A simplified approach to seismic assessment of existing masonry structures using few analyses

Still nowadays masonry structures represent most of the global built environment in seismic regions. Despite their diffusion and long age, their dynamic behavior under earthquake loads is still extremely hard to predict, since it depends on several site-dependent factors, such as local empirical expertise, that are difficult to generalize. Furthermore, considerable and often economically disproportionate efforts are usually required to achieve a sufficient knowledge level for characterizing the basic variables affecting their response. The problem is challenging and the recent earthquakes have highlighted the extreme urgency to provide structural engineers with reliable yet simple procedures to seismically assess such buildings. This work intends to propose a new approach for dealing with ex-isting masonry structures, by expressing their seismic vulnerability in terms of failure probability, using only two (or three, if needed) sim-plified non-linear deterministic analyses, where the standard devia-tions of a selected number of variables are appropriately combined. The method has been applied to five Structural Units, where two types of wall connections and four masonry types were considered. Numeri-cal models are purposely developed in spreadsheets, to calculate the base shear/displacement response of each floor and then build the global response of the equivalent SDOF system. For the purpose of comparison, the proposed approach was validated against a fully probabilistic analysis by including all uncertainties affecting the struc-tural response. The probabilistic response of each considered structural unit is rep-resented through Capacity/Demand (C/D) ratios and exceedance prob-abilities. Sensitivity analyses are used to quantify and rank the effects of each variable on the global response. The viability of the overall procedure is commented upon, with due attention to the ensuing er-rors, which are deemed to be more than acceptable, given that only a few analyses have to be carried out.