Seismic damage on merlons in masonry fortified buildings: A parametric analysis for overturning mechanism

Abstract

The observation of the damage occurred to ancient masonry buildings is the necessary first step to understand the seismic behavior of the elements that compose them. Looking at the recent seismic events in Italy, a severe damage could be noticed on a wide range of historical buildings, in some cases even for low values of peak ground acceleration. In particular, the present paper focuses on ancient fortified architectures, characterizing the historic city centers and landscapes, investigating the seismic vulnerability of its most typical element: the merlon.The analysis of the observed damage on the fortified building typology, collected and catalogued in previous works, clearly points out that merlons are frequently damaged, particularly by out-of-plane mechanisms and even for low accelerations. Given the fact that these elements are particularly vulnerable and, at the same time, particularly meaningful from a historical and cultural point of view, the present work focuses specifically on the out-of-plane damage mechanisms suffered by these protruding elements, in order to better understand their behavior during earthquakes, to quantify their vulnerability and to provide simple instruments for their seismic protection.Indeed, though the collapse of merlons is rather common, it has received little attention in the literature.The present paper analyses both merlons on towers and on walls, in clay brick masonry or in stone masonry, and describes, through a parametric analysis, their behavior as the features change. A simple linear elastic model was adopted to identify the activation of the out of plane mechanisms, while the subsequent collapse was analyzed with a non-linear kinematic model. Moreover, appropriate filtering equations were chosen to modify the response spectrum at the ground, thus taking into consideration the seismic filtering effect exerted by the supporting wall or tower. The proposed procedure is discussed and validated by means of three different case studies: the San Felice sul Panaro Fortress (damaged in the Emilia 2012 earthquake), the Arquata del Tronto Fortress, and the Rancia Castle (both damaged in the 2016 Central Italy earthquake). By changing the parameters (geometries, materials, soil) between extreme but realistic values, the curves that relate the slenderness of the merlons to the PGA that leads to the activation of the mechanism (or collapse) are plotted. These graphs supply ranges of vulnerable conditions, representing a straightforward and reliable instrument, also for practitioners and public bodies in charge of heritage preservation, useful to define priority lists for interventions and to optimize the resources for the prevention of future damage.