Viscoelastic damper for vibration mitigation of footbridges.

Abstract

Footbridges are among long-span light-weight structures that because of their low damping ratio are susceptible to vibration. Excessive vibration in footbridges usually occurs when they are subjected to rhythmic dynamic loads caused by human activities like walking and running. In order to mitigate the human induced vibrations in footbridges, an increase in the damping ratio is often suggested as the most economical approach. Tuned mass dampers have been widely used for this purpose, however, their installation and maintenance costs are high. This has encouraged researchers to examine the efficiency of the other types of dampers. Viscoelastic dampers have been successfully employed for vibration mitigation of structures against wind and earthquake loads. However, their efficiency for reducing human induced vibration in footbridges has not been addressed. In this study, a real footbridge with a free span of 22.5 m and a width of 2.3 m was selected for numerical investigations. SAP2000 program was used to establish the finite element (FE) model of the footbridge. The established FE model was validated by comparing its natural frequencies with those measured on the field. FE model results indicated that the acceleration response of the footbridge exceeded the code specified limit. Therefore, a viscoelastic damper was designed and installed under the footbridge in order to reduce the acceleration response below the allowable level. Installation of the viscoelastic damper significantly decreased the vibrations. It was concluded that viscoelastic dampers were an economical and efficient solution for vibration problems in footbridges.