Development of a proposed design method for discontinuous columns in braced frames

Abstract

A column design method has been developed for use in braced frames with discontinuous columns using flexible cap and base plates and floor beams that are either simply supported or continuous. The proposed method is intended to be used with shallow floor construction with concrete or steel/concrete composite slabs in which the floor slab occupies the depth of the floor beams and is fully grouted to the beams so that the slab restrains the full depth of the beams. It was developed to simplify the design of square hollow sections discontinuous columns in frames using asymmetric beam (ASB) type floor construction. Floor beams are designed to carry the floor loads without interaction with the columns; columns are then designed to resist the floor beam reactions assuming a deformed shape derived from end-rotations equal to the slope of the floor beams at the top or bottom of the column, whichever is the greater. The method incorporates the elasto-plastic behaviour of columns subject to axial compression and large end-rotations and has been verified by physical tests on full-scale square hollow sections columns and finite element analysis using non-linear geometry and material properties and including residual stresses.