Seismic vulnerability assessment at urban scale: state of the art and perspectives

Italian territory is particularly sensitive to seismic actions. The Amatrice earthquake on August 24th 2016 confirmed this aspect. Such an event, nothing but extraordinary, has been able to cause huge and tragic damages. The direct knowledge of building features is the only prior measure to face seismic events. In order to get a realistic scenario of the urban damage distribution, the determination of useful seismic vulnerability assessment tools at urban scale becomes a priority. The widespread application of seismic vulnerability assessment sheets and the related data transformation into urban damage distribution plans is exactly what municipalities need. Main advantages are both in the chance of prior knowing the most affected areas to focus on for retrofitting interventions and in the possibility of organizing optimal emergency plans. In European framework, in the last decade, the Risk-UE project has played an important role. The Risk-UE project has proposed two methods for vulnerability assessment at urban scale: LM1 method (macroseismic) and LM2 method (mechanical). The two methods provide, with different approaches, seismic vulnerability ssessment of existing buildings. In LM1, seismic input is simulated by a given seismic intensity. In LM2, seismic input is given by a predetermined response spectrum. On the basis of the two proposed methods, many countries have adjusted their evaluation forms. Seismic vulnerability assessment in Italy is carried out through the application of appropriate forms (level 0, level 1, level 2), prepared by GNDT. The three gradually more detailed forms provide all the core information for seismic assessment of analysed buildings. The two methods proposed by Risk UE project are particularly advanced and founded on solid theoretical basis. Their application over the last few years and, in particular, a recent detailed study on the reliability of the methods, carried out by Canton of Valais (Switzerland), together with local research centre Crealp, University of Genova and École Polytechnique Fédérale de Lausanne, have shown some nebulous aspects that deserve further studies. The paper deals with the main features of the two methods and tries to point out the aspects that need to be improved for a better reliability of results.