Design and experimental analysis of an externally prestressed steel and concrete footbridge equipped with vibration mitigation devices

A 142-m, three-span continuous footbridge over the Esino River (Italy) is considered as a case study to illustrate a number of challenging aspects in its static and dynamic design. The adoption of an optimized steel deck with a variable cross section together with the use of external prestressing tendons in the central span allows a substantial reduction of structural weights. The resulting footbridge requires a proper model for the assessment of its behavior up to the ultimate limit state as well as attention to vibration control under pedestrian loading at the service limit state. The former issue is addressed through the use of a specifically developed material and geometric nonlinear finite-element formulation. Regarding vibration control, an original combination of two different systems is used, i.e., high damping rubber (HDR) stripes and tuned mass dampers (TMDs). The HDR stripes, applied between the steel deck and the concrete floor, increase the overall damping of the footbridge, whereas the TMDs significantly reduce the accelerations at the most critical frequencies. The design of this nonconventional solution for vibration control is discussed, and the results of experimental tests in the early stage of the footbridge construction are illustrated. The experimental results allow the validation of the structural model used in the design as well as the evaluation of the influence of the HDR stripes and of the nonstructural components on the modal properties of the completed footbridge, permitting fine-tuning of the TMDs before they are installed.