Non-linear FE Modelling of UR Masonry Buildings: Shear-Flexural Behaviour of Piers and Spandrels

Numerous studies focus on analysing the dynamic behaviour of URM buildings under horizontal forces and interpreting potential in-plane collapse modes. Understanding the mechanical behaviour of masonry structures remains challenging due to their intrinsic heterogeneity and the various possibilities of material combinations. Consequently, the modelling phase becomes crucial for seismic vulnerability assessments of masonry buildings, particularly concerning differences in the shear-flexural behaviour of piers and spandrels. In this paper, after briefly reviewing the Equivalent Frame (EF) and Finite Element (FE) approaches, simple masonry elements such as piers have been modelled using these methods under various loading and constraint conditions. By comparing the results obtained issues related to shear behaviour were detected. All models were developed in SAP2000 using two different approaches: lumped-plasticity and distributed-plasticity. Notably, the software automatically defines shear behaviour based on flexural behaviour without offering modification options. Therefore, a simplified method for primally considering the shear collapse is proposed. By analysing the stress-state due to vertical loads and evaluating the strength domain of the analysed pier, a layered shell element section with appropriate geometric and mechanical properties can be defined for the pier, based on internal equilibrium conditions. This approach permits determining the minimum strength value for the modelled pier basing on its strength domain, considering the predominant behaviour (either shear or flexure) and enabling visualization of the related deformed shape. Comparisons between theoretical and numerical results are provided with the aim of better calibrating the proposed method.