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
