Modelling of the seismic behaviour of wall-to-horizontal diaphragm connections in historical constructions: Application to a case study

Out of plane mechanisms in historical earthquake-prone buildings are frequently due to weak wall-to-wall and wall-to-horizontal diaphragm connections solely designed for gravitational loads and generally neglected in the seismic analysis of unreinforced masonry buildings. Accurate modeling of structural connections is generally hard and nonlinear behavior can only be estimated when experimental data are available. This paper studies the influence of plain and strengthened wall-to-horizontal diaphragm connections on global and local analysis by developing and using simplified and advanced connections models calibrated upon experimental cyclic curves. The beneficial effects of the strengthened solution under study are demonstrated by means of global nonlinear static and incremental dynamic analysis, as well as local analysis based on the virtual work principle, but also advanced stability of rigid blocks. Hysteretic numerical models, accounting for strength degradation and energy dissipation capacity, are developed on the basis of available experimental results seeking to simulate the nonlinear behaviour of wall-to-horizontal diaphragm connections. This study aims at providing an innovative procedure at the forefront of the global and local analysis of structural connections in historical constructions. The behaviour of the building modelled with nonlinear connections is in between that of the building modelled with (i) poor and (ii) perfect connections commonly adopted in favor of simplified analysis. Results reveal that simplifications may imply errors up to 70% of the overall capacity of the building.