The Role of Dynamic Response in Design

Weight reduction, obtained by utilising materials with high mechanical features and by formally adopting visually transparent structures, led to designing buildings with limited self weight and thus sensitive to the effects of live loads.

This sensitivity is particularly marked in the case of footbridges where the pedestrian traffic translates into dynamic forces that, should they have frequencies that are close to self vibrations of the structure itself, can lead to resonance.

The footbridge over the river Adige at Legnago, designed by the authors, once construction had been completed, showed a marked sensitivity to repeated horizontal forces that were able to cause torsional vibrations around its longitudinal axis.

This paper examines how an analysis of self frequencies and modal response enabled the excessive deformability of the piers to be identified as the key cause of the structure behaving overall in this way and, as a result, geared the design solution towards constructing a more sound connection between the head of the new piers and the existing ones.

The experimental frequency identification enabled the efficacy of the design solution to be checked, demonstrating the excellent ability of the FEM model used to predict dynamic structural behaviour.