Influence of steel mechanical properties on EBF seismic behaviour

Among the resisting systems suitable for the design of ductile steel structures, Eurocode 8 proposes MRFs and EBFs. The formers are considered more efficient in terms of ductility, but they suffer a strong weakness in the lateral stiffness, with following cumbersome design procedures to avoid excessive lateral displacements maintaining a quite high ductile behaviour under seismic actions. Often, the design process leads to not optimized structural members, oversized with respect to the minimum seismic requirements due to lateral deformation limitations. EBFs combine high lateral stiffness, due to bracing elements, and high dissipative capacities, provided by the plastic hinges developed in links. Eurocode 8 proposes a design procedure for EBF structures in which iterative checks are required to design links with a defined level resistance dependent on all the other links’ strength. The present paper investigates the seismic behaviour of EBFs using Incremental Dynamic Analyses (IDA) to explore their mechanical response under increasing seismic action. IDAs are executed considering the influence of variability of steel mechanical properties on the behaviour of EBFs, using seven artificial accelerograms according to Eurocode 8. The aims of IDAs are the probabilistic assessment of the response of the system with respect to the variability of the material properties, the analysis of structural safety and the ability of the structures to internally redistribute plastic phenomena during the earthquake. Structural safety conditions will be defined according to a multi-level performance approach. The paper presents also some final suggestions for possible improvements and design simplifications.