Seismic Stability of Steel Wide Flange Columns in Concentrically Braced Frames: Response and Design Recommendations

Abstract This paper evaluates the seismic stability response of wide flange steel concentrically braced frame (CBF) columns and proposes drift-based stability design recommendations for such columns under seismic loading. Four full-scale tests were conducted on seismically compact W 250 × 101 under axial compression and lateral displacement histories representative of demands expected in CBF structures experiencing drift concentration. The tests confirmed that braced frame columns can maintain stable and ductile behavior under combined axial force and lateral deformation demands surpassing those expected under design-level earthquakes. A comprehensive parametric study was then performed using corroborated 3D finite-element (FE) model. The results of the numerical simulations identified four instability modes for wide flange steel CBF columns: flexural, local, local-flexural, and local-flexural-torsional buckling. The study established that ductility demand, axial load level, cross-sectional compactness, and member slenderness ratio are the key parameters governing the stability of CBF columns. Predictive equations were proposed to relate drift capacity and drift-based ductility to the axial load level, flange compactness, and member slenderness ratio. The proposed drift capacity and drift-based ductility equations can be used to evaluate seismic stability response of seismically compact and compact wide flange steel CBF columns.