Forced vibration tests carried out on a laminated timber footbridge: comparisons five years apart

The aim of this work concerns the analysis and comparison of those modal parameters which are obtained by assessing two forced vibration tests, experienced on a laminated timber footbridge. The two tests were carried out five years apart to verify if the dynamic characteristics of the structure change considerably during its use. In particular, modal damping of the footbridge increases (that means an effective structural deterioration), whereas modal frequencies are substantially constant . It is noticeable that the analysis of the first test [1] highlighted that the natural frequencies of the structure were included in the range between 1 and 2 Hz, more similar to the frequency of the human step. This can entail possible amplifications of the oscillations of the structure during the passing of pedestrians (low comfort level for users). The analysis of the structural durability is necessary because the ordinary maintenance of the footbridge is not usually made, although the structure is subject to hard weather condition.