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SEISMIC VULNERABILITY OF MERLONS IN ANCIENT FORTIFIED BUILDINGS Erica LENTICCHIA1, Eva COÏSSON2, Daniele FERRETTI3 ABSTRACT The paper investigates the seismic vulnerability of a typical element of the fortified architecture: the merlons. Indeed, the last seismic events in Italy have caused severe damage to a wide range of historical buildings, in some cases even for low values of peak ground acceleration. Among those, the crenellations typical of historical fortified buildings were particularly affected. Based on previous works, in which the seismic damage phenomena on the fortified building typology were collected and catalogued, the merlons proved to be particularly vulnerable elements. For this reason, the present work focuses specifically on the damage mechanisms suffered by these protruding elements, in order to understand their behavior in case of earthquake, to quantify their vulnerability and to provide instruments for their seismic protection. Different case studies referring to merlons, both on crenellated fortified walls and towers, were illustrated. Examples showed that free-standing merlons are mainly subjected to out-of-plane overturning; however if merlons support a roof, as often happens in castles which were subjected to a civil reuse in the course of time, also in plane shear failure can occur. Furthermore, some of the case studies analyzed presented seismic retrofitting interventions, whose behaviour under the seismic actions is described and discussed. Case studies showed that the collapse of merlons can occur even with low values of peak ground accelerations (PGA). Though the collapse of merlons is rather common, it received little attention in the literature. The present work focuses specifically on the out-of-plane overturning of merlons. The behavior of the merlons was studied by means of simple mechanical models. In particular, a simple linear elastic model was used to identify the activation of the mechanisms. The subsequent collapse by overturning was studied by means of a non-linear kinematic model. The seismic filtering effect, which is exerted by the supporting wall or tower, influences the behavior of the merlons. For this reason, proper filtering equations that modify the response spectrum at the ground were chosen. The proposed approach was used for a parametric analysis with merlons and supporting walls. Results permitted to plot curves that relate the slenderness of the merlons to the PGA that leads to their collapse. The proposed work thus defines a simple but reliable procedure than can be adopted by the practitioner for the seismic assessment of merlons and that could be used at a territorial scale in order to identify the most vulnerable cases and optimize the limited economic resources for the prevention of future damage on these elements, which might seem of minor importance but which are particularly meaningful both from the historical and aesthetical point of view. Keywords: masonry buildings; fortified buildings; seismic vulnerability; merlons 1. INTRODUCTION The last seismic events in Italy have shown the significant vulnerability of a typical element of the landscape and city centers skylines: the ancient fortified buildings. Fortified architecture is a generic 1Post-doc Research Fellow, Department of Structural, Geotechnical and Building Engineering, Politecnico di Torino, Torino, Italy, [email protected] 2Associate Professor, Department of Engineering and Architecture, Università degli Studi di Parma, Parma, Italy, [email protected] 3Associate Professor, Department of Engineering and Architecture, Università degli Studi di Parma, Parma, Italy, [email protected] term, which indicates a very wide variety of buildings, usually characterized by the presence of towers, defensive walls, and other characteristic elements. Frequently, among these features, the presence of a specific type of protruding element particularly characterizes this building typology: the merlons. The merlons are the solid standing part of a battlement or crenellated parapet, typical of medieval architectures or fortifications. They are an essential element for the battlements and have been used for centuries, not only for defensive purpose, but also as decorations in order to highlight the social status or the alliance of the castellan. In fact, in more recent configurations, fortified buildings sometimes present false decorative battlements. Based on previous works (Cattari, et al., 2014) (Coïsson, Ferretti, & Lenticchia, 2017), in which the seismic damage phenomena on the fortified building typology were collected and catalogued, the merlons proved to be particularly vulnerable elements. For this reason, the present work focuses specifically on the damage mechanisms suffered by these protruding elements, in order to understand their behavior in case of earthquake, to quantify their vulnerability and to provide indications for interventions aimed at their seismic protection. 1.1 Role of merlons in fortified buildings The crenellation of a defensive wall or tower is a defensive technique that was employed since the Ancient Times, but only during the Middle Ages, when the process of castellation spread through the whole Europe, they became a distinctive element of the fortified buildings. In fact, with the spread of the process of castellation through the whole Europe, the crenellation soon became a symbol of fortification, and starting from the Carolingian Empire it was necessary to obtain a license of crenellation in order to build a fortification. A license to crenellate was supposedly a grant that gave permission for a building to be fortified (Davis, 2007). It was employed as a way to control the construction of fortified buildings, and preventing local lords to become too powerful. In medieval England, the license to crenellate was also a tool to demonstrate the lords’ alliance to its monarch (Coulson, 2003). (a) (b) Figure 1: (a) Merlons and crenels of a battlement (Viollet-le-Duc, 1854 ) (b) Ghibelline crenellation with a wooden panel (Nigra, 1937) Though the shape and dimensions of the merlons, together with the width of the crenels (the space between two merlons) varied enormously, their purpose was the same: the crenel allowed defenders to shoot arrows and throw down missiles, while the merlons offered shelter from the assailants’ shootings (Figure 1). The geometrical features of merlons depend on the geographical location, the period of construction of the fortification and, most important, by the evolution of the weapons employed. In fact, if at first fortified buildings, and consequently the merlons, were built in wood, during the Middle Ages castles started to be built in stone masonry, and only during the Renaissance in brick masonry. These transformations were a consequence of warfare. During the Roman Empire, the walls of the Empire were mostly represented by its legions (Settia, 2017): castra were a temporary shelter for the Roman legions, and indeed, in ancient warfare, it was preferred to fight battles in open battlefield than to start 2 a siege. The siege warfare became a common feature of the Middle Ages, when fortified cities, fortresses and strongholds were necessary to maintain control on a certain area. Crenellations soon became a fundamental defensive element and merlons were designed as thin elements, more tall than wide. Usually, their wideness was sufficient to shelter a couple of men, and they could be provided with loopholes of various dimensions and shapes. This configuration persisted until the introduction of gunpowder artillery. Historians argue about the origins and the initial diffusion of gunpowder. The cannon first appears in the European iconography in an English manuscript of 1326 (Milemete, 1326), represented as an urn-like object. In the fifteenth century, gunpowder artillery came to play a regular, but only occasionally decisive, part in fortress warfare (Duffy, 1979). However, in general the development of cannons and gunpowder made revolutionary changes to siege warfare throughout Europe. If, at first, the artillery was employed in rare occasions, its employment in war became more frequent and, consequently, fortified buildings built in previous periods showed their vulnerability to this new type of action. In fact, when originally the primary strength in fortified wall constructions was due to their height, this then became its weakness since cannonballs could easily damage slender elements. With the introduction of gunpowder artillery, the configuration of defensive walls and merlons changed abruptly: walls became less regular in plan, grew in thickness, and lowered in height; similarly, merlons assumed a stocky shape and their thickness was increased. Merlons have been used until the artillery made them ineffective or even dangerous for defenders. However, they soon started to be employed as a decorative element. Fake merlons and battlements were largely used in the Neo-Gothic Style of the 19th century. Different decorations were used already in the Middle Ages, in order to indicate the alliance to a particular faction. A famous configuration was the one adopted for the Guelf and the Ghibelline factions: the former adopted a normal rectangular shape, while the latter adopted a merlon that ended in the upper part with a swallow-tailed form. In the Middle-East regions, instead, usually merlons were rounded, triangular or shaped with steps tapered at the end (Figure 2). (a) (b) Figure 2: (a) various forms of merlons (b) the crenellation

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