Serviceability Assessment of a Retrofitted Footbridge Prone to Lateral Vibration

This paper describes the results of a numerical investigation carried out on the dynamic behavior of a footbridge recently built in Milan, Italy. Following excessive vibrations under crowd loading, experimental tests under ambient-induced vibrations were carried out on the footbridge, and the structure was strengthened through the addition of diagonal braces in the piers. The objective of the different analyses illustrated in the paper is to assess the dynamic characteristics of the bridge, as well as the expected vibration level induced by crowd loading, in order to evaluate the risk of discomfort problems, and to evaluate the effectiveness of the strengthening strategy adopted. The structural behavior was studied by carrying out modal and linear dynamic analyses, as well as through the application of a simple and straightforward criterion. The modal analysis shows good agreement with the measurements, and the adopted strengthening solution is shown to greatly reduce the likelihood of vibration problems under crowd loading.