large dams via modal identification Antonella Frigerio*, Elia Bon* 5th International Conference on Dam Engineering Lisbona, 14-16 Febbraio 2007 * CESI RICERCA The construction industry at European level is increasingly involved in the safety reassessment and rehabilitation of existing structures considering the limited available resources for new constructions and the greater environmental awareness. To this aim reliable mathematical models of civil engineering structures could play a key rule because of the help they could provide to conjugate structural safety, rehabilitation design and life extension. However, it has to be kept in mind that for older structures these models often do not exist and for newer projects “as-built” information often does not accurately reflect the work done on site. Given the shortcomings in design data and surveys as a basis for structural models, it is clear that non- destructive methods are particularly useful in order to create more reliable models. The HISTRIDE methodology here presented greatly extends and simplifies a non-destructive identification approach based on modal structural response. Physical parameters of the Finite Element model of a structure are modified to reduce the error between experimental modal features and computed ones. HISTRIDE is a software environment running on a desktop PC, developed in the frame of EC ESPRIT Programme. The Least Squares Algorithm of the HISTRIDE identification process has been recently improved (thanks to the public research funding for the Italian electric sector): in order to avoid divergent oscillations that move away from the structural response, the Coupled Local Minimizers (CLM) method has been implemented. In the paper HISTRIDE will be presented with reference to a full scale validation test carried out with reference to a concrete arch dam. Keywords: modal identification, updating of Finite Element models, optimisation methods