The Role of Vibration Analysis in the Design of the Pedestrian Walkway Extension of the Principe Umberto Bridge in Legnago, Italy

This paper describes the design and construction of a new pedestrian walkway extension to the Principe Umberto bridge in Legnago (Italy), testing of vibration, and work carried out to improve its performance in serviceability condition. This walkway showed a marked responsiveness to repetitive horizontal forces, which tended to excite transversal and torsional vibration around the longitudinal axis of the structure. To overcome this problem a new static condition was created. This was based on analysing the response of the structure to human-induced dynamic loading by pedestrian movement (walking, running or jumping). Vibrations derived from such human-induced loads can cause disturbance to pedestrians (the serviceability problem) or, in more severe cases, resonance of the structure. According to technical literature and various design codes, there are two factors to be considered in overcoming these phenomena: the natural frequencies of the structure must be made to fall outside the range of human-pacing frequencies, and the maximum acceleration at any point of the structure must be not greater than a threshold value. On that basis, both modal and dynamic analyses were performed on the Legnago Bridge and the results made it possible to identify the cause of the excessive deformability. These analyses were then used to develop a design solution and to re-verify the structural project, which consisted of a variation to the static design.