Analysis of the behavior of the masonry Medici tower resorting on a hybrid discrete-kinematic methodology

This study presents a novel integrated discrete-analytical approach for analyzing the collapse behavior of the masonry Medici tower (L'Aquila, Italy). Due to their slenderness, masonry towers are characterized by high susceptibility to seismic actions and several approaches can be adopted to analyze their seismic vulnerability. Generally, engineers-practitioners and researchers study the local and global collapse mechanisms based on simplified kinematic analysis, as prescribed by national and international construction codes or, alternatively, more sophisticated approaches such as nonlinear finite element methods have been adopted to simulate the response of masonry towers. Although successful in some applications, these methods are limited in accurately capturing crack distributions and fracture mechanisms. In fact, they completely ignore the damage propagation phenomenon, starting from the trigger of the fracture up to the complete structural failure condition, that is instead fundamental aiming to analyze intermediate damage states for the check of serviceability limit states or to individuate a more realistic structural crack distribution in ultimate conditions. This work proposes a hybrid discrete-kinematic approach: first, the Lattice Discrete Particle Model (LDPM), that simulates masonry at meso-scale, is used to individuate the actual collapse mechanism; next, the individuated cracked configuration is used in the kinematic analysis for the analysis in ultimate conditions. The results show that the collapse of the Medici tower due to the 2009 L'Aquila earthquake is well predicted by LDPM and the corresponding limit analyses demonstrate the efficiency of the proposed hybrid approach applied to this case study. Additional results point out that different load configurations, more specifically variations in the direction of the seismic action, provoke in certain cases a more diffused damage and a clear failure pattern can not be identified for kinematic analyses. In these cases, relying mainly on comprehensive numerical models, such as LDPM, is fundamental to study the fracturing process from the cracks trigger up to the ultimate complex collapse mechanism.