Collapse of the clock-tower in Finale Emilia after the Emilia-Romagna seismic events in May 2012: a numerical insight

The two main seismic events, occurred on May 20 and 29, were characterized by the presence of low frequency ground motions, with relevant vertical components, as typical of near field earthquakes. As a consequence, from a structural point of view, structures having natural periods greater than those typical of ordinary buildings -such as the one analyzed- have been severely damaged. As a consequence of the first tremor (on the 20th of May), the clock-tower was sheared in two, with one half collapsing into rubble and the other standing precariously. The subsequent strong aftershock caused the almost total failure of the structure. In the paper, a number of different numerical models are critically compared, in order to have an insight into the causes which led to the collapse of the structure. Different numerical analyses have been performed, including linear and nonlinear static analyses. To this purpose, a full three-dimensional (3D) detailed finite element model (FEM) has been developed, starting from the available documentation (photographs and existing drawings), trying different directions for the seismic load and its distribution. Experimental data available have been employed to calibrate elastic and inelastic masonry parameters, to be used within the FEM non-linear analyses. From the numerical results, both the role played by the actual geometry and the insufficient resistance of the constituent materials are envisaged, also in light of the actual failure mechanism. In all cases, the numerical analyses provide a valuable picture of all possible failure mechanisms, thus giving useful hints for the reconstruction of the tower.