Exploring behaviour factors and chord rotation in RC MRF structures: Nonlinear analysis based on second generation of Eurocode 8

Eurocode 8 is undergoing revisions, including introducing new ductility classes and displacement-based design methods alongside traditional force-based ones. Additionally, new detailing provisions for local ductility are being considered. A notable change in the second generation of Eurocode 8 is that it no longer requires direct verification of concrete core confinement at the base of columns when detailing for local ductility. This study examines these changes concerning moment-resisting frames that are regular in plan and elevation and non-torsionally flexible. The behaviour factor ( q ) components q R , q D and q S , and chord rotation (displacement-based) are analysed using nonlinear analysis and compared with the current and second-generation of the Eurocode 8. A mathematical model based on nonlinear analysis models has been developed to understand the implications of forfeiting the direct verification of concrete core confinement at the base of columns. Nonlinear analysis reveals higher behaviour factor values than those prescribed by the code, highlighting the safety characteristics of the second generation of Eurocode 8 and the implications of three-dimensional modelling. Results show that chord rotation models preconised in the second generation of Eurocode 8 demonstrate good approximation to the ones obtained by nonlinear analysis, with minor differences observed for the structures under analysis. The strong correlation observed in the developed mathematical model for concrete core confinement indicates that displacement-based design alone sufficiently ensures the safety of core confinement at the base of columns. This research innovatively validates the new ductility classes of Eurocode 8. It introduces a mathematical model that eliminates the need to verify concrete core confinement at column bases. Nonlinear analysis confirms that displacement-based design ensures safety, streamlines the design process and enhances understanding of structural behaviour under seismic loads. • The behaviour factor component q R for various structures exceeds the recommended value. • The behaviour factor component q S exceeds the recommended values overstrength due to all other sources. • The behaviour factor component q D increases when the ductility classes, number of stories or seismic action increase. • The behaviour factor values ( q ) obtained from nonlinear static analysis exceed the code-prescribed values. • Confinement calculated through chord rotation is more conservative than verification through EN 1998-1:2004.