Long-term monitoring of Sesia high speed railway bridge

Long-term monitoring has been recognized to be one of the most reliable approach to real-time control of bridge behavior, assuring structural safety and optimizing repairing and maintenance operations. Many different typologies of monitoring systems aimed at the evaluation of structural health condition, identification of possible damages in real time or analysis of strain/stress spectra on structural members have been installed on roadway/railway short to long span bridges. Type, number and configuration of sensors, position of acquisition units, quantity of data collected and eventually processed in real time depends on the kind of structural response monitored. Besides the realization of new high-speed (HS) railways across Europe, as well as in many other countries, has required the development of monitoring systems for many bridges and viaducts, among witch there are classical concrete solutions and new steel-concrete composite typologies characterized by light and cheap structures. In this paper, a long-term dynamical monitoring of the Sesia viaduct, a medium span double box composite bridge of the new Italian HS network, is exposed and analyzed. Modal proper-ties, e.g. frequencies and mode shapes, are observed in order to determine the real-time structural behavior and the effects of dynamic interaction between train and bridge deck. A suitable procedure, based on the correlation between video and dynamic data, is applied to determine typology, length and velocity of train vehicles passing on bridge, to obtain a reliable evaluation of real traffic spectra of HS bridge superstructures.