Reviewing and redefining the dynamic amplification factor of a simply supported beam of a road bridge

The dynamic amplification factor (DAF) is a key parameter for evaluating the dynamic performance of bridges under vehicular loading. Although it has been extensively studied, accurately determining DAF remains challenging due to the combined influence of multiple parameters and the absence of a unified evaluation methodology. In this study, the concept of DAF is revisited, and a new definition based on dynamic displacement difference is proposed to better capture the physical mechanisms governing bridge dynamic responses. A review of existing DAF definitions, calculation methods and design code provisions is first presented. Subsequently, a vehicle–bridge interaction framework is adopted to investigate the dynamic responses of a multi-span simply supported bridge subjected to different vehicle models. Numerical simulations are conducted to evaluate the sensitivity of bridge responses and DAF values to vehicle modelling assumptions and road roughness effects. The results indicate that conventional DAF definitions may overestimate or underestimate dynamic effects under certain conditions, whereas the proposed DAF formulation provides a more consistent and physically meaningful representation of dynamic amplification. This study clarifies the effects of vehicle modelling assumptions and road roughness on DAF evaluation and provides a rational basis for improving DAF assessment in bridge design and analysis.