Identificazione dinamica di una passerella pedonale strallata mediante algoritmi nel dominio delle frequenze

Footbridge are normally slender structures; limited level of live loads usually provides for effective bridges, when static behaviour is concerned, but characterized by fundamental vibration frequencies in the range of 1-5 Hz. On the other side, the dynamic behaviour of footbridges subject to pedestrian loads is still a matter of research. Furthermore, the frequency range mainly involved in the dynamic pedestrian actions is in the range of natural frequencies of the action on the bridge, caused by running, stepping, walking of pedestrian. For this reason, the dynamic properties of footbridges must be analyzed in order to define a proper humanfootbridge interaction model. The main purpose of this study is the characterization of the dynamic properties of a cable stayed footbridge, with particular reference to the pedestrian dynamic action. Dynamic tests have been carried out on a 45 m long footbridge, recently built in Imola (Bologna). Different experimental tests have been carried out: free vibrations have been recorded after releasing external loads; a wide number of pedestrian dynamic loading conditions have been considered on the structure, by walking with different passing frequencies, such as simple walking, running, etc. in order to excite the different structural natural modes. Some tests have been repeated by using different number of people. The experimental data have been used to find the dynamic properties of the structure (frequencies, mode shapes and damping ratios) by using two different frequency domain techniques (the Enhanced Frequency Domain Decomposition - EFDD and the MDOF Circlefit method), in order to verify and compare the reliability of different identification methodologies.