Potentially Plastic Zones Details in Bottom Storey Columns of Concentrically Braced Frames

The present paper is intended to illustrate the advantages and disadvantages of different structural details for the potentially plastic zones located near the bottom end of the first storey columns in concentrically braced frames. Several structural details were analysed, considering: reduced flanges cross-sections and/or transversal and longitudinal stiffeners for the bottom zone of the columns. The features of the proposed alternative details are analysed for four concentrically braced frames. The considered frames had six and respectively ten storey and were located in Bucharest, Romania. The frames had two spans of 6.0 m and the storey height was 3.5 m. Built-up I-shaped cross-sections were used for all types of structural members: braces, columns and girders. All connections among different kind of structural members, as well as the connections to the foundation were considered as fixed. Dynamic nonlinear analyses were performed for each structural configuration using acceleration records of three Vrancea earthquakes, calibrated all to a peak ground acceleration value of 0.3 times the acceleration of gravity. The maximum values of the bending moments, the axial forces and the plastic deformations in the potentially plastic zones at the bottom end of the first-storey columns were compared. The buckling resistance of first-storey columns was compared for the most unfavourable loading states recorded during dynamic nonlinear analyses.