Seismic performance assessment of masonry buildings requires a nonlinear response analysis to achieve a reliable understanding of the possible effects of future earthquakes in terms of damage and losses. Equivalent frame (EF) modelling combined with nonlinear static procedures has been recognized as an efficient tool, which was validated in several studies through both experimental data and post-earthquake damage inspections. In this paper, a new macroelement based on a fibre formulation is implemented into a matrix analysis approach to build up a nonlinear EF model and to perform incremental static (pushover) analysis with response control. For each step of the analysis, the stiffness matrix of the structure is updated using the novel macroelement model, accounting for geometric and mechanical nonlinearities both in terms of flexural and shear behaviour. Floor systems are modelled with truss elements, the stiffness of which can be varied in order to consider either rigid or flexible floors. In addition, the capacity model can simulate different degrees of connection at wall intersections and can easily be adapted to consider structural elements made of reinforced concrete, steel, wood, or other materials. The capacity modelling procedure proposed in this study was first validated by simulating the in-plane lateral behaviour of a full-scale masonry wall with opening, and then, implemented to run pushover analysis of existing masonry buildings representative of those located in the Campania region (southern Italy).
Differential settlements during earthquake ground shaking at the base of framed buildings located on the crest of slopes can produce heavy damage. This reflects the importance of considering ground shaking and co-seismic vertical displacements as interacting hazards in seismic fragility assessment. Slow-moving landslides are indeed secondary hazards of earthquakes that can induce significant damage accumulation, increasing the seismic vulnerability of structures. This paper presents the main findings of a seismic fragility analysis that was carried out on RC framed structures representative of low-rise, pre-code, residential Italian buildings. The methodology behind this study made use of fibre-based structural models and sequential nonlinear static analysis, which allowed the simulation of structural response to both earthquake ground motion and differential settlements with acceptable computational cost. Based on multivariate regression models available in the literature and random sampling of structures, seismically-induced settlements at the base of each structure were simulated considering multiple intensity measures (IMs) of seismic ground shaking. The correlation between the selected IMs was derived through a recent database of 250 accelerograms, which allow a wide representation of seismic hazard in the whole Italian territory for seismic risk assessment. The buildings were analysed with OpenSees software, assuming four performance limit states for characterization of seismic fragility at multiple levels of structural damage. The comparison between fragility curves associated with earthquake ground shaking only and those derived considering differential settlements allows the impact of cumulative damage to be evaluated.
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