Structural Health Monitoring of historical buildings: preventive and post-earthquake controls

Structural health monitoring (SHM) has been recently more and more exploited in the study of cultural heritage (CH) buildings, as a key activity to increase the knowledge on their structural behavior and to have a deeper insight on their conditions. This knowledge allows to carry out with more confidence and only if necessary a strengthening intervention, but also to prevent the execution of intrusive repair works, if they are not justified by an experimentally demonstrated worsening of the structural conditions. The use of monitoring systems applied under ordinary conditions and installed on CH structures allows to: (i) validate the functioning of the adopted structural models; (ii) identify the ongoing damaging processes; (iii) validate the effectiveness of the strengthening interventions. The effectiveness of this approach is demonstrated by the installation of SHM systems on four important monuments in northern Italy (Verona Arena and the stone tomb of “Cansignorio della Scala” in Verona, the “Bertoliana” library in Vicenza and the church of S. Sofia in Padova) and on the Qutb Minar in New Delhi. In case of a seismic event, SHM can furthermore prove its usefulness in order to: (i) evaluate quantitatively the progression of the damage pattern, (ii) design effective and urgent interventions if an unsafe displacement patterns is recorded; (iii) define an early warning procedure for the safety of the workers employed in the strengthening interventions. Monitoring can also be effective when implemented on seriously damaged buildings, if the time schedule for the interventions is difficult to be a priori planned. A low cost diffused monitoring system permits to proceed more urgently on selected cases, if a worsening of their structural conditions is noted, or to postpone the interventions in a successive phase, if the assessed damage pattern maintains an acceptable stability. In this framework, the authors and the university of Padova in collaboration with the officer of the Cultural Heritage Authority, the university of Nagoya (Japan), the National Institute of the Conservation and Restoration (ISCR) and the Veneto region designed and installed SHM systems on six representative and emblematic CH buildings in l’Aquila after the devastating earthquake occurred on the 6th of April 2009 in the Abruzzo Region. The selected case studies (S. Agostino church, S. Biagio church and S.Giuseppe oratory, S. Marco church, Civic Tower and Spanish Fortress) give the possibility to validate the use of monitoring during and after the emergency activities in case of a seismic event.