Prediction of seismic demands for ancillary elements in vertically irregular steel frames

This paper investigates the elastic and inelastic seismic response of non-structural ancillary components within multi-storey steel frames exhibiting typical vertical irregularities. For this purpose, a large set of 188 steel moment framed structures, characterised by various combinations of setbacks within their elevations, is considered. The frames, which are designed according to European code provisions, are described in detail in terms of their configurations, member sizes, and dynamic characteristics. Within these structures, non-structural components, characterised by various periods and strength reduction factors are mounted at individual floors and assessed in terms of both their displacement and acceleration response under seismic loading. Detailed nonlinear dynamic time-history analyses are carried out using a suite of 100 ground motion records from both far-field and near-field sources, selected from the PEER NGA database in accordance with FEMA-695 requirements, scaled at intensity levels consistent with both elastic and inelastic conditions. The results are used to assess the suitability of existing models which are primarily developed to predict the seismic response of non-structural components in regular frames. The results reveal, with 95 % confidence, that frame irregularities have a direct and significant effect on the seismic response of non-structural components, and therefore, various modifications to current models are necessary to capture adequately the influence of vertical frame irregularities. Based on the findings, unified analytical models are proposed and shown to predict, well within an accuracy of 10 %, the seismic displacement and acceleration response of non-structural components mounted within the floors of both regular and irregular multi-storey steel frames. • The seismic response of non-structural components in irregular steel frames is investigated. • An extensive range of frame and ancillary component characteristics is considered. • The displacement and acceleration demands are examined under far-field and near-field records. • Detailed nonlinear dynamic time history assessments are carried out. • The influence of inelasticity in both the components and the frames is evaluated. • Unified prediction models for component response in regular and irregular frames are proposed.