Evaluation of Partial Safety Factors for the Structural Assessment of Existings Masonry Buildings

The assessment of existing structures and infrastructures is a primary task in modern engineering, both for its key economic significance and for the extent and the significance of the built environment, nonetheless operational rules and standards for existing structures are often missing or insufficient, especially for masonry constructions. Existing masonry buildings, even in limited geographical regions, are characterized by many masonry types, differing in basic material, mortar, block shape, block texture, workmanship, degree of decay and so on. For these reasons, relevant mechanical parameters of masonry are often very uncertain; their rough estimation thus leads to inaccurate conclusions about the reliability of the investigated structure. In this work, a methodology to derive a refined probabilistic description of masonry parameters is first outlined starting from the analysis of a database of in-situ tests results collected by the authors. In particular, material classes, representing low, medium and high-quality masonry, are identified for a given masonry typology by means of the definition of a Gaussian Mixture Model. The probability density functions so obtained are the fundamental basis for the implementation of probabilistic analysis methods. In particular, the study will focus on the evaluation of masonry classes for compressive strength of stone masonry, considering a relevant database of semi-destructive, double flat jacks, in-situ test results. The statistical properties of the identified masonry classes, which can be used for the direct probabilistic assessment of structural performance of masonry walls under vertical loads, are finally considered for the evaluation of suitable partial safety factors, γ_M, to be used in the engineering practice.