Semi-probabilistic calibration of material partial safety factors for the capacity assessment of existing masonry structures

Abstract

A practical procedure is presented for the calibration of partial safety factors (PSF) related to material properties, with a focus on unreinforced masonry structures. The methodology addresses the propagation of material and model uncertainties through a calibration based on the First Order Reliability Method (FORM) in the context of nonlinear static analysis approaches. The so-called Star Design with Central Point (SDCP) method is adopted for the computation of sensitivity coefficients and corresponding PSF for material uncertainty (γm). First, it is demonstrated how such calibration is affected by the geometry of the structure, by the pre-compression load level, and by the dominant failure mode. Second, it is evidenced that the most influential parameters on the structural response vary depending on the adopted modelling strategy (macro- or micro-modelling) for masonry discretisation. Third, the relative importance of model uncertainties is evidenced, for which a dataset of numerical predictions for the in-plane capacity of masonry panels is collected from the literature and discussed. Lastly, a comparison of different strategies to propagate uncertainty is provided, which emphasises the promising potential of the proposed procedure.