Dynamic performance assessment of timber-steel composite pedestrian bridges

As lightweight, slender footbridge designs gain popularity, pedestrian-induced vibrations are becoming a prominent concern in modern bridge engineering. The reduced mass and stiffness of these structures make them flexible and, hence, more vulnerable to dynamic oscillations, impacting pedestrian comfort and structural serviceability. Timber-steel bridges, in particular, have recently gained attention as an efficient and eco-friendly solution for footbridges. However, the dynamic behavior of these structures under pedestrian and other dynamic loads remains underexplored, as current research has predominantly focused on steel, concrete, and timber-only footbridges. Addressing this gap, the current study investigates the dynamic performance of three timber-steel footbridges, providing new insights into their behavior under dynamic loads. The research scope encompasses a thorough analysis of comfort criteria, focusing on vibration serviceability for pedestrian-induced loads per CSA S7 guidelines. Various pedestrian load models were applied for all critical modes that were identified. Consideration was given to human-structure interaction effects and pedestrian-structure lock-in. Additional evaluations assess bridge responses to wind and seismic forces to give a comprehensive overview of the dynamic performance of timber-steel pedestrian bridges. Results reveal that timber-steel footbridges, while offering favorable load-bearing characteristics, require careful vibration control to meet comfort standards, particularly under pedestrian-induced loading. The study also evaluates the effectiveness of passive control devices, such as Tuned Mass Dampers (TMDs), demonstrating their utility in enhancing the dynamic response of these structures. Such configurations were found to be effective in mitigating vibrations and maintaining desirable comfort levels. To sum up, this work serves as a means to increase the understanding and knowledge regarding the dynamic performance of timber-steel footbridges under various loading conditions and to suggest practical measures to overcome any serviceability issues.