Inelastic stability of compression flange plates in three-way moment connections

Abstract

Abstract In three-way moment connections, where two major axis beams frame into the column flanges and a minor axis beam frames into the column web, there is always fear that connecting beam flanges directly to the column web may cause unwanted out-of-plane web deflections which may be accentuated by the presence of large axial column loads leading to premature buckling. It has been argued, however, that good practice dictates that only the web of the minor axis beam need be connected directly to the column web; the flanges may be cut-off and connected, instead, to plates which are attached to the column flanges only. This arrangement reduces significantly out-of-plane column web deflections. These plates also act as column stiffeners to stresses from the major axis beams. This paper investigates the plastic stability of the flange plates subject to compression in three directions. It has been shown through finite element plastic bifurcation analysis that the magnitudes of the maximum stresses from the major axis beams, which the flange plate can support before it buckles, are highly sensitive to the magnitudes of stresses induced in the plate by the minor axis beam. This necessitates applying a higher safety factor for stresses induced in the plate by the minor axis beam.