Influence of Cyclic Degradation on Inelastic Seismic Demands in Steel Moment Frames

Abstract eng:
This paper assesses the influence of the cyclic strength and stiffness degradation on the global and local inter-storey drift demands in moment resistant steel frames (MRF) designed according to Eurocode 8. The underlying question that motivated this research is whether refined structural modelling techniques such as those able to simulate steel degradation phenomena are relevant at the most typical design level, in order to satisfy the No-Collapse requirements imposed by the seismic code. For this purpose a set of low-rise and mid-rise MRFs, designed to European guidelines, were subjected to incremental dynamic analyses (IDA) using a suite of 56 far-field ground motion records. Two main modelling approaches were considered: (i) distributed plasticity modelling with fibre sections and elasto-plastic hardening material, and (ii) concentrated plasticity modelling with plastic hinges characterized by a constitutive model that includes deterioration effects. The results obtained from this set of analysis suggest that in the case of low-rise frames, cyclic degradation does not significantly affect the structural response, measured in terms of inter-storey drifts, while in the case of medium-rise frames degradation modelling is more relevant, resulting in up to 40% higher inter-storey drifts values. It is concluded, based on the findings of this study, that detailed assessments would be required in order to quantify the influence of cyclic degradation modelling in the structural response of medium-rise moment frame with various typologies.

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