Special Lecture: The role of monitoring and identification techniques on the preservation of historic towers

The historic towers today we observe survived the initial period in which they could have been not so far from a bearing capacity collapse, due to lack of strength. And due to uneven settlements, they appear today to survive at an alarming angle of inclination, in some cases not so far from the danger of a leaning instability, due to lack of stiffness of the soil. Since these towers are quite often the symbol of the town and sometime they represent the local community as a whole, their preservation deserves special attention and efforts. Within the context of the restoration principles, preserving the whole integrity of the monument should be a well accepted concept and this requires not to rush in deciding the stabilizing measures until the behaviour of the monument is properly understood. A long term monitoring should then be aimed at identifying the causes of movements and their potential increase in rate in order to distinguish the normal physiological behaviour from deviations. In addition, these observations can be complemented with experimental identification analyses, performed in the presence of ambient vibration, that allow to explore in a rather effective way the response of the structure and its interaction with the soil.