On the collapse of the masonry Medici tower: An integrated discrete-analytical approach

Masonry towers are characterized by a high susceptibility to seismic actions. For this task different approaches exist and they are selected depending on the desired level of accuracy of the analysis. The identification of the correct collapse configuration is however complex and necessitates thorough on-site surveys. Construction codes usually require the study of local and global collapse mechanisms based on simplified kinematic analysis. More elaborated approaches such as nonlinear finite element methods have been used to simulate the response of masonry towers. Although successful in many applications, these methods are limited in accurately capturing crack distributions and fracture mechanisms. In this work, an integrated discrete-analytical approach is proposed. First, the Lattice Discrete Particle Model (LDPM), which simulates masonry at the stone level and has a superior capability in capturing fracturing processes, is adopted to simulate masonry towers subjected to seismic excitation. The numerical model is used to predict the actual collapse mechanism. Next, the final fractured configuration is used in the kinematic analysis for the calculation of the ultimate condition. The proposed method is used to analyze the collapse of the Medici tower that collapsed during the 2009 L'Aquila earthquake. The simulations are able to predict the induced damage and the crack contours, which are used then to identify six different failure configurations. The subsequent kinematic analyses take into account the relative position of openings and fracture locations. The results show that the collapse of the Medici tower is well replicated by LDPM and the corresponding kinematic analyses demonstrate the efficiency of the proposed hybrid approach applied to this case study. The paper also points out that different load configurations, more specifically the direction of the seismic action, result in certain cases in more diffused damage and a clear failure pattern cannot be identified for kinematic analyses. In these cases, it appears fundamental to rely mainly on comprehensive numerical models, such as LDPM, to study the fracturing process from the cracks trigger to the ultimate complex collapse mechanism.