On the Dynamic Assessment of a Cable-Stayed Footbridge: The Iron Bridge

Abstract Human-induced loads may produce resonance when the forcing frequency coincides with the natural frequency of the system. In this work, the dynamic assessment of a pedestrian cable-stayed bridge in Uppsala, Sweden is presented. The dynamic properties of the system have been identified and a loading scenario is evaluated. A comparison between the theoretical and measured acceleration of the bridge is made using a detailed finite element model. Different modelling aspects are considered and evaluated by studying their influence on the natural frequencies of the system such as the tie rods system, railings, and boundary conditions. Moreover, a parametric analysis of the elastic modulus of the cast iron material with respect to the boundary conditions of the system is presented to quantify the uncertainties of the system. Special focus is given to the resonant response of the first natural frequency of the bridge potentially compromising the serviceability limit state of the structure. Furthermore, the scenario of a single pedestrian jogging on the spot is evaluated and a hypothetical standing crowd is considered to illustrate the benefits of taking into account the human-structure interaction effect. A considerable reduction of the dynamic response of the system is found, highlighting the importance of the human-structure-interaction effect.