Advanced Modelling of Masonry Wall Structures under Earthquake Loading

Unreinforced masonry (URM) is a heterogeneous material with a complex response characterised by strong nonlinearity, dependent on the properties of its constituents and their arrangement. Furthermore, when analysing masonry-infilled frames, the complexity even increases, as it involves the representation of the ever-changing interaction between the frame and the infill. These aspects make modelling these structures a particularly challenging task. This PhD thesis focuses on addressing the critical issue of modelling the complex behaviour of brick masonry wall structures under earthquake loading, assessing the application of refined strategies for the analysis of URM and masonry-infilled frame structures while proposing a reliable yet efficient tool, which can be applied for accurate studies of the response of real-sized structures. The research work starts from a comparison of finite element descriptions formulated according to different scales of representation for URM modelling, investigating the nonlinear response up to collapse of unreinforced masonry wall components and structures under seismic loading. The results of macro and mesoscale simulations are compared against experimental findings to assess the ability to represent the cyclic hysteretic response. Great emphasis is laid upon the objectivity of the definition and calibration of the model material parameters with the aim of critically assessing how the response predictions are affected by their selection. The research then progresses to the modelling of masonry-infilled frames under horizontal actions, employing a sophisticated multidimensional approach, where masonry infills are represented using either mesoscale or continuum macroscale methods. The implemented models are assessed against experimental data, demonstrating their capability in capturing the complex frame-infill interaction and successfully replicating both global responses and local mechanisms. The objective calibration of material parameters is explored, accompanied by the conduction of parametric analyses to identify the most influential characteristics. Furthermore, the influence of openings is examined, offering valuable insights into how their presence affects the response, particularly in terms of strength and stiffness variations. Since the strategies previously employed may not be suitable for analysing real-sized structures due to their computational cost, a three-dimensional macroelement is developed to provide a tool that combines reliability and computational efficiency. A thorough validation is conducted, focusing on applications for both URM and masonry-infilled frame structures under monotonic and cyclic loadings. The validation extends to evaluating the out-of-plane response, crucial for a comprehensive assessment of the seismic performance of existing masonry buildings. Additionally, the model's ability to account for the presence of openings in masonry-infilled frames is assessed by comparing its outcomes from those obtained from continuum macro-scale models. The strategy is finally applied to assess the seismic vulnerability of a real irregular RC structure, originally designed without seismic provisions. The analysis includes evaluating the significant impact of infills on seismic response, potentially enhancing performance but also introducing further vulnerabilities. It is highlighted that, for an accurate description of the response in existing RC structures, these non-structural components must be carefully examined through the adoption of a reliable modelling strategy.