Human-structure dynamic interactions: Identification of two-degrees-of-freedom walking human model

Single-degree-of-freedom (SDOF) models are widely used as a first approximation to simulate dynamic interactions of a walking human body with a vertically vibrating structure. However, the parameters identified in the literature for such SDOF models are distinctly different for different structures and even different modes of a structure. This study hypothesises that these differences can be attributed to different modes of a human body being dominant when subjected to different vibration frequencies. A 2DOF mass-spring-damper model with two modes of vibration is proposed to simulate a walking human dynamics. The 2DOF model parameters were identified using iterative Agent-based simulations in a way that the analytical FRF of the occupied structure matches the corresponding experimental FRF measured from a series of walking tests on a lightweight floor structure. It was found that a 2DOF human model with modal frequencies 4.3Hz and 11.0Hz and modal damping ratios of 19% and 0.52% for modes one and two, respectively, generates the least error in estimated FRFs. The validation of the identified 2DOF model on a post-tensioned concrete footbridge with different walking traffic regime showed that the model can estimate the natural frequency and damping ratio of both vibration modes of the occupied structure with maximum error of 0.4% and 6%, respectively. This is the first study of its kind that proposes a physical model of a walking human that consistently simulates the dynamics of a walking human for different structures and different modes of a structure, and addresses the discrepancy in the identified parameters of the SDOF walking human model in the literature.