Influence of the measurement mesh on the spread of the modal parameters of a stadium grandstand, identified via Operational Modal Analysis techniques

Operational modal analysis offers a powerful tool to the aim of structural health monitoring of civil structures. Vibration data gathered during the structure normal life can be used to identify a set of modal parameters and so to keep their evolution under control. Anyway this kind of modal analysis leads to results that are affected by a higher spread if compared to the ones given by the traditional experimental modal analysis performed using known forcing. This is mainly due to the forcing nature, which is assumed to be white noise but this is often a wide assumption, and to the external parameters values, such as temperature or structure loading which are changing from one identification to the others and are seldom measurable. The aim of this paper is to investigate the influence of the number of measurement points on the spread in the identification of the modal parameters of one of the Milano Stadium grandstands. At the moment only two accelerometers per stand are installed in the stadium as permanent monitoring transducers to provide an indication of the reached maximum vibration levels, the idea is to exploit the same system to the aim of monitoring the modal parameters evolution. In this work the advantages of increasing the number of sensors per stand is investigated studying its influence on the spread of the identified parameters. © 2009 Society for Experimental Mechanics Inc