Il collasso di un edificio industriale durante il terremoto del 2012 in Emilia Romagna

In May 2012, Emilia-Romagna (Northern Italy) was hit by a sequence of earthquakes. The two main shocks took place on May 20, (ML 5.9) and on May 29 (ML 5.8), with a sequence of aftershocks in between and after. In the epicentral area there were many small villages with a large amount of industrial plants. According to the Seismic Italian Codes up to 2003 the region was considered to be of such a low seismicity that no seismic design was required. In this scenario, many precast buildings failed during the two main events, causing many victims. One of the most dramatic cases, a large building (60  80 m2 in plan) partially failed in the small town of Medolla on May 29, killing four workers that were back to work after eight days of stop. The building was designed in 2002, and thus no seismic provisions were enforced. The Italian Legal Authority appointed the authors as experts to investigate the reasons of the collapse. In particular, the authors had to clarify why the building did not collapse on May 20 and (partially) failed catastrophically on May 29. The investi-gations have covered first of all the sequence of earthquakes hitting the building, that was very close to the earthquake epicentre in both dates. A numerical model of the building has been devised to: (a) obtain a reasonable estimate of the periods of the first natural mode; (b) analyze the modal shapes and compare them with the actual collapse mechanism; (c) determine a reasonable value of the demand in terms of strength and ductility posed on columns, that appear to be the critical elements in the collapse; (d) analyze the effects of the variation of a few parameters on the numerical response. The in-site damage observations provide a check of the goodness-of-fit of the developed numerical models. The results of this investigation, that will be summarized in the paper, help to explain the behaviour of this particular building and offer a significant contribution on the assessment procedures for the class of precast industrial buildings (quite relevant in Italy) not designed for seismic actions.