Evaluation of Uncertainties in the Seismic Assessment of Existing Masonry Buildings

The assessment of existing masonry buildings is an important issue in earthquake prone countries like Italy. The current Italian building code, which adopts the approach proposed by Eurocode 8, includes an assessment procedure based on the use of confidence factors, whose values depend on the level of knowledge of the structure. These factors are intended to take into account all possible uncertainties related to the incomplete knowledge of the structure. This article investigates the reliability of the code-based procedure for the assessment of existing masonry buildings and pinpoints some problematic aspects. The approach followed is the simulation of the entire code-based assessment procedure, with the flow of decisions that an engineer would face in the assessment of an existing building schematized in the form of a logic tree. The proposed simulated procedure accounts for different sources of epistemic uncertainty like the selection of the level of knowledge, uncertainty in the results and location of in-situ tests, identification of several structural details, etc. A Monte Carlo procedure allows the simulation of a large number of random assessments intended to be performed by different virtual engineers. The results are then compared with those coming from the assessment of the "perfectly known" structure, used as a benchmark, providing an estimate of the validity of the codified assessment methodology.