New techniques and materials allow designing bridges and elevated pedestrian crossings with longer spans. Adopting slender geometries leads to low vibration frequencies, close to the walking frequency of pedestrians. This may induce pedestrians to synchronise their step with the motions of the structure and, hence, to resonance and to an excessive level of vibrations. London’s Millenium Bridge is a well-known example.
Principia has carried out studies of vibrations and dynamic amplification for several such structures in their design phase. One of them is the Pedro Arrupe crossing, in Bilbao, spanning 150 m. The studies were based on a finite-element model, which allowed calculating the modal shapes and frequencies, as well as the dynamic amplification undergone by the pedestrian excitation. The work concluded with the design of four absorption devices (TMD: Tuned Mass Dampers) to limit the levels of vibration.