Serviceability response of a bench-mark cable-stayed footbridge: comparison of available methods

In previous Footbridge Conferences, the focus of researchers has been on the representation of pedestrian actions (vertical and lateral) to design footbridges, on the proposal of methodologies for the analysis in service of these structures and on the description of the serviceability response of particular footbridges. Nonetheless, none of these research works have been focused on the magnitude of the serviceability response of footbridges according to its structural type. This paper characterises the response of footbridges with stayed cables as main structural type. Based on a compiled dataset of cable-stayed footbridges (developed for this research work), the paper presents the geometrical and structural characteristics of a footbridge that can be regarded as representative of this structural type. Considering the best methodologies available for the assessment of its response in vertical and lateral direction, the paper describes the magnitude of the serviceability performance of this bridge under a wide range of pedestrian scenarios. This description familiarises designers at early stages of their design with the order of magnitude of the serviceability response of cable-stayed footbridges with an arrangement similar to that commonly used for this structural type

Serviceability limit state of vibrations in under-deck cable-stayed bridges accounting for vehicle-structure interaction

Verification of the serviceability limit state of vibrations due to traffic live loads can be neglected in conventional types of concrete road bridges but becomes critical in the design of slender structures like under-deck cable-stayed bridges. The novelty of the work presented in this article is that an innovative vehicle-bridge interaction model is employed, in which realistic wheel dimensions of heavy trucks, road roughness profiles and the cross slope of the road are considered in nonlinear dynamic analyses of detailed three-dimensional finite element models. An extensive parametric study is conducted to explore the influence of the bridge parameters such as the longitudinal and transverse cable arrangement and the support conditions, in addition to the load modelling, road quality, the wheel size, the transverse road slope and the vehicle position and speed on the response of under-deck cable-stayed bridges. It has been observed that the vibrations perceived by pedestrians can be effectively reduced by concentrating the cable-system below the deck at the bridge centreline. The Fourier amplitude spectrum of the acceleration at critical positions along the deck proved that the response of under-deck cable-stayed bridges is not dominated only by contributions at the fundamental mode and, consequently, the conventional deflection-based methods are not valid to assess the users comfort. Instead, Vehicle-Bridge Interaction analyses are recommended for detailed design, considering the wheel dimensions if the pavement quality is bad and/or if the wheel radius is large. Finally, we verify through multiple approaches that the comfort of pedestrian users is more critical than that of vehicle users. However, the comfort of vehicle users is shown to be significantly affected when the road quality is poor

Dynamical behaviour of an under-deck cablestayed footbridge under the action of pedestrian transit

In recent years, the new trends in the construction of footbridges have led to the design of innovative bridge types, such as under-deck cable-stayed bridges, with slender and lighter decks. This tendency has made the serviceability limit state of vibrations relevant in the design of footbridges. The natural frequencies of these bridge types, in many occasions, fall within the range of the frequencies of the dynamic forces induced by pedestrians. Therefore, the accelerations induced by pedestrian transit are not admissible when the users‘ comfort has to be guaranteed. In this paper, the dynamical behaviour of an under-deck cable-stayed footbridge under pedestrian action is presented. Both vertical and lateral components of the pedestrian action have been considered. For the analysis of the vertical component, the under-deck cable-stayed footbridge is loaded with groups of pedestrians moving across the footbridge with two different velocities. For the analysis of the lateral component, the frequencies of the lateral forces induced by the pedestrians are taken from the range 0.7-1.2Hz. (Bachmann, 2002). The verification criteria for the serviceability limit state of vibrations established by Eurocode are considered, and the response of the under-deck cable-stayed footbridge was compare with these design standards.Results of the analyses carried out shows the acceleration values of the footbridge in both horizontal and vertical direction. The important of the application of a bracing system on the horizontal acceleration due to laterally induced pedestrians‘ action. The effect of density on the vertical and horizontal acceleration values of the footbridge due to induced pedestrians‘ action. Finally, the result of the effect of speed and different phase time in the induced pedestrians‘ action is shown