Seismic drift demands in steel moment resisting frames

This thesis focuses on assessing the seismic performance of steel moment resisting frames (MRFs), with particular emphasis on inelastic drift demands. The development of reliable predictive models for engineering demand parameters (EDPs), which represent structural and non-structural damage, is pivotal to improving the performance-based design procedures of modern structural systems for any given seismic hazard scenario. Extensive literature is available in relation to the key structural characteristics that control the inelastic response of buildings when subjected to seismic loads. However, most of this research has been limited to single-degree-of freedom (SDOF) representations. Also, when dealing with multi-degree-of-freedom systems (MDOF) several simplifications are typically made, including on the strength and stiffness distribution in order to simplify the behaviour. Similarly, the influence of important earthquake characteristics such as the frequency content and duration has not been adequately considered or even totally disregarded in previous research as well as in seismic design guidelines. Moreover, the vast majority of available studies have not considered the effects of stiffness and strength degradation produced under cyclic loading which occur primarily due to local buckling and lateral instability. The main objectives of this thesis is to provide detailed insights and predictive models for inelastic drift demands in steel moment frames, with due account for the influence of the structural configuration as well as realistic earthquake characteristics. To represent a wide range of structural characteristics, a set of 54 multi-storey frames designed to comply with Eurocode 8 provisions is considered throughout the thesis, in which the number of stories, steel profiles, seismic hazard and compliance criteria are varied. Detailed incremental dynamic analyses are performed on the full set of frames using a suite of 56 far-field ground motion records, which are scaled appropriately to achieve different levels of inelastic demand or equivalent behaviour factors. The seismic performance is evaluated in terms of maximum roof drift, maximum inter-storey drift, beam chord rotations and maximum residual drift demands. Statistical assessments are carried out to propose predictive relationships for each EDP investigated. In a subsequent study, a second set of 144 spectrally equivalent ground motion records is collated and employed in order to examine the effect of earthquake duration, whilst isolating this from the influence of spectral shape and amplitude. Finally, the implications of the findings of the research presented in this thesis on current seismic design provisions are discussed, and proposals for modifications and improvements are outlined. The main conclusions and observations from the thesis are also summarised alongside suggestions for future research.Open Acces