Finite element investigation of stability bracing force demands of steel moment resisting frame columns under cyclic loading

This thesis examines the out-of-plane stability bracing of deep wide flange steel columns in moment resisting frames (MRFs) under cyclic loading. This is performed through a detailed continuum finite element analysis including a validation process and a parametric study with thorough consideration of the boundary conditions. A literature review highlights theoretical models with their evolution and limitations. Strength and stiffness requirements for various national standards (SIA 263, EN 1993-1-1, CSA S16:19, AISC-360-16 ) are exposed and put in perspective with research. The finite element results show that local geometric imperfections should imperatively be accounted for. The maximum brace force demand is found to be dependent on the member slenderness, as stocky members L/ry < 50 lead to higher force demands. Moreover, the level of axial load impacts negligibly the maximum brace demand. However, the peak demand occurs at smaller story drift ratios (SDR) for higher axial loads. Furthermore, the orientation of geometric imperfections, the offset due to out-of-straightness and the brace axial stiffness are examined. Key recommendations are established regarding the force and stiffness requirements of the reviewed standards. Our suggestions are to adapt the current provisions in order to account for the axial yield strength of the column rather than the axial load. The AISC-360-16 stiffness requirement showed satisfactory results and it is suggested to generalize it to the other standards