Closed-form expressions for partial safety factors used in the seismic assessment of existing RC buildings

Abstract

A new set of partial safety factors is proposed for the seismic safety assessment of existing reinforced concrete buildings. These safety factors are derived using a framework that focuses on the determination of the uncertainty in the limit state capacities. Existing seismic safety assessment standards, such as EN1998-3 or ASCE 41-17, follow a component-based approach that consider limit-state acceptance criteria based on capacity-related parameters to verify the safety of ductile and brittle failure modes. Despite their similar limit-state philosophy, these standards consider different conceptual formats for introducing the effects of uncertainties: the current version of EN1998-3 adopts confidence factors (CF) that factorize the mean values of material strength, while ASCE 41-17 uses a knowledge factor (k) to reduce the capacity of the component. The CF-based approach of EN1998-3 has been seen to lead to unclear levels of safety that may not reflect the impact of all the uncertainties about the different parameters or the sensitivity of different capacity models to these parameters. To address these issues, the proposed framework establishes a set of partial safety factors derived using an approach similar to that of ASCE 41-17, and involves recent capacity models, their uncertainties and a clear uncertainty management strategy. Furthermore, these new partial safety factors can also be seen to be compatible with the safety format proposed by the upcoming second-generation EN1998-3.