Controlling the Human-Induced Longitudinal Vibrations of a Nielsen-Truss Footbridge Via the Modification of Its Natural Frequencies

This paper describes a case-study where the human-induced vibrations of a footbridge have been controlled by means of the modification of its natural frequencies. The structure, a Nielsen variable depth truss, is located over a highway on the outskirts of Malaga (Spain), so that it was designed to withstand low pedestrian densities and its dynamic behavior was just analyzed according to Spanish standards at the date of construction. However, the presence of a nearby sports pavilion originated unexpected large pedestrian flows. This new service condition was not properly anticipated, leading to significant longitudinal vibration levels. To overcome this problem, experimental and numerical studies were carried out, with the aim of finding a low cost solution that yet maintained the footbridge aesthetic appearance. Following these studies, corrective measures that increased its stiffness were then adopted. Subsequently, experimental tests and a finite element model tuning were performed to obtain: (i) its modified modal parameters; and (ii) a more accurate estimation of its dynamic behavior under different pedestrian flows. Presently, the footbridge has been in service for more than four years, maintaining an adequate comfort level.