Shear lag effects on pedestrian-induced vibration and TMD-based vibration control of footbridges

The shear lag effect (SLE) is one of the vital mechanical characteristics of structures with thin-walled box sections. While most existing studies of the SLE focus on the static response of footbridges, pedestrian-induced vibration deserves more attention since it represents the actual response of footbridges during their practical service process. A theoretical framework is proposed to consider the corresponding SLE. Firstly, the SLE on the natural frequencies of the structure can be considered with a reduction ratio to the corresponding case without considering the SLE. Results show it is more necessary to consider the SLE for footbridges with smaller span-width ratios, smaller section thickness-width ratios and lower height-width ratios. The SLE may result in significant reductions in the natural frequencies of the structures. These reductions in the predicted natural frequencies due to the SLE may further result in inaccuracy in the prediction of pedestrian-induced vibrations of footbridges. Furthermore, the most often applied mitigation measures may not be reliably designed. This may result in very significant reduction in the effectiveness of vibration mitigation measures. To consider the SLE on pedestrian-induced vibration and tuned-mass-damper-based vibration control of typical footbridges with thin-walled box sections, a simplified strategy is proposed.