Structural behaviour and design criteria of under-attack cable-supported foorbridges

Under-deck cable-supported footbridges are slender and effective structures comprising of cables located underneath the deck. They can be sorted into under-deck cable-stayed (UDCS), under-deck suspension (UDS) and stress-ribbon (SR) footbridges. All of them promote the axial behaviour and reduce the amount of required construction materials. In addition, to their high structural efficiency and sustainability they also possess aesthetic and construction advantages compared to conventional footbridges for covering medium spans. Nevertheless, they become more prone to vibrations that can be activated from the passage of pedestrians during service. In the present work, the dynamic response of UDCS, UDS, and SR footbridges under pedestrian loading in service was examined in detail. Due to the shortcomings of the current codes of practice to represent realistically human-induced vibrations, a stochastic pedestrian load model was implemented. This model simulates the actions induced by individuals, taking into account the inter-subject and intra-subject variability as well as the pedestrian-structure and pedestrian-pedestrian interaction. The pedestrian load model was applied to representative UDCS, UDS and SR benchmark footbridges in order to investigate their dynamic response. The effects of different sources of non-linearities were examined. As for all the benchmark footbridge configurations, when designed to fulfil only ultimate limit states, the acceleration response was found unsatisfactory, yielding to minimum comfort for their users, extensive parametric studies were carried out aiming to find critical design parameters able to improve their dynamic behaviour. Based on the investigation of the benchmark configurations and the parametric studies a set of comprehensive design criteria and recommendations for UDCS, UDS, and SR footbridges were proposed. For all those cases, decreasing the deck slenderness was found the most cost-effective way to improve the dynamic response and increase users’ comfort within appropriate design limits.Open Acces