Dynamic identification of a timber footbridge subject to vibration tests

Over the last thirty years timber bridges and footbridges have been found considerable use especially by their versatility, good durability and pleasing aesthetic view. First the development of new technology and materials, as the laminated timber, second the use of innovative building, assembling and connection techniques and third the expansion of efficient, certain and inexpensive products for timber protection, have allowed the employ of this type of structure. In this paper the results obtained from two forced vibration tests, carried out in 2000 and 2005, define the dynamic behaviour of a laminated timber footbridge, which has been excited by means of vibrodyne. The first test has been made in the 2000, immediately after the building launch and before its use, whereas the second test has been replicated after five years using the same test set up adopted in the first one. The aim has been to estimate, with hindsight, the dynamic characteristics of the footbridge natural frequencies, dampings, mode shapes, etc.) and their possible variations. The free vibrations of the system, acquired during only the first test, have been analyzed afterwards to define the modal parameters through the Wavelet Transform. This kind of survey is necessary due both to the material used in the building and the particular using conditions of the footbridge: in fact, it is subjected to particular weather conditions, because it is situated near to the Adriatic Sea.