Vibration serviceability often governs the dynamic design of pedestrian structures. Reliable prediction of pedestrian-induced vibrations is essential to the vibration serviceability evaluation in the design stage. Many models have been developed to evaluate vibration serviceability of pedestrian structures under human excitations. However, among these models, simplifying assumptions are often adopted as follows: (1) modal properties of structures are assumed constant in the structural system identification; (2) effects of pedestrian-structure interaction are not considered or considered based on linear dynamic behaviour of pedestrian body; (3) inter- and intra-subject variabilities in walking parameters and walking forces are neglected or not fully considered.
To address some aspects of these simplifying assumptions, extensive field tests are carried out on a footbridge. Firstly, effective natural frequencies and damping ratios are obtained from a least-square fit between the measured structural responses and the calculated acceleration responses of an equivalent SDOF system. In the response calculations, the equivalent SDOF system is subjected to the measured shaker excitation forces. Next, to identify the dynamic properties of the pedestrian body, the empty structure is excited by the shaker at the fundamental natural frequency. After the structure reaches full steady response, the pedestrian starts walking on the structure at a specific step frequency. In the measurements, during pedestrian passing, the structural acceleration responses are recorded. Also, the time-variant positions of the crossing person are monitored. In the calculations of the pedestrian-induced vibrations, the pedestrian body is represented by a SDOF system. The SDOF system of the human body is moving along the structure in accordance with the registered positions of the person. The dynamic properties of the pedestrian body are identified based on good agreement between the measured and calculated acceleration responses of the coupled pedestrian-structure interaction system in time domain. Based on the real situations in the field studies, an identification strategy is proposed to obtain the pedestrian body dynamics. An illustrative example and extensive sensitivity analysis are performed to verify the validity of the proposed method. Furthermore, this contribution investigates some simplifying aspects that may affect the accuracy of the identified pedestrian body dynamics.
Results show that the modal parameters of the structure are identified to be not constant or deterministic. To obtain best identification accuracy for pedestrian body dynamics, step frequency should not be close to resonance frequency. Also, higher acceleration amplitude should be excited to obtain relative less effect from the ‘noise’ induced by the pedestrian walking. It also shows that simplifying assumptions such as the assumed constant modal properties of the structure in the system identification procedures result in inaccuracy of the pedestrian body dynamics identification. Furthermore, these simplifying assumptions lead to inaccurate/unreliable predictions of pedestrian-induced vibration levels.        
 

human-induced vibrations; pedestrian structures; vibration serviceability assessment; structural system identification; nonlinear natural frequency and damping ratio; identification of human body dynamics; simplifying assumptions