Human-induced vibrations on footbridges

Abstract

In structural design there is a tendency towards more slender and challenging architectural structures. Footbridges become more slender with an increasing high ratio live load to dead weight. A consequence of this increased slenderness of footbridges in an increased susceptibility to human-induced vibrations. The evaluation of the serviceability of footbridges therefore becomes more important. The first aim of this study was to provide a good basis and overview of the critical aspects in the evaluation of human-induced vibrations in footbridges. From a literature study, the discussions with engineering companies and an impact study it became clear that there are four critical aspects particularly relevant for further study at the moment: vandal loading, structural damping,additional mass and damping by pedestrians and probability of occurrence of accelerations and the consequences for comfort of the pedestrians. The second part of this study was focused on the question whether a probability-based approach can demonstrate that the Eurocode is conservative in the evaluation of human-induced vibrations in footbridges. Hereto, a probability-based analysis has been performed for the vibration serviceability of footbridges and implemented in a case study with three simply supported footbridges. Instead of looking at the maximum acceleration that is expected for the bridge deck, the accelerations which individual pedestrians experience when crossing the bridge have been investigated. Four scenarios have been compared to the approach prescribed by the Eurocode. The pedestrian loading has been modeled based on two assumptions for the scenarios: scenarios based on densities of the pedestrian ?ow and scenarios based on group formation. The conducted research based on assumptions for the pedestrian traf?c and a ?xed criterion for human comfort, has given valuable insight in the use of a more realistic evaluation of human-induced vibrations in footbridges. This insight has been obtained for the incoming pedestrian traf?c and the exposure to vibrations for individual pedestrians. The adopted probability-based approach contributes to demonstrate potential conservatism in the Eurocode regarding the evaluation of human-induced vibrations in footbridges.