The authors have investigated practical application of beam-to-column connection with exterior diaphragm assembled by high-strength bolts. When horizontal loads due to bending moments of beams act at this connection under seismic force, local out-of-plane deformation of square hollow section (SHS) columns may occur. In this paper, experiment and FEM analysis with a part of SHS column were conducted to verify the effects of several parameters on local deformation behavior. Furthermore, based on the stress distribution obtained by the FEM analysis, a method of evaluating the strength of SHS by local deformation was proposed.
