Analysis of retrofitting solutions to enhance the seismic behavior of masonry-to-timber connections in historical constructions

The modelling and interpretation of retrofitting solutions in seismically vulnerable buildings is complex and uncertain but fundamental for understanding their actual influence in the global and local seismic performance of buildings. Historical buildings are frequently prone to earthquakes, especially developing out of plane local mechanisms of structural elements. This tendency is due to weak wall-to-wall and wall- to-horizontal diaphragm (WD) connections, mainly solely designed for gravitational loads. Global analysis of unreinforced masonry buildings is conventionally carried out neglecting the nonlinear properties of structural connections, while local analysis is commonly performed through simplified connection models, possibly leading to overconservative results. In this thesis, the influence of WD connections is studied through simplified and advanced numerical analyses on a benchmark building, on the bases of a comprehensive literature review and available experimental data. Hysteretic numerical models, calibrated upon cyclic experimental curves, carefully fit the force-displacement backbone curves, the strength degradation and the energy dissipation capacity. Global analysis is performed through nonlinear-static and nonlinear dynamic analyses, capable of including WD connections, and providing the overall capacity of the building and the corresponding damage pattern. On the other hand, local analysis, based on the virtual work principle, is applied as an efficient, rapid and simple procedure for the assessment of existing and strengthened WD connections. A more advanced approach, based on the dynamic stability of rigid block is further adopted to better highlight the possible dynamic effects of out-of-plane mechanisms including nonlinear WD connections. The strengthened solution under study reveals to be a prominent and low-invasive solution capable of strongly increasing the seismic safety index of out-of-plane mechanisms. Displacement-based assessment, through kinematic analysis, accounting for possible dynamic amplification of the seismic load reveals to be one of the most simple and basic design procedures capable of providing the necessary knowledge of the current state and the design parameters of the strengthened solution.