Toward fib model code 2020: Partial safety factor for resisting model uncertainties in plane stress nlfem analyses of R.C. systems

Fib Model Code 2010 describes different safety formats for non-linear analyses of reinforced concrete structures. Each safety format makes it possible to account for random uncertainties (i.e., random variability of material properties) and epistemic uncertainties (i.e., model uncertainty) through the definition of two appropriate partial safety factors. In general, the partial factor accounting for the material uncertainties is derived according to the aleatory variability of material properties (e.g., as a function of the coefficient of variation of the main variables). This does not happen for the partial factor related to the model uncertainty. In fact, toward the definition of new Model Code 2020, becomes necessary the reliability-based calibration of the partial safety factor accounting for the model uncertainty. This study is focused on the estimation of the partial safety factor corresponding to the resisting model uncertainty in plane stress non-linear finite element method analyses (NLFEMAs) of reinforced concrete structures considering different structural typologies with different behaviours and failure modes (i.e., beams, walls, deep beams, panels). Several experimental tests with outcomes known from the literature have been considered and reproduced by means of two-dimensional NLFEM models. For each structure, nine different structural models have been developed in order to differentiate the possible solution strategies available to the engineers. Defining the resisting model uncertainty as the ratio between experimental to NLFEM outcomes, the resisting model uncertainty random variable has been calibrated by means of a Bayesian updating. Finally, in agreement with the safety formats for NLFEMAs of reinforced concrete structures, the partial safety factor is proposed.