a moving load with a speed equalling the human walking speed. Following a generalised description of the developed numerical approach and footfall loads, an example is given. In this example, three cases involving two people walking along two perpendicular directions on the top floor of the structure are simulated, respectively. The dynamic responses of the displacement of the structure and the acoustic pressure in the acoustic volume are obtained. The calculated results are compared and discussed to illustrate the developed method and to reveal the mechanism of low-frequency vibration produced by human footfall impacts. The advantages of the proposed method are summarised to provide some guidelines to house designs.

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