Vertical Crowd-Structure Interaction Modeling: Numerical and Experimental Assessment of a Cable-Stayed Footbridge

Low-damped lightweight footbridges usually present excessive human-induced vibrations. Hence, several experimental and numerical studies have been conducted over the years to propose easy-to-apply load models to represent pedestrian actions for vibration serviceability studies. In this sense, an experimental campaign of an in-service cable-stayed footbridge subjected to different pedestrian-stream scenarios has been carried out. The experimental results have been compared with numerical results involving direct time-integration analyses with and without considering human-structure interaction (HSI). As the application of interacting load models is time consuming and difficult to apply in practical engineering, a simplified frequency-domain interacting model based on the two degree-of-freedom equivalent coupled crowd-structure system is proposed and validated with the time-domain results. Furthermore, the effects of synchronization between pedestrians through the consideration of several statistical distributions for the synchronization angle is evaluated using direct time-integration with HSI and compared with the results of the simplified frequency-domain model in which the interpedestrian synchronization is considered by the equivalent number of pedestrians. Finally, showing the advantages of using the equivalent crowd-structure system, a parametric study of the influence of pedestrian dynamic properties on the structure response is carried out. Nowadays, footbridges tend to be slender and are designed using lighter materials than in the past. When footbridges are lightweight, the coupling vertical effect of pedestrians and the structure, called the human-structure interaction phenomenon that causes a reduction in the structure accelerations, is very significant. Therefore, it is of crucial importance to consider this in the design process of new footbridges. However, these models are complex and not geared to engineering practice. In this paper, a simplified method that allows for this phenomenon to be considered is proposed. It is based on simple algebraic operations between transfer functions which are obtained in the frequency-domain in a straightforward manner. The model is compared with another more complex model formulated in the time-domain and with experimental tests yielding very similar results. Furthermore, it is also compared with the noninteracting models proposed in guidelines. These models clearly overestimate acceleration response in lightweight footbridges, leading to a structural oversizing in the design stage.