Comparative Evaluation of Crowd Walking Load Models for Structural Vibration Serviceability

The vibration serviceability of large-span footbridges under crowd loading has become a governing design criterion. However, the significant divergence among existing load models introduces substantial uncertainty into response prediction. This study presents a comparative evaluation of ten representative crowd walking load models from international codes and the relevant literature. It objectively evaluates their theoretical mechanisms regarding crowd synchronization and structural damping. Initial parametric sensitivity analyses are conducted utilizing single-degree-of-freedom systems. Subsequently, the predictive capabilities of these models are evaluated against field measurements from four footbridges under resonant and off-resonant conditions. The investigation reveals that response-based amplification models (e.g., M1–M3) assume high synchronization and thus overestimate accelerations under natural unrestricted resonant flows. However, these models perform reasonably well under off-resonant high-frequency conditions. In contrast, load-based models that incorporate the square-root growth law and explicit damping terms (e.g., M8–M10) better represent uncorrelated crowd flows under resonant conditions. These observations, while derived from a limited set of validation cases, provide indicative guidance and illustrate that accounting for phase randomness and structural damping is important for serviceability assessment.