Comparative analysis of code-based approaches for seismic assessment of existing steel moment resisting frames

Nowadays, there is a lack of adequate code provisions for the seismic performance and risk assessment of steel structures to be used within European countries. At the same time, in several occasions, existing steel moment resisting frames (MRFs) have demonstrated to be very fragile with respect to seismic actions due to their inadequate ductility capacity. This combination highlights the urgent need for an update of the current Eurocode 8 – Part 3 (EC8-3), thus promoting a reliable assessment of existing steel structures. To this aim, the present study provides a comprehensive and quantitative comparison of the EC8-3 with the three versions of the American ASCE 41 (i.e., ASCE 41-06, -13 and -17), which are here assumed as a reference, as they reflect the evolution of ‘similar’ assessment procedures during the last two decades. The comparison of the capacity values provided by the codes for different engineering demand parameters (EDPs) highlights significant differences pointing out drawbacks of the EC8-3. In addition, the comparison is made by assessing the seismic performance of two existing steel MRFs, by performing Incremental Dynamic Analyses and deriving fragility curves in a probabilistic approach which considers local EDPs which are compliant with the codes, and that are conventionally used in deterministic studies, e.g., chord rotations in beams and columns, shear strain in panel zones. The comparison of the codes, and the probabilistic assessment of the case studies by using code-based (i.e., local) EDPs, provide significant insights and directions for revision of the EC8-3.