A method for large-scale vulnerability assessment of historic towers

The methods commonly pursued for vulnerability or risk analysis, when carried out at large scale (territorial, regional), are mainly based on qualitative parameters, due to the necessity of processing a huge number of structures. As a matter of fact, the final target of these methods is the correlation of the most representative parameters of the structural behaviour, so as to finally rank the same structures according to their level of vulnerability or associated risk. These methods are undoubtedly effective for large-scale analyses and statistical elaborations, although affected by a certain level of subjectivity. Moreover, the vulnerability is commonly defined by hybrid indices (more often obtained as score assignment or expert opinions) that do not represent physical entities. A validation of these methods can be pursued by data on earthquake damage, which are very helpful for calibrating the analysis and formulating fragility curves. Experimental data and in situ investigations can also help to enhance the effectiveness of the method and to finally calibrate the same results. These are particularly needed for very slender structures, as towers and similar structures, the behaviour of which is strongly influenced by the dynamic performance. This paper presents a new method, named Vulnerability of Towers (VULNeT), for assessing the seismic vulnerability of slender structures (particularly towers) according to two different levels of accuracy. The method is based on qualitative parameters, collected through a new survey form, on purpose developed with an online data storage, capable of running speedy analyses. Once the method has been introduced, some applications on different samples are shown and the result compared with those of other recent works obtained from the literature on the topic. The final part of this paper provides a general framework on possible enhancements of VULNeT. Data on the dynamic behaviour of the structure obtained through experimental campaigns and structural modelling are introduced, and these are conceived for validating the results achieved as well as to check the feasibility of the possible failure mechanisms included in the form. Finally, the first results obtained on a pilot application on the Febonio tower of Trasacco (Abruzzo, Italy, where in situ investigations and F.E. structural modelling were carried out), are presented, and some conclusions are drawn on the future development of the work.