Non-linear Finite Element modelling for the out-of-plane analysis of masonry walls

A Finite Element (FE) model implemented in SAP2000 is presented in this paper to analyze Out-Of-Plane (OOP) behaviour of masonry walls under horizontal actions. According to current Italian building code, the vulnerability of masonry walls regarding OOP may be assessed through linear and non-linear kinematic analyses. Nevertheless, these methods - even if efficient – might be tedious when applied to more complex OOP mechanisms or even for considering more complex phenomena (e.g., corner detachments). For this purpose, a numerical model based on the equivalent frame idealization is here proposed. Within this model, the non-linearity is considered concentrated at the base of the frame elements introducing plastic hinges. Modelling flexural hinges, several and/or multiple out-of-plane mechanisms may be activated in the model related to various parameters, for instance, external boundary conditions. Simple overturning and combined flexural mechanisms as well as various loading scenarios have been adopted for evaluating the application range of the proposed model. Evaluating the results, the proposed model allows to determine the development of the appropriate failure mechanism deriving from the input parameters. Furthermore, typical seismic strengthening interventions (e.g., steel ties, reinforced concrete ring beams) have been considered for each mechanism, leading to analyse the same geometry in both pre-intervention (IS) and post-intervention (PS) configurations hypothesized. The comparison with the analytical results still confirms the reliability and effectiveness of the proposed model.