Vertical irregularity in RC MRF and wall structures: Evaluation and proposal of irregularity levels and impacts on behaviour factor

Eurocode 8 is currently undergoing revision on several aspects, such as ductility classes, damage limitation thresholds, local ductility requirements and their corresponding detailing provisions, and criteria for structural irregularities. This work assessed the impact of irregularity in elevation on seismic response by analysing regular in plan DCM (Ductility Class Medium) frame and wall structures. The increase in ground floor height implemented the irregularity to produce shifts in the inter-storey lateral stiffness. The design of those models was performed following the current generation Eurocode 8 (EC8) guidelines, using ETABS22® and the nonlinear analysis was assessed by an adaptive pushover analysis in SeismoStruct v2025. Additionally, this study examines the changes in behaviour factor calculus methodology in the first and second generations of EC8 in those models. The main purpose of this work is to propose an intermediate behaviour factor, considering the hypothesis that different levels of seismic response of irregular structures exist. The outcomes of this research revealed that, for DCM structures, irregular elevation impacts the seismic response substantially. Moreover, it is proposed for the second generation of Eurocode 8 a classification of regular, irregular and strongly irregular structures, with a corresponding reduction of 20 % of ( q ) for irregular structures and 30 % for strongly irregular structures.