Monitoring historic structures, from their past to their future

The aim of this paper is to inspect the role of structural monitoring in the knowledge and also in the conservation process of the built historical heritage, bearing in mind that knowledge and conservation should always go hand in hand. One of the most interesting, and in some ways innovative, contents in the recent Directive on the seismic protection of cultural heritage is certainly the role ascribed, in the evaluation of seismic risk, to the observation of the buildings and to their control, and thus to their "monitoring." Indeed, the Directive defines the "regular monitoring of construction" as "a practice highly desirable because it is the main instrument for the conscious conservation". Moreover, it adds that "in some cases, when the possible collapse mechanism is well understood and safety thresholds can be reliably defined, monitoring can constitute a valid alternative to strengthening interventions"[DPCM, 2011, 15, 19]. On the other hand, the same concept was expressed, at the end of the 80s, by the Commission Ballardini-Gavarini, which emphasized as "from this data series [monitoring] can derive an indication on the building global behavior, considering the phenomena that have taken place over time as a direct experimentation, at a real scale, very indicative and conclusive" [Ballardini, Gavarini, 1989, 16]. Indeed, monitoring is not only a matter of understanding what has happened in the past: it can also assume an active role in the conservation of historical buildings. A methodology of "slow" experimental investigation is particularly suitable for the historic buildings, as it allows to calibrate a reliable model of the structure, which is not only able to understand better its "normal" behaviour but also to simulate responses to various accidental events (earthquakes, wind, temperature variations and changes in structural constraints). This procedure allows a constant evaluation of the cracks and damges and the ability to run short and long term forecasts and simulations on the behavior of the monument, also assessing the actual effectiveness (or possible recalibration) of interventions, which are proposed or even put in practice. Indeed, monitoring is based on the most reliable “model” available to date of the real structural behavior: the real response of the building and its deep observation.